Multiomics approach to profiling Sertoli cell maturation during development of the spermatogonial stem cell niche

Spermatogonial stem cells (SSCs) are the basis of spermatogenesis, a complex process supported by a specialized microenvironment, called the SSC niche. Postnatal development of SSCs is characterized by distinct metabolic transitions from prepubertal to adult stages. An understanding of the niche factors that regulate these maturational events is critical for the clinical application of SSCs in fertility preservation. To investigate the niche maturation events that take place during SSC maturation, we combined different '-omics' technologies. Serial single cell RNA sequencing analysis revealed changes in the transcriptomes indicative of niche maturation that was initiated at 11 years of age in humans and at 8 weeks of age in pigs, as evident by Monocle analysis of Sertoli cells and peritubular myoid cell (PMC) development in humans and Sertoli cell analysis in pigs. Morphological niche maturation was associated with lipid droplet accumulation, a characteristic that was conserved between species. Lipidomic profiling revealed an increase in triglycerides and a decrease in sphingolipids with Sertoli cell maturation in the pig model. Quantitative (phospho-) proteomics analysis detected the activation of distinct pathways with porcine Sertoli cell maturation. We show here that the main aspects of niche maturation coincide with the morphological maturation of SSCs, which is followed by their metabolic maturation. The main aspects are also conserved between the species and can be predicted by changes in the niche lipidome. Overall, this knowledge is pivotal to establishing cell/tissue-based biomarkers that could gauge stem cell maturation to facilitate laboratory techniques that allow for SSC transplantation for restoration of fertility.

Metabolic transitions define spermatogonial stem cell maturation

STUDY QUESTION

Do spermatogonia, including spermatogonial stem cells (SSCs), undergo metabolic changes during prepubertal development?

SUMMARY ANSWER

Here, we show that the metabolic phenotype of prepubertal human spermatogonia is distinct from that of adult spermatogonia and that SSC development is characterized by distinct metabolic transitions from oxidative phosphorylation (OXPHOS) to anaerobic metabolism.

WHAT IS KNOWN ALREADY

Maintenance of both mouse and human adult SSCs relies on glycolysis, while embryonic SSC precursors, primordial germ cells (PGCs), exhibit an elevated dependence on OXPHOS. Neonatal porcine SSC precursors reportedly initiate a transition to an adult SSC metabolic phenotype at 2 months of development. However, when and if such a metabolic transition occurs in humans is ambiguous.

STUDY DESIGN, SIZE, DURATION

To address our research questions: (i) we performed a meta-analysis of publicly available and newly generated (current study) single-cell RNA sequencing (scRNA-Seq) datasets in order to establish a roadmap of SSC metabolic development from embryonic stages (embryonic week 6) to adulthood in humans (25 years of age) with a total of ten groups; (ii) in parallel, we analyzed single-cell RNA sequencing datasets of isolated pup (n = 3) and adult (n = 2) murine spermatogonia to determine whether a similar metabolic switch occurs; and (iii) we characterized the mechanisms that regulate these metabolic transitions during SSC maturation by conducting quantitative proteomic analysis using two different ages of prepubertal pig spermatogonia as a model, each with four independently collected cell populations.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Single testicular cells collected from 1-year, 2-year and 7-year-old human males and sorted spermatogonia isolated from 6- to 8-day (n = 3) and 4-month (n = 2) old mice were subjected to scRNA-Seq. The human sequences were individually processed and then merged with the publicly available datasets for a meta-analysis using Seurat V4 package. We then performed a pairwise differential gene expression analysis between groups of age, followed by pathways enrichment analysis using gene set enrichment analysis (cutoff of false discovery rate < 0.05). The sequences from mice were subjected to a similar workflow as described for humans. Early (1-week-old) and late (8-week-old) prepubertal pig spermatogonia were analyzed to reveal underlying cellular mechanisms of the metabolic shift using immunohistochemistry, western blot, qRT-PCR, quantitative proteomics, and culture experiments.

MAIN RESULTS AND THE ROLE OF CHANCE

Human PGCs and prepubertal human spermatogonia show an enrichment of OXPHOS-associated genes, which is downregulated at the onset of puberty (P < 0.0001). Furthermore, we demonstrate that similar metabolic changes between pup and adult spermatogonia are detectable in the mouse (P < 0.0001). In humans, the metabolic transition at puberty is also preceded by a drastic change in SSC shape at 11 years of age (P < 0.0001). Using a pig model, we reveal that this metabolic shift could be regulated by an insulin growth factor-1 dependent signaling pathway via mammalian target of rapamycin and proteasome inhibition.

LARGE SCALE DATA

New single-cell RNA sequencing datasets obtained from this study are freely available through NCBI GEO with accession number GSE196819.

LIMITATIONS, REASONS FOR CAUTION

Human prepubertal tissue samples are scarce, which led to the investigation of a low number of samples per age. Gene enrichment analysis gives only an indication about the functional state of the cells. Due to limited numbers of prepubertal human spermatogonia, porcine spermatogonia were used for further proteomic and in vitro analyses.

WIDER IMPLICATIONS OF THE FINDINGS

We show that prepubertal human spermatogonia exhibit high OXHPOS and switch to an adult-like metabolism only after 11 years of age. Prepubescent cancer survivors often suffer from infertility in adulthood. SSC transplantation could provide a powerful tool for the treatment of infertility; however, it requires high cell numbers. This work provides key insight into the dynamic metabolic requirements of human SSCs across development that would be critical in establishing ex vivo systems to support expansion and sustained function of SSCs toward clinical use.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the NIH/NICHD R01 HD091068 and NIH/ORIP R01 OD016575 to I.D. K.E.O. was supported by R01 HD100197. S.K.M. was supported by T32 HD087194 and F31 HD101323. The authors declare no conflict of interest.

Testicular organoids to study cell-cell interactions in the mammalian testis

BACKGROUND

Over the last ten years, three-dimensional organoid culture has garnered renewed interest, as organoids generated from primary cells or stem cells with cell associations and functions similar to organs in vivo can be a powerful tool to study tissue-specific cell-cell interactions in vitro. Very recently, a few interesting approaches have been put forth for generating testicular organoids for studying the germ cell niche microenvironment.

AIM

To review different model systems that have been employed to study germ cell biology and testicular cell-cell interactions and discuss how the organoid approach can address some of the shortcomings of those systems.

RESULTS AND CONCLUSION

Testicular organoids that bear architectural and functional similarities to their in vivo counterparts are a powerful model system to study cell-cell interactions in the germ cell niche. Organoids enable studying samples in humans and other large animals where in vivo experiments are not possible, allow modeling of testicular disease and malignancies and may provide a platform to design more precise therapeutic interventions.

Xenografting of isolated equine (Equus caballus) testis cells results in de novo morphogenesis of seminiferous tubules but not spermatogenesis

The study of spermatogenesis in the horse is challenging because of the absence of an in vitro system that is capable of reproducing efficient spermatogenesis and because of the difficulties and costs associated with performing well-controlled studies in vivo. In an attempt to develop novel methods for the study of equine spermatogenesis, we tested whether cells from enzymatically digested pre-pubertal equine testicular tissue were capable of de novo tissue formation and spermatogenesis following xenografting under the back skin of immunocompromised mice. Testes were obtained from normal pre-pubertal colts and dissociated into cell suspensions using trypsin/collagenase digestion. Resulting cell pellets, consisting of both somatic and germ cells, were injected into fascial pockets under the back skin of immunocompromised, castrated mice and maintained for between 1 and 14 months. Mice were killed and grafts were recovered and analyzed. As has been reported for testis cell suspensions from pigs, mice, cattle, and sheep, de novo formation of equine testicular tissue was observed, as evidenced by the presence of seminiferous tubules and an interstitial compartment. There was an increased likelihood of de novo testicular formation as grafting period increased. Using indirect immunofluorescence, we confirmed the presence of spermatogonia in de novo formed seminiferous tubules. However, we found no evidence of meiotic or haploid cells. These results indicate that dissociated pre-pubertal equine testis cells are capable of reorganizing into the highly specialized endocrine and spermatogenic compartments of the testis following ectopic xenografting. However, in spite of the presence of spermatogonia within the seminiferous tubules, spermatogenesis does not occur. Although this technique does allow access to the cells within the seminiferous tubule and interstitial compartments of the equine testis prior to reaggregation, the absence of spermatogenesis will limit its use as a method for the study of testicular function in the horse.

Stirred suspension bioreactors as a novel method to enrich germ cells from pre-pubertal pig testis

To study spermatogonial stem cells the heterogeneous testicular cell population first needs to be enriched for undifferentiated spermatogonia, which contain the stem cell population. When working with non-rodent models, this step requires working with large numbers of cells. Available cell separation methods rely on differential properties of testicular cell types such as expression of specific cell surface proteins, size, density, or differential adhesion to substrates to separate germ cells from somatic cells. The objective of this study was to develop an approach that allowed germ cell enrichment while providing efficiency of handling large cell numbers. Here, we report the use of stirred suspension bioreactors (SSB) to exploit the adhesion properties of Sertoli cells to enrich cells obtained from pre-pubertal porcine testes for undifferentiated spermatogonia. We also compared the bioreactor approach with an established differential plating method and the combination of both: SSB followed by differential plating. After 66 h of culture, germ cell enrichment in SSBs provided 7.3 ± 1.0-fold (n = 9), differential plating 9.8 ± 2.4-fold (n = 6) and combination of both methods resulted in 9.1 ± 0.3-fold enrichment of germ cells from the initial germ cell population (n = 3). To document functionality of cells recovered from the bioreactor, we demonstrated that cells retained their functional ability to reassemble seminiferous tubules de novo after grafting to mouse hosts and to support spermatogenesis. These results demonstrate that the SSB allows enrichment of germ cells in a controlled and scalable environment providing an efficient method when handling large cell numbers while reducing variability owing to handling.

Germline modification of domestic animals

Genetically-modified domestic animal models are of increasing significance in biomedical research and agriculture. As authentic ES cells derived from domestic animals are not yet available, the prevailing approaches for engineering genetic modifications in those animals are pronuclear microinjection and somatic cell nuclear transfer (SCNT, also known as cloning). Both pronuclear microinjection and SCNT are inefficient, costly, and time-consuming. In animals produced by pronuclear microinjection, the exogenous transgene is usually inserted randomly into the genome, which results in highly variable expression patterns and levels in different founders. Therefore, significant efforts are required to generate and screen multiple founders to obtain animals with optimal transgene expression. For SCNT, specific genetic modifications (both gain-of-function and loss-of-function) can be engineered and carefully selected in the somatic cell nucleus before nuclear transfer. SCNT has been used to generate a variety of genetically modified animals such as goats, pigs, sheep and cattle; however, animals resulting from SCNT frequently suffer from developmental abnormalities associated with incomplete nuclear reprogramming. Other strategies to generate genetically-modified animals rely on the use of the spermatozoon as a natural vector to introduce genetic material into the female gamete. This sperm mediated DNA transfer (SMGT) combined with intracytoplasmatic sperm injection (ICSI) has relatively high efficiency and allows the insertion of large DNA fragments, which, in turn, enhance proper gene expression. An approach currently being developed to complement SCNT for producing genetically modified animals is germ cell transplantation using genetically modified male germline stem cells (GSCs). This approach relies on the ability of GSCs that are genetically modified in vitro to colonize the recipient testis and produce donor derived sperm upon transplantation. As the genetic change is introduced into the male germ line just before the onset of spermatogenesis, the time required for the production of genetically modified sperm is significantly shorter using germ cell transplantation compared to cloning or embryonic stem (ES) cell based technology. Moreover, the GSC-mediated germline modification circumvents problems associated with embryo manipulation and nuclear reprogramming. Currently, engineering targeted mutations in domestic animals using GSCs remains a challenge as GSCs from those animals are difficult to maintain in vitro for an extended period of time. Recent advances in genome editing techniques such as Zinc-Finger Nucleases (ZFNs), Transcription Activator-like Effector Nucleases (TALENs) and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) greatly enhance the efficiency of engineering targeted genetic change in domestic animals as demonstrated by the generation of several gene knock-out pig and cattle models using those techniques. The potential of GSC-mediated germline modification in making targeted genetic modifications in domestic animal models will be maximized if those genome editing techniques can be applied in GSCs.

268 ROLE OF ATPase MOTOR CYTOPLASMIC DYNEIN AND PRIMARY CILIA IN TESTICULAR MORPHOGENESIS

In vertebrates, the primary cilium is a nearly ubiquitous organelle present in somatic cells, but little is known about its function in the male gonad. We investigated the role of primary cilia in testis cells using in vitro formation of seminiferous tubules and in vitro culture of testicular somatic cells by inhibiting the primary cilium with CiliobrevinD, a cell-permeable, reversible chemical modulator that inhibits the major component of the organelle: ATPase motor cytoplasmic dynein. We analysed in vitro cultures for the presence of primary cilia and the activation of hedgehog signalling through translocation of Gli2 to the nuclei; in vitro tubule formation was evaluated by length and width of tubules formed. Methods: testicular cells were harvested from neonatal pigs by 2-step enzymatic digestion. Cells (50 × 106 mL–1) were plated on 100 mm Petri dishes in 15 mL of DMEM + 5% FBS + 50 U of penicillin and incubated at 37°C in 5% CO2 in air overnight, cells remaining in suspension and those slightly attached were removed and the somatic cells attached were trypsinized to obtain a single cell suspension, and then submitted to two different protocols: in vitro culture (A) or in vitro tubule formation (B), n = 5 replicates each. For A, somatic cells were replated on coverslips in 24-well plates and cultured in serum free media for 48 h, then for the treated group, 10 mM of CiliobrevinD was added for 24 h, attached cells from control and treated groups were fixed in 4% PFA and characterised by immunocytochemistry for ARL13B, Vimentin, and Gli2. For B: 1 × 106 cells were added to 24-well plates coated with 1 : 1 diluted Matrigel, the control group was kept in serum free media and to the treated group was added 20 mM CiliobrevinD at Day 0. Results: A) primary cilia were present in 89.3 ± 2.3% of cells cultured in serum-free media for the control group and Gli2 was located in the nuclei of 90.2 ± 1.2% of cells; in the CiliobrevinD-treated group the percentage of primary cilia decreased (P < 0.05) to 3.1 ± 2.5% and nuclear Gli2 to 3.9 ± 0.7; B) tubules formed in the control group were significantly longer and wider than the ones formed when CiliobrevinD was added (9.91 ± 0.35 v. 5.540 ± 1.08 mm and 339.8 ± 55.78 v. 127.2 ± 11.9 µm, respectively, P < 0.05 by Student's t-test). In conclusion, the inhibition of ATPase motor cytoplasmic dynein perturbs formation of primary cilia in testicular somatic cells, blocks Hedgehog signalling, and impairs in vitro tubule formation. Therefore, primary cilia on testicular somatic cells appear to be essential for testicular morphogenesis.Research was supported by 5 R01 OD016575-13.

74 GERM CELLS AND TESTICULAR SOMATIC CELLS HAVE DIFFERENT SENSITIVITY TO CRYOPRESERVATION

Spermatogonial stem cells (SSC) are the foundation of spermatogenesis. Undifferentiated spermatogonia, containing SSC, represent only 2 to 5% of cells recovered from immature mammalian testis. Cryopreservation in liquid nitrogen allows for long-term storage of cells. Preservation of germ cells can serve as a means of genetic preservation from immature males when sperm storage is not an option. Studies have investigated the effects of cryopreservation on the spermatogenic potential of SSC and the efficiency of various cryopreservation protocols. Preliminary observations indicated that germ cells may survive cryopreservation better than testicular somatic cells, resulting in a post-thaw cell population enriched in germ cells. However, this has not been critically evaluated. The objective of this study was to test the hypothesis that germ cells are less susceptible to cryo-damage than testicular somatic cells. Cells were harvested from the testes of 1-wk-old piglets by 2-step enzymatic digestion. The initial cell suspension was subjected to differential adhesion to enrich the cell population for germ cells. Cells were plated in DMEM + 5% fetal bovine serum and incubated at 37°C in 5% CO2 in air. After 18 h, cells in suspension and cells slightly attached were recovered by trypsinization (1 : 10 trypsin-ethylenediaminetetraacetic acid) for 30 s and replated. This was repeated 24 and 36 h after initial plating. The enriched population was placed into cryovials at a concentration of 30 × 106 cells in freezing media (70% DMEM + 20% fetal bovine serum + 10% dimethyl sulfoxide), kept for 24 h at –80°C in a cryogenic freezing container and transferred to liquid nitrogen for 1 week. Aliquots of cells before freezing and after thawing at 37°C followed by incubation at 37°C in 5% CO2 in air for 1 h were analyzed for viability by propidium iodide (PI) exclusion and immunofluorescence for the germ cell marker VASA to identify viable germ cells (VASA+/PI–), nonviable germ cells (VASA+/PI+), viable somatic cells (VASA–/PI–), and nonviable somatic cells (VASA–/PI+). The percentage of viable germ cells after freezing and thawing was compared to the percentage of viable somatic cells by ANOVA. After enrichment by differential plating, the cell population had 95.6 ± 0.9% viability and contained 27.1 ± 7.4% germ cells (n = 3 replicates). After cryopreservation, the overall cell viability was 77.5 ± 1.6%, and 25.8 ± 8.0% were germ cells. The overall viability after cryopreservation could potentially have benefited from the 1-h incubation prior to analysis. The viability of the germ cell population after freezing and thawing was higher (92.1 ± 3.1%) than somatic cell viability (72.3 ± 1.7%; P < 0.01). These results indicate that porcine germ cells survive cryopreservation better than do testicular somatic cells. Therefore, cryostorage of germ cells can be an efficient means for preservation of male genetic material. Supported by NIH ORIP/DCM RR17359.

Non-viral transfection of goat germline stem cells by nucleofection results in production of transgenic sperm after germ cell transplantation

Germline stem cells (GSCs) can be used for large animal transgenesis, in which GSCs that are genetically manipulated in vitro are transplanted into a recipient testis to generate donor-derived transgenic sperm. The objectives of this study were to explore a non-viral approach for transgene delivery into goat GSCs and to investigate the efficiency of nucleofection in producing transgenic sperm. Four recipient goats received fractionated irradiation at 8 weeks of age to deplete endogenous GSCs. Germ cell transplantations were performed 8-9 weeks post-irradiation. Donor cells were collected from testes of 9-week-old goats, enriched for GSCs by Staput velocity sedimentation, and transfected by nucleofection with a transgene construct harboring the human growth hormone gene under the control of the goat beta-casein promoter (GBC) and a chicken beta-globin insulator (CBGI) sequence upstream of the promoter. For each recipient, transfected cells from 10 nucleofection reactions were pooled, mixed with non-transfected cells to a total of 1.5 × 10(8) cells in 3 ml, and transplanted into one testis (n = 4 recipients) by ultrasound-guided cannulation of the rete testis. The second testis of each recipient was removed. Semen was collected, starting at 9 months after transplantation, for a period of over a year (a total of 62 ejaculates from four recipients). Nested genomic PCR for hGH and CBGI sequences demonstrated that 31.3% ± 12.6% of ejaculates were positive for both hGH and CBGI. This study provides proof-of-concept that non-viral transfection (nucleofection) of primary goat germ cells followed by germ cell transplantation results in transgene transmission to sperm in recipient goats.

Establishment of goat embryonic stem cells from in vivo produced blastocyst-stage embryos

Embryonic stem (ES) cells with the capacity for germ line transmission have only been verified in mouse and rat. Methods for derivation, propagation, and differentiation of ES cells from domestic animals have not been fully established. Here, we describe derivation of ES cells from goat embryos. In vivo-derived embryos were cultured on goat fetal fibroblast feeders. Embryos either attached to the feeder layer or remained floating and expanded in culture. Embryos that attached showed a prominent inner cell mass (ICM) and those that remained floating formed structures resembling ICM disks surrounded by trophectodermal cells. ICM cells and embryonic disks were isolated mechanically, cultured on feeder cells in the presence of hLIF, and outgrown into ES-like colonies. Two cell lines were cultured for 25 passages and stained positive for alkaline phosphatase, POU5F1, NANOG, SOX2, SSEA-1, and SSEA-4. Embryoid bodies formed in suspension culture without hLIF. One cell line was cultured for 2 years (over 120 passages). This cell line differentiated in vitro into epithelia and neuronal cells, and could be stably transfected and selected for expression of a fluorescent marker. When cells were injected into SCID mice, teratomas were identified 5-6 weeks after transplantation. Expression of known ES cell markers, maintenance in vitro for 2 years in an undifferentiated state, differentiation in vitro, and formation of teratomas in immunodeficient mice provide evidence that the established cell line represents goat ES cells. This also is the first report of teratoma formation from large animal ES cells.

318 EFFECT OF 6-N-PROPYL-2-THIOURACIL-INDUCED HYPOTHYROIDISM IN THE HOST MOUSE ON THE DEVELOPMENT OF BOVINE TESTIS XENOGRAFTS

In rodents, thyroid hormones inhibit Sertoli cell proliferation, promote Sertoli cell differentiation, and accelerate lumen formation in the seminiferous tubules. Conversely, transient hypothyroidism prolongs Sertoli cell proliferation, leading to increased Sertoli cell number and testicular size. In order to evaluate whether 6-N-propyl-2-thiouracil (PTU)-induced hypothyroidism in the host mouse would affect seminiferous tubule development and germ cell differentiation, and subsequently increase spermatogenesis in bovine testis xenografts, fragments (∼1 mm3) of testes from 1-wk-old Holstein calves (n = 6) were transplanted ectopically to castrated immunodeficient male mice (n = 6/donor). Mice (n = 3/donor) were treated with 0.1% (w/v) PTU in drinking water for 4 weeks or left as control. At 5 and 7 months after grafting, grafts were analyzed by morphometry and immunohistochemistry for expression of protein gene product 9.5 (PGP 9.5) as a germ cell marker, and Mullerian-inhibiting substance (MIS) and androgen receptor (AR) to assess Sertoli cell maturation. For each variable, averages of each group were compared at each collection point by t-test PTU treatment to the drinking water for 1 month suppressed thyroid hormone levels (T4) in host mice without negative systemic effects (0.3 ± 0.2 v. 4 ± 0.3 μg dL-1 at 4 weeks in treated v. control mice, respectively, P < 0.05). Spermatogenesis in recovered grafts was arrested at meiosis regardless of treatment and collection time. Graft weight was lower in treated mice than in controls (21 ± 4 v. 42 ± 5 and 24 ± 9 v. 51 ± 5 mg, at 5 and 7 months, respectively, P < 0.05). Volume density of the tubular and intertubular compartments, and seminiferous epithelium, was not affected by treatment (P > 0.05); however, treatment reduced lumen density compared to controls (9 ± 2 v. 19 ± 3 and 12 ± 1 v. 24 ± 4%) and tubular diameter (121 ± 3 v. 140 ± 7 and 144 ± 2v. 170 ± 2 (im, at 5 and 7 months, respectively (P < 0.05). Tubule length per milligram was not different at 5 months between control and treated groups (P > 0.05) but was increased at 7 months in the treated grafts (50 ± 1 v. 30 ± 1 cm, P < 0.05). Number of Sertoli cells per milligram was not affected by treatment (P > 0.05). However, Sertoli cell volume was increased in controls (440 ± 19 v. 341 ± 14 and 504 ± 6 v. 388 ± 18 μm3, at 5 and 7 months, respectively, P < 0.05). The number of germ cells per 100 Sertoli cells was not different between groups at any collection time (P > 0.05). Sertoli cells showed variable MIS expression and lack of or weak AR expression regardless of treatment and collection time, indicating an immature phenotype. In conclusion, suppression of thyroid hormone levels in host mice affects seminiferous tubule development in bovine testis xenografts, demonstrating that endocrine manipulation of the mouse host will affect xenografts in a predictable manner. However, treatment did not affect number and differentiation of germ cells. Rather, incomplete Sertoli cell maturation appears to lead to incomplete germ cell differentiation in bovine testis xenografts. Supported by USDA (2007-35203-18213).

Preservation and transplantation of porcine testis tissue

Grafting of immature mammalian testis tissue to mouse hosts can preserve the male germline. To make this approach applicable to a clinical or field situation, it is imperative that the testis tissue and/or spermatozoa harvested from grafted tissue are preserved successfully. The aim of the present study was to evaluate protocols for the preservation of testis tissue in a porcine model. Testis tissue was stored at 4 degrees C for short-term preservation or cryopreserved by slow-freezing, automated slow-freezing or vitrification for long-term storage. Preserved tissue was transplanted ectopically to mouse hosts and recovered xenografts were analysed histologically. In addition, spermatozoa were harvested from xenografts and cryopreserved. Total cell viability and germ cell viability remained high after tissue preservation. Complete spermatogenesis occurred in xenografts preserved by cooling up to 48 h, whereas spermatogenesis progressed to round spermatids in the xenografts that were frozen-thawed before grafting. Approximately 50% of spermatozoa harvested from xenografts remained viable after freezing and thawing. The in vivo developmental potential of cryopreserved tissue was reduced despite high post-thaw viability. Therefore, it is important to evaluate germ cell differentiation in vivo in addition to cell viability in vitro when optimising freezing protocols for testis tissue.

Male germ cell transplantation

Transplantation of male germ line stem cells from a donor animal to the testes of an infertile recipient was first described in 1994. Donor germ cells colonize the recipient's testis and produce donor-derived sperm, such that the recipient male can distribute the genetic material of the germ cell donor. Germ cell transplantation represents a functional reconstitution assay for male germ line stem cells and as such has vastly increased our ability to study the biology of stem cells in the testis and define phenotypes of infertility. First developed in rodents, the technique has now been used in a number of animal species, including domestic mammals, chicken and fish. There are three major applications for this technology in animals: first, to study fundamental aspects of male germ line stem cell biology and male fertility; second, to preserve the reproductive potential of genetically valuable individuals by male germ cell transplantation within or between species; third, to produce transgenic sperm by genetic manipulation of isolated germ line stem cells and subsequent transplantation. Transgenesis through the male germ line has tremendous potential in species in which embryonic stem cells are not available and somatic cell nuclear transfer has limited success. Therefore, transplantation of male germ cells is a uniquely valuable approach for the study, preservation and manipulation of male fertility in animals.

288 THE EXPRESSION PATTERN OF ACETYLATED ALPHA-TUBULIN IS CONSERVED IN PORCINE AND MURINE SPERMATOGONIAL STEM CELLS

During mammalian spermatogenesis, spermatogonial stem cells (SSCs) reside in the stem cell niche on the basement membrane where they undergo self-renewing divisions. Differentiating daughter cells are located progressively more toward the tubular lumen where they ultimately form spermatozoa. The mechanisms responsible for maintenance of SSCs at the basement membrane are unclear. Microtubules consisting of α/β-tubulin heterodimers are associated with many cellular functions. Reversible acetylation of α-tubulin at Lys40 has been implicated in regulating microtubule stability and function. Acetylation of α-tubulin is abundant in stable microtubules but absent from dynamic cellular structures. Deacetylation of α-tubulin is controlled by histone deacetylase 6 which is predominantly expressed in mouse testis. Here, we tested the hypothesis that differential acetylation of α-tubulin might be involved in maintenance of SSCs. Immunohistochemistry for acetylated α-tubulin (Ac-α-Tu) and the spermatogonia specific proteins PGP 9.5, DAZL, and PLZF were used to characterize the expression pattern of Ac-α-Tu in porcine and murine germ cells at different stages of testis development. In immature boar testes, Ac-α-Tu was present exclusively in gonocytes but not in other testicular cells at 1 week of age, and in a subset of spermatogonia at 10 weeks of age. At this age, spermatogonia are migrating to the basement membrane of the seminiferous tubules, and Ac-α-Tu appeared to be polarized toward the basement membrane. In immature mouse testes, Ac-α-Tu was present in germ cells and Sertoli cells at 6 days of age, whereas at 2 weeks of age, Ac-α-Tu expression was stronger in spermatogonia co-expressing PGP 9.5 and in spermatocytes than in Sertoli cells or PGP 9.5-negative spermatogonia. In adult boar and mouse testes, Ac-α-Tu was detected in a few single or paired spermatogonia expressing PGP 9.5 localized on the basement membrane as well as in spermatocytes, spermatids, and spermatozoa. Spermatogonia with high levels of Ac-α-Tu expressed PLZF but did not express DAZL, suggesting that only undifferentiated spermatogonia maintain a high level of Ac-α-Tu. When seminiferous tubules from 1-week-old and adult boar testes were maintained in vitro for 1–2 days, high levels of Ac-α-Tu were detected in single or paired round spermatogonia with a large nucleus, compared to low levels in elongated paired and aligned spermatogonia. The unique expression pattern of Ac-α-Tu in undifferentiated germ cells during postnatal development appears to be conserved in mammalian testes. Since Ac-α-Tu is a component of long-lived stable microtubules and reducing acetylation of α-tubulin enhances cell motility, these results suggest that stabilization of microtubules might contribute to the maintenance of spermatogonial stem cells. This work was supported by 1R01 RR 17359-05.

Germ cell transplantation for the propagation of companion animals, non-domestic and endangered species

The transplantation of spermatogonial stem cells between males results in a recipient animal producing spermatozoa carrying a donor's haplotype. First pioneered in rodents, this technique has now been used in several animal species. Importantly, germ cell transplantation was successful between unrelated, immuno-competent large animals, whereas efficient donor-derived spermatogenesis in rodents requires syngeneic or immuno-compromised recipients. Transplantation requires four steps: recipient preparation, donor cell isolation, transplantation and identifying donor-derived spermatozoa. There are two main applications for this technology. First, genetic manipulation of isolated germ line stem cells and subsequent transplantation will result in production of transgenic spermatozoa. Transgenesis through the male germ line has tremendous potential in species in which embryonic stem cells are not available and somatic cell nuclear transfer and reprogramming pose several problems. Second, spermatogonial stem cell transplantation within or between species offers a means of preserving the reproductive potential of genetically valuable individuals. This might have significance in the captive propagation of non-domestic animals of high conservation value. Transplantation of germ cells is a uniquely valuable approach for the study, preservation and manipulation of male fertility in mammalian species.

Determination of acrosin amidase activity in equine spermatozoa

Acrosin amidase activity of spermatozoa has been been associated with in vitro fertilization success in humans and has been proposed as an additional method for assessing sperm function in vitro. In this study, acrosin amidase activity was determined in equine spermatozoa by the hydrolysis of an arginine amide substrate. This assay includes a detergent to release acrosomal enzymes into a medium of basic pH to activate proacrosin to acrosin, which subsequently hydrolyses N-alpha-benzoyl-DL-arginine para-nitroanilide-HCl (BAPNA) to a chromogenic product. Spermatozoa (n = 3 ejaculates from each of 4 stallions) were washed free from seminal plasma by centrifugation through Ficoll and incubated with a detergent-substrate mixture (BAPNA in triton X-100; pH = 8.0) at room temperature for 3 h in the dark. At the end of the 3-h incubation, benzamidine was added to test samples to stop the reaction, and samples were centrifuged to remove spermatozoa. Absorbance at 410 nm was measured to determine acrosin amidase activity (microIU acrosin/10(6) sperm). Acrosin amidase activity increased with sperm concentration (P < 0.001; r(2) = 0.75), and there were significant effects (P < 0.001) of stallion and ejaculate within stallion on acrosin activity. Acrosin activity detectable in equine seminal plasma was 312 +/- 49 microU/ml (n = 3 ejaculates). Addition of a cryopreservation medium containing egg yolk, skim-milk, glycerol and sucrose to equine spermatozoa and subsequent cryopreservation significantly (P < 0.05) increased acrosin amidase activity compared with spermatozoa from raw semen. This result is in contrast to that previously reported for frozen-thawed human spermatozoa. Determination of acrosin amidase activity in equine spermatozoa may provide an alternative method for assessing sperm function in vitro; however, further studies are needed to determine the relationship between acrosin activity and fertility in the horse.

1 XENOGRAFTING OF ADULT MAMMALIAN TESTIS TISSUE

Testis tissue grafting presents an option for preservation of genetic material when sperm recovery is not possible. Grafting of testis tissue from sexually immature males to immunodeficient mice results in germ cell differentiation and production of fertilization-competent sperm from different mammalian species (Honaramooz et al. 2002 Nature 418, 778–781). However, the efficiency of testis tissue xenografting from adult donors has not been critically evaluated. Spermatogenesis was arrested at meiosis in grafts from mature horses (Rathi et al. 2006 Reproduction 131, 1091–1098) and hamsters (Schlatt et al. 2002 Reproduction 124, 339–346), and no germ cell differentiation occurred in xenografts of adult human testis tissue (Schlatt et al. 2006 Hum. Reprod. 21, 384–389). The objective of this study was to investigate survival and germ cell differentiation of testis xenografts from sexually mature donors of different species. Small fragments of testis tissue from 10 donor animals of 5 species were grafted under the back skin of immunodeficient, castrated male mice (n = 37, 2–6/donor). Donors were pig (8 months old), goat (18 months old and 4 years old) (n = 2), bull (3 years old), donkey (13 months old), and rhesus monkey (3, 6, 11, and 12 years old). At the time of grafting, donor tissue contained elongated spermatids, albeit to different degrees (&gt;75% of seminiferous tubules in testis tissue from pig, goat, bull, and 6–12-year-old monkeys, and 33 or 66% of tubules in tissue from donkey or 3-year-old monkey, respectively). Grafts were recovered &lt;12 weeks (n = 14 mice), 12–24 weeks (n = 16 mice), and &gt;24 weeks (n = 7 mice) after grafting and classified histologically as completely degenerated (no tubules found), degenerated tubules (only hyalinized seminiferous tubules observed), or according to the most advanced type of germ cell present. Grafts from pig, goat, bull, and 6–12-year-old monkeys contained &gt;60% degenerated tubules or were completely degenerated at all time points analyzed. In contrast, in grafts from the 3-year-old monkey, only 18% of tubules were degenerated, 14% contained Sertoli cells only, 64% contained meiotic, and 4% haploid germ cells at 24 weeks after grafting. Similarly, donkey testis grafts recovered 12–24 weeks after grafting contained &lt;2% degenerated tubules, 46% of tubules had Sertoli cells only, 45% contained meiotic, and 7% haploid germ cells. These results show that survival and differentiation of germ cells in testis grafts from sexually mature mammalian donors is poor. However, better graft survival and maintenance of spermatogenesis occurred in donor tissue from donkey and 3-year-old monkey that were less mature at the time of grafting. Therefore, species and age-related differences appear to exist with regard to germ cell survival and differentiation in xenografts from adult donors. This work was supported by USDA/CSREES 03-35203-13486, NIH/NCRR 5-R01-RR17359-05, the Spanish Ministry of Education, and Science (BES-2004-4112).

Transplantation of germ line stem cells for the study and manipulation of spermatogenesis

Transplantation of male germ line stem cells from a fertile donor to the testis of an infertile recipient restores donor-derived spermatogenesis in the recipient testis and the resulting sperm pass the donor genotype to the offspring of the recipient. Germ cell transplantation has been an invaluable tool to elucidate the biology of male germ line stem cells and their niche in the testis, develop systems to isolate and culture spermatogonial stem cells, examine defects in spermatogenesis, correct male infertility and introduce genetic changes into the male germ line. Although most widely studied in rodents, germ cell transplantation has been applied to larger mammals, including primates. Recently, ectopic grafting of testis tissue from diverse donor species, including primates, into a mouse host has opened an additional possibility to study spermatogenesis and to produce fertile sperm from immature donors. Testis xenografts are ideally suitable to study toxicants or drugs with the potential to enhance or suppress male fertility without the necessity of performing experiments in the target species. Therefore, transplantation of germ cells or xenografting of testis tissue represent powerful approaches for the study, preservation, and manipulation of male fertility.

Germ cell development in equine testis tissue xenografted into mice

Grafting of testis tissue from immature animals to immunodeficient mice results in complete spermatogenesis, albeit with varying efficiency in different species. The objectives of this study were to investigate if grafting of horse testis tissue would result in spermatogenesis, and to assess the effect of exogenous gonadotropins on xenograft development. Small fragments of testis tissue from 7 colts (2 week to 4 years of age) were grafted under the back skin of castrated male immunodeficient mice. For 2 donor animals, half of the mice were treated with gonadotropins. Xenografts were analyzed at 4 and 8 months post-transplantation. Spermatogenic differentiation following grafting ranged from no differentiation to progression through meiosis with appearance of haploid cells. Administration of exogenous gonadotropins appeared to support post-meiotic differentiation. For more mature donor testis samples where spermatogenesis had progressed into or through meiosis, after grafting an initial loss of differentiated germ cells was observed followed by a resurgence of spermatogenesis. However, if haploid cells had been present prior to grafting, spermatogenesis did not progress beyond meiotic division. In all host mice with spermatogenic differentiation in grafts, increased weight of the seminal vesicles compared to castrated mice showed that xenografts were releasing testosterone. These results indicate that horse spermatogenesis occurs in a mouse host albeit with low efficiency. In most cases, spermatogenesis arrested at meiosis. The underlying mechanisms of this spermatogenic arrest require further investigation.

Male germ cell transplantation in livestock

Male germ cell transplantation is a powerful approach to study the control of spermatogenesis with the ultimate goal to enhance or suppress male fertility. In livestock animals, applications can be expanded to provide an alternative method of transgenesis and an alternative means of artificial insemination (AI). The transplantation technique uses testis stem cells, harvested from the donor animal. These donor stem cells are injected into seminiferous tubules, migrate from the lumen to relocate to the basement membrane and, amazingly, they can retain the capability to produce donor sperm in their new host. Adaptation of the mouse technique for livestock is progressing, with gradual gains in efficiency. Germ cell transfer in goats has produced offspring, but not yet in cattle and pigs. In goats and pigs, the applications of germ cell transplantation are mainly in facilitating transgenic animal production. In cattle, successful male germ cell transfer could create an alternative to AI in areas where it is impractical. Large-scale culture of testis stem cells would enhance the use of elite bulls by providing a renewable source of stem cells for transfer. Although still in a developmental state, germ cell transplantation is an emerging technology with the potential to create new opportunities in livestock production.

93 CALCIUM REMOVAL INCREASES THE PROTECTIVE EFFECTS OF β-CYCLODEXTRIN PLUS CHOLESTEROL ON PORCINE SPERM DURING COLD SHOCK

Porcine sperm are extremely sensitive to the damaging effects of cold shock and cryopreservation. Cholesterol-binding molecules, such as 2-hydroxypropyl-�-cyclodextrin (HBCD), improve post-thaw and post-cooling porcine sperm viability when added to an egg yolk-based extender, but also enhance sperm capacitation in other species. Depending upon the environmental cholesterol content, HBCD can act either as a cholesterol shuttle or sink to increase or decrease, respectively, sperm plasma membrane cholesterol content. Increasing the sperm cholesterol to phospholipid ratio reduces cold shock sensitivity whereas decreasing the ratio initiates the process of sperm capacitation. An increase in protein tyrosine phosphorylation correlates with sperm capacitation and has been shown to be dependent upon the presence of extracellular calcium. Sperm intracellular calcium also increases during cold shock. The objective of this study was to determine the combined effects of extracellular calcium and membrane cholesterol manipulation on porcine sperm viability and protein tyrosine phosphorylation following cold shock (10�C for 10 min). Viability was assessed using CFDA/propidium iodide staining. Protein tyrosine phosphorylation, previously shown to correlate with porcine sperm capacitation, was evaluated via antiphosphotyrosine (clone 4G10) immunoblots. We report here that following cold shock, porcine sperm incubated in defined medium containing both 0.8 mM HBCD and 0.5 mM cholesterol 3-sulfate (ChS) incubated in the absence of added extracellular calcium and the presence of 6 mM EGTA have significantly improved viability (90.5 � 6.3%, n = 3) when compared with cold-shocked sperm incubated in either the same medium with calcium (46.1 � 3.8%), without HBCD or ChS (26.5 � 7.4% with calcium; 46.5 � 13.1% without calcium), or with HBCD alone (17.0 � 7.4% with calcium, 36.8 � 7.5% without calcium). As we have found previously, treatment with 0.8 mM HBCD plus 0.5 mM ChS completely inhibited the increase in protein tyrosine phosphorylation induced by the cold shock treatment. Although protein tyrosine phosphorylation correlates with porcine sperm capacitation, the ability of cold shock treatment to induce the same phosphorylation pattern indicates that other processes or pathways may contribute to its appearance. Removing extracellular calcium consistently decreased, but did not completely eliminate, the protein tyrosine phosphorylation induced by cold shock. These results indicate that cold shock-induced protein tyrosine phosphorylation is not dependent upon, but can be modulated by, extracellular calcium. The combined effects of calcium, HBCD and ChS on viability suggest that porcine sperm viability following cold shock is best maintained by removing extracellular calcium and increasing membrane cholesterol content via the cholesterol shuttle activity of HBCD. This work was supported by grants from PA Dept. Ag. (ME 443291) and the NIH (5-K08-HD041430).

371 EVALUATION OF ENRICHMENT STRATEGIES FOR PORCINE SPERMATOGONIA BY EXPRESSION OF PROTEIN GENE PRODUCT 9.5, A SPERMATOGONIA-SPECIFIC MARKER IN THE PIG TESTIS

Transplantation of genetically altered male germ cells is under investigation as a novel route to generate transgenic animal models. Identification and isolation of spermatogonial stem cells are a prerequisite for this strategy. The objectives of this study were to validate a marker for identification of undifferentiated porcine spermatogonia, and to use this marker to develop a practical enrichment strategy for spermatogonia from pig testis. We established that expression of protein gene product (PGP) 9.5 is a spermatogonia-specific marker in porcine testis through analysis of its expression pattern in testis cells, by comparison with the expression of the cell-type specific proteins GATA-4 (expressed in Sertoli cells) or PLZF (expressed in undifferentiated mouse spermatogonia) in seminiferous tubules at different ages, and by comparison of expression levels of PGP 9.5 and the germ cell-specific protein VASA in different cell fractions after differential plating. Using expression of PGP 9.5 as a marker, we characterized enrichment of porcine spermatogonia from two-week-old (2wo) and 10-week-old (10wo) pigs by immunofluorescence either after differential plating only or after velocity sedimentation at unit gravity followed by differential plating. After differential plating with overnight culture to deplete testicular somatic cells that firmly attach to culture dishes, spermatogonia (mean � SEM per 1000 cells) were 5-fold enriched (P < 0.05) in cells remaining in suspension (fraction I) (2wo: 54.0 � 9.1; 10wo: 162.7 � 30.5) and in populations slightly attached to the culture plate (fraction II) (2wo: 92.7 � 8; 10wo: 159.5 � 22.5) compared to the initial samples (2wo: 12.3 � 2.7; 10wo: 27.2 � 2.9). Slightly attached spermatogonia appear to be superior for future experiments due to higher viability (>90%) than spermatogonia remaining in suspension (<50%). Cell populations containing up to 70% spermatogonia with good viability (>80%) were achieved by velocity sedimentation isolation followed by differential plating. These results indicate that expression of PGP 9.5 is a useful marker for identification of undifferentiated porcine germ cells. Simple differential adhesion culture of testis cells harvested from pre-pubertal boars can supply cell populations enriched in spermatogonia for subsequent genetic manipulation and transplantation. This work was supported by 1 R01 RR17359-01.

197 PRODUCTION OF IN VITRO- AND IN VIVO-DERIVED CAT BLASTOCYSTS FOR THE ESTABLISHMENT OF FELINE EMBRYONIC STEM CELLS

Identification and characterization of spontaneously occurring genetic diseases in cats has permitted the development of valuable models for testing potential treatments of similar human diseases. With the near completion of the feline genome project, establishment of pluripotential feline embryonic stem (ES) cells would facilitate the targeting of specific genetic loci to produce new feline medical models. Two approaches were used to produce feline blastocysts in an attempt to establish feline ES cells in culture. Naive queens were superovulated with an intramuscular (i.m.) injection of 150 IU of equine chorionic gonadotropin (eCG) followed by an i.m. injection of 100 IU of human chorionic gonadotropin (hCG) 80 h later; follicles were aspirated laparoscopically 24-26 h later for subsequent in vitro fertilization (IVF). On average, 29 mature cumulus oocyte cell complexes (COCs) were recovered from each queen. IVF was performed in 50 microliter drops of complete Hams F-10 medium containing 30 000 fresh, motile sperm. COCs were cultured overnight in 5% carbon dioxide at 38�C, and residual adherent cumulus cells were removed 12 to 16 h later by trituration in 0.1% hyaluronidase. Embryos were cultured in fresh drops of Hams F-10, and on average 25% developed to the early blastocyst stage after 7 days. Alternatively, estrus was induced in queens with a single i.m. injection of 100 IU of eCG, and then 72 h later queens were permitted six supervised matings with a fertile tom over the next two days. Queens underwent ovariohysterectomy 7 days after their first copulation, and compacted morulae and early blastocysts were flushed from the oviducts and uterine horns. On average, eight embryos were recovered from the reproductive tract of each queen. Both in vivo- and in vitro-matured blastocysts were subsequently cultured in standard mouse ES cell medium on inactivated mouse embryonic fibroblasts. When they failed to hatch in culture after 3 days, a 0.5% pronase solution was used to dissolve the zonae pellucidae under microscopic visualization. Denuded expanded blastocysts adhered to the heterotypic feeder layer and primary inner cell mass (ICM) outgrowths formed within 4 days. Outgrowths were mechanically disaggregated into small clusters of 15 to 20 cells and re-plated on fresh feeders. These colonies grew slowly and were transferred after one week onto new feeder layers. The addition of murine or human recombinant leukemia inhibitory factor had no effect on the survival and proliferation of primary outgrowths or subsequent colonies. After 3 weeks, all colonies derived from both in vivo- and in vitro-matured blastocysts had either differentiated or died. Additional experiments are ongoing to test the effects of homotypic feeder layers and alternative growth factors on promoting the establishment and survival of feline ES cell lines. Ultimately, germline transmission of any putative feline ES cell lines will need to be demonstrated in vivo for their utility in gene targeting experiments to be realized.

Germ cell transplantation in pigs--advances and applications

Transplantation of germ cells from fertile donor mice to the testes of infertile recipient mice results in donor-derived spermatogenesis and transmission of the donor haplotype to offspring of recipient animals. In the pig, germ cells can be transplanted to a recipient testis by ultrasound-guided cannulation of the rete testis with delivery of cells by gravity flow. It is important to note that germ cell transplantation was successful between unrelated, immuno-competent pigs, whereas transplantation in rodents requires syngeneic or immuno-compromised recipients. Efficiency of colonization of the recipient testis by donor-derived germ cells can be improved by pretreatment of the recipient animal to deplete endogenous germ cells. Genetic manipulation of isolated germ line stem cells and subsequent transplantation will result in production of transgenic sperm. Transgenesis through the male germ line has tremendous potential in species like pigs where embryonic stem cell technology is not available and current options to generate transgenic animals are inefficient. Introduction of a genetic change prior to fertilization will circumvent problems associated with manipulation of early embryos and developmental abnormalities associated with somatic cell nuclear transfer and reprogramming. Viral transduction of germ cells prior to transplantation has been used to generate transgenic rodents and has also shown early promising results in pigs. Current research is directed toward improving protocols for isolation and culture of porcine male germ cells to increase efficiency of transgene transmission and to allow for gene targeting prior to germ cell transplantation. It is expected that germ cell transplantation will then provide a viable alternate approach to generate germ line transgenic pigs.

309 THE SPERMATOGENIC CYCLE IN MAMMALIAN TESTIS XENOGRAFTS

Grafting of immature testis tissue from different mammalian donor species into mouse hosts results in production of spermatozoa from the donor species. Xenografting of testis tissue from rhesus monkeys, pigs, and sheep accelerates sperm production. To determine whether this shortened time to sperm production is due to the reduced spermatogenic cycle length, we applied bromodeoxyuridine (BrdU) incorporation to analyze the spermatogenic cycle in porcine and ovine testis xenografts. Testes from 1-2-week-old Yorkshire cross pigs and 1-week-old Suffolk sheep were cut into small fragments (approximately 1 � 1 � 2 mm) and eight fragments were grafted under the back skin of each castrated male immunodeficient NCR nude recipient mouse (n = 7 for pig, n = 5 for sheep). Mice were given BrdU (100 mg/kg i.p.) at 7 months (porcine tissue) or 6 months (ovine tissue) post-transplantation. Mice carrying porcine tissue were sacrificed 1 h, 9 days or 18 days after BrdU injection. Mice with ovine testicular tissue were sacrificed 1 h, 11 days or 22 days after BrdU injection. Analysis time points were chosen based on the reported length of the spermatogenic cycle in pigs and sheep (approximately 9 days and 11 days, respectively). All eight stages of the spermatogenic cycle were analyzed to identify the most advanced germ cells labeled in each time period after BrdU injection. All seminiferous tubules containing full spermatogenesis were analyzed. Histologically, 51.8% (range 7 to 98%, n = 2040 tubules) of seminiferous tubules from porcine grafts, and 64.4% (range 2 to 92%, n = 2903 tubules) of seminiferous tubules from ovine grafts presented complete spermatogenesis. In porcine grafts, the most advanced germ cells labeled 1 h after BrdU injection were primary spermatocytes in pre-leptotene/leptotene at stage I of the spermatogenic cycle. At 9 days and 18 days after injection, the most advanced labeled germ cells were primary spermatocytes at pachytene at stage I and elongating spermatids at late stage II, respectively. In ovine grafts, the most advanced labeled germ cells at 1 h, 11 days and 22 days were pre-leptotene/leptotene at stage II, primary spermatocytes at the pachytene at stage I and elongating spermatids at stage II, respectively. These results indicate that each spermatogenic cycle in porcine and ovine testis xenografts lasts around 9 days and 11 days, respectively. Therefore, the length of the spermatogenic cycle is conserved in porcine and ovine testis xenografts and shortened time to sperm production is likely due to accelerated maturation of the testicular somatic components, such as Sertoli cells. This work was supported by NIH R01 RR17359-01.

Limited survival of adult human testicular tissue as ectopic xenograft

BACKGROUND

Grafting of testicular tissue into immunodeficient mice has become an interesting and promising scientific tool for the generation of gametes and the study of testicular function. This technique might potentially be used to generate sperm from patients whose testes need to be removed or are destroyed due to therapeutic intervention or as a consequence of disease. Here we explore whether adult human testicular tissue from patients with different testicular pathologies survives as xenograft.

METHODS AND RESULTS

Testis tissue from adult patients with varying degrees of spermatogenesis was grafted into two strains of immunodeficient mice (severe combined immunodeficiency, Nu/Nu). Tissue with active spermatogenesis prior to grafting largely regressed. However, testicular tissue survival was better in cases where spermatogenesis was suppressed prior to grafting and occasionally spermatogonial stem cells survived. Cases with spermatogenic disruption were not corrected by the xenografting.

CONCLUSION

Superior survival of the germinal epithelium and spermatogonia when spermatogenesis was suppressed prior to grafting could provide a novel strategy for germline preservation in pre-pubertal cancer patients. This approach could also be valuable to study the early stages of human spermatogenesis.

267 TESTIS TISSUE XENOGRAFTING AS A BIOASSAY FOR GERM CELL DEVELOPMENTAL POTENTIAL IN EQUINE CRYPTORCHID TESTES

In domestic animals, spermatogenic differentiation is blocked in abdominally retained testes exposed to core body temperature. It is not known if undifferentiated germ cells are retained in long-term cryptorchid equine testes, nor is it known whether any surviving germ cells retain their ability to progress through spermatogenesis. If functional germ cells do persist in equine abdominal testes, then the possibility exists that offspring could be derived even from bilaterally cryptorchid individuals. Previously, we reported an in vivo model where completion of spermatogenesis with production of spermatozoa capable of fertilization occurred in fragments of testicular tissue from immature mice, domestic animals, and monkeys grafted under the skin of immunodeficient mice. Therefore, spermatogenic development in testis tissue xenografts can serve as an in vivo assay system for the developmental potential of germ cells. The objective of this study was to investigate if cryptorchid horse testes that had been exposed to core body temperature for 1–3 years had retained developmentally competent germ cells. Small fragments of abdominally cryptorchid testis tissue (about 1 mm3) from three donor horses (1-, 2-, and 3-year-old Quarterhorse) were grafted under the back skin of castrated male immunodeficient mice (n = 8, 6, and 3 recipient mice, respectively). At the time of grafting, donor tissue did not contain differentiated germ cells. Histological examination of the testis xenografts was performed between 5 and 45 weeks post-transplantation. Weight of the seminal vesicles in the host mouse was recorded as an indicator of bioactive testosterone produced by the xenografts. By 28 weeks after grafting, pachytene spermatocytes were observed in xenografts from all cryptorchid donor testes. While haploid gametes would be expected to be present in xenografted testis tissue from descended equine testes by 35 weeks after grafting, spermatogenesis did not progress through meiosis in the cryptorchid grafts. In all recipient animals where spermatogenic differentiation occurred, the weight of the seminal vesicles in the castrated host mice was restored to pre-castration values, indicating that xenografts were capable of releasing biologically active testosterone. These results indicate that even after 3 years of exposure to core body temperature, equine cryptorchid testes contain germ cells capable of differentiation. It remains to be investigated if supplementation of exogenous gonadotropins might support post-meiotic differentiation of germ cells in cryptorchid equine testes xenografts. This work was supported by USDA 03-35203-13486.

107 INITIAL RESULTS FROM MALE GERM CELL TRANSFER BETWEEN CATTLE BREEDS

Male germline cell transfer has produced offspring in mice (Brinster & Zimmerman 1994 PNAS 91, 11 298–11 302). Recently the first livestock animal, a goat, was produced (Honaramooz et al. 2003 Mol. Reprod. Dev. 64 422–64 428.), and early results in cattle are promising (Izadyar et al. 2003 Reproduction 126, 765–774; Oatley et al. 2002 J. Anim. Sci. 80, 1925–1931). We have assessed the outcome of male germ cell transfer between breeds of cattle and the efficacy of two vital dyes as markers of donor cells following transfer. Testis cells from three Bos taurus (Angus) bull calves were used as donor cells to transfer into six Bos indicus cross (predominantly Brahman bloodline) bull calves. Each of the calves was prepubertal and aged between 5 and 7 months. The calves were castrated; then a single-cell suspension of testis cells was prepared enzymatically using collagenase, DNAase, and trypsin. Prior to transfer into the recipient calves, the testis cell suspensions were dyed with one of two long-term vital dyes (PKH26 or CFDA). Approximately 300 million cells were injected into the rete of each testis under ultrasonographic guidance. In four of the six recipients, CFDA was injected into one testis and PKH26 into the other. These four recipients were castrated at 2, 4, 6, and 8 weeks after transfer. The other two recipients received either CFDA or PKH26 into both testes and were castrated at 8 weeks after transfer. Following castration, PKH positive donor cells were found in freshly isolated tubules of each of the five recipients that received PKH-dyed cells, while no CFDA-positive donor cells were conclusively identified in any of the recipients. In the freshly isolated tubules, clumps of PKH-positive donor cells were observed, which indicated either cell division or substantial local colonization of certain areas of the tubules. Frozen sections were used to further localize the PKH positive donor cells. Positive cells were located on the seminiferous tubule basement membrane, which indicates these cells had successfully migrated from the tubule lumen and were likely to be spermatogonia. There was variation in the amount of fluorescence for individual cells, which indicated either cell division or variable uptake of the stain during the staining procedure. We were disappointed to find no conclusive evidence of CFDA stained cells as we encountered high background fluorescence from the majority of testis cells. Although this fluorescence was quenched within 10 s, we were unable to find positive cells with any certainty. We have concluded that PKH26 was more suitable for labeling donor testis cells and that donor cells can be identified for at least 2 months following transfer. Each of the recipients that received PKH26 stained cells retained these cells in the tubule epithelium, which suggests that transfer between different animals, and indeed between breeds, can be achieved. Further studies will aim to demonstrate that donor cells are able to undergo spermatogenesis in the recipient animals.

268 GERM CELL DEVELOPMENT IN EQUINE TESTIS TISSUE XENOGRAFTED INTO MICE

Grafting of testis tissue from immature animals under the back skin of immunodeficient mice results in complete spermatogenesis, albeit with different levels of efficiency in different species. While spermatogenesis develops comparably to that in the donor species in xenografts from pigs, sheep and goats, spermatogenic differentiation is less efficient in testis tissue from cats and bulls. Testicular maturation was significantly accelerated in rhesus monkey testis grafts whereas timing was similar to that in the donor species in cats and bulls. The objective of this study was to investigate if grafting of immature horse testis tissue would result in spermatogenesis in a mouse host. Small fragments of testis tissue (about 1 mm3) from four sexually immature colts (2-week-old Standardbred, 5- and 8-month-old ponies, 10-month-old Warmblood) were grafted under the back skin of castrated male immunodeficient mice (n = 5, 5, 10 and 5 recipient mice, respectively). Histological examination of the testis xenografts was performed between 14 and 50 week post-transplantation. Weight of the seminal vesicles in the host mouse was recorded as an indicator of bioactive testosterone produced by the xenografts. At the time of grafting, the seminiferous cords of the donor testis tissue form 2-week-, 5-month- and 8-month-old colts contained only immature Sertoli cells and gonocytes. No spermatogenic differentiation occurred in xenografts from the 2-week-old colt and testosterone production was minimal. Pachytene spermatocytes were observed in testis grafts from the 5- and 8-month-old donors from 14 weeks onward. Spermatogenesis did not proceed through meiosis in grafts from the 5-month-old donor. Recipient mice carrying xenografts from the 8-month-old donor received exogenous gonadotropins (equine chorionic gonadotropin and human chorionic gonadotropin, 10 I.U./day for 2 months, beginning 14 weeks after grafting) and condensing spermatids were observed by 35 weeks after grafting. In donor tissue from the 10-month-old colt, pachytene spermatocytes were present in about 50% of tubules at the time of grafting. After 14 weeks, xenografts showed fewer differentiated germ cells than the donor tissue. However, at 35 weeks after grafting, condensing spermatids were observed, indicating that differentiated germ cells were initially lost and spermatogenesis was subsequently reinitiated. In all castrated host mice where spermatogenic differentiation occurred, the weight of the seminal vesicles was restored to pre-castration values showing that xenografts were releasing bioactive testosterone. These results indicate that horse spermatogenesis can occur in a mouse host albeit with low efficiency. Testicular maturation was not accelerated. In most cases, spermatogenesis appeared to become arrested at meiosis. The underlying mechanisms of this spermatogenic arrest require further investigation. Although equine testis xenografts produced testosterone, supplementation of exogenous gonadotropins might support post-meiotic differentiation. This work was supported by USDA 03-35203-13486.

193 TESTIS TISSUE XENOGRAFTING TO PRESERVE GERM CELLS FROM A CLONED BANTENG CALF

In April 2003, two banteng (Bos javonicus) calves were born after heterologous nuclear transfer of donor cells from a genetically valuable individual frozen in 1978. One of the cloned banteng calves died at one week of age. The calf was found to have one scrotal and one abdominally cryptorchid testis. In an attempt to preserve male germ cells from this valuable animal, parts of each testis were shipped on ice to the University of Pennsylvania for xenografting. Grafting of testis tissue from immature domestic animals and monkeys under the back skin of immunodeficient mice can result in complete spermatogenesis, albeit with different levels of efficiency in different species. The objective of this experiment was to investigate if grafting of immature banteng testis tissue would result in spermatogenesis in a mouse host. Small fragments of tissue (about 1 mm, 3 each) from both testes were grafted under the back skin (4 pieces of scrotal testis on the right side and 4 pieces of retained testis on the left side) of 6 castrated male immunodeficient mice. Histological examination of the testis xenografts was performed 3, 6, 9, 12, and 15 months after transplantation. Weight of the seminal vesicles in the host mouse was recorded as an indicator of bioactive testosterone produced by the xenografts. At the time of grafting, both testes contained seminiferous cords with immature Sertoli cells and gonocytes. At 3, 6, and 9 months after grafting, pachytene spermatocytes were present in the xenografts of the scrotal testis whereas no germ cell differentiation was observed in grafts from the retained testis. However, spermatogenesis in grafts of the scrotal testis did not proceed further through meiosis in grafts analyzed at 12 and 15 months after grafting, with pachytene spermatocytes still the most advanced germ cell type present in grafts recovered 15 months after grafting. The weight of the seminal vesicles in the castrated host mice was restored to pre-castration values showing that xenografts were releasing bioactive testosterone. These results indicate that banteng spermatogenesis was initiated in the mouse host but became arrested at meiosis as observed previously in xenografts of immature bovine or equine testis. Therefore, haploid germ cells could not be recovered. This represents the first example of trying to preserve fertility from a rare, valuable newborn animal by testis tissue xenografting. While xenografting presents a previously unavailable option for preservation of male germ cells from immature individuals, the efficiency of sperm production in testis xenografts appears to be variable and has to be determined empirically for different donor species. This work was supported by USDA 03-35203-13486.

205A GAME OF CAT AND MOUSE: XENOGRAFTING OF TESTIS TISSUE FROM DOMESTIC KITTENS RESULTS IN COMPLETE CAT SPERMATOGENESIS IN A MOUSE HOST

Loss of genetic diversity due to infertility or the premature death of valuable individuals is a significant problem in the conservation of rare and endangered felid species, as well as in the maintenance of lines of cats used to study inherited feline and human disease. Attempts to overcome loss of genetic diversity have focused on freezing sperm;; however, sperm cannot be collected from immature males. Previously, we reported completion of spermatogenesis in testis tissue from newborn pigs and goats grafted ectopically into host mice (Honaramooz A et al., 2002 Nature 418, 778–781). Xenografting of testis tissue not only serves as a powerful system for the study of spermatogenesis and testicular maturation, but it also provides a previously unavailable system to obtain sperm from immature animals. The objective of the present study was to extend the technique of testis tissue xenografting to the domestic cat as a model animal for felid species. Testes from 1- to 5-wk-old domestic short-haired kittens (n=8) were cut into small fragments (about 1×3mm each), and up to eight fragments were grafted under the back skin of each castrated immunodeficient host mouse (n=12). Histological examination of the testis xenografts was performed between 14 and 36 weeks post-transplantation. From 8 of the 12 recipient mice, 93% of testis tissue grafts were recovered. No grafts were recovered from the remaining 4 mice. At the time of grafting, the seminiferous cords of the donor testis tissue contained only immature Sertoli cells and gonocytes. At 14 weeks after grafting, tubular expansion was evident, caused by the proliferation of Sertoli cells and tubular lumen formation. By 18 weeks after transplantation, the seminiferous epithelium contained spermatocytes, and by 20 weeks, round spermatids were the most advanced types of germ cells. By 36 weeks after transplantation, xenografts of cat testis tissue had completed spermatogenesis and mature sperm were present. In all recipient animals where xenografts were recovered, the weight of the seminal vesicles in the castrated host mice was restored to pre-castration values, indicating that xenografts were capable of releasing biologically active testosterone. These results demonstrate the potential of xenografting to achieve full spermatogenesis in testis tissue from kittens without the necessity of exogenous hormonal stimulation. It was shown previously that sperm recovered from testis xenografts can support fertilization and development (Shinohara T et al., 2002 Hum. Reprod. 17, 3039–3045; Schlatt S et al., 2003 Biol. Reprod. 68, 2331–2335). Therefore, sperm production in a mouse host can provide an alternative for germ line preservation from immature felids where sperm cryopreservation is not an option. Sperm recovered from xenografts can be used for assisted reproduction, thereby making it possible to produce offspring from immature males.

Effect of the GnRH-agonist leuprolide on colonization of recipient testes by donor spermatogonial stem cells after transplantation in mice

Gonadotropin-releasing hormone (GnRH)-agonist or antagonist treatment supports recovery of spermatogenesis after irradiation damage in the rat and appears to be beneficial to colonization of recipient testes after spermatogonial transplantation from fertile donors to the testes of infertile recipients in rats and mice. In the present study, we quantified the effect of treatment of recipient mice with the GnRH-agonist leuprolide acetate on the extent of colonization by donor spermatogonial stem cells in the recipient testis. Testis cells from mice carrying transgenes, which produce beta-galactosidase in spermatogenic cells, were used as donor cells for transplantation to allow for quantification of donor spermatogenesis in the recipient testis by staining for enzyme activity. Donor cell colonization 3 months after transplantation was compared between recipients receiving leuprolide in different treatment protocols and untreated control mice. Two injections of leuprolide 4 weeks apart prior to transplantation with as little as 3.8 mg/kg resulted in a pronounced improvement in the number of donor-derived spermatogenic colonies as well as in the in the area of recipient seminiferous tubules occupied by donor cell spermatogenesis. Improved colonization efficiency by treatment with GnRH-agonist can make the technique of spermatogonial transplantation applicable to situations when only low numbers of donor cells are available.

Germ cell transplantation from large domestic animals into mouse testes

Donor-derived spermatogenesis after spermatogonial transplantation to recipient animals could serve as a novel approach to manipulate the male germ line in species where current methods of genetic modification are still inefficient. The objective of the present study was to investigate germ cell transplantation from boars, bulls, and stallions, which are economically important domestic animals, to mouse recipients. Donor testis cells (fresh, cryopreserved, or cultured for 1 month) were transplanted into testes of immunodeficient recipient mice in which endogenous spermatogenesis had been destroyed. Recipient testes were analyzed from 1 to > 12 months after transplantation for the presence of donor germ cells by donor-specific immunohistochemistry. Donor cells were present in most recipient testes with species-dependent differences in pattern and extent of colonization. Porcine donor germ cells formed chains and networks of round cells connected by intercellular bridges but later stages of donor-derived spermatogenesis were not observed. Transplanted bovine testis cells initially appeared similar but then developed predominantly into fibrous tissue within recipient seminiferous tubules. Few equine germ cells proliferated in mouse testes with no obvious difference between cells recovered from a scrotal or a cryptorchid donor testis. The pattern of colonization after transplantation of cultured cells did not resemble spermatogonial proliferation. These results indicate that fresh or cryopreserved germ cells from large animals can colonize the mouse testis but do not differentiate beyond the stage of spermatogonial expansion. Species-specific differences in the compatibility of large animal donors and mouse recipients were detected which cannot be predicted solely on the basis of phylogenetic distance between donor and recipient species.

Transplantation of male germ line stem cells restores fertility in infertile mice

Azoospermia or oligozoospermia due to disruption of spermatogenesis are common causes of human male infertility. We used the technique of spermatogonial transplantation in two infertile mouse strains, Steel (Sl) and dominant white spotting (W), to determine if stem cells from an infertile male were capable of generating spermatogenesis. Transplantation of germ cells from infertile Sl/Sld mutant male mice to infertile W/Wv or Wv/W54 mutant male mice restored fertility to the recipient mice. Thus, transplantation of spermatogonial stem cells from an infertile donor to a permissive testicular environment can restore fertility and result in progeny with the genetic makeup of the infertile donor male.

Transplantation of germ cells from rabbits and dogs into mouse testes

Spermatogonial stem cells of a fertile mouse transplanted into the seminiferous tubules of an infertile mouse can develop spermatogenesis and transmit the donor haplotype to progeny of the recipient mouse. When testis cells from rats or hamsters were transplanted to the testes of immunodeficient mice, complete rat or hamster spermatogenesis occurred in the recipient mouse testes, albeit with lower efficiency for the hamster. The objective of the present study was to investigate the effect of increasing phylogenetic distance between donor and recipient animals on the outcome of spermatogonial transplantation. Testis cells were collected from donor rabbits and dogs and transplanted into testes of immunodeficient recipient mice in which endogenous spermatogenesis had been destroyed. In separate experiments, rabbit or dog testis cells were frozen and stored in liquid nitrogen or cultured for 1 mo before transplantation to mice. Recipient testes were analyzed, using donor-specific polyclonal antibodies, from 1 to >12 mo after transplantation for the presence of donor germ cells. In addition, the presence of canine cells in recipient testes was demonstrated by polymerase chain reaction using primers specific for canine alpha-satellite DNA. Donor germ cells were present in the testes of all but one recipient. Donor germ cells predominantly formed chains and networks of round cells connected by intercellular bridges, but later stages of donor-derived spermatogenesis were not observed. The pattern of colonization after transplantation of cultured cells did not resemble spermatogonial proliferation. These results indicate that fresh and cryopreserved germ cells can colonize the mouse testis but do not differentiate beyond the stage of spermatogonial expansion.

Generation of an equine oviductal epithelial cell line for the study of sperm-oviduct interactions

Equine oviductal epithelial cells (OEC) were transformed with simian virus 40 large T antigen (SV 40 T-ag) to create a cell line for the study of the interaction of equine spermatozoa with oviductal epithelium. One cell line was established based on the expression of the SV 40 T-ag and extended lifespan in culture. Immortalized equine OEC retained the characteristics of differentiated OEC such as the formation of monolayers with characteristic epithelial morphology and cell polarization as well as expression of cytokeratin and equine major histocompatibility complex I. Monolayers of immortalized equine OEC retained their functional competence to bind equine spermatozoa in a dose-dependent manner comparable to that of primary equine OEC cultures. This immortalized cell line of equine OEC provides a uniform, readily available system for sperm-OEC co-cultures, and may be a useful model for the study of sperm-oviduct interactions in the horse.

Recipient preparation is critical for spermatogonial transplantation in the rat

Testis cell transplantation from mice or rats into recipient mouse seminiferous tubules results in donor cell-derived spermatogenesis in nearly all host testes. Normal spermatozoa are produced and, in the most successful mouse transplantations, the donor haplotype is transmitted to progeny of the recipient. However, few studies have been performed in other species. In this report, we demonstrate that rat and mouse testis cells will generate donor cell-derived spermatogenesis in recipient rat seminiferous tubules. Depletion of endogenous spermatogenesis before donor cell transplantation was more difficult in rat than reported for mouse recipients. A protocol employing treatment of neonatal rats with busulfan was most effective in preparing recipients and allowed more than 90% of testes to be colonized by donor cells. Transplantation of mouse testis cells into rat seminiferous tubules was most successful in recipients made cryptorchid and treated with busulfan. In the best experiments, about 55% of rat testes were colonized by mouse cells. Both rat and mouse donor cell-derived spermatogenesis were improved by treatment of rat recipients with leuprolide, a gonadotropin-releasing hormone agonist. The studies indicated that recipient preparation for spermatogonial stem cell transplantation was critical in the rat and differs from the mouse. However, modification of currently used techniques should allow male germ line stem cell transplantation in many species.

Computer assisted image analysis to assess colonization of recipient seminiferous tubules by spermatogonial stem cells from transgenic donor mice

Transplantation of spermatogonial stem cells from fertile, transgenic donor mice to the testes of infertile recipients provides a unique system to study the biology of spermatogonial stem cells. To facilitate the investigation of treatment effects on colonization efficiency an analysis system was needed to quantify colonization of recipient mouse seminiferous tubules by donor stem cell-derived spermatogenesis. In this study, a computer-assisted morphometry system was developed and validated to analyze large numbers of samples. Donor spermatogenesis in recipient testes is identified by blue staining of donor-derived spermatogenic cells expressing the E. coli lacZ structural gene. Images of seminiferous tubules from recipient testes collected three months after spermatogonial transplantation are captured, and stained seminiferous tubules containing donor-derived spermatogenesis are selected for measurement based on their color by color thresholding. Colonization is measured as number, area, and length of stained tubules. Interactive, operator-controlled color selection and sample preparation accounted for less than 10% variability for all collected parameters. Using this system, the relationship between number of transplanted cells and colonization efficiency was investigated. Transplantation of 10(4) cells per testis only rarely resulted in colonization, whereas after transplantation of 10(5) and 10(6) cells per testis the extent of donor-derived spermatogenesis was directly related to the number of transplanted donor cells. It appears that about 10% of transplanted spermatogonial stem cells result in colony formation in the recipient testis. The present study establishes a rapid, repeatable, semi-interactive morphometry system to investigate treatment effects on colonization efficiency after spermatogonial transplantation in the mouse.

Xenogeneic spermatogenesis following transplantation of hamster germ cells to mouse testes

It was recently demonstrated that rat spermatogenesis can occur in the seminiferous tubules of an immunodeficient recipient mouse after transplantation of testis cells from a donor rat. In the present study, hamster donor testis cells were transplanted to mice to determine whether xenogeneic spermatogenesis would result. The hamster diverged at least 16 million years ago from the mouse and produces spermatozoa that are larger than, and have a shape distinctly different from, those of the mouse. In four separate experiments with a total of 13 recipient mice, hamster spermatogenesis was identified in the testes of each mouse. Approximately 6% of the tubules examined demonstrated xenogeneic spermatogenesis. In addition, cryopreserved hamster testis cells generated spermatogenesis in recipients. However, abnormalities were noted in hamster spermatids and acrosomes in seminiferous tubules of recipient mice. Hamster spermatozoa were also found in the epididymis of recipient animals, but these spermatozoa generally lacked acrosomes, and heads and tails were separated. Thus, defects in spermiogenesis occur in hamster spermatogenesis in the mouse, which may reflect a limited ability of endogenous mouse Sertoli cells to support fully the larger and evolutionarily distant hamster germ cell. The generation of spermatogenesis from frozen hamster cells now adds this species to the mouse and rat, in which spermatogonial stem cells also can be cryopreserved. This finding has immediate application to valuable animals of many species, because the cells could be stored until suitable recipients are identified or culture techniques devised to expand the stem cell population.

Leuprolide, a gonadotropin-releasing hormone agonist, enhances colonization after spermatogonial transplantation into mouse testes

Spermatogonial stem cells can be transplanted from a fertile donor mouse to the testis of an infertile recipient where they establish spermatogenesis and produce spermatozoa. In the present study we investigated whether treatment of recipient mice with the gonadotropin-releasing hormone (GnRH) agonist leuprolide acetate could alter the efficiency of colonization by donor spermatogonial stem cells in the recipient testis. Six recipient mice were treated with busulfan to destroy endogenous spermatogenesis followed by injection of leuprolide acetate to three of the mice. Testis cells from mice carrying the ZFlacZ transgene, which produces beta-galactosidase in spermatids, were used as donor cells for transplantation to allow for identification of donor spermatogenesis in the recipient testis by staining for enzyme activity. The extent of donor cell colonization was compared between leuprolide treated recipients and untreated control mice 3 months after transplantation. Efficiency of colonization by donor cells was markedly enhanced in recipient mice treated with the GnRH agonist leuprolide acetate, which makes the technique of spermatogonial transplantation applicable to a wide range of experimental situations. The present study also indicates that this technique can be used as a biological assay system to investigate factors controlling the establishment and progression of spermatogenesis.

Isolation and characterization of a protein with homology to angiotensin converting enzyme from the periacrosomal plasma membrane of equine spermatozoa

The periacrosomal plasma membrane of spermatozoa is involved in sperm binding to oviductal epithelial cells and to the zona pellucida. A protein of 68-70 kD molecular mass was purified biochemically from the isolated periacrosomal plasma membrane of equine spermatozoa as a possible receptor for adhesion of spermatozoa to oviductal epithelial cells. A polyclonal antibody raised in rabbits against the purified equine sperm membrane protein recognized the 70 kD and an antigenically related to 32 kD protein in preparations of isolated periacrosomal sperm plasma membrane and in detergent extracted ejaculated and epididymal spermatozoa. A larger protein (approximately 110 kD) was detected in equine testis. Two antigenically related proteins (64 and 45 kD) were recognized on the plasma membrane of cynomolgus macaque spermatozoa. In vitro sperm-binding assays were performed in the presence of antigen-binding fragments or IgG purified from the polyclonal antiserum to investigate a possible function to the isolated protein in binding of equine spermatozoa to homologous oviductal epithelial cells or zona pellucida. Incubation with antigen-binding fragments or IgG purified from the antiserum did not inhibit binding of equine spermatozoa either to oviductal epithelial cells or the zona pellucida. On ultrastructural examination, the antibody bound exclusively to the cytoplasmic side of the periacrosomal plasma membrane of equine and macaque spermatozoa. Microsequence analysis of 13 residues of sequence showed strong homology with a number of angiotensin converting enzymes: An 84% identity was identified with testis specific and somatic forms of human and mouse angiotensin-converting enzyme. Immunocytochemistry and immunoblot analysis established that the protein is specific for the periacrosomal membrane of ejaculated, epididymal, and testicular stallion spermatozoa.

Distribution of glycoconjugates in the uterine tube (oviduct) of horses

OBJECTIVE

To examine glycoconjugates in the isthmic and ampullar regions of the uterine tube (oviduct) of horses during estrus, diestrus, and pregnancy.

SAMPLE POPULATION

Oviductal samples from 17 mares.

PROCEDURE

Oviducts were collected during estrus (n = 3), diestrus (n = 3), or pregnancy (n = 3), embedded, and snap frozen in liquid nitrogen. Frozen sections (5 to 6 microns in thickness) were stained with 100 micrograms/ml of fluorescein-isothiocyanate-conjugated lectin (30 min at 38.5 C) and were evaluated by use of epifluorescence microscopy and video image analysis. Specificity of lectins was established by blocking with the corresponding carbohydrate. Dolichos biflorus agglutinin (DBA)-affinity studies on western blots of oviductal lavage fluid, oviductal explant conditioned media, and apical membrane proteins from isthmic and ampullar regions of oviducts were used to identify glycoproteins with galactosyl residues.

RESULTS

Use of 4 lectins resulted in differential labeling of the luminal surface of the oviductal epithelium. Both DBA and soybean agglutinin labeled the apical epithelium of the isthmus, but not the ampullar oviduct. Soybean agglutinin resulted in more-intensely labeled epithelium in the isthmic region of oviducts during estrus and pregnancy than during diestrus. The DBA labeled a number of glycoproteins in conditioned media from both regions of the oviduct. These glycoproteins ranged from 14 to 200 kd, with major glycoproteins identified at 31 and 57 kd.

CONCLUSIONS

The predominant glycoconjugates in the oviduct of horses are galactosyl residues. There are regional differences in the distribution of these galactosyl glycoconjugates in the isthmic and ampullar oviduct.

Membrane contact with oviductal epithelium modulates the intracellular calcium concentration of equine spermatozoa in vitro

Interaction of equine spermatozoa with oviductal epithelial cells (OEC) prolongs sperm viability and maintains low intracellular calcium concentration ([Ca2+]i) in spermatozoa. Experiments were designed to investigate 1) whether release of spermatozoa from OEC in vitro is associated with elevated [Ca2+]i and 2) whether soluble products from OEC or direct membrane contact between spermatozoa and OEC mediates the effects of OEC on sperm [Ca2+]i. In the first experiment, changes in [Ca2+]i in spermatozoa loaded with indo-1 acetoxymethylester were determined in motile spermatozoa released from OEC monolayers after 4 h of culture compared to [Ca2+]i in spermatozoa still attached to OEC. In addition, [Ca2+]i was determined in spermatozoa incubated with OEC-conditioned medium for 6 h compared to that in spermatozoa incubated in control medium. [Ca2+]i was higher in motile spermatozoa released from OEC than in spermatozoa still attached to OEC after 4 h of incubation. Incubation in OEC-conditioned medium resulted in lower sperm [Ca2+]i only at 4 h of incubation, but not at 0.5, 2, or 6 h of incubation. In the second experiment, a suspension of apical plasma membrane vesicles (AMV) isolated from isthmic oviductal epithelium was used to study the specific effect of sperm contact with OEC membranes on sperm viability, capacitation, and [Ca2+]i. Direct membrane contact between spermatozoa and AMV prolonged sperm viability, delayed capacitation, and maintained low [Ca2+]i in spermatozoa. These results indicated that membrane contact between equine spermatozoa and OEC is required to maintain low [Ca2+]i, delay capacitation, and prolong viability of spermatozoa in vitro. Modulation of capacitation rate for spermatozoa stored in the isthmic sperm reservoir might ensure the availability of a competent sperm population at the time of fertilization.

Antibody directed against plasma membrane components of equine spermatozoa inhibits adhesion of spermatozoa to oviduct epithelial cells in vitro

Before fertilization, equine spermatozoa adhere to oviduct epithelial cells (OEC) of the mare. The biochemical basis for this adhesion has not been determined. Our objective was to produce an antiserum to block this interaction. Ejaculated spermatozoa were subjected to nitrogen cavitation and spermatozoal plasma membranes enriched by sucrose density gradient centrifugation; membrane enrichment was confirmed by comparative alkaline phosphatase analysis, electron microscopy, and one- and two-dimensional PAGE. Periacrosomal plasma membrane was used as an immunogen for the production of an antiserum, which recognized several components of spermatozoal plasma membrane on Western blots. Antigen-binding fragments (Fab) were isolated by papain digestion from a specific antiserum and from nonimmunized rabbit IgG (control). The periacrosomal regions of epididymal and ejaculated spermatozoa were immunolabeled with antiserum Fab but not control Fab. The immunoneutralizing activity of antiserum Fab was tested in fluorescent cell-binding assays by competitive inhibition of the binding of spermatozoa to OEC monolayers or explants. In both assays, binding of spermatozoa to OEC was reduced as the concentration of specific Fab increased. These results suggest that one or more protein or glycoprotein components of the rostral spermatozoal plasma membrane mediate adhesion between spermatozoa and oviduct epithelium in vitro.

Role of carbohydrates in the attachment of equine spermatozoa to uterine tubal (oviductal) epithelial cells in vitro

OBJECTIVE

To test the hypotheses that the attachment of equine spermatozoa to uterine tubal (oviductal) epithelial cells (OEC) in vitro is mediated by glycoproteins, and that proteins with carbohydrate-binding properties are present in the periacrosomal plasma membrane of equine spermatozoa.

ANIMALS

4 reproductively sound stallions, and 1 mare in estrus.

PROCEDURES

In experiment 1a, fluorescent-labeled spermatozoa were cocultured with monolayers of OEC in the presence of 50 mM glucose, fructose, galactose, mannose, N-acetyl glucosamine, N-acetyl galactosamine, or N-acetyl neuraminic acid, or 10 mg of fetuin or asialofetuin/ml in modified Tyrode's solution (TALP), or in TALP alone. After 2 hours of coculture, numbers of attached spermatozoa were counted by fluorescence microscopy and analysis of digitized images. In experiment 1b, progressive motility, viability, acrosomal integrity, and capacitation status were determined in spermatozoa incubated for 2 hours in the presence of the respective monosaccharides and glycoproteins or in TALP alone. In experiment 2, proteins isolated from the periacrosomal plasma membrane of equine spermatozoa were subjected to galactose affinity chromatography and subsequent one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining.

RESULTS

Numbers of spermatozoa attached to OEC were reduced (P < 0.05) after all treatments except N-acetyl glucosamine, compared with incubation in TALP alone. The lowest numbers of spermatozoa were bound in cultures incubated in the presence of galactose and asialofetuin. Spermatozoal motility was lower (P < 0.05) after incubation for 2 hours in the presence of fetuin, compared with control, and incubation in the presence of fetuin or asialofetuin caused a significant (P < 0.05) increase in the percentage of capacitated spermatozoa, compared with control. Affinity chromatography of periacrosomal plasma membrane proteins revealed a galactose-binding protein of about 66 kd.

CONCLUSION

Recognition of glycoconjugates with exposed galactosyl residues on OEC by galactose-binding proteins on the periacrosomal plasma membrane of equine spermatozoa could mediate the attachment of equine spermatozoa to OEC in vitro.