Immunophenotype profile by flow cytometry reveals different subtypes of extracellular vesicles in porcine seminal plasma

BACKGROUND

Porcine seminal plasma (SP) is endowed with a heterogeneous population of extracellular vesicles (sEVs). This study evaluated the immunophenotypic profile by high-sensitivity flow cytometry of eight sEV subpopulations isolated according to their size (small [S-sEVs] and large [L-sEVs]) from four different SP sources, namely three ejaculate fractions (the first 10 mL of the sperm rich fraction [SRF-P1], the remaining SRF [SRF-P2], and the post-SRF [PSRF]) and entire ejaculate (EE).

METHODS

Seminal EVs were isolated using a size exclusion chromatography-based protocol from six SP pools (five ejaculates/pool) of each SP source and characterized using complementary approaches including total protein (BCA™assay), particle size distribution (dynamic light scattering), morphology (transmission electron microscopy), and purity (albumin by Western blot). Expression of CD9, CD63, CD81, CD44 and HSP90β was analyzed in all sEV subpopulations by high-sensitivity flow cytometry according to MIFlowCyt-EV guidelines, including an accurate calibration, controls, and discrimination by CFSE-labelling.

RESULTS

Each sEV subpopulation exhibited a specific immunophenotypic profile. The percentage of sEVs positive for CD9, CD63, CD81 and HSP90β differed between S- and L-sEVs (P < 0.0001). Specifically, the percentage of sEVs positive for CD9 and CD63 was higher and that for CD81 was lower in S- than L-sEVs in the four SP sources. However, the percentage of HSP90β-positive sEVs was lower in S-sEVs than L-sEVs in the SRF-P1 and EE samples. The percentage of sEVs positive for CD9, CD63, and CD44 also differed among the four SP sources (P < 0.0001), being highest in PSRF samples. Notably, virtually all sEV subpopulations expressed CD44 (range: 88.04-98.50%).

CONCLUSIONS

This study demonstrated the utility of high-sensitivity flow cytometry for sEV immunophenotyping, allowing the identification of distinct sEV subpopulations that may have different cellular origin, cargo, functions, and target cells.

Seminal extracellular vesicles subsets modulate gene expression in cumulus cells of porcine in vitro matured oocytes

Seminal plasma (SP), a fluid composed mainly by secretions from accessory sex glands, contains a heterogenous population of extracellular vesicles (EVs), involved in several reproductive physiological processes. Seminal plasma has been found to modulate ovary function, in terms of hormone secretion and immune regulation. This study evaluated the potential effect of SP-EV-subsets on the modulation of cumulus-oocyte-complex (COCs) physiology during in vitro maturation (IVM). Two SP-EV-subsets, small-EVs (S-EVs) and large-EVs (L-EVs), were isolated from pig SP by size-exclusion-chromatography. Next, COCs were IVM in the absence (control) or presence of each SP-EV-subset to evaluate their uptake by COCs (PKH67-EVs labelling) and their effect on oocyte and cumulus cells (CCs) (gene expression, and progesterone and estradiol-17β levels). S-EVs and L-EVs were able to bind CCs but not oocytes. Supplementation with L-EVs induced changes (P ≤ 0.05) in the transcript levels of oocyte maturation- (HAS2) and steroidogenesis-related genes (CYP11A1 and HSD3B1) in CCs. No effect on nuclear oocyte maturation and progesterone and estradiol-17β levels was observed when COCs were IVM with any of the two SP-EV-subsets. In conclusion, while SP-EV-subsets can be integrated by CCs during IVM, they do not affect oocyte maturation and only L-EVs are able to modulate CCs function, mainly modifying the expression of steroidogenesis-related genes.

Establishment of a male fertility prediction model with sperm RNA markers in pigs as a translational animal model

BACKGROUND

Male infertility is an important issue that causes low production in the animal industry. To solve the male fertility crisis in the animal industry, the prediction of sperm quality is the most important step. Sperm RNA is the potential marker for male fertility prediction. We hypothesized that the expression of functional genes related to fertilization will be the best target for male fertility prediction markers. To investigate optimum male fertility prediction marker, we compared target genes expression level and a wide range of field data acquired from artificial insemination of boar semen.

RESULTS

Among the genes related to acrosomal vesicle exocytosis and sperm-oocyte fusion, equatorin (EQTN), zona pellucida sperm-binding protein 4 (ZP4), and sperm acrosome membrane-associated protein 3 exhibited high accuracy (70%, 90%, and 70%, respectively) as markers to evaluate male fertility. Combinations of EQTN-ZP4, ZP4-protein unc-13 homolog B, and ZP4-regulating synaptic membrane exocytosis protein 1 (RIMS1) showed the highest prediction value, and all these markers are involved in the acrosome reaction.

CONCLUSION

The EQTN-ZP4 model was efficient in clustering the high-fertility group and may be useful for selection of animal that has superior fertility in the livestock industry. Compared to the EQTN-ZP4 model, the ZP4-RIMS1 model was more efficient in clustering the low-fertility group and may be useful in the diagnosis of male infertility in humans and other animals. The appointed translational animal model and established biomarker combination can be widely used in various scientific fields such as biomedical science.

Advanced bioengineering of male germ stem cells to preserve fertility

In modern life, several factors such as genetics, exposure to toxins, and aging have resulted in significant levels of male infertility, estimated to be approximately 18% worldwide. In response, substantial progress has been made to improve in vitro fertilization treatments (e.g. microsurgical testicular sperm extraction (m-TESE), intra-cytoplasmic sperm injection (ICSI), and round spermatid injection (ROSI)). Mimicking the structure of testicular natural extracellular matrices (ECM) outside of the body is one clear route toward complete in vitro spermatogenesis and male fertility preservation. Here, a new wave of technological innovations is underway applying regenerative medicine strategies to cell-tissue culture on natural or synthetic scaffolds supplemented with bioactive factors. The emergence of advanced bioengineered systems suggests new hope for male fertility preservation through development of functional male germ cells. To date, few studies aimed at in vitro spermatogenesis have resulted in relevant numbers of mature gametes. However, a substantial body of knowledge on conditions that are required to maintain and mature male germ cells in vitro is now in place. This review focuses on advanced bioengineering methods such as microfluidic systems, bio-fabricated scaffolds, and 3D organ culture applied to the germline for fertility preservation through in vitro spermatogenesis.

Acrosome and chromatin integrity, oxidative stress, and expression of apoptosis-related genes in cryopreserved mouse epididymal spermatozoa treated with L-Carnitine

Oxidative stress is believed to be an important cause of sperm damage during freezing. l-Carnitine (LC) may have the potential to improve sperm quality after frozen-thawed process. The present study aimed to investigate the effect of LC supplementation in cryoprotectant media of mouse epididymal sperm on post-thaw sperm quality and expression of apoptosis-related genes. Male BALB/cJ mice spermatozoa were cryopreserved in a cryoprotectant medium containing 2.5 or 5 mM LC. The untreated group was cryopreserved with the cryoprotectant medium only. Six months following cryopreservation, the samples were thawed and sperm quality parameters, chromatin and acrosome integrity, reactive oxygen species (ROS) and glutathione (GSH) levels, mitochondrial activity, and mRNA expression of Bax and Bcl-2 were assessed. The results demonstrated that the concentration of 5 mM LC in cryoprotectant media exhibited higher values for the sperm quality parameters and integrity of chromatin and acrosome in post-thaw spermatozoa than those of the untreated group. Furthermore, sperm ROS levels decreased while GSH and mitochondrial activity levels increased in 5 mM LC group compared to those in the untreated group (P < 0.01). In 5 mM LC-treated group, Bax was down-regulated (P < 0.05) while Bcl-2 was up-regulated (P < 0.001) compared to the untreated group. Collectively, LC supplementation of cryoprotectant medium improved the quality of frozen-thawed mouse epididymal spermatozoa, as showed reduced ROS level and Bax expression as well as increased GSH, mitochondrial activity, and Bcl-2 expression.

The Effect of N-N-Dimethylformamide on the Membrane Characteristics of Canine Spermatozoa After Cryopreservation, and its Relationship With Post-Thaw Motility

Some studies have demonstrated that glycerol is superior to amides in preserving sperm motion characteristics of canine sperm; however, little is known about the effect of these cryoprotectants on the membrane characteristics of canine spermatozoa after freezing/thawing. In this study, the effects of using either N-N-dimethylformamide (DMF) or glycerol (GLY) on the integrity and function of the canine sperm, after cryopreservation were determined. We hypothesized that the use of a multiparametric approach for assessing the effect of DMF on the membranes of canine sperm would explain the lower values reported for post-thaw motility. Ejaculates from 12 dogs were collected, split into 2 groups, and frozen using a tris-fructose-citrate-egg yolk-based extender containing either 7% (v/v) GLY or 7% (v/v) DMF. Frozen straws (n = 120) were thawed and analyzed for subjectively-assessed sperm progressive motility, normal morphology, plasma membrane integrity, plasma membrane function (HOST+), acrosome membrane integrity, high mitochondrial membrane potential, and simultaneous assessment of sperm membrane integrity and function by a triple-staining fluorescent procedure. Overall, sperm motility and membrane intactness/function were higher when GLY was used as a cryoprotectant, as compared to DMF (P < .05). A model to explain the variation in progressive motility using the values obtained from the sperm integrity and function parameters was designed. The percent HOST+ sperm and high mitochondrial membrane potential sperm were mostly associated with the changes observed in the progressive motility (r² = 0.84; P = .043) when either GLY or DMF were used as cryoprotectants. These results may explain the overall reduced sperm quality observed after cryopreservation, as a reflection of sublethal damage sustained by the sperm membranes.

Characterization and population dynamics of germ cells in adult macaque testicular cultures

BACKGROUND

From a biological and clinical perspective, it is imperative to establish primate spermatogonial cultures. Due to limited availability of human testicular tissues, the macaque (Macaca fascicularis) was employed as non-human primate model. The aim of this study was to characterize the expression of somatic as well as germ cell markers in testicular tissues and to establish macaque testicular primary cell cultures.

MATERIALS AND METHODS

Characterization of macaque testicular cell population was performed by immunohistochemical analyses for somatic cell markers (SOX9, VIM, SMA) as well as for germ cell markers (UTF1, MAGEA4, VASA). Testicular cells from adult macaque testes (n = 4) were isolated and cultured for 21 days using three stem cell culture media (SSC, PS and SM). An extended marker gene panel (SOX9, VIM, ACTA2; UTF1, FGFR3, MAGEA4, BOLL, DDX4) was then employed to assess the changes in gene expression levels and throughout the in vitro culture period. Dynamics of the spermatogonial population was further investigated by quantitative analysis of immunofluorescence-labeled MAGEA4-positive cells (n = 3).

RESULTS

RNA expression analyses of cell cultures revealed that parallel to decreasing SOX9-expressing Sertoli cells, maintenance of VIM and ACTA2-expressing somatic cells was observed. Expression levels of germ cell marker genes UTF1, FGFR3 and MAGEA4 were maintained until day 14 in SSC and SM media. Findings from MAGEA4 immunofluorescence staining corroborate mRNA expression profiling and substantiate the overall maintenance of MAGEA4-positive pre- and early meiotic germ cells until day 14.

CONCLUSIONS

Our findings demonstrate maintenance of macaque germ cell subpopulations in vitro. This study provides novel perspective and proof that macaques could be used as a research model for establishing in vitro germ cell-somatic cell cultures, to identify ideal culture conditions for long-term maintenance of primate germ cell subpopulation in vitro.

Iodixanol supplementation during sperm cryopreservation improves protamine level and reduces reactive oxygen species of canine sperm

The objective of this study was to analyze the protective effects of iodixanol on dog spermatozoa during cryopreservation. The optimal concentration of iodixanol, 1.5%, was determined using fresh spermatozoa and was applied in the following experiments. The 1.5% iodixanol group showed significantly increased sperm motility from that in the control (p < 0.05). Lower mitochondrial reactive oxygen species (ROS) modulator (ROMO1) and pro-apoptotic gene (BAX) expressions, together with higher expressions of protamine-2 (PRM2), protamine-3 (PRM3), anti-apoptotic B-cell lymphoma-2 (BCL2), and sperm acrosome associated-3 (SPACA3) genes were detected in the iodixanol-treated group. In addition, decreased protamine deficiency and cryocapacitation were observed in the treatment group. Our results show that supplementation with 1.5% iodixanol is ideal for reducing production of ROS and preventing detrimental effects during the canine sperm cryopreservation process, effects manifested as increased motility and reduced cryocapacitation in frozen-thawed spermatozoa.

Effect of sphingosine-1-phosphate on cryopreserved sheep testicular explants cultured in vitro

Complete spermatogenesis has been achieved in vitro in mouse testicular explants with resulting sperm used to produce pups after Intra Cytoplasm Sperm Injection and Embryo Transfer. In the present study, we evaluated the influence of sphingosine-1-phosphate (S1P) on spermatogenesis of frozen-thawed lamb testis explants in vitro. Thawed testicular pieces were cultured for 12 d on agarose blocks in serum-free growth medium containing 0, 2, 5 or 10 μM S1P. At the end of D6 and D12, some pieces were fixed and processed for histology. Other pieces were processed for RNA isolation and quantitation of proliferation (PCNA, Ki67) and differentiation (PLZF) markers and genes involved in S1P signaling (S1PR1, SGPL1, SGPP1, AKT1 and NFKBIA) by qPCR. Histology revealed an increase (P < 0.05) in seminiferous cord (SC) diameter under all culture conditions, except 5 and 10 μM S1P by D6. In the presence of 5 μM S1P, percentage of gonocytes decreased (P < 0.05) by D6 (control, 24.9% vs. S1P, 10.3%) with a concomitant increase (P < 0.05) in spermatogonia formation (control, 74.4% vs. S1P, 88.1%). S1P induced PCNA or Ki67 expression by D6, whereas PLZF was up-regulated (P < 0.05) by D6 in 2 μM S1P and D12 in 5 & 10 μM S1P. Expression of SGPL1 and SGPP1 increased 4-12-fold in tissues cultured in 10 μM S1P by D12 compared to D12 control. AKT1 and NFKBIA mRNA expression was low (P < 0.05) in 5 and or 10 μM S1P treatments on D6. These results demonstrate that S1P promotes germ cell proliferation during first week of culture and may exert an anti-apoptotic influence on the seminiferous cord in sheep testicular explants in vitro.

Preservation of female fertility in humans and animal species

A detailed understanding of the cryobiology of gametes and complex tissues has led to the development of methods that facilitate the successful low temperature banking of isolated mature human oocytes, or immature oocytes in situ within fragments of human ovarian cortex. Although many outstanding research challenges remain to be addressed, the successful development of new treatments to preserve female fertility for a range of clinical indications has largely been underpinned by the conduct of extensive, fundamental research on oocytes and ovarian tissues from a number of laboratory and commercially important farm species. Indeed, the most recent evidence from large animals suggests that it is also possible to cryopreserve intact whole ovaries along with their supporting vasculature for later auto-transplantation and restoration of natural fertility. This review will explore how the methods developed to preserve human oocytes and ovarian tissues can now be used strategically to support the development of conservation strategies aimed at safeguarding the genetic diversity of commercially important domestic animals and also of preserving the female germplasm for wild animals and endangered species.

Cryosurvival of isolated testicular cells and testicular tissue of tench Tinca tinca and goldfish Carassius auratus following slow-rate freezing

Experiments were carried out to test the efficiency of cryopreservation of whole testicular tissue in tench Tinca tinca and goldfish Carassius auratus and compare it to cryopreservation of isolated testicular cells. Additionally, effects of three cryoprotectants (dimethyl sulphoxyde - Me₂SO, methanol - MeOH and ethylene glycol - EG) at three concentrations (1M, 2M and 3M) on post-thaw cell viability were assessed. Tissue pieces/isolated testicular cells were diluted in cryomedia and cryopreserved by slow-rate freezing (1°C/min to -80°C followed by a plunge into the liquid nitrogen). In both species Me₂SO and EG generally yielded higher cryosurvival of early-stage germ cells than MeOH, while spermatozoa of neither species displayed such a pattern. In most cases a 3M>2M>1M viability pattern emerged in both species for both sample types regardless of the cryoprotectant used. Sample type (dissociated testicular cells vs testicular tissue) did not seem to affect viability rates of tench early-stage germ cells and goldfish spermatozoa, while the opposite was observed for tench spermatozoa and goldfish early-stage germ cells. Additionally, through histological analysis we displayed that tissue structure mainly remained unaltered after thawing in goldfish. These results indicate that cryopreservation of whole testicular tissue is indeed a valid alternative method to cryopreservation of dissociated testicular cells. Early-stage germ cells obtained from cryopreserved testis can be further used in different purposes such as transplantation into suitable donors while viable sperm might be used for fertilization when feasible.

Biobanking efforts and new advances in male fertility preservation for rare and endangered species

Understanding and sustaining biodiversity is a multi-disciplinary science that benefits highly from the creation of organized and accessible collections of biomaterials (Genome Resource Banks). Large cryo-collections are invaluable tools for understanding, cataloging, and protecting the genetic diversity of the world's unique animals and plants. Specifically, the systematic collection and preservation of semen from rare species has been developed significantly in recent decades with some biobanks now being actively used for endangered species management and propagation (including the introduction of species such as the black-footed ferret and the giant panda). Innovations emerging from the growing field of male fertility preservation for humans, livestock species, and laboratory animals are also becoming relevant to the protection and the propagation of valuable domestic and wild species. These new approaches extend beyond the “classical” methods associated with sperm freezing to include testicular tissue preservation combined with xenografting or in vitro culture, all of which have potential for rescuing vast amounts of unused germplasm. There also are other options under development that are predicted to have a high impact within the next decade (stem cell technologies, bio-stabilization of sperm cells at ambient temperatures, and the use of genomics tools). However, biobanking efforts and new fertility preservation strategies have to expand the way beyond mammalian species, which will offer knowledge and tools to better manage species that serve as valuable biomedical models or require assistance to reverse endangerment.

Maintaining canine sperm function and osmolyte content with multistep freezing protocol and different cryoprotective agents

Cryopreservation procedures cause osmotic stress to spermatozoa following cryoinjury and reduce their content of osmolytes. Conventional method for cryoprotectant loading and dilution on canine semen freezing which could be categorized in single step protocol, makes decreasing in sperm performance such as motility, morphology and viability. Therefore, the objective of the present study was to determine if a multistep protocol using glycerol or ethylene glycol can be used to overcome the osmotic sensitivity of canine spermatozoa, and to identify osmolytes that were involved in regulation of osmotic stress. A multistep protocol, comprising serial loading and dilution of cryoprotective agents by dividing the total volume of extender into 4 steps (14%, 19%, 27%, and 40%) every 30s, was compared to a single step method. Frozen-thawed spermatozoa in the multistep group showed superior quality (P<0.05) compared with the single step process in progressive motility (23.3 ± 1.3% vs. 12.5 ± 1.6%), intact membranes (66.5 ± 2.8% vs. 49.5 ± 2.6%) and bent tail (29.2 ± 3.2% vs. 46.2 ± 1.9%). Multistep also succeeded in minimizing loss of the osmolytes carnitine (20.6 ± 2.0 nmol/U G6PDH vs. 10.8 ± 2.1 nmol/U G6PDH) and glutamate (18.4 ± 1.6 nmol/U G6PDH vs. 14.4 ± 0.8 nmol/U G6PDH) compared to the single step group. Moreover, glycerol with multistep was more advantageous for maintaining sperm quality than ethylene glycol. In conclusion, the multistep protocol with glycerol can be used to improve the morphology, motility and osmolytes content of frozen-thawed canine spermatozoa.

Xenotransplantation models to study the effects of toxicants on human fetal tissues

Many diseases that manifest throughout the lifetime are influenced by factors affecting fetal development. Fetal exposure to xenobiotics, in particular, may influence the development of adult diseases. Established animal models provide systems for characterizing both developmental biology and developmental toxicology. However, animal model systems do not allow researchers to assess the mechanistic effects of toxicants on developing human tissue. Human fetal tissue xenotransplantation models have recently been implemented to provide human-relevant mechanistic data on the many tissue-level functions that may be affected by fetal exposure to toxicants. This review describes the development of human fetal tissue xenotransplant models for testis, prostate, lung, liver, and adipose tissue, aimed at studying the effects of xenobiotics on tissue development, including implications for testicular dysgenesis, prostate disease, lung disease, and metabolic syndrome. The mechanistic data obtained from these models can complement data from epidemiology, traditional animal models, and in vitro studies to quantify the risks of toxicant exposures during human development.

Mammalian fertility preservation through cryobiology: value of classical comparative studies and the need for new preservation options

Human-related fertility preservation strategies have enormous potential for helping sustain and protect other species, especially to assist managing or 'rescuing' the genomes of genetically valuable individuals, including endangered species. However, wider-scale applications are limited by significant physiological variations among species, as well as a lack of fundamental knowledge of basic reproductive traits and cryosensitivity. Systematic and comparative cryopreservation studies (e.g. on membrane biophysical properties and resilience to freezing temperatures) are required to successfully recover gametes and gonadal tissues after thawing and eventually produce healthy offspring. Such data are currently available for humans and a few laboratory and livestock animals, with virtually all other species, including wildlife, having gone unstudied. Interestingly, there also are commonalities among taxa that allow a protocol developed for one species to provide useful information or guidance for another. However, when a rare animal unexpectedly dies there is no time for a prospective understanding of that species' biophysical traits. Because the odds of success will be much lower in such instances, it is essential that more fundamental studies be directed at more species. But also worthwhile is thinking beyond these systematic characterisations to consider the potential of a 'universal preservation protocol' for animal biomaterials.

Recent advances and prospects in germplasm preservation of rare and endangered species

Fertility preservation strategies using cryopreservation have enormous potential for helping sustain and protect rare and endangered species, especially to assist managing or 'rescuing' the genomes of genetically valuable individuals. However, wide-scale applications are still limited by significant physiological variations among species and a sheer lack of fundamental knowledge about basic reproductive traits as well as in germplasm cryobiology. Cryo-studies have been conducted in more species (mainly vertebrates) in the recent years but a vast majority still remains un-studied. Semen cryopreservation represents the most extensive effort with live births reported in more and more species after artificial insemination. Oocyte freezing remains challenging and unsuccessful in wild species and will require more research before becoming a standard procedure. As an alternative to fully grown gametes, gonadal tissue preservation has become a promising option in vertebrates. Yet, more fertility preservation options are necessary to save species so a change in strategy might be required. It is worthwhile thinking beyond systematic characterizations and considering the application of cutting edge approaches to universally preserve the fertility of a vast array of species.

Production of live offspring from testicular tissue cryopreserved by vitrification procedures in Japanese quail (Coturnix japonica)

Cryopreservation of testicular tissue can be used for ex situ conservation of male germplasm of avian species. The possibility of using vitrification and transplantation of testicular tissue for fertility preservation and recovery was tested in Japanese quail. Testes were removed from 1-wk-old Japanese quail; transfixed on acupuncture needles; equilibrated with dimethyl sulphoxide, ethylene glycol, and sucrose; plunged into liquid nitrogen; and stored in 2-ml straws. Cryopreserved tissue was warmed in sucrose solution at room temperature or at 40°C. Fresh and cryopreserved tissue were transplanted subcutaneously into castrated, 1-wk-old recipients. Twenty of 21 recipients survived the surgery, and 18 had viable transplants at maturity, with no difference in transplantation success between fresh and cryopreserved tissue. Fluid extrusion from 11 of the transplants was collected and inseminated surgically into the magnum of 22 quail hens, and 10 inseminations included foam from the proctodeal gland of the same recipients. Egg production in the 2 wk after insemination was reduced, and none of the hens inseminated with foam produced fertile eggs. Five hens inseminated without foam produced a total of eight live offspring; four of these hens had been inseminated with fluid extrusion from cryopreserved tissue. Histological examination showed spermatogenesis in the transplants, and the tubules, lumens, and epithelium of the seminiferous tubules were of comparable size to those of testicular tissue from intact males. These results demonstrate that testicular tissue of Japanese quail can be preserved using vitrification procedures and recovered through transplantation.

Comparative cryobiological traits and requirements for gametes and gonadal tissues collected from wildlife species

A major challenge to retaining viability of frozen gametes and reproductive tissues is to understand and overcome species-specificities, especially because there is substantial diversity in cryobiological properties and requirements among cell types and tissues. Systematic studies can lead to successful post-thaw recovery, especially after determining: 1) membrane permeability to water and cryoprotectant, 2) cryoprotectant toxicity, 3) tolerance to osmotic changes, and 4) resistance to cooling and freezing temperatures. Although species-dependency ultimately dictates the ability of specific cells and tissues to survive freeze-thawing, there are commonalities between taxa that allow a protocol developed for one species to be useful information for another. This is the reason for performing comparative cryopreservation studies among diverse species. Our laboratory has compared cellular cryotolerance, especially in spermatozoa, in a diverse group of animals-from corals to elephants-for more than 30 yrs. Characterizing the biophysical traits of gametes and tissues is the most efficient way to develop successful storage and recovery protocols, but, such data are only available for a few laboratory, livestock, and fish species, with virtually all others (wild mammals, birds, reptiles, and amphibians) having gone unstudied. Nonetheless, when a rare animal unexpectedly dies, there is no time to understand the fundamentals of biophysics. In these emergencies, it is necessary to rely on experience and the best data from taxonomically-related species. Fortunately, there are some general similarities among most species, which, for example, allow adequate post-thaw viability. Regardless, there is a priority for more information on biophysical traits and freezing tolerance of distinctive biomaterials, especially for oocytes and gonadal tissues, and even for common, domesticated animals. Our colleague, Dr John Critser was a pioneer in cryobiology, earning that moniker because of his advocacy and devotion to understanding the differences (and similarities) among species to better store living genetic material.

Cryopreservation of human testicular diploid germ cell suspensions

For patients with threatened fertility, preservation of it is a major concern. Although promising results have been obtained in animal models using testicular germ cell suspensions, in humans, it is crucial to first develop an efficient method of cryopreservation to be able to apply to transplantation. Thus, four reliable and available cryopreservation techniques in any fertility centre were tested to cryopreserve an enriched fraction of diploid germ cells isolated from human testicular biopsies. The protocols were evaluated based on cell viability, and the results showed significant differences between the four methods. The semen and tissue cryopreservation methods appeared to be inadequate for diploid germ cell suspensions, and programmed slow freezing gave significantly lower results than open pulled straw vitrification; the latter was found to be the protocol that best preserved cell viability. The vitrification of isolated human diploid germ cells is innovative and constitutes valuable information for cryopreservation in cases of transplants or in vitro maturation.

Separating spermatogonia from cancer cells in contaminated prepubertal primate testis cell suspensions

BACKGROUND

Chemotherapy and radiation treatments for cancer and other diseases can cause male infertility. There are currently no options to preserve the fertility of prepubertal boys who are not yet making sperm. Cryopreservation of spermatogonial stem cells (SSCs, obtained via testicular biopsy) followed by autologous transplantation back into the testes at a later date may restore fertility in these patients. However, this approach carries an inherent risk of reintroducing cancer.

METHODS

To address this aspect of SSC transplantation safety, prepubertal non-human primate testis cell suspensions were inoculated with MOLT4 T-lymphoblastic leukemia cells and subsequently sorted for cell surface markers CD90 (THY-1) and CD45.

RESULTS

Cancer cells segregated to the CD90-/CD45+ fraction and produced tumors in nude mice. Nearly all sorted DEAD box polypeptide 4-positive (VASA+) spermatogonia segregated to the CD90+/CD45- fraction. In a preliminary experiment, a purity check of the sorted putative stem cell fraction (CD90+/CD45-) revealed 0.1% contamination with cancer cells, which was sufficient to produce tumors in nude mice. We hypothesized that the contamination resulted from mis-sorting due to cell clumping and employed singlet discrimination (SD) in four subsequent experiments. Purity checks revealed no cancer cell contamination in the CD90+/CD45- fraction from three of the four SD replicates and these fractions produced no tumors when transplanted into nude mouse testes.

CONCLUSIONS

We conclude that spermatogonia can be separated from contaminating malignant cells by fluorescence-activated cell sorting prior to SSC transplantation and that post-sorting purity checks are required to confirm elimination of malignant cells.

Optimizing potential for fertility: fertility considerations for the pediatrician

Whether for the prepubertal or pubertal child, the goal of fertility preservation is to obtain cells or tissues to be used to produce future children. For the prepubertal child, preservation efforts involve germ cells, earlier forms of sperm, and immature follicles, rather than mature spermatozoa or follicles. Options for prepubertal children include for boys freezing testicular tissue and extracting testicular sperm or for girls obtaining ovarian cortical or follicular tissue for storage. These procedures involve extraction and storage of immature gametes for subsequent in vitro maturation, although attempts for sperm currently involve only animal studies. For adolescent subjects who have sufficient gonadal development and reserve, sperm, oocytes, and ovarian cortex can be retrieved as among adults.

Recent advances in application of male germ cell transplantation in farm animals

Transplantation of isolated germ cells from a fertile donor male into the seminiferous tubules of infertile recipients can result in donor-derived sperm production. Therefore, this system represents a major development in the study of spermatogenesis and a unique functional assay to determine the developmental potential and relative abundance of spermatogonial stem cells in a given population of testis cells. The application of this method in farm animals has been the subject of an increasing number of studies, mostly because of its potential as an alternative strategy in producing transgenic livestock with higher efficiency and less time and capital requirement than the current methods. This paper highlights the salient recent research on germ cell transplantation in farm animals. The emphasis is placed on the current status of the technique and examination of ways to increase its efficiency through improved preparation of the recipient animals as well as isolation, purification, preservation, and transgenesis of the donor germ cells.

Xenografting of human fetal testis tissue: a new approach to study fetal testis development and germ cell differentiation

BACKGROUND

Abnormal fetal testis development can result in disorders of sex development (DSDs) and predispose to later testicular dysgenesis syndrome (TDS) disorders such as testicular germ cell tumours. Studies of human fetal testis development are hampered by the lack of appropriate model, and intervention systems. We hypothesized that human fetal testis xenografts can recapitulate normal development.

METHODS

Human fetal testes (at 9 weeks, n = 4 and 14-18 weeks gestation, n = 6) were xenografted into male nude mice for 6 weeks, with or without hCG treatment of the host, and evaluated for normal cellular development and function using immunohistochemistry, triple immunofluorescence and testosterone assay. The differentiation and proliferation status of germ cells within xenografts was quantified and compared with age-matched controls.

RESULTS

Xenografts showed >75% survival with normal morphology. In the first-trimester xenografts seminiferous cord formation was initiated and in first- and second-trimester grafts normal functional development of Sertoli, Leydig and peritubular myoid cells was demonstrated using cell-specific protein markers. Grafts produced testosterone when hosts were treated with hCG (P = 0.004 versus control). Proliferation of germ cells and differentiation from gonocytes (OCT4(+)) into pre-spermatogonia (VASA(+)) occurred in grafts and quantification showed this progressed comparably with age-matched ungrafted controls.

CONCLUSIONS

Human fetal testis tissue xenografts demonstrate normal structure, function and development after xenografting, including normal germ cell differentiation. This provides an in vivo system to study normal human fetal testis development and its susceptibility to disruption by exogenous factors (e.g. environmental chemicals). This should provide mechanistic insight into the fetal origins of DSDs and TDS disorders.

Modulating testicular mass in xenografting: a model to explore testis development and endocrine function

The hypothalamic-pituitary-gonadal (HPG) axis is involved in both the regulation of growth of the developing testis and in controlling spermatogenic and steroidogenic activity in the adult testis. Here, we develop a novel testicular xenografting model to examine to which degree testicular growth and function are controlled by intra- and extratesticular factors. Two or eight halves of neonatal Djungarian hamster testes were implanted into intact, hemicastrated, or castrated nude mouse recipients, and the development of the grafts under reduced or increased competition of testicular tissue was monitored and analyzed. We hypothesized that the outgrowth of the testicular grafts is influenced by the total amount of testicular tissue present in a host and that less testicular tissue in a host would result in more extended outgrowth of the grafts. Our results reveal that the hypothesis is wrong, because implanted hamster testis tissue irrespectively of the grafting condition grows to a similar size revealing an intrinsic mechanism for testicular growth. In contrast, similar size of seminal vesicle as bio-indicator of androgen levels in all hosts revealed that the steroidogenic activity is independent from the mass of testicular tissue and that steroid levels are extrinsically regulated by the recipient's HPG axis. We propose that the model of testicular xenografting provides highly valuable options to explore testicular growth and endocrine regulation of the HPG axis.

Effects of medium and hypothermic temperatures on preservation of isolated porcine testis cells

The effects of medium and hypothermic temperatures on testis cells were investigated to develop a strategy for their short-term preservation. Testes from 1-week-old piglets were enzymatically dissociated for cell isolation. In Experiment 1, testis cells were stored at either room (RT) or refrigeration (RG) temperature for 6 days in one of 13 different media. Live cell recovery was assayed daily using trypan blue exclusion. In Experiment 2, three media at RG were selected for immunocytochemical and in vitro culture studies. Live cell recovery was also assayed daily for 6 days using both trypan blue exclusion and a fluorochrome assay kit. For all media tested, significantly or numerically more live cells were maintained at RG than RT. On preservation Day 3 at RG (cell isolation day as Day 0), 20% FBS-Leibovitz resulted in the highest live cell recovery (89.5 + or - 1.7%) and DPBS in the lowest (60.3 + or - 1.9%). On Day 6 at RG, 20% FBS- Leibovitz also resulted in the best preservation efficiency with 80.9 + or - 1.8% of Day 0 live cells recovered. There was no difference in live cell recovery detected by the two viability assays. After preservation, the proportion of gonocytes did not change, whereas that of Sertoli and peritubular cells increased and decreased, respectively. After 6 days of hypothermic preservation, testis cells showed similar culture potential to fresh cells. These results show that testis cells can be preserved for 6 days under hypothermic conditions with a live cell recovery of more than 80% and after-storage viability of 88%.

Donor-host involvement in immature rat testis xenografting into nude mouse hosts

Immature testicular tissue of a wide variety of mammalian species continues growth and maturation when ectopically grafted under the dorsal skin of adult nude mouse recipients. Tissues from most donor species fully mature, exhibiting complete spermatogenesis within months. The connection to the recipient's vascular system is mandatory for graft development, and failure of vascularization leads to necrosis in the grafted tissue. In the present study, we analyze to what extent 1) the xenografted immature donor tissue and 2) the recipient's cells and tissues contribute to the functional recovery of a "testicular xenograft." We address whether recipient cells migrate into the testicular parenchyma and whether the circulatory connection between the donor testicular tissue and the recipient is established by ingrowing host or outgrowing donor blood vessels. Although this issue has been repeatedly discussed in previous xenografting studies, so far it has not been possible to unequivocally distinguish between donor and recipient tissues and thus to identify the mechanisms by which the circulatory connection is established. To facilitate the distinction of donor and recipient tissues, herein we used immature green fluorescent protein-positive rat testes as donor tissues and adult nude mice as graft recipients. At the time of graft recovery, donor tissues could be easily identified by the GFP expression in these tissues, allowing us to distinguish donor- and recipient-derived blood vessels. We conclude that the circulatory connection between graft and host is established by a combination of outgrowing small capillaries from the donor tissue and formation of larger vessels by the host, which connect the graft to subcutaneous blood vessels.

Optimizing potential for fertility: fertility preservation considerations for the pediatric endocrinologist

Whether for the prepubertal or pubertal child, the goal of fertility preservation is to obtain cells or tissues to be used to produce future children. For the prepubertal child, preservation efforts involve germ cells, earlier forms of sperm, and immature follicles, rather than mature spermatozoa or follicles. Options for prepubertal children include for boys freezing testicular tissue and extracting testicular sperm or for girls obtaining ovarian cortical or follicular tissue for storage. These procedures involve extraction and storage of immature gametes for subsequent in vitro maturation, although attempts for sperm currently involve only animal studies. For adolescent subjects who have sufficient gonadal development and reserve, sperm, oocytes, and ovarian cortex can be retrieved as among adults.

New horizons for in vitro spermatogenesis? An update on novel three-dimensional culture systems as tools for meiotic and post-meiotic differentiation of testicular germ cells

Culture and differentiation of male germ cells has been performed for various purposes in the past. To date, none of the studies aimed at in vitro spermatogenesis has resulted in a sufficient number of mature gametes. Numerous studies have revealed worthy pieces of information, building up a body of information on conditions that are required to maintain and mature male germ cells in vitro. In this review, we report on previously published and unpublished experiments addressing murine germ cell differentiation in three-dimensional (3D) in vitro culture systems. In a systematic set of experiments, we examined the influence of two different matrices (soft agar and methylcellulose) as well as the need for gonadotrophin support. For the first time, we demonstrate that pre-meiotic male germ cells [revealed by the absence of meiotic marker expression (e.g. Boule)] obtained from immature mice pass through meiosis in vitro. After several weeks of culture, we obtained morphologically normal spermatozoa embedded in the matrix substance. Complete maturation relied on support from somatic testicular cells and the presence of gonadotrophins but appeared independent from the matrix in a 3D culture environment. Further research efforts are required to reveal the applicability of this culture technique for human germ cells and the functionality of the spermatozoa for generating offspring.

Fertility preservation techniques: laboratory and clinical progress and current issues

Human fertility is dependent on maturation of germ cells through meiosis and their association with supporting cells, which in the female are also the source of sex steroids. These processes are sensitive to both chemotherapy and radiotherapy thus can be damaged by anti-cancer treatments. The uterus is also sensitive to radiotherapy. Our understanding of and the ability to manipulate fertility has increased together with survival rates from many cancers, particularly those affecting children, younger men, and women. The growth of interest in fertility preservation for cancer patients is a natural union of these two fields. Sperm banking has been available for many years, and is a recognized and evidence-based option for men that should be available to all. Options for women and pre-pubertal boys and girls are, however, more experimental, other than for women of committing oocytes to fertilization and cryopreservation as embryos. This Focus Issue of Reproduction aims to address the current status of some of the clinical and laboratory aspects of this burgeoning subspecialty to highlight not only areas of progress but also areas of uncertainty where future developments are required to allow the provision of accurate information, and safe and effective treatments.