Generation and in vitro differentiation of a spermatogonial cell line

Preserving the reproductive potential of men and boys with cancer: current concepts and future prospects

The introduction of ICSI has totally changed the reproductive prospects for boys and men who are treated for cancer. With post-pubertal boys and adult men, semen cryopreservation should be offered to every patient undergoing a cancer treatment since preservation of fertility cannot be guaranteed for an individual patient and treatment may shift to a more sterilizing regimen. In the ICSI era, all semen samples, even those containing only a few motile sperm, should be accepted for cryopreservation. Patients who are azoospermic at the time cancer is diagnosed may be offered testicular sperm extraction and cryopreservation of testicular tissue. With pre-pubertal boys, no prevention of sterility by sperm banking is possible since no active spermatogenesis is present. However, in the next decade, prevention of sterility in childhood cancer survivors will become a major challenge for reproductive medicine. In theory, testicular stem cell banking is the only way of preserving the future fertility of boys undergoing a sterilizing chemotherapy. In animal models, testicular stem cell transplantation has proved to be effective; however, it remains to be shown that this technique is clinically efficient as well, especially when frozen-thawed cells are to be transplanted. Malignancy recurrence prevention is an important prerequisite for any clinical application of testicular stem cell transplantation. Although still at the experimental stage, cryobanking of testicular tissue from pre-pubertal boys may now be considered an acceptable strategy.

Testis-specific transcriptional control

In the testis, tissue-specific transcription is essential for proper expression of the genes that are required for the reproduction of the organism. Many testis-specific genes are required for mitotic proliferation of spermatogonia, spermatocytes undergoing genetic recombination and meiotic divisions, and differentiation of haploid spermatids. In this article we describe some of the genes that are transcribed in male germinal cells and in non-germinal testis cells. Because significant progress has been made in examination of promoter elements and their cognate transcription factors that are involved in controlling transcription of the testis-specific linker histone H1t gene in primary spermatocytes, this work will be reviewed in greater detail. The gene is transcriptionally active in spermatocytes and repressed in all other germinal and non-germinal cell types and, therefore, it serves as a model for study of regulatory mechanisms involved in testis-specific transcription.

Rat Sertoli cells express epithelial but also mesenchymal genes after immortalization with SV40

A new immortal Sertoli cell line from pubertal rat testis was established and characterized. We have generated the clonal line SCIT-C8 expressing established markers for Sertoli cells (SC) like transferrin, clusterin and steel factor/stem cell factor (SCF). Additionally, the immortalized cells express afadin, a protein which is a member of tight and adherens junctions, therefore the cells may be useful for studies of the blood-testis barrier (BTB) in vitro. In contrast to primary SC, the immortalized cells lost expression of androgen receptor and responsiveness to androgens and follicle-stimulating hormone. Surprisingly, we found mRNA expression and protein secretion of the mesenchymal markers, fibronectin and entactin-1, which we also observed for the immortalized SC lines, ASC-17D and 93RS2. In comparison to primary SC, the immortalized cells demonstrated enhanced adhesion in vitro. This correlated with the expression of entactin-1 because adhesion was strongly reduced by antibody perturbation experiments. Additionally, we found the alternatively spliced and primarily muscle cell-specific long variant of TGF-beta2 not only in peritubular cells (PC), but also in the primary and immortalized SC. Furthermore, all immortalized cell lines secreted higher amounts of TGF-beta2 than primary SC. In conclusion, the immortalized SC lines from different developmental stages showed a similar pattern of epithelial and mesenchymal markers.

Effects of follicle-stimulating hormone and androgen on proliferation of cultured testicular germ cells of embryonic chickens

A germ-Sertoli cell coculture model was established to study effects of follicle-stimulating hormone (FSH) and testosterone (T) on testicular germ cell proliferation of the embryonic chickens. Germ and somatic cells were dispersed from 18-day-old embryonic testes and cultured in 96-well plates. Germ cells were characterized by expression of stem cell factor receptor c-kit. Germ cell proliferation was assessed by an increase in cell number and expression of proliferating cell nuclear antigen (PCNA). Results showed that the germ and Sertoli cells kept alive in serum-free McCoy's 5A medium supplemented with insulin, transferrin, and selenite (ITS medium). Germ cells adhered to the free surface of Sertoli cells that spread the filopodia and formed a monolayer in ITS medium. In the serum-containing medium, Sertoli cells displayed an increment with a flat squamous form and only a few very large germ cell masses were found in the free surface of Sertoli cells. Many germ cells showed apoptosis in the McCoy's 5A medium without ITS or serum. Only germ cells showed positive staining for c-kit in the coculture. Ovine FSH (0.25-1.0 IU/ml) significantly increased the number of germ cells, and PCNA-labeling index (P < 0.05). FSH also induced stronger c-kit expression compared with the control. In the FSH-treated groups, germ cells were manifested distinct knob-like form. Similar stimulating effect was found in the germ cell number by T treatments (10(-7)-10(-6)M). Furthermore, FSH (0.5 IU/ml) combined with T significantly promoted higher testicular germ cell proliferation (P < 0.05) compared with either FSH or T alone, which indicated that interaction of FSH and T might be additive. The above results showed that the serum-free germ-Sertoli cell coculture model allowed evaluating hormonal regulation of testicular germ cell proliferation. FSH and T promoted testicular germ cell proliferation probably through indirect effects on Sertoli cells.

In vivo and in vitro differentiation of male germ cells in the mouse

Primordial germ cells appear in the embryo at about day 7 after coitum. They proliferate and migrate towards the genital ridge. Once there, they undergo differentiation into germ stem cells, known as ‘A spermatogonia’. These cells are the foundation of spermatogenesis. A spermatogonia commit to spermatogenesis, stay undifferentiated or degenerate. The differentiation of primordial germ cells to migratory, postmigratory and germ stem cells is dependent on gene expression and cellular interactions. Some of the genes that play a crucial role in germ cell differentiation areSteel, c-Kit,VASA, DAZL, fragilis, miwi, mili, mil1andmil2. Their expression is stage specific, therefore allowing solid identification of germ cells at different developmental phases. In addition to the expression of these genes, other markers associated with germ cell development are nonspecific alkaline phosphatase activity, the stage specific embryonic antigen, the transcription factorOct3/4and β1- and α6-integrins. Commitment of cells to primordial germ cells and to A spermatogonia is also dependent on induction by the bone morphogenetic protein (BMP)-4. With this knowledge, researchers were able to isolate germ stem cells from embryonic stem cell-derived embryoid bodies, and drive these into gametes eitherin vivoorin vitro. Although no viable embryos were obtained from these gametes, the prospects are that this goal is not too far from being accomplished.

Male germline-specific histones in mouse and man

In mice and humans, the production of male gametes is a result of a complex multistep process of stem cell differentiation. The final product, the mature spermatozoon, is designed for the safe delivery of a haploid copy of the paternal genetic information to the oocyte in a structural state suitable for zygote formation and embryogenesis. A remarkable structural reorganization of chromosomes in germline cells during mammalian spermatogenesis has been characterized. The most important steps are connected with the recombination events during meiosis and the final packaging of the haploid genome in the genetically inert, compacted nucleus of the sperm. Underlying the changes in chromatin organization is the appearance of testis-specific histones. Although the existence of such histones has been known for decades, their exact functions still are not established. Deciphering of the mouse and human genomes has allowed a more detailed description of the organization and regulation of the testis-specific histone genes. In addition, it has facilitated the discovery of previously unknown proteins. This review summarizes contemporary information on these germline-specific/enriched histones in both the mouse and human and outlines early achievements in the identification of their functions.

Patterns, mechanisms, and functions of translation regulation in mammalian spermatogenic cells

Translational regulation is a fundamental aspect of the atypical patterns of gene expression in mammalian meiotic and haploid spermatogenic cells. Every mRNA is at least partially translationally repressed in meiotic and haploid spermatogenic cells, but the extent of repression of individual mRNA species is regulated individually and varies greatly. Many mRNA species, such as protamine mRNAs, are stored in translationally repressed free-mRNPs in early haploid cells and translated actively in late haploid cells. However, translation does not regulate developmental expression of all mRNAs. Some mRNAs appear to be partially repressed for the entire period that the mRNA is expressed in meiotic and haploid cells, while other mRNAs, some of which are expressed at high levels, are almost totally inactivated in free-mRNPs and/or generate little or no protein. This distinctive phenomenon can be explained by the hypothesis that translational repression is used to prevent the potentionally deleterious effects of overproduction of proteins encoded by overexpressed mRNAs. Translational regulation also appears to be frequently altered by the widespread usage of alternative transcription start sites in spermatogenic cells. Many ubiquitously expressed genes generate novel transcripts in somatic spermatogenic cells containing elements, uORFs and secondary structure that are inhibitory to mRNA translation, while the ribosomal proten L32 mRNA lacks a repressive element that is present in somatic cells. Very little is known about the mechanisms that regulate mRNA translation in spermatogenic cells, largely because few labs have utilized in vivo genetic approaches, although there have been important insights into the repression and activation of protamine 1 mRNA, and the role of Y-box proteins and poly(A) lengthening in mRNA-specific translational activation mediated by the cytoplasmic poly(A) element binding protein and a testis-specific isoform of poly(A) polymerase. A very large literature by evolutionary biologists suggests that the atypical patterns of gene expression in spermatogenic cells are the consequence of the powerful and unusual selective pressures on male reproductive success.

Establishment of a normal medakafish spermatogonial cell line capable of sperm production in vitro

Spermatogonia are the male germ stem cells that continuously produce sperm for the next generation. Spermatogenesis is a complicated process that proceeds through mitotic phase of stem cell renewal and differentiation, meiotic phase, and postmeiotic phase of spermiogenesis. Full recapitulation of spermatogenesis in vitro has been impossible, as generation of normal spermatogonial stem cell lines without immortalization and production of motile sperm from these cells after long-term culture have not been achieved. Here we report the derivation of a normal spermatogonial cell line from a mature medakafish testis without immortalization. After 140 passages during 2 years of culture, this cell line retains stable but growth factor-dependent proliferation, a diploid karyotype, and the phenotype and gene expression pattern of spermatogonial stem cells. Furthermore, we show that this cell line can undergo meiosis and spermiogenesis to generate motile sperm. Therefore, the ability of continuous proliferation and sperm production in culture is an intrinsic property of medaka spermatogonial stem cells, and immortalization apparently is not necessary to derive male germ cell cultures. Our findings and cell line will offer a unique opportunity to study and recapitulate spermatogenesis in vitro and to develop approaches for germ-line transmission.

Pathways of post-transcriptional gene regulation in mammalian germ cell development

Male germ cell development is orchestrated by complex and disparate patterns of gene expression operating in different cell types. The mechanisms of gene expression underlying these have been dissected in the mouse because of its readily available genetics. These analyses have shown that as well as the traditional transcriptional mechanisms, post-transcriptional regulatory pathways of gene expression are essential for mouse spermatogenesis. Proteins essential for germ cell development have been identified which operate at different points throughout the life cycle of RNA from pre-mRNA splicing to translation and RNA decay in the cytoplasm. Recent data suggests that these post-transcriptional pathways respond to environmental cues via signalling pathways.

Post-meiotic gene products as targets for male contraception

Post-meiotic stages of male germ cell maturation represent an interesting target system for the development of novel male contraceptive agents. In the human, these stages represent a period of only about 16 days differentiation, and thus targeting these cells would represent a contraceptive approach with a relatively rapid onset and equivalent recovery. Results from the Human Genome Project suggest that these cells also express a high number of very specific transcripts, though whether all of these are functional and/or essential for sperm differentiation and function requires more research. Until recently, however, these haploid stages were relatively inaccessible to molecular research because of the lack of appropriate model systems and methods. This situation has recently improved, with several new techniques involving manipulation of primary cells and seminiferous tubules, germ cell transplantation and the development of new immortalized cell-lines. Also, new biochemical approaches are yielding more information about haploid-specific transcription factors, such as GCNF. It is therefore to be expected that soon several new targets for a potential post-meiotic male contraceptive will become available for pharmaceutical development.

Transgenic zebrafish produced by retroviral infection of in vitro-cultured sperm

Transgenic modification of sperm before fertilization has distinct advantages over conventional transgenic methods. The primary advantage is that the mosaicism inherent in those other techniques is avoided. A culture system using primary cultures of zebrafish male germ cells, in which the differentiation from spermatogonia to functional sperm can occur in vitro, provides the opportunity for genetic modification of sperm in vitro. Here, we report the production of transgenic zebrafish from cultured sperm. The sperm were differentiated from premeiotic germ cells infected with a pseudotyped retrovirus in vitro. The collected sperm were used to perform successful in vitro fertilizations, and transgenic embryos were identified. The transgenic fish transmitted the proviral integration to the next generation in a Mendelian fashion. We report the generation of a transgenic animal by cultured sperm and open the door to many exciting possibilities for the rapid generation of transgenic lines in model organisms such as zebrafish or other animal systems that are otherwise intractable to transgenesis.

Transient expression analysis of the mouse ornithine decarboxylase antizyme haploid-specific promoter using in vivo electroporation

The testicular isoform of the ornithine decarboxylase antizyme (OAZt) gene is expressed exclusively in the haploid spermatids of mice. The 357-bp region, which includes a TATA-less promoter and an untranslated region, is sufficient for OAZt gene expression in the spermatids of transgenic mice. In this study, in vivo transient transfection to living mouse testes was used to define the transcriptional regulatory elements of the OAZt gene promoter. We found that the 10-bp element that contains an initiator (Inr) plays a central role as the core promoter, in combination with a downstream element, while two cyclic adenosine monophosphate-responsive element (CRE)-like sites in the upstream region also contribute to promoter activity. The electrophoretic mobility shift assay showed binding of the testis-specific factors to these elements. Our results show that the in vivo DNA transfer technique enables detailed analysis of haploid germ cell-specific gene regulation in mice.

Derivation and morphological characterization of mouse spermatogonial stem cell lines

Spermatogonial stem cells (SSCs), having yet to possess decisive markers, can only be detected retrospectively by transplantation assay. It was reported recently that mouse gonocytes collected from DBA/2 and ICR neonates propagated in vitro. This cultured germ cell, named the germline stem cell (GS cell), produced functional sperm to make progeny when transplanted into recipient mouse testes. Here we show that GS cell lines can be established not only from neonatal testes but also from the testis of adult mice. We also confirmed that GS cells once transplanted into a host testis can be recovered to resume in vitro expansion, indicating that they are convertible mutually with SSCs in adult testes. Confocal laser microscopic examination showed GS cells resemble undifferentiated spermatogonia in the adult testis. This unique cell line could be useful for research in germ cell biology and applicable as a new tool for the genetic engineering of animals.

Spermatogonial depletion in adult Pin1-deficient mice

Spermatogonia in the mouse testis arise from early postnatal gonocytes that are derived from primordial germ cells (PGCs) during embryonic development. The proliferation, self-renewal, and differentiation of spermatogonial stem cells provide the basis for the continuing integrity of spermatogenesis. We previously reported that Pin1-deficient embryos had a profoundly reduced number of PGCs and that Pin1 was critical to ensure appropriate proliferation of PGCs. The current investigation aimed to elucidate the function of Pin1 in postnatal germ cell development by analyzing spermatogenesis in adult Pin1-/- mice. Although Pin1 was ubiquitously expressed in the adult testis, we found it to be most highly expressed in spermatogonia and Sertoli cells. Correspondingly, we show here that Pin1 plays an essential role in maintaining spermatogonia in the adult testis. Germ cells in postnatal Pin1-/- testis were able to initiate and complete spermatogenesis, culminated by production of mature spermatozoa. However, there was a progressive and age-dependent degeneration of the spermatogenic cells in Pin1-/- testis that led to complete germ cell loss by 14 mo of age. This depletion of germ cells was not due to increased cell apoptosis. Rather, detailed analysis of the seminiferous tubules using a germ cell-specific marker revealed that depletion of spermatogonia was the first step in the degenerative process and led to disruption of spermatogenesis, which resulted in eventual tubule degeneration. These results reveal that the presence of Pin1 is required to regulate proliferation and/or cell fate of undifferentiated spermatogonia in the adult mouse testis.

Morphological characterization of the spermatogonial subtypes in the neonatal mouse testis

Spermatogenesis is the process of differentiation of diploid type A spermatogonia to haploid spermatozoa. Several subtypes of A spermatogonia have been characterized in the adult mouse testis. These include A-single (A(s)), A-paired (A(pr)), A-aligned (A(al)), and A1-A4. However, in the immature testis, very little information is available on subtypes and morphological features of type A spermatogonia. Six-day-old mouse testes, fixed either in Bouin solution or 5% glutaraldehyde, were embedded in paraffin and Epon, respectively. Thick sections (approximately 1 microm) of Epon-embedded tissue were stained with toluidine blue and revealed three subtypes of spermatogonia by light microscopy. The smallest spermatogonia (subtype I) appeared as single cells and exhibited a round or oval flattened nucleus with one or two prominent dense nucleoli and a characteristic unstained round and centrally located vacuole. These cells bound toluidine blue more avidly and appeared darker in comparison with the other cell types. Electron microscopy of thin sections (90 nm) revealed a finely granulated chromatin homogeneously distributed in the nucleus and sparse organelles in the cytoplasm. The second subtype of spermatogonia (subtype II) also displayed dark staining but was larger than subtype I; there was no central vacuole in the nucleus and heterochromatin clumps were observed. The largest subtype of spermatogonia (subtype III) showed large heterochromatin clumps and a pale staining nucleus. Intercellular bridges were noted between subtypes II and III. Based on the dye avidity, the three subtypes were classified as dark, transitional, and pale spermatogonia, respectively. Image analyses of 30 different cells of each subtype revealed a decline in gray-scale intensity from subtype I to III. Five-micrometer sections of paraffin-embedded tissue were immunoassayed with an antibody against the glial cell-derived neurotrophic factor family receptor alpha-1 (GFRalpha-1) receptor, a putative marker for undifferentiated spermatogonia, showing positive reaction only in germ cells. The pattern of GFRalpha-1 expression, coupled to the overall morphology of the cells, indicates that at this stage of development, mouse seminiferous tubules contain essentially A(s), A(pr), and possibly A(al) spermatogonia. Thus, the present study indicates the presence of subtypes of type A spermatogonia in the immature mouse testis similar to that described previously in adult monkey and man.

Long-term culture and transplantation of murine testicular germ cells

The objectives of this study were to develop an in vitro culture system to optimize germ cell proliferation and to measure the potential of the cultured germ cells to produce mature spermatozoa after transplantation into a recipient. Donor germ cells isolated from ROSA26 male mice were cultured with a STO feeder cell layer in Dulbecco's minimal essential medium (DMEM) supplemented with fetal bovine serum (FBS), stem cell factor, leukemia inhibitory factor, basic fibroblast growth factor, insulin-like growth factor 1, interleukin-11, L-glutamine, sodium pyruvate, 2-mercaptoethanol, murine oncostatin M, and platelet-derived growth factor. Donor germ cells formed colonies in the primary cultures after 8-21 days. These cultured colonies were maintained for 4 weeks or longer without subculture and proliferated for up to 8 passages over a period of 3 months. These colonies had alkaline phosphatase activity and incorporated 5-bromo-2'-deoxyuridine. These colonies were positive partially when screened with antibody for germ cell nuclear antigen and c-kit. Germ cells cultured with this supplemented medium showed enhanced colonization vs controls cultured with DMEM and FBS. Cultured germ cells from Rosa26 donors were transplanted into testes and were identified by X-gal staining and histological screening. The cells cultured in the supplemented medium colonized the tubules and initiated spermatogenesis in the recipient mice. This is an improved method for culturing germ cells and may be useful in gene therapy and the production of transgenic animals.

Seminolipid and its precursor/degradative product, galactosylalkylacylglycerol, in the testis of saposin A- and prosaposin-deficient mice

Sphingolipid activator proteins (saposins A, B, C, and D) are derived from a common precursor protein (prosaposin) and specifically activate in vivo degradation of glycolipids with short carbohydrate chains. A mouse model of prosaposin deficiency (prosaposin-/-) closely mimics the human disease with an elevation of multiple glycolipids. The recently developed saposin A-/- mice showed a chronic form of globoid cell leukodystrophy, establishing the essential in vivo role of saposin A as an activator for galactosylceramidase to degrade galactosylceramide. Seminolipid, the principal glycolipid in spermatozoa, and its precursor/degradative product, galactosylalkylacylglycerol (GalEAG), were analyzed in the testis of the two mouse mutants by electrospray ionization mass spectrometry. Saposin A-/- mice showed the normal seminolipid level, while that of prosaposin-/- mice was approximately 150% of the normal level at the terminal stage. In contrast, GalEAG increased up to 10 times in saposin A-/- mice, whereas it decreased with age in the wild-type as well as in prosaposin-/- mice. These analytical findings on the two saposin mutants may shed some light on the physiological function of seminolipid and GalEAG.

Long-term proliferation in culture and germline transmission of mouse male germline stem cells

Spermatogenesis is a complex process that originates in a small population of spermatogonial stem cells. Here we report the in vitro culture of spermatogonial stem cells that proliferate for long periods of time. In the presence of glial cell line-derived neurotrophic factor, epidermal growth factor, basic fibroblast growth factor, and leukemia inhibitory factor, gonocytes isolated from neonatal mouse testis proliferated over a 5-month period (>10(14)-fold) and restored fertility to congenitally infertile recipient mice following transplantation into seminiferous tubules. Long-term spermatogonial stem cell culture will be useful for studying spermatogenesis mechanism and has important implications for developing new technology in transgenesis or medicine.

Mouse round spermatids developed in vitro from preexisting spermatocytes can produce normal offspring by nuclear injection into in vivo-developed mature oocytes

It has been shown that mature oocytes injected with nuclei from round spermatids collected from mouse testis can generate normal offspring and that round spermatids can develop in vitro. An undetermined issue is whether spermatids developed in vitro are capable of generating fertile offspring by nuclear injection into oocytes. Herein, we report the production of normal and fertile offspring by nuclear injection using haploid spermatid donors derived from mouse primary spermatocyte precursors cocultured with Sertoli cells. Cocultured spermatogonia and spermatocytes were characterized by their nuclear immunoreactive patterns determined by an antibody to phosphorylated histone H2AX (gamma-H2AX), a marker for DNA double-strand breaks. Cocultured round spermatid progenies display more than one motile flagellum, whose axonemes were recognized by antitubulin immunostaining. Flagellar wavelike movement and flagellar-driven propulsion of round spermatids developed in vitro were documented by videomicroscopy (http://www.sci.ccny.cuny.edu/ approximately kier). We also show that breeding of male and female mouse offspring generated by spermatid nuclear injection produced fertile offspring. In addition to their capacity to produce fertile offspring, cocultured, flagellated round spermatids can facilitate the analysis of the mechanisms of centriolar polarity, duplication, assembly, and flagellar growth, including the intraflagellar transport of cargo proteins.

Identification and characterization of stem cells in prepubertal spermatogenesis in mice

The stem cell properties of gonocytes and prospermatogonia at prepubertal stages are still largely unknown: it is not clear whether gonocytes and prospermatogonia are a special cell type or similar to adult undifferentiated spermatogonia. To characterize these cells, we have established transgenic mice carrying EGFP (enhanced green fluorescence protein) cDNA under control of an Oct4 18-kb genomic fragment containing the minimal promoter and proximal and distal enhancers; Oct4 is reported to be expressed in undifferentiated spermatogonia at prepubertal stages. Generation of transgenic mice enabled us to purify gonocytes and prospermatogonia from the somatic cells of the testis. Transplantation studies of testicular cells so far have been done with a mixture of germ cells and somatic cells. This is the first report that establishes how to purify germ cells from total testicular cells, enabling evaluation of cell-autonomous repopulating activity of a subpopulation of prospermatogonia. We show that prospermatogonia differ markedly from adult spermatogonia in both the size of the KIT-negative population and cell cycle characteristics. The GFP(+) KIT(-) fraction of prospermatogonia has much higher repopulating activity than does the GFP(+)KIT(+) population in the adult environment. Interestingly, the GFP(+)KIT(+) population still exhibits repopulating activity, unlike adult KIT-positive spermatogonia. We also show that ALCAM, activated leukocyte cell adhesion molecule, is expressed transiently in gonocytes. Sertoli cells and myoid cells also express ALCAM at the same stage, suggesting that ALCAM may contribute to gonocyte-Sertoli cell adhesion and migration of gonoyctes toward the basement membrane.

Specific binding of nuclear proteins to a bifunctional promoter element upstream of the H1/AC box of the testis-specific histone H1t gene

The testis-specific histone H1t gene is transcribed exclusively in primary spermatocytes during spermatogenesis. Studies with transgenic mice show that 141 base pairs (bp) of the H1t proximal promoter accompanied with 800 bp of downstream sequence are sufficient for tissue-specific transcription. Nuclear proteins from testis and pachytene spermatocytes produce footprints spanning the region covering the repressor element (RE) from 100 to 125 nucleotides upstream of the H1t transcriptional initiation site. Only testis nuclear proteins bind to the 5'-end of the element and produce a unique, low-mobility complex in electrophoretic mobility shift assays. This testis complex is distinct from the complex formed by a repressor protein derived from several cell lines that binds to the 3'-end of the element. The testis complex band is formed when using nuclear proteins from primary spermatocytes, where the H1t gene is transcribed, and band intensity drops 70%-80% when using nuclear proteins from early spermatids, where H1t gene transcription ceases. Protein-DNA cross-linking experiments using testis nuclear proteins produce electrophoretic bands of 59, 52, and 50 kDa on SDS/PAGE gels.

Progeny from sperm obtained after ectopic grafting of neonatal mouse testes

Ectopic grafting of testicular tissue is a promising new approach that can be used to preserve testicular function. This technique has been used recently to differentiate the neonatal testes of different species, up to the level of complete spermatogenesis. This approach can be applied successfully to generate live progeny using sperm extracted from grafts originating from testes of newborn donors. The sperm are capable of supporting normal development and producing fertile male and female offspring after intracytoplasmic injection into mouse oocytes and embryo transfer into surrogate mothers. The grafted tissue was also capable of significantly normalizing reproductive hormone levels in the castrated recipients. This technique presents new avenues for experimentation. The recipient mouse can be regarded as a living incubator and a culture system of testicular tissue, allowing the experimental manipulation of several aspects of testis development and spermatogenesis. The successful generation of pups indicates that this technique can be used to study the testicular phenotype and to breed mutant or transgenic mouse strains with lethal postnatal phenotypes. The ability to generate sperm from the germ line ex vivo also paves the way for the development of new strategies for preserving fertility in boys undergoing cancer therapy.

New insights into the rat spermatogonial proteome: identification of 156 additional proteins

Despite the essential role played by spermatogonia in testicular function, little is known about these cells. To improve our understanding of their biology, our group recently identified a set of 53 spermatogonial proteins using two-dimensional (2-D) gel electrophoresis and mass spectrometry. To continue this work, we investigated a subset of the spermatogonial proteome using narrow range immobilized pH gradients to favor the detection of less abundant proteins. A 2-D reference map of spermatogonia in the pH range 4-9 was created, and protein entities fractionated in a pH 5-6 2-D gel were further processed for protein identification. A new set of 156 polypeptides was identified by peptide mass fingerprinting and tandem mass spectrometry. These polypeptides corresponded to 102 different proteins, which reflect the complexity of post-translational modifications. Seventy-nine of these proteins were identified for the first time in spermatogonia. All identified proteins were classified into functional groups. This work represents a first step toward the establishment of a systematic spermatogonia protein database.

Male germ line stem cells: from cell biology to cell therapy

Research using stem cells has several applications in basic biology and clinical medicine. Recent advances in the establishment of male germ line stem cells provided researchers with the ability to identify, isolate, maintain, expand and differentiate the spermatogonia, the primitive male germ cells, as cell lines under in vitro conditions. The ability to culture and manipulate stem cell lines from male germ cells has gradually facilitated research into spermatogenesis and male infertility, to an extent beyond that facilitated by the use of somatic stem cells. After the introduction of exogenous genes, the spermatogonial cells can be transplanted into the seminiferous tubules of recipients, where the transplanted cells can contribute to the offspring. The present review concentrates on the origin, life cycle and establishment of stem cell lines from male germ cells, as well as the current status of transplantation techniques and the application of spermatogonial stem cell lines.

Prospects for spermatogenesis in vitro

In recent years, extraordinary progress has been made in a broad range of reproductive technologies, including spermatogonial transplantation in the male. However, effective procedures for the complete recapitulation of spermatogenesis in vitro, including meiosis, have remained elusive. Such procedures have the potential to facilitate (1) mechanistic studies of spermatogenesis, (2) directed genetic modification of the male germ line, and (3) treatment of male factor infertility. Early studies demonstrated the importance of germ cell-Sertoli association for germ cell survival in vitro. Recently, evidence for male germ cell survival and progression through meiosis has been reported for the rat, mouse, and man. We demonstrated the expression of spermatid-specific genes (protamine and transition protein 1) by alginate-encapsulate neonatal bull testis cells after 10 weeks in culture, suggesting that meiosis had occurred. Although identifiable germ cells in these cultures were very sparse, some indication of acrosome development was observed. Following round spermatid injection (ROSI) with presumptive spermatids produced in vitro, 50% of blastocysts produced were diploid and 37% were Y-chromosome positive. Improved culture conditions, which promote germ cell survival, differentiation, and proliferation, are essential for in vitro spermatogenesis (IVS) to become a useful technology. Other approaches to male germ cell manipulation and spermatid production are discussed.

Mouse models of male infertility

Spermatogenesis is a complex process that involves stem-cell renewal, genome reorganization and genome repackaging, and that culminates in the production of motile gametes. Problems at all stages of spermatogenesis contribute to human infertility, but few of them can be modelled in vitro or in cell culture. Targeted mutagenesis in the mouse provides a powerful method to analyse these steps and has provided new insights into the origins of male infertility.