Immortalization of murine male germ cells at a discrete stage of differentiation by a novel directed promoter-based selection strategy

YTHDF2 promotes spermagonial adhesion through modulating MMPs decay via m6A/mRNA pathway

As the foundation of male fertility, spermatogenesis is a complicated and highly controlled process. YTHDF2 plays regulatory roles in biological processes through accelerating the degradation of target mRNAs. However, the function of YTHDF2 in spermatogenesis remains elusive. Here, we knocked out Ythdf2 in mouse spermatogonia via CRISPR/Cas9, and found that depletion of Ythdf2 mainly downregulated the expression of matrix metallopeptidase (MMPs), thus affecting cell adhesion and proliferation. m⁶A-IP-PCR and RIP-PCR analysis showed that Mmp3, Mmp13, Adamts1 and Adamts9 were modified with m⁶A and simultaneously interacted with YTHDF2. Moreover, inhibition of Mmp13 partially rescued the phenotypes in Ythdf2-KO cells. Taken together, YTHDF2 regulates cell-matrix adhesion and proliferation through modulating the expression of Mmps by the m⁶A/mRNA degradation pathway.

Atp7a and Atp7b regulate copper homeostasis in developing male germ cells in mice

The maintenance of copper homeostasis is critical for all cells. As learned from mice with disturbed copper metabolism, this trace element is also important for spermatogenesis. The experiments conducted in yeasts have demonstrated that appropriate copper level must be preserved to enable meiosis progression; however, increased copper level is toxic for cells. This study aims to analyze the expression profile of Atp7a and Atp7b and other genes encoding copper-related proteins during spermatogenesis in mice. Using the transcripts and protein detection techniques, we demonstrate that within seminiferous tubuli, ATP7A is mainly present in early meiotic germ cells (leptotene to pachytene spermatocytes) and in Sertoli cells (SCs). During spermatogenesis, the progression Atp7a expression profile corresponds to Slc31a1 (encoding copper importer CTR1) and Atox1 (encoding chaperon protein, which delivers copper from CTR1 to ATP7A and ATP7B) expression, suggesting that male germ cells retrieve copper and ATP7A protects them from copper overdose. In contrast, ATP7B protein is observed in SCs and near elongated spermatids; thus, its function seems to be related to copper extraction during spermiogenesis. This is the first study to give a comprehensive view on the activity of copper-related genes during spermatogenesis in mice.

Establishment and applications of male germ cell and Sertoli cell lines

Within the seminiferous tubules there are two major cell types, namely male germ cells and Sertoli cells. Recent studies have demonstrated that male germ cells and Sertoli cells can have significant applications in treating male infertility and other diseases. However, primary male germ cells are hard to proliferate in vitro and the number of spermatogonial stem cells is scarce. Therefore, methods that promote the expansion of these cell populations are essential for their use from the bench to the bed side. Notably, a number of cell lines for rodent spermatogonia, spermatocytes and Sertoli cells have been developed, and significantly we have successfully established a human spermatogonial stem cell line with an unlimited proliferation potential and no tumor formation. This newly developed cell line could provide an abundant source of cells for uncovering molecular mechanisms underlying human spermatogenesis and for their utilization in the field of reproductive and regenerative medicine. In this review, we discuss the methods for establishing spermatogonial, spermatocyte and Sertoli cell lines using various kinds of approaches, including spontaneity, transgenic animals with oncogenes, simian virus 40 (SV40) large T antigen, the gene coding for a temperature-sensitive mutant of p53, telomerase reverse gene (Tert), and the specific promoter-based selection strategy. We further highlight the essential applications of these cell lines in basic research and translation medicine.

BET Protein BRDT Complexes With HDAC1, PRMT5, and TRIM28 and Functions in Transcriptional Repression During Spermatogenesis

The expression of BRDT, a member of the BET sub-family of double bromodomain-containing proteins, is restricted to the male germ line, specifically to pachytene-diplotene spermatocytes and early spermatids. We previously showed that loss of the first bromodomain of BRDT by targeted mutagenesis (Brdt(ΔBD1) ) resulted in sterility and abnormalities in spermiogenesis, but little is known about BRDT's function at the molecular level. As part of studies designed to identify BRDT-interacting proteins we stably introduced a FLAG-tagged BRDT cDNA into 293T cells, which do not normally express BRDT. Affinity-purification of FLAG-tagged BRDT complexes indicated that BRDT has novel interactions with the histone deacetylase HDAC1, the arginine-specific histone methyltransferase 5 PRMT5, and the Tripartite motif-containing 28 protein TRIM28. Immunofluorescent microscopy revealed that BRDT co-localized with each of these proteins in round spermatids and co-immunoprecipitation of testicular extracts showed that these proteins interact with BRDT. Furthermore, they bind the promoter of H1t, a putative target of BRDT-containing complexes. This binding of H1t was lost in mice expressing the Brdt(ΔBD1) mutant protein and concomitantly, H1t expression was elevated in round spermatids. Our study reveals a role for BRDT-containing complexes in the repression of gene expression in vivo that correlates with dramatic effects on chromatin remodeling and the progression of spermiogenesis.

Lrrc34, a novel nucleolar protein, interacts with npm1 and ncl and has an impact on pluripotent stem cells

The gene Lrrc34 (leucine rich repeat containing 34) is highly expressed in pluripotent stem cells and its expression is strongly downregulated upon differentiation. These results let us to suggest a role for Lrrc34 in the regulation and maintenance of pluripotency. Expression analyses revealed that Lrrc34 is predominantly expressed in pluripotent stem cells and has an impact on the expression of known pluripotency genes, such as Oct4. Methylation studies of the Lrrc34 promoter showed a hypomethylation in undifferentiated stem cells and chromatin immunoprecipitation-quantitative polymerase chain reaction analyses of histone modifications revealed an enrichment of activating histone modifications on the Lrrc34 promoter region. Further, we could verify the nucleolus-the place of ribosome biogenesis-as the major subcellular localization of the LRRC34 protein. We have verified the interaction of LRRC34 with two major nucleolar proteins, Nucleophosmin and Nucleolin, by two independent methods, suggesting a role for Lrrc34 in ribosome biogenesis of pluripotent stem cells. In conclusion, LRRC34 is a novel nucleolar protein that is predominantly expressed in pluripotent stem cells. Its altered expression has an impact on pluripotency-regulating genes and it interacts with proteins known to be involved in ribosome biogenesis. Therefore we suggest a role for Lrrc34 in ribosome biogenesis of pluripotent stem cells.

Sp1 transcription factor and GATA1 cis-acting elements modulate testis-specific expression of mouse cyclin A1

Cyclin A1 is a male germ cell-specific cell cycle regulator that is essential for spermatogenesis. It is unique among the cyclins by virtue of its highly restricted expression in vivo, being present in pachytene and diplotene spermatocytes and not in earlier or later stages of spermatogenesis. To begin to understand the molecular mechanisms responsible for this narrow window of expression of the mouse cyclin A1 (Ccna1) gene, we carried out a detailed analysis of its promoter. We defined a 170-bp region within the promoter and showed that it is involved in repression of Ccna1 in cultured cells. Within this region we identified known cis-acting transcription factor binding sequences, including an Sp1-binding site and two GATA1-binding sites. Neither Sp1 nor GATA1 is expressed in pachytene spermatocytes and later stages of germ cell differentiation. Sp1 is readily detected at earlier stages of spermatogenesis. Site-directed mutagenesis demonstrated that neither factor alone was sufficient to significantly repress expression driven by the Ccna1 promoter, while concurrent binding of Sp1, and most likely GATA1 and possibly additional factors was inhibitory. Occupancy of Sp1 on the Ccna1 promoter and influence of GATA1-dependent cis-acting elements was confirmed by ChIP analysis in cell lines and most importantly, in spermatogonia. In contrast with many other testis-specific genes, the CpG island methylation status of the Ccna1 promoter was similar among various tissues examined, irrespective of whether Ccna1 was transcriptionally active, suggesting that this regulatory mechanism is not involved in the restricted expression of Ccna1.

Transgenic Mouse Studies to Understand the Regulation, Expression and Function of the Testis-Specific Protein Y-Encoded (TSPY) Gene

The TSPY gene, which encodes the testis-specific protein, Y-encoded, was first discovered and characterized in humans, but orthologous genes were subsequently identified on the Y chromosome of many other placental mammals. TSPY is expressed in the testis and to a much lesser extent in the prostate gland, and it is assumed that TSPY serves function in spermatogonial proliferation and/or differentiation. It is further supposed that TSPY is involved in male infertility and exerts oncogenic effects in gonadal and prostate tumor formation. As a member of the TSPY/SET/NAP protein family, TSPY is able to bind cyclin B types, and stimulates the cyclin B1-CDK1 kinase activity, thereby accelerating the G₂/M phase transition of the cell cycle of target cells. Because the laboratory mouse carries only a nonfunctional Y-chromosomal Tspy-ps pseudogene, a knockout mouse model for functional research analyses is not a feasible approach. In the last decade, three classical transgenic mouse models have been developed to contribute to our understanding of TSPY regulation, expression and function. The different transgenic mouse approaches and their relevance for studying TSPY regulation, expression and function are discussed in this review.

Molecular and functional characterization of the murine ldh2 promoter region: Sp-binding GC-box domains are the key cis-elements regulating ldh2 gene expression during spermatogenesis

The goal of the present study was to elucidate the specific transcriptional mechanisms that regulate ldh2 gene expression during the early stages of spermatogenesis. DNA sequence analysis of the 1.0-kb ldh2 promoter region directly upstream of the transcriptional start site indicated the presence of three SP-protein binding GC-box elements and the absence of TATA and CAAT boxes. Functional characterization studies of the mouse ldh2 promoter were performed in the SV40 transformed mouse spermatogonial cell line, GC-1 spg. Transfection/transient expression studies using full-length and truncated ldh2 promoter/luciferase reporter constructs revealed that all three of the SP-binding cis-regulatory GC-box elements are required for optimal ldh2 promoter activity. Additional site-directed mutagenesis studies indicated that the two most proximal GC-box sites play essential regulatory roles in mediating basal ldh2 promoter activity. These studies suggest that the expression of the ldh2 gene in spermatogonia and early spermatocytes are regulated by SP-mediated transcriptional mechanisms.

In vitro culture of testicular germ cells: regulatory factors and limitations

Spermatogenesis is regulated mainly by endocrine factors and also by testicular paracrine/autocrine growth factors. These factors are produced by Sertoli cells, germ cells, peritubular cells and interstitial cells, mainly Leydig cells and macrophages. The interactions and the ratio between Sertoli and germ cells in the seminiferous tubules ensure successful spermatogenesis. In order to culture spermatogonial stem cells (SSCs) in vitro, researchers tried to overcome some of the obstacles -- such as the low number of stem cells in the testis, absence of specific markers to identify SSCs -- in addition to difficulties in keeping the SSCs alive in culture. Recently, some growth factors important for the proliferation and differentiation of SSCs were identified, such as glial cell line derived neurotrophic factor (GDNF), stem cell factor (SCF) and leukemia inhibitory factor (LIF); also, markers for SSCs at different stages were reported. Therefore, some groups succeeded in culturing SSCs (under limitations), or more differentiated cells and even were able to produce in vitro germ cells from embryonic stem cells. Thus, success in culturing SSCs is dependent on understanding the molecular mechanisms behind self-renewal and differentiation. Culture of SSCs should be a good tool for discovering new therapeutic avenue for some infertile men or for patients undergoing chemotherapy/radiotherapy (pre-puberty or post-puberty).

Spermatogonial stem cells: characteristics and experimental possibilities

The continuation of the spermatogenic process throughout life relies on a proper regulation of self-renewal and differentiation of the spermatogonial stem cells. These are single cells situated on the basal membrane of the seminiferous epithelium. Only 0.03% of all germ cells are spermatogonial stem cells. They are the only cell type that can repopulate and restore fertility to congenitally infertile recipient mice following transplantation. Although numerous expression markers have been helpful in isolating and enriching spermatogonial stem cells, such as expression of THY-1 and GFRalpha-1 and absence of c-kit, no specific marker for this cell type has yet been identified. Much effort has been put into developing a protocol for the maintenance of spermatogonial cells in vitro. Recently, coculture systems of testicular cells on various feeder cells have made it possible to culture spermatogonial stem cells for a long period of time, as was demonstrated by the transplantation assay. Even expansion of testicular cells, including the spermatogonial stem cells, has been achieved. In these culture systems, hormones and growth factors are investigated for their role in the process of proliferation of spermatogonial stem cells. At the moment the best culture system known still consists of a mixture of testicular cells with about 1.33% spermatogonial stem cells. Recently pure SV40 large T immortalized spermatogonial stem cell lines have been established. These c-kit-negative cell lines did not show any differentiation in vitro or in vivo. A telomerase immortalized c-kit-positive spermatogonial cell line has been established that was able to differentiate in vitro. Spermatocytes and even spermatids were formed. However, spermatogonial stem cell activity by means of the transplantation assay was not tested for this cell line. Both the primary long-term cultures and immortalized cell lines have represented a major step forward in investigating the regulation of spermatogonial self-renewal and differentiation, and will be useful for identifying specific molecular markers.

Characterization of a human TSPY promoter

Human TSPY is a candidate oncogene and is supposed to function as a proliferation factor during spermatogenesis. It is the only mammalian protein-coding gene known to be organized as a tandem repeat gene family. It is expressed at highest level in spermatogonia and to a lower amount in primary spermatocytes. To characterize the human TSPY promoter we used the luciferase reporter system in a mouse spermatogonia derived cell line (GC-1 spg) and in a GC-4 spc cell line, that harbour prophase spermatocytes of the preleptotene and early pachytene stage. We isolated a 1303 bp fragment of the 5'-flanking region of exon 1 that shows significant promoter activity in GC-1 spg and reduced activity in GC-4 spc cells. In order to gain further insight into the organization of the TSPY-promoter, stepwise truncations of the putative promoter sequence were performed. The resulting fragments were cloned into the pGL 3-vector and analysed for reporter gene activity in the murine germ cell lines GC-1 spg and GC-4 spc, leading to the characterization of a core promoter (--159 to--1), an enhancing region (--673 to--364) and a silencing region (--1262 to--669). Database research for cis-active elements yielded two putative SOX-like binding sites in the enhancing region and reporter gene activity was drastically reduced when three nucleotides of the AACAAT SOX core sequence were mutated. Our findings strongly suggest that testis-specific expression of human TSPY is mediated by Sox proteins.

Efforts to create an artificial testis: culture systems of male germ cells under biochemical conditions resembling the seminiferous tubular biochemical environment

Induction of meiotic and post-meiotic alterations of male germ cells in vitro has been the target of several research efforts since 1960. However, to date, the establishment of an ideal culture system in which spermatogonial stem cells can be maintained and directed to proliferate and undergo meiosis and complete spermiogenesis does not exist. This is attributed to the difficulties concerning the isolation and purification of defined subpopulations of germ cells and the establishment of male germ cell lines. In addition, there is no adequate knowledge regarding the optimal biochemical conditions that promote the survival and differentiation of germ cells in long-term cultures. This review focuses on the methodologies that have been proved sufficient to achieve differentiation of cultured male germ cells. Furthermore, the factors regulating spermatogenesis and the technical prerequisites to achieve differentiation of cultured male germ cells are described. Finally, the role of in vitro cultures of immature diploid germ cells in the therapeutic management of men negative for haploid cells in their testes and the subsequent potential genetic and epigenetic risks are discussed.

A Cre gene directed by a human TSPY promoter is specific for germ cells and neurons

The testis-specific protein Y-encoded (TSPY) gene is a candidate for the gonadoblastoma locus on the Y chromosome and is expressed in normal testicular germ cells and gonadoblastoma cells of XY sex-reversed females. Although TSPY expression has been demonstrated in gonadoblastoma tissues, it is uncertain if such expression is involved in a causative or consequential event of the oncogenic process. We postulate that if TSPY is involved in gonadoblastoma development, its promoter should be functional in the female gonad before and/or at early stages of tumorigenesis. To test this hypothesis, we generated several lines of transgenic mice harboring a Cre-recombinase transgene directed by a 2.4-kb hTSPY promoter. These mice were crossed with the Z/EG reporter line that expresses EGFP only after a Cre-mediated recombination. Our results showed that hTSPY-Cre;Z/EG double transgenic mice expressed EGFP specifically in the germ cells of both male and female gonads. Further, neurons of the central and peripheral nervous systems also expressed EGFP as early as E12.5 embryonic stage. EGFP was particularly observed in the trigeminal nerve, trigeminal ganglion, dorsal root of the ganglia, and in postnatal and adult brains. These observations support the hypothesis that TSPY plays an active role in gonadoblastoma. The tissue-specific expression of the hTSPY-Cre transgene should also be useful in studies utilizing Cre-mediated gene activation/inactivation strategies in gamatogenesis and/or neurogenesis.

Testicular cell lines

The range of in vivo or in vitro immortalized cell lines currently available provides a variety of model systems for studies of normal and pathological cell functions. The cell lines have been derived from spontaneous or experimentally induced tumors, or through in vitro immortalization. The transgenic (TG) techniques provide a powerful approach, allowing the production of in vivo animal models for a variety of diseases, including malignant tumors, through tissue-specific expression of oncogenes or other tumor-promoting genes. The TG techniques also enable the production of cell lines with specific characteristics, through insertion of desired genes into specific cell types, which can then be immortalized upon cell culture. The use of temperature-sensitive immortalizing genes offers an additional advantage of controlling gene expression, including the proliferation and differentiation of the cells to be immortalized. As regards the male reproductive system, a number of cell lines of testicular somatic cells are currently available. This review covers mainly the immortalized cell lines of testicular Leydig and Sertoli cells, with special reference to murine cell lines for the study of testicular endocrine function and tumorigenesis. These cell lines also provide useful tools to investigate the molecular basis of hormone actions and testicular cell interactions.

Novel role for a sterol response element binding protein in directing spermatogenic cell-specific gene expression

Sperm are highly specialized cells, and their formation requires the synthesis of a large number of unique mRNAs. However, little is known about the transcriptional mechanisms that direct male germ cell differentiation. Sterol response element binding protein 2gc (SREBP2gc) is a spermatogenic cell-enriched isoform of the ubiquitous transcription factor SREBP2, which in somatic cells is required for homeostatic regulation of cholesterol. SREBP2gc is selectively enriched in spermatocytes and spermatids, and, due to its novel structure, its synthesis is not subject to cholesterol feedback control. This suggested that SREBP2gc has unique cell- and stage-specific functions during spermatogenesis. Here, we demonstrate that this factor activates the promoter for the spermatogenesis-related gene proacrosin in a cell-specific manner. Multiple SREBP2gc response elements were identified within the 5'-flanking and proximal promoter regions of the proacrosin promoter. Mutating these elements greatly diminished in vivo expression of this promoter in spermatogenic cells of transgenic mice. These studies define a totally new function for an SREBP as a transactivator of male germ cell-specific gene expression. We propose that SREBP2gc is part of a cadre of spermatogenic cell-enriched isoforms of ubiquitously expressed transcriptional coregulators that were specifically adapted in concert to direct differentiation of the male germ cell lineage.

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.

Protein products of human Gas2-related genes on chromosomes 17 and 22 (hGAR17 and hGAR22) associate with both microfilaments and microtubules

The human Gas2-related gene on chromosome 22 (hGAR22) encodes two alternatively spliced mRNA species. The longer mRNA encodes a protein with a deduced molecular mass of 36.3 kDa (GAR22alpha), whereas the shorter mRNA encodes a larger protein with a deduced molecular mass of 72.6 kDa (GAR22beta). We show that both hGAR22 proteins contain a calponin homology actin-binding domain and a Gas2-related microtubule-binding domain. Using rapid amplification of cDNA ends, we have cloned the mouse orthologue of hGAR22, mGAR22, and found its protein products to be extremely well conserved. We also report the cDNA cloning of a human Gas2-related gene on chromosome 17 (hGAR17). hGAR17 also encodes two protein isoforms. The overall cytoskeletal binding properties of the hGAR17 and hGAR22 proteins are remarkably similar. hGAR17 mRNA expression is limited to skeletal muscle. Although hGAR22 and mGAR22 mRNAs are expressed nearly ubiquitously, mGAR22 protein can only be detected in testis and brain. Furthermore, only the beta isoform is present in these tissues. GAR22beta expression is induced in a variety of cultured cells by growth arrest. The absolute amounts of GAR22beta protein expressed are low. The beta isoforms of hGAR17 and hGAR22 appear to be able to crosslink microtubules and microfilaments in transfected cells. This finding suggests that the physiological functions of these proteins may involve integration of these two components of the cytoskeleton.

TSPY-LTA transgenic mice develop endocrine tumors of the pituitary and adrenal gland

In an attempt to determine the susceptibility of spermatogonia to malignant transformation transgenic mice were generated harboring a 1.3 kb 5'-flanking region of the germ cell specific expressed human testis specific protein, Y-encoded gene fused with the simian virus 40 large T antigen (TAg). Unexpectedly, TAg expression in transgenic mice was also detected in somatic tissues. Between days 65 and 85 after birth most of the transgenic mice developed anterior lobe tumors of the pituitary gland and to a less extent medulla type tumors of the adrenal gland. In addition, a few older transgenic mice developed tumors of the seminal vesicle, but no testicular tumors were observed in transgenic mice up to an age of 5 months. The pituitary tumors were immunoreactive for anti-prolactin (PRL) and anti-adrenocorticotropic hormone (ACTH). PRL and corticosterone concentrations in serum of transgenic mice were significantly increased. Taken together, our studies provide a novel mouse model for pituitary adenomas displaying a unique combination of hormone expression by tumor cells secreting PRL and ACTH.

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.

The murine BTB/POZ zinc finger gene Znf131: predominant expression in the developing central nervous system, in adult brain, testis, and thymus

The Znf131/ZNF131 protein belongs to the superfamily of POK proteins containing a BTB/POZ domain in its N-terminal part and 5 typical C2H2 zinc fingers and an additional C2HC zinc finger structure in its C-terminal region. In mouse and human two alternatively spliced transcripts are expressed from the Znf131/ZNF131 gene, resulting from intraexonic splicing. While the longer transcript encodes for three double zinc finger structures the shorter transcript lacks the region coding for the first zinc finger. Although the murine Znf131 gene is ubiquitously expressed, expression analysis applying whole mount in situ hybridization showed a predominant expression in the developing central nervous system with strongest signals in the forebrain, midbrain, and hindbrain areas and in the neural tube. Further dominant expression was seen in embryonic limb buds. In human adult tissues a predominant expression of ZNF131 was seen in different brain areas, i.e., the occipital and temporal lobe, the nucleus caudatus, hippocampus, and the cerebellum as well as in testis and thymus. Therefore, it is possible that Znf131/ZNF131 plays a role during development and organogenesis as well as in the function of the adult central nervous system.

Identification and characterization of a novel murine multigene family containing a PHD-finger-like motif

The genes Phf5a and Phf5b-ps are the first two members of a novel murine multigene family that is highly conserved during evolution and belongs to the superfamily of PHD-finger genes. The Phf5 gene family contains an active locus on mouse chromosome 15, region E and several processed pseudogenes on different chromosomes. The active locus, Phf5a, is expressed ubiquitously in pre- and postnatal murine tissues and encodes a protein of 110 amino acids. The protein is localized in the nucleus in a non-homogenous pattern as the nucleolar subcompartment is almost free of Phf5a. The molecular and biological functions of Phf5a are unknown up-to-date, but the systematic deletion of its yeast homolog is lethal, pointing out that the protein is required for cell viability. Interpretation of our data and review of the literature suggest both basic and essential cellular functions of the Phf5a protein, possibly acting as a chromatin-associated protein.

Establishment of cell lines with rat spermatogonial stem cell characteristics

Spermatogonial cell lines were established by transfecting a mixed population of purified rat A(s) (stem cells), A(pr) and A(al) spermatogonia with SV40 large T antigen. Two cell lines were characterized and found to express Hsp90alpha and oct-4, specific markers for germ cells and A spermatogonia, respectively. Expression of c-kit, normally expressed in A spermatogonia from late A(al) spermatogonia onwards, could not be detected in either cell line. Furthermore, no expression of vimentin (Sertoli cell marker) and alpha-smooth muscle actin (peritubular cell marker) could be found. Upon transplantation of these cell lines into recipient mice, the cells were found to be able to migrate to the basement membrane and to colonize seminiferous tubules. Taken together, we conclude that our cell lines have spermatogonial stem cell characteristics. These first spermatogonial cell lines with stem cell characteristics can now be used to study spermatogonial gene expression in comparison with more advanced germ cells.