Postnatal Male Germ Cells Research Articles

DOT1L regulates chromatin reorganization and gene expression during sperm differentiation

Spermatozoa have a unique genome organization. Their chromatin is almost completely devoid of histones and is formed instead of protamines, which confer a high level of compaction and preserve paternal genome integrity until fertilization. Histone‐to‐protamine transition takes place in spermatids and is indispensable for the production of functional sperm. Here, we show that the H3K79‐methyltransferase DOT1L controls spermatid chromatin remodeling and subsequent reorganization and compaction of the spermatozoon genome. Using a mouse model in which Dot1l is knocked‐out (KO) in postnatal male germ cells, we found that Dot1l‐KO sperm chromatin is less compact and has an abnormal content, characterized by the presence of transition proteins, immature protamine 2 forms and a higher level of histones. Proteomic and transcriptomic analyses performed on spermatids reveal that Dot1l‐KO modifies the chromatin prior to histone removal and leads to the deregulation of genes involved in flagellum formation and apoptosis during spermatid differentiation. As a consequence of these chromatin and gene expression defects, Dot1l‐KO spermatozoa have less compact heads and are less motile, which results in impaired fertility.

Intermitochondrial cement (IMC) harbors piRNA biogenesis machinery and exonuclease domain-containing proteins EXD1 and EXD2 in mouse spermatocytes.

Germ granules are large cytoplasmic ribonucleoprotein complexes that emerge in the germline to participate in RNA regulation. The two most prominent germ granules are the intermitochondrial cement (IMC) in meiotic spermatocytes and the chromatoid body (CB) in haploid round spermatids, both functionally linked to the PIWI-interacting RNA (piRNA) pathway. In this study, we clarified the IMC function by identifying proteins that form complexes with a well-known IMC protein PIWIL2/MILI in the mouse testis. The PIWIL2 interactome included several proteins with known functions in piRNA biogenesis. We further characterized the expression and localization of two of the identified proteins, Exonuclease 3'-5' domain-containing proteins EXD1 and EXD2, and confirmed their localization to the IMC. We showed that EXD2 interacts with PIWIL2, and that the mutation of Exd2 exonuclease domain in mice induces misregulation of piRNA levels originating from specific pachytene piRNA clusters, but does not disrupt male fertility. Altogether, this study highlights the central role of the IMC as a platform for piRNA biogenesis, and suggests that EXD1 and EXD2 function in the IMC-mediated RNA regulation in postnatal male germ cells.

Retinoic Acid Receptor Alpha Is Essential in Postnatal Sertoli Cells but Not in Germ Cells.

Retinoic acid signaling is indispensable for the completion of spermatogenesis. It is known that loss of retinoic acid nuclear receptor alpha (RARA) induces male sterility due to seminiferous epithelium degeneration. Initial genetic studies established that RARA acts in Sertoli cells, but a recent paper proposed that RARA is also instrumental in germ cells. In the present study, we have re-assessed the function of RARA in germ cells by genetically ablating the Rara gene in spermatogonia and their progenies using a cell-specific conditional mutagenesis approach. We show that loss of Rara in postnatal male germ cells does not alter the histology of the seminiferous epithelium. Furthermore, RARA-deficient germ cells differentiate normally and give rise to normal, living pups. This establishes that RARA plays no crucial role in germ cells. We also tested whether RARA is required in Sertoli cells during the fetal period or after birth. For this purpose, we deleted the Rara gene in Sertoli cells at postnatal day 15 (PN15), i.e., after the onset of the first spermatogenic wave. To do so, we used temporally controlled cell-specific mutagenesis. By comparing the testis phenotypes generated when Rara is lost either at PN15 or at embryonic day 13, we show that RARA exerts all of its functions in Sertoli cells not at the fetal stage but from puberty.

Overactive type 2 cannabinoid receptor induces meiosis in fetal gonads and impairs ovarian reserve

Type 2 cannabinoid receptor (CB2R) has been proposed to promote in vitro meiotic entry of postnatal male germ cells and to maintain the temporal progression of spermatogenesis in vivo. However, no information is presently available on the role played by CB2R in male and female fetal gonads. Here we show that in vitro pharmacological stimulation with JWH133, a CB2R agonist, induced activation of the meiotic program in both male and female fetal gonads. Upon stimulation, gonocytes initiated the meiotic program but became arrested at early stages of prophase I, while oocytes showed an increased rate of meiotic entry and progression toward more advanced stage of meiosis. Acceleration of meiosis in oocytes was accompanied by a strong increase in the percentage of γ-H2AX-positive pachytene and diplotene cells, paralleled by an increase of TUNEL-positive cells, suggesting that DNA double-strand breaks were not correctly repaired during meiosis, leading to oocyte apoptosis. Interestingly, in vivo pharmacological stimulation of CB2R in fetal germ cells through JWH133 administration to pregnant females caused a significant reduction of primordial and primary follicles in the ovaries of newborns with a consequent depletion of ovarian reserve and reduced fertility in adult life, while no alterations of spermatogenesis in the testis of the offspring were detected. Altogether our findings highlight a pro-meiotic role of CB2R in male and female germ cells and suggest that the use of cannabis in pregnant female might represent a risk for fertility and reproductive lifespan in female offspring.

DNA methylation and gene expression dynamics during spermatogonial stem cell differentiation in the early postnatal mouse testis.

BackgroundIn the male germline, neonatal prospermatogonia give rise to spermatogonia, which include stem cell population (undifferentiated spermatogonia) that supports continuous spermatogenesis in adults. Although the levels of DNA methyltransferases change dynamically in the neonatal and early postnatal male germ cells, detailed genome-wide DNA methylation profiles of these cells during the stem cell formation and differentiation have not been reported.ResultsTo understand the regulation of spermatogonial stem cell formation and differentiation, we examined the DNA methylation and gene expression dynamics of male mouse germ cells at the critical stages: neonatal prospermatogonia, and early postntal (day 7) undifferentiated and differentiating spermatogonia. We found large partially methylated domains similar to those found in cancer cells and placenta in all these germ cells, and high levels of non-CG methylation and 5-hydroxymethylcytosines in neonatal prospermatogonia. Although the global CG methylation levels were stable in early postnatal male germ cells, and despite the reported scarcity of differential methylation in the adult spermatogonial stem cells, we identified many regions showing stage-specific differential methylation in and around genes important for stem cell function and spermatogenesis. These regions contained binding sites for specific transcription factors including the SOX family members.ConclusionsOur findings show a distinctive and dynamic regulation of DNA methylation during spermatogonial stem cell formation and differentiation in the neonatal and early postnatal testes. Furthermore, we revealed a unique accumulation and distribution of non-CG methylation and 5hmC marks in neonatal prospermatogonia. These findings contrast with the reported scarcity of differential methylation in adult spermatogonial stem cell differentiation and represent a unique phase of male germ cell development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1833-5) contains supplementary material, which is available to authorized users.

Role of Pten deletion and BRafV600E mutation in the generation of testicular germ cell tumors

Testicular germ cell tumors (TGCT) represent the most common solid malignancy affecting males between the ages of 15 and 35, while ovarian germ cell tumours (OGCT) are a type of ovarian neoplasm principally affecting young women. Germ cell tumors (GCTs) account for about 95 % of testicular cancer cases and for only 2-3% of ovarian cancer cases (Siegel et al., 2011). Most TGCT are potentially curable, however approximately 5% of patients with TGCT develop chemoresistance and die from the disease. PTEN deletion and mutational activation of BRAF are frequent genetic alterations found in human TGCTs, suggesting that they might be directly involved in germ cell tumorigenesis. Furthermore, BRAF mutation positively correlates with the acquisition of resistence to cisplatin, the most commonly chemotherapic agent employed for the treatment of human TGCTs. We obtained heterozygous floxed Ptenloxp/+ BRafCA Spo11Cre mice showing ovarian teratomas and testicular tumors with an incidence of about 30% at 20 days post partum (dpp) . Since Spo- 11Cre is active at around 13.5 days post coitum (dpc) in female germ cells and at around 7 dpp in male germ cells (18), these results suggest that ovarian teratomas origin from early meiotic germ cells in the fetal period whereas GCT formation in males can be a postnatal event. By histological inspection, we found that cancer cells in testes showed features reminiscent of seminoma such as a diffuse, confluent multinodular pattern. However, by immunohistochemical staining, we observed that the cells within the tumor showed heterogeneous positivity for the pluripotency markers Oct4, Sox2, Nanog, Kit and Prdm14, suggesting that they can represent a mixed form of seminoma and embryonal carcinoma cells. Our results indicate that deregulated MAP and PI3 Kinase activation can lead to postnatal male germ cells transformation.

FGF9 - Nodal signaling negatively control meiotic entry of postnatal male germ cells

Fibroblast growth factor 9 (FGF9) produced by the somatic cells of the testis acts directly on germ cells to inhibit meiosis by upregulating levels of the RNA binding protein Nanos2, both in fetal and postnatal gonad [1]. Several studies have recently demonstrated that the anti-meiotic effect of FGF9 in the fetal testis is mediated by Nodal, a member of the TGF-Beta morphogen family. In fetal male germ cells FGF9 upregulates Cripto, which is a Nodal co-receptor, making these cells unable to enter meiosis [2]. However it is currently unknown how FGF9 acts postnatally to inhibit entry into meiosis of male mitotic germ cells. We first investigated which was the signal transduction pathway activated by FGF9 on postnatal mouse spermatogonia. We found that FGF9 signaling is dependent on ERK but not on AKT activation, which is instead triggered by Kit ligand (an inducer of meiotic entry that cooperates with retinoic acid). By qRT-PCR we found that Nodal and Cripto are expressed in postnatal spermatogonia and that FGF9 (but not Kit ligand) treatment promotes their upregulation. By western blot we found that phospho-Smad2, an indicator of active Nodal signaling, is increased in spermatogonia upon FGF9 treatment, suggesting that Nodal mediates FGF9 action also in postnatal male germ cells.

Deregulated Sex Chromosome Gene Expression with Male Germ Cell-Specific Loss of Dicer1

MicroRNAs (miRNAs) are a class of endogenous, non-coding RNAs that mediate post-transcriptional gene silencing by inhibiting mRNA translation and promoting mRNA decay. DICER1, an RNase III endonuclease encoded by Dicer1, is required for processing short 21–22 nucleotide miRNAs from longer double-stranded RNA precursors. Here, we investigate the loss of Dicer1 in mouse postnatal male germ cells to determine how disruptions in the miRNA biogenesis pathway may contribute to infertility. Reduced levels of Dicer1 transcripts and DICER1 were confirmed in germ cell knock-out (GCKO) testes by postnatal day 18 (P18). Compared to wild-type (WT) at 8 weeks, GCKO males had no change in body weight; yet showed significant reductions in testis mass and sperm number. Histology and fertility tests confirmed spermatogenic failure in GCKO males. Array analyses at P18 showed that in comparison to WT testes, 75% of miRNA genes and 37% of protein coding genes were differentially expressed in GCKO testes. Among these, 96% of miRNA genes were significantly down-regulated, while 4% miRNA genes were overexpressed. Interestingly, we observed preferential overexpression of genes encoded on the sex chromosomes in GCKO testes, including more than 80% of previously identified targets of meiotic sex chromosome inactivation (MSCI). Compared to WT, GCKO mice showed higher percentages of germ cells at early meiotic stages (leptotene and zygotene) but lower percentages at later stages (pachytene, diplotene and metaphase I) providing evidence that deletion of Dicer1 leads to disruptions in meiotic progression. Therefore, deleting Dicer1 in early postnatal germ cells resulted in deregulation of transcripts encoded by genes on the sex chromosomes, impaired meiotic progression and led to spermatogenic failure and infertility.

DNA Methylation Defects in Prenatal and Postnatal Germ Cells of Dnmt3L Haploinsufficient Male Mice.

The enzyme DNA methyltransferase 3-like (DNMT3L) is essential for the acquisition of DNA methylation patterns in germ cells as well as normal germ cell development and has been reported as the first paternal effect gene in mammals. Although Dnmt3L heterozygous males are fertile, they have abnormalities in X chromosome compaction, postmeiotic gene expression and sire an increased number of pups with XO monosomy. To examine the postulated epigenetic basis of the paternal effects, we examined DNA methylation acquisition at intergenic (non-CpG island, non-repeat) sites along chromosome 9 in male germ cells isolated during the prenatal and postnatal periods. At 16.5 dpc (days post coitum), 42% of intergenic loci examined were hypomethylated, by 20–30%, in Dnmt3L heterozygotes as compared to Dnmt3L wildtype mice. By day 1 after birth DNA methylation differences in spermatogonia between the two genotypes had resolved for 67% of the sites; in contrast, 33% of sites showed residual hypomethylation, in the range of 10%, associated with Dnmt3L haploinsufficiency. By postnatal days 4 and 6, germ cell DNA methylation levels were similar in the heterozygous and wildtype mice and remained similar later in spermatogenesis in spermatozoa. The findings suggest that germ cell DNA methylation differences between the genotypes resolve shortly after birth before the spermatogonia begin to divide. To confirm and extend these results, higher resolution studies using Reduced Representation Bisulphite Sequencing (RRBS) are being carried out to examine methylation differences at 3-5 million CpG sites across the genome. The DNA methylation defects described here in prenatal and early postnatal male germ cells of Dnmt3L heterozygous mice are the earliest epigenetic perturbation yet identified for a mammalian paternal effect gene and may influence downstream epigenetic and genetic events that lead to the previously observed abnormalities during spermatogenesis and paternal effects in the offspring. (Supported by CIHR).

SOHLH1 and SOHLH2 control Kit expression during postnatal male germ cell development

How Kit expression is regulated in the germline remains unknown. SOHLH1 and SOHLH2, two bHLH transcription factors specifically expressed in germ cells, are involved in spermatogonia and oocyte differentiation. In the male, deletion of each factor causes loss of Kit-expressing spermatogonia in the prepuberal testis. In the female, SOHLH1 and SOHLH2 ablations cause oocyte loss in the neonatal ovary. To investigate whether Kit expression is regulated by these two factors in male germ cells, we examined SOHLH1 and SOHLH2 expression during fetal and postnatal mouse development. We found a strong positive correlation between Kit and the two transcription factors only in postnatal spermatogonia. SOHLH2 was enriched in undifferentiated spermatogonia, whereas SOHLH1 expression was maximal at Kit-dependent stages. Expression of SOHLH1, but not SOHLH2, was increased in postnatal mitotic germ cells by treatment with all-trans retinoic acid. We found that E-box sequences within the Kit promoter and its first intron can be transactivated in transfection experiments overexpressing Sohlh1 or Sohlh2. Co-transfection of both factors showed a cooperative effect. EMSA experiments showed that SOHLH1 and SOHLH2 can independently and cooperatively bind an E-box-containing probe. In vivo co-immunoprecipitations indicated that the two proteins interact and overexpression of both factors increases endogenous Kit expression in embryonic stem cells. SOHLH1 was found by ChIP analysis to occupy an E-box-containing region within the Kit promoter in spermatogonia chromatin. Our results suggest that SOHLH1 and SOHLH2 directly stimulate Kit transcription in postnatal spermatogonia, thus activating the signaling involved in spermatogonia differentiation and spermatogenetic progression.

SOHLH1 and SOHLH2 control Kit expression during postnatal male germ cell development.

How Kit expression is regulated in the germline remains unknown. SOHLH1 and SOHLH2, two bHLH transcription factors specifically expressed in germ cells, are involved in spermatogonia and oocyte differentiation. In the male, deletion of each factor causes loss of Kit-expressing spermatogonia in the prepuberal testis. In the female, SOHLH1 and SOHLH2 ablations cause oocyte loss in the neonatal ovary. To investigate whether Kit expression is regulated by these two factors in male germ cells, we examined SOHLH1 and SOHLH2 expression during fetal and postnatal mouse development. We found a strong positive correlation between Kit and the two transcription factors only in postnatal spermatogonia. SOHLH2 was enriched in undifferentiated spermatogonia, whereas SOHLH1 expression was maximal at Kit-dependent stages. Expression of SOHLH1, but not SOHLH2, was increased in postnatal mitotic germ cells by treatment with all-trans retinoic acid. We found that E-box sequences within the Kit promoter and its first intron can be transactivated in transfection experiments overexpressing Sohlh1 or Sohlh2. Co-transfection of both factors showed a cooperative effect. EMSA experiments showed that SOHLH1 and SOHLH2 can independently and cooperatively bind an E-box-containing probe. In vivo co-immunoprecipitations indicated that the two proteins interact and overexpression of both factors increases endogenous Kit expression in embryonic stem cells. SOHLH1 was found by ChIP analysis to occupy an E-box-containing region within the Kit promoter in spermatogonia chromatin. Our results suggest that SOHLH1 and SOHLH2 directly stimulate Kit transcription in postnatal spermatogonia, thus activating the signaling involved in spermatogonia differentiation and spermatogenetic progression.

Chromatoid body and small RNAs in male germ cells

The chromatoid body (CB) is a germ granule in the cytoplasm of postmeiotic haploid round spermatids that is loaded with RNA and RNA-binding proteins. Following the discovery of small non-coding RNA-mediated gene regulation and the identification of PIWI-interacting RNAs (piRNAs) that have crucial roles in germ line development, the function of the CB has slowly begun to be revealed. Male germ cells utilise small RNAs to control the complex and specialised process of sperm production. Several microRNAs have been identified during spermatogenesis. In addition, a high number of piRNAs are present both in embryonic and postnatal male germ cells, with their expression being impressively induced in late meiotic cells and haploid round spermatids. At postmeiotic stage of germ cell differentiation, the CB accumulates piRNAs and proteins of piRNA machinery, as well as several other proteins involved in distinct RNA regulation pathways. All existing evidence suggests a role for the CB in mRNA regulation and small RNA-mediated gene control, but the mechanisms remain uncharacterised. In this review, we summarise the current knowledge of the CB and its association with small RNA pathways.

Dispensable role of PTEN in mouse spermatogenesis

PTEN (phosphatase and tensin homologue deleted on chromosome ten) plays critical roles in multiple cellular processes, including cell proliferation, survival, migration and transformation. A role of PTEN in mammalian spermatogenesis, however, has not been explored. To address this question, we generated a mouse model with PTEN conditional knockout in postnatal male germ cells. We found that spermatogenesis was normal in PTEN-deleted male germ cells. PTEN conditional mutant males produced sperm and sired offspring as competently as wild-type littermates. Moreover, our biochemical analysis also indicated that the Akt (acutely transforming retrovirus AKT8 in rodent T cell lymphoma) signalling pathway was not affected in mutant testis. Taken together, these findings demonstrate that PTEN is dispensable in mouse spermatogenesis.

Microgravity Promotes Differentiation and Meiotic Entry of Postnatal Mouse Male Germ Cells

A critical step of spermatogenesis is the entry of mitotic spermatogonia into meiosis. Progresses on these topics are hampered by the lack of an in vitro culture system allowing mouse spermatogonia differentiation and entry into meiosis. Previous studies have shown that mouse pachytene spermatocytes cultured in simulated microgravity (SM) undergo a spontaneous meiotic progression. Here we report that mouse mitotic spermatogonia cultured under SM with a rotary cell culture system (RCCS) enter into meiosis in the absence of any added exogenous factor or contact with somatic cells. We found that isolated Kit-positive spermatogonia under the RCCS condition enter into the prophase of the first meiotic division (leptotene stage), as monitored by chromosomal organization of the synaptonemal complex 3 protein (Scp3) and up-regulation of several pro-meiotic genes. SM was found to activate the phosphatidyl inositol 3 kinase (PI3K) pathway and to induce in Kit-positive spermatogonia the last round of DNA replication, typical of the preleptotene stage. A PI3K inhibitor abolished Scp3 induction and meiotic entry stimulated by RCCS conditions. A positive effect of SM on germ cell differentiation was also observed in undifferentiated (Kit-negative) spermatogonia, in which RCCS conditions stimulate the expression of Kit and Stra8. In conclusion, SM is an artificial environmental condition which promotes postnatal male germ cell differentiation and might provide a tool to study the molecular mechanisms underlying the switch from mitosis to meiosis in mammals.

169. SERTOLI CELL-SPECIFIC DISRUPTION OF THE ANDROGEN RECEPTOR DNA-BINDING DOMAIN REVEALS DIFFERENTIAL TEMPORAL CONTROL OF DISTINCT ANDROGEN-REGULATED GENES

Androgen receptor (AR) actions are vital for spermatogenesis. However, in postnatal development male germ cells do not express AR, highlighting its key role in testicular somatic cells. We recently used a Cre-loxP strategy to determine the in vivo requirement of AR DNA-binding in Sertoli cell (SC) function. Transgenic (Tg) mice with Cre expression targeted by SC-specific AMH or Abp promoters were crossed with floxed-Ar (Arflox) mice for Cre-loxP inframe deletion of Ar exon 3, which encodes a zinc finger essential for the DNA-binding domain (DBD). SC-specific mutated ARΔex3 (SCARΔex3) produced infertile AMH.SCARΔex3 and Abp.SCARΔex3 males. Testes from adult homozygous TgCre(+/+) AMH.SCARΔex3 or Abp.SCARΔex3 males were 30% of normal size and exhibited meiotic arrest, whereas testes from hemizygous TgCre(+/–) Abp.SCARΔex3 males were larger (47% normal) with more postmeiotic germ cell development. Despite marked Leydig cell hypertrophy, testicular expression of the adult Leydig marker Hsd3b6 (RT-PCR) and normal intratesticular testosterone levels (LC-MS/MS) in SCARΔex3 males indicated the presence of morphologically distinct but functional adult Leydig cells. SC-specific mutated AR Δex3 was predicted to disrupt classical AR-regulated pathways via loss of direct DNA interaction. Androgen-repressed testicular Ngfr expression (known to be via non-classical AR pathways) was not upregulated in SCARΔex3 testes, suggesting maintenance of a non-classical mechanism independent of AR-DBD. In contrast, SC-specific Rhox5 and Eppin transcription, regulated by divergent or classical androgen-response elements respectively, were both decreased in postnatal SCARΔex3 vs. control testes, demonstrating SC-specific AR function as early as postnatal day 5. However, Rhox5 expression declined dose-dependently, whereas Eppin expression increased, in adult TgCre(+/−) and TgCre(+/+) SCARΔex3 testes, revealing differential temporal control for distinct AR-regulated transcripts. Thus, our SCARΔex3 paradigm displayed dose-dependent TgCre-disruption of meiotic competence and post-meiotic development as well as gene expression, and represents a unique model to selectively differentiate AR-regulated genes.

Tudor-related proteins TDRD1/MTR-1, TDRD6 and TDRD7/TRAP: Domain composition, intracellular localization, and function in male germ cells in mice

The germ-line cells of many animals possess a characteristic cytoplasmic structure termed nuage or germinal granules. In mice, nuage that is prominent in postnatal male germ cells is also called intermitochondrial cement or chromatoid bodies. TDRD1/MTR-1, which contains Tudor domain repeats, is a specific component of the mouse nuage, analogously to Drosophila Tudor, a constituent of polar granules/nuage in oocytes and embryos. We show that TDRD6 and TDRD7/TRAP, which also contain multiple Tudor domains, specifically localize to nuage and form a ribonucleoprotein complex together with TDRD1/MTR-1. The characteristic co-localization of TDRD1, 6 and 7 was disrupted in a mutant of mouse vasa homologue/ DEAD box polypeptide 4 ( Mvh/ Ddx4), which encodes another evolutionarily conserved component of nuage. In vivo over-expression experiments of the TDRD proteins and truncated forms during male germ cell differentiation showed that a single Tudor domain is a structural unit that localizes or accumulates to nuage, but the expression of the truncated, putative dominant negative forms is detrimental to meiotic spermatocytes. These results indicate that the Tudor-related proteins, which contain multiple repeats of the Tudor domain, constitute an evolutionarily conserved class of nuage components in the germ-line, and their localization or accumulation to nuage is likely conferred by a Tudor domain structure and downstream of Mvh, while the characteristic repeated architecture of the domain is functionally essential for the differentiation of germ cells.

RNF17, a component of the mammalian germ cell nuage, is essential for spermiogenesis

Nuages are found in the germ cells of diverse organisms. However, nuages in postnatal male germ cells of mice are poorly studied. Previously, we cloned a germ cell-specific gene named Rnf17, which encodes a protein containing both a RING finger and tudor domains. Here, we report that RNF17 is a component of a novel nuage in male germ cells--the RNF17 granule, which is an electron-dense non-membrane bound spherical organelle with a diameter of 0.5 mum. RNF17 granules are prominent in late pachytene and diplotene spermatocytes, and in elongating spermatids. RNF17 granules are distinguishable from other known nuages, such as chromatoid bodies. RNF17 is able to form dimers or polymers both in vitro and in vivo, indicating that it may play a role in the assembly of RNF17 granules. Rnf17-deficient male mice were sterile and exhibited a complete arrest in round spermatids, demonstrating that Rnf17 encodes a novel key regulator of spermiogenesis. Rnf17-null round spermatids advanced to step 4 but failed to produce sperm. These results have shown that RNF17 is a component of a novel germ cell nuage and is required for differentiation of male germ cells.

Molecular markers for the assessment of postnatal male germ cell development in the mouse

A proliferation marker, proliferating cell nuclear antigen (PCNA), a Sertoli cell specific transcription factor, GATA-1 and the male germ cell specific, RNA binding motif (RBM), were used to identify different cellular populations during postnatal development of the mouse testis. Immunohistochemistry, RT-PCR and real-time quantitative RT-PCR (QRT-PCR) were used. PCNA was expressed in pre-Sertoli and germ cells on the day of birth. Both pre-meiotic germ cells and spermatocytes expressed RBM throughout postnatal development. RBM-positive cell counts and QRT-PCR of RBM showed that average level of RBM per cell is highest in juvenile males between 14 and 21 days. From 42 days onward, there was a dramatic decrease in RBM expression in individual pre-meiotic and meiotic germ cells. These markers were used to correlate cell proliferative capability, gene expression profile and anatomic location within the developing mouse testis. The majority of germ cells start active proliferation once they have migrated to the basement membrane or immediately before. RBM is more highly expressed during the first wave of spermatogenesis versus subsequent waves, suggesting that there may be a change in the activity of RBM.

Molecular markers for the assessment of postnatal male germ cell development in the mouse

A proliferation marker, proliferating nuclear antigen (PCNA), a Sertoli cell specific marker, the transcription factor GATA-1 and a male germ cell specific RNA processing marker, RNA binding motif (RBM), help to gain insight into the postnatal development of the mouse testis.

Acquisition of theH19Methylation Imprint Occurs Differentially on the Parental Alleles during Spermatogenesis

The imprinted mouseH19gene is hypomethylated on the expressed maternal allele and hypermethylated on the silent paternal allele. A 2-kb region of differential methylation located from −2 to −4 kb relative to theH19transcriptional start site has been proposed to act as the imprinting mark since hypermethylation in this region is inherited from sperm and retained on the paternal allele throughout development. Here, we describe a temporal analysis of the methylation patterns at theH19locus during postnatal male germ cell development. The 2-kb region is methylated on the paternal allele throughout spermatogenesis, suggesting that methylation is acquired in this region prior to the resumption of mitosis in postnatal male mice. Likewise, more than half of the maternal alleles are hypermethylated prior to the resumption of mitosis. However, the remaining maternal alleles are not hypermethylated until the completion of meiosis I, indicating thatde novomethylation in this region is a continuous process. Sequences proximal to theH19promoter, which are methylated in spermatozoa and on the paternal allele in somatic cells, are differentially methylated in diploid, mitotic spermatogonia. The maternal allele becomes hypermethylated in this region during meiotic prophase. Thus, the parentalH19alleles acquire methylation differentially in the male germline.