Potential role of Nanos3 in maintaining the undifferentiated spermatogonia population

Functional annotation of a hugely expanded nanos repertoire in Lytechinus variegatus, the green sea urchin

Nanos genes encode essential RNA-binding proteins involved in germline determination and germline stem cell maintenance. When examining diverse classes of echinoderms, typically three, sometimes four, nanos genes are present. In this analysis, we identify and annotate nine nanos orthologs in the green sea urchin, Lytechinus variegatus (Lv). All nine genes are transcribed and grouped into three distinct classes. Class one includes the germline Nanos, with one member: Nanos2. Class two includes Nanos3-like genes, with significant sequence similarity to Nanos3 in the purple sea urchin, Strongylocentrotus purpuratus (Sp), but with wildly variable expression patterns. The third class includes several previously undescribed nanos zinc-finger genes that may be the result of duplications of Nanos2. All nine nanos transcripts occupy unique genomic loci and are expressed with unique temporal profiles during development. Importantly, here we describe and characterize the unique genomic location, conservation, and phylogeny of the Lv ortholog of the well-studied Sp Nanos2. However, in addition to the conserved germline functioning Nanos2, the green sea urchin appears to be an outlier in the echinoderm phyla with eight additional nanos genes. We hypothesize that this expansion of nanos gene members may be the result of a previously uncharacterized L1-class transposon encoded on the opposite strand of a nanos2 pseudogene present on chromosome 12 in this species. The expansion of nanos genes described here represents intriguing insights into germline specification and nanos evolution in this species of sea urchin.

Generation of germ cell-deficient pigs by NANOS3 knockout

NANOS3 is an evolutionarily conserved gene expressed in primordial germ cells that is important for germ cell development. Germ cell deletion by NANOS3 knockout has been reported in several mammalian species, but its function in pigs is unclear. In the present study, we investigated the germline effects of NANOS3 knockout in pigs using CRISPR/Cas9. Embryo transfer of CRISPR/Cas9-modified embryos produced ten offspring, of which one showed wild-type NANOS3 alleles, eight had two mutant NANOS3 alleles, and the other exhibited mosaicism (four mutant alleles). Histological analysis revealed no germ cells in the testes or ovaries of any of the nine mutant pigs. These results demonstrated that NANOS3 is crucial for porcine germ cell production.

The germ cell-specific RNA binding protein RBM46 is essential for spermatogonial differentiation in mice

Control over gene expression is exerted, in multiple stages of spermatogenesis, at the post-transcriptional level by RNA binding proteins (RBPs). We identify here an essential role in mammalian spermatogenesis and male fertility for 'RNA binding protein 46' (RBM46). A highly evolutionarily conserved gene, Rbm46 is also essential for fertility in both flies and fish. We found Rbm46 expression was restricted to the mouse germline, detectable in males in the cytoplasm of premeiotic spermatogonia and meiotic spermatocytes. To define its requirement for spermatogenesis, we generated Rbm46 knockout (KO, Rbm46-/-) mice; although male Rbm46-/- mice were viable and appeared grossly normal, they were infertile. Testes from adult Rbm46-/- mice were small, with seminiferous tubules containing only Sertoli cells and few undifferentiated spermatogonia. Using genome-wide unbiased high throughput assays RNA-seq and 'enhanced crosslinking immunoprecipitation' coupled with RNA-seq (eCLIP-seq), we discovered RBM46 could bind, via a U-rich conserved consensus sequence, to a cohort of mRNAs encoding proteins required for completion of differentiation and subsequent meiotic initiation. In summary, our studies support an essential role for RBM46 in regulating target mRNAs during spermatogonia differentiation prior to the commitment to meiosis in mice.

NANOS3 suppresses premature spermatogonial differentiation to expand progenitors and fine-tunes spermatogenesis in mice

In the mouse testis, sperm originate from spermatogonial stem cells (SSCs). SSCs give rise to spermatogonial progenitors, which expand their population until entering the differentiation process that is precisely regulated by a fixed time-scaled program called the seminiferous cycle. Although this expansion process of progenitors is highly important, its regulatory mechanisms remain unclear. NANOS3 is an RNA-binding protein expressed in the progenitor population. We demonstrated that the conditional deletion of Nanos3 at a later embryonic stage results in the reduction of spermatogonial progenitors in the postnatal testis. This reduction was associated with the premature differentiation of progenitors. Furthermore, this premature differentiation caused seminiferous stage disagreement between adjacent spermatogenic cells, which influenced spermatogenic epithelial cycles, leading to disruption of the later differentiation pathway. Our study suggests that NANOS3 plays an important role in timing progenitor expansion to adjust to the proper differentiation timing by blocking the retinoic acid (RA) signaling pathway.

Discovery of Nanos1 and Nanos2/3 as Germ Cell Markers During Scallop Gonadal Development

Nanos are conserved genes involved in germline cell specification and differentiation. However, little is known about the role of different members of Nanos family in germ cell development in mollusks. In the present study, we conducted genome-wide identification of Nanos family in an economically important scallop Patinopecten yessoensis, and detected their expression in adult tissues and during early development. Two Nanos genes (PyNanos1, PyNanos2/3) were identified, both of which have the N-terminal NOT1-interacting motif and C-terminal (CCHC)₂ zinc finger domain. Expression profiles showed that PyNanos1 and PyNanos2/3 were primarily expressed in the gonads, with PyNanos1 being localized in the oogonia, oocytes, and spermatogonia, while PyNanos2/3 being specifically in spermatogonia. The results suggest that PyNanos are germ cell specific and may play crucial roles in gametogenesis in the scallop. PyNanos1 is a maternal gene, which is distributed uniformly at early cleavage, and restricted to 2-3 cell clusters from blastulae to trochophore larvae, suggesting its potential role in the formation of PGCs. Zygotically expressed PyNanos2/3 displayed a similar signal with PyNanos1 in the trochophore larvae, suggesting it may also participate in the formation and/or maintenance of PGCs. This study will benefit germplasm exploitation and conservation in bivalves, and facilitate a better understanding of the evolution of Nanos family and the role of different Nanos in germ cell development in mollusks.

A large and diverse autosomal haplotype is associated with sex-linked colour polymorphism in the guppy

Male colour patterns of the Trinidadian guppy (Poecilia reticulata) are typified by extreme variation governed by both natural and sexual selection. Since guppy colour patterns are often inherited faithfully from fathers to sons, it has been hypothesised that many of the colour trait genes must be physically linked to sex determining loci as a ‘supergene’ on the sex chromosome. Here, we phenotype and genotype four guppy ‘Iso-Y lines’, where colour was inherited along the patriline for 40 generations. Using an unbiased phenotyping method, we confirm the breeding design was successful in creating four distinct colour patterns. We find that genetic differentiation among the Iso-Y lines is repeatedly associated with a diverse haplotype on an autosome (LG1), not the sex chromosome (LG12). Moreover, the LG1 haplotype exhibits elevated linkage disequilibrium and evidence of sex-specific diversity in the natural source population. We hypothesise that colour pattern polymorphism is driven by Y-autosome epistasis.

Extreme colour pattern variation in male Trinidadian guppies are influenced by natural selection and sexual selection. Here, the authors phenotype and genotype four guppy lineages finding that colour pattern is associated with a diverse haplotype on an autosome.

Overexpression of bmp4, dazl, nanos3 and sycp2 in Hu Sheep Leydig Cells Using CRISPR/dcas9 System Promoted Male Germ Cell Related Gene Expression

Simple Summary

Male germ cell development plays a crucial role in male reproduction, and gene expression also presents an essential regulatory role in its development. Many studies have been devoted to the induction and differentiation of pluripotent stem cells into germ cells in vitro. However, the culture system for pluripotent stem cells from domestic animals is not stable, especially in sheep. Our study attempted to transdifferentiate sheep somatic cells into germ cells in vitro by the overexpression of key germ cell related genes, with the aim of perfecting the construction of germ cell research models in vitro. Therefore, we explored the expression pattern of four crucial genes, bmp4, dazl, nanos3 and sycp2, in Hu sheep testicular development, and investigated the potential efficiency of overexpression of the four candidate genes using the CRISPR/dcas9 system in Leydig cells. We revealed that the overexpression of bmp4, dazl, nanos3 and sycp2 can promote the expression of male germ cell related genes. To the best of our knowledge, this is the first study to construct an overexpression induction system using CRISPR/dcas9 technology, and to induce sheep somatic cells into germ cells in vitro.

Abstract

Male germ cells directly affect the reproduction of males; however, their accurate isolation and culture in vitro is extremely challenging, hindering the study of germ cell development and function. CRISPR/dcas9, as an efficient gene reprogramming system, has been verified to promote the transdifferentiation of pluripotent stem cells into male germ cells by editing target genes. In our research, we explored the expression pattern of the germ cell related genes bmp4, dazl,nanos3 and sycp2 in Hu sheep testicular development and constructed the overexpression model using the CRISPR/dcas9 system. The results indicated that four genes showed more expression in testis tissue than in other tissues, and that bmp4, dazl and sycp2 present higher expression levels in nine-month-old sheep testes than in three-month-olds, while nanos3 expressed the opposite trend (p < 0.05). In addition, the expression of four potential genes in spermatogenic cells was slightly different, but they were all expressed in sheep Leydig cells. To verify the potential roles of the four genes in the process of inducing differentiation of male germ cells, we performed cell transfection in vitro. We found that the expression of the germ cell related genes Prdm1, Prdm14, Mvh and Sox17 were significantly increased after the overexpression of the four genes in Leydig cells, and the co-transfection effect was the most significant (p < 0.05). Our results illustrate the crucial functions of bmp4, dazl, nanos3 and sycp2 in Hu sheep testis development and verified the effectiveness of the overexpression model that was constructed using the CRISPR/dcas9 system, which provided a basis for further male germ cell differentiation in vitro.

Gene Alterations and Expression Spectrum of NANOS3 in Nonobstructive Azoospermia

Nanos3, a zinc finger RNA-binding protein, suppresses the apoptosis in primordial germ cells (PGCs) during migration to gonads and maintains the PGC population. The genetic variations and expression of NANOS3 in patients with non-obstructive azoospermia (NOA) were evaluated in this study. The study included 100 idiopathic infertile men with NOA and 100 fertile men as the as the case and control groups, respectively. NANOS3 gene variations were analyzed using the standard polymerase chain reaction (PCR) and sequencing. For mRNA and protein expression analysis, testicular biopsy specimens from 27 patients including 9 obstructive azoospermia (OA), 9 maturation arrest (MA), and 9 Sertoli cell-only syndromes (SCOS) were collected and evaluated using the real-time PCR technique and immunohistochemistry. Although the evaluation of the 5`UTR regulatory region has shown the significant difference in the numbers of TG repeats in rs11182456 between groups, the odd ratio was not strong enough to consider that as a certain risk factor lead to azoospermia and infertility. Meanwhile, NANOS3 expression at mRNA level had a significant difference among OA, SCOS, and MA groups.

Roles of Stra8 and Tcerg1l in retinoic acid induced spermatogonial differentiation in mouse†

Retinoic acid (RA) induces spermatogonial differentiation, but the mechanism by which it operates remains largely unknown. We developed a germ cell culture assay system to study genes involved in spermatogonial differentiation triggered by RA. Stimulated by RA 8 (Stra8), a RA-inducible gene, is indispensable for meiosis initiation, and its deletion results in a complete block of spermatogenesis at the pre-leptotene/zygotene stage. To interrogate the role of Stra8 in RA mediated differentiation of spermatogonia, we derived germ cell cultures from the neonatal testis of both wild type and Stra8 knock-out mice. We provide the first evidence that Stra8 plays a crucial role in modulating the responsiveness of undifferentiated spermatogonia to RA and facilitates transition to a differentiated state. Stra8-mediated differentiation is achieved through the downregulation of a large portfolio of genes and pathways, most notably including genes involved in the spermatogonial stem cell self-renewal process. We also report here for the first time the role of transcription elongation regulator-1 like (Tcerg1l) as a downstream effector of RA-induced spermatogonial differentiation.

Genetic and structural analysis of the in vivo functional redundancy between murine NANOS2 and NANOS3

NANOS2 and NANOS3 are evolutionarily conserved RNA-binding proteins involved in murine germ cell development. NANOS3 is required for protection from apoptosis during migration and gonadal colonization in both sexes, whereas NANOS2 is male-specific and required for the male-type differentiation of germ cells. Ectopic NANOS2 rescues the functions of NANOS3, but NANOS3 cannot rescue NANOS2 function, even though its expression is upregulated in Nanos2-null conditions. It is unknown why NANOS3 cannot rescue NANOS2 function and it is unclear whether NANOS3 plays any role in male germ cell differentiation. To address these questions, we made conditional Nanos3/Nanos2 knockout mice and chimeric mice expressing chimeric NANOS proteins. Conditional double knockout of Nanos2 and Nanos3 led to the rapid loss of germ cells, and in vivo and in vitro experiments revealed that DND1 and NANOS2 binding is dependent on the specific NANOS2 zinc-finger structure. Moreover, murine NANOS3 failed to bind CNOT1, an interactor of NANOS2 at its N-terminal. Collectively, our study suggests that the inability of NANOS3 to rescue NANOS2 function is due to poor DND1 recruitment and CNOT1 binding.

The Molecular Machinery of Gametogenesis in Geodia Demosponges (Porifera): Evolutionary Origins of a Conserved Toolkit across Animals

All animals are capable of undergoing gametogenesis. The ability of forming haploid cells from diploid cells through meiosis and recombination appeared early in eukaryotes, whereas further gamete differentiation is mostly a metazoan signature. Morphologically, the gametogenic process presents many similarities across animal taxa, but little is known about its conservation at the molecular level. Porifera are the earliest divergent animals and therefore are an ideal phylum to understand evolution of the gametogenic toolkits. Although sponge gametogenesis is well known at the histological level, the molecular toolkits for gamete production are largely unknown. Our goal was to identify the genes and their expression levels which regulate oogenesis and spermatogenesis in five gonochoristic and oviparous species of the genus Geodia, using both RNAseq and proteomic analyses. In the early stages of both female and male gametogenesis, genes involved in germ cell fate and cell-renewal were upregulated. Then, molecular signals involved in retinoic acid pathway could trigger the meiotic processes. During later stages of oogenesis, female sponges expressed genes involved in cell growth, vitellogenesis, and extracellular matrix reassembly, which are conserved elements of oocyte maturation in Metazoa. Likewise, in spermatogenesis, genes regulating the whole meiotic cycle, chromatin compaction, and flagellum axoneme formation, that are common across Metazoa were overexpressed in the sponges. Finally, molecular signals possibly related to sperm capacitation were identified during late stages of spermatogenesis for the first time in Porifera. In conclusion, the activated molecular toolkit during gametogenesis in sponges was remarkably similar to that deployed during gametogenesis in vertebrates.

RNA-binding protein Ptbp1 regulates alternative splicing and transcriptome in spermatogonia and maintains spermatogenesis in concert with Nanos3

PTBP1, a well-conserved RNA-binding protein, regulates cellular development by tuning posttranscriptional mRNA modification such as alternative splicing (AS) or mRNA stabilization. We previously revealed that the loss of Ptbp1 in spermatogonia causes the dysregulation of spermatogenesis, but the molecular mechanisms by which PTBP1 regulates spermatogonium homeostasis are unclear. In this study, changes of AS or transcriptome in Ptbp1-knockout (KO) germline stem cells (GSC), an in vitro model of proliferating spermatogonia, was determined by next generation sequencing. We identified more than 200 differentially expressed genes, as well as 85 genes with altered AS due to the loss of PTBP1. Surprisingly, no differentially expressed genes overlapped with different AS genes in Ptbp1-KO GSC. In addition, we observed that the mRNA expression of Nanos3, an essential gene for normal spermatogenesis, was significantly decreased in Ptbp1-KO spermatogonia. We also revealed that PTBP1 protein binds to Nanos3 mRNA in spermatogonia. Furthermore, Nanos3^+/−;Ptbp1^+/− mice exhibited abnormal spermatogenesis, which resembled the effects of germ cell-specific Ptbp1 KO, whereas no significant abnormality was observed in mice heterozygous for either gene alone. These data implied that PTBP1 regulates alternative splicing and transcriptome in spermatogonia under different molecular pathways, and contributes spermatogenesis, at least in part, in concert with NANOS3.

Investigation of VASA Gene and Protein Expression in Neonate and Adult Testicular Germ Cells in Mice In Vivo and In Vitro

Objective

We aimed to examine the expression levels of the VASA gene and protein in testis sections of neonate and adult mice as well as testicular cell cultures.

Materials and Methods

In this experimental study, in order to investigate the expression of this germ cell marker gene in more detail, we analyzed the expression of VASA by immunocytochemistry, immunohistochemistry and fluidigm reverse transcription-polymerase chain reaction (RT-PCR).

Results

The immunohistochemical assays showed that the VASA protein was exclusively expressed in germ cells in the seminiferous tubules of the neonate and adult testis and not in somatic cells. VASA was not detectable in PLZF positive spermatogonial stem cells (SSCs), was weakly expressed in proliferating spermatogonia, and became abundant in spermatocytes and round spermatozoa. Counting VASA-positive cells in the seminiferous tubules of the neonate and adult testis depicted significant higher expression (P<0.05) of VASA in the adult testis in comparison to its neonate counterpart. SSC colonies were established in vitro after digestion of the testis and characterized by immunocytochemistry for CD90 and stage-specific embryonic antigens 3 (SSEA3). Immunocytochemistry confirmed that in contrast to the not detectable signal in vivo, VASA protein was strongly localized in the cytoplasm of both neonate and adult mouse SSCs under in vitro conditions. The results of Fluidigm RT-PCR revealed a significant higher expression of the germ cell gene VASA in adult SSCs in comparison to neonate SSCs in cell culture (P<0.05).

Conclusion

The VASA protein is, therefore, an extremely specific marker of testicular germ cell differentiation in vivo and mostly expressed in the adult testis in spermatocytes and round spermatids. The immunohistochemical signal in spermatogonia is very low. So, PLZF positive SSCs are negative for VASA in vivo, while in contrast, once isolated from the testicular niche VASA is also strongly expressed in SSCs under in vitro conditions.

Comprehensive analysis of long noncoding RNA and mRNA expression patterns in sheep testicular maturation

Long noncoding RNAs (LncRNAs) have been identified as important regulators of testis development; however, their expression patterns and roles in sheep are not yet clear. Thus, we used stranded specific RNA-seq to profile the testis transcriptome (lncRNAs and mRNAs) in premature and mature sheep. Hormone levels and the testis index were examined, and histological analyses were performed at five stages of testis development, 5-day-old (D5), 3-month-old (3M), 6-month-old (6M), 9-month-old (9M), and 2-year-old (2Y), the results of which indicate a significant difference in hormone levels and testis morphometries between the 3M and 9M stages (P < 0.05). Based on the comparison between 3M and 9M samples, we found 1,118 differentially expressed (DE) lncRNAs and 7,253 DE mRNAs in the testes, and qRT-PCR analysis showed that the results correlated well with the transcriptome data. Furthermore, we constructed lncRNA-protein-coding gene interaction networks. Forty-seven DE lncRNA-targeted genes enriched for male reproduction were obtained by cis- and trans-acting; 51 DE lncRNAs and 45 cis-targets, 2 DE lncRNAs and 2 trans-targets were involved in this network. Of these, 5 lncRNAs and their targets, PRKCD, NANOS3, SERPINA5, and CYP19A1, were enriched for spermatogenesis and male gonad development signaling pathways. We further examined the expression levels of 5 candidate lncRNAs and their target genes during testis development. Lastly, the interaction of lncRNA TCONS__00863147 and its target gene PRKCD was validated in vitro in sheep Leydig cells. This study provides a valuable resource for further study of lncRNA function in sheep testis development and spermatogenesis.

Perinatal Exposure to Glyphosate and a Glyphosate-Based Herbicide Affect Spermatogenesis in Mice

Glyphosate is the most widely used herbicide in the world. Several studies have investigated the effects of glyphosate and glyphosate-based herbicides (GBHs) on male reproduction, but there is still little and conflicting evidence for its toxicity. In this study, we analyzed the effects of glyphosate, alone or in formula, on the male reproductive system. Pregnant mice were treated from E10.5 to 20 days postpartum by adding glyphosate or a GBH (Roundup 3 Plus) to their drinking water at 0.5 (the acceptable daily intake, ADI dose), 5 and 50 mg/kg/day. Male offspring derived from treated mice were sacrificed at 5, 20, and 35 days old (d.o.) and 8 months old (m.o.) for analysis. Our result showed that exposure to glyphosate, but not GBH, affects testis morphology in 20 d.o. and decrease serum testosterone concentrations in 35 d.o. males. We identified that the spermatozoa number decreased by 89% and 84% in 0.5 and 5 mg/kg/day of GBH and glyphosate groups, respectively. Moreover, the undifferentiated spermatogonia numbers were decreased by 60% in 5 mg/kg/day glyphosate group, which could be due to the alterations in the expression of genes involved in germ cell differentiation such as Sall4 and Nano3 and apoptosis as Bax and Bcl2. In 8 m.o. animals, a decreased testosterone level was observed in GBH groups. Our data demonstrate that glyphosate and GBHs could cause endocrine-disrupting effects on male reproduction at low doses. As glyphosate has effects at the ADI level, our data suggest that the current ADI for glyphosate could be overestimated.

PUM1 and PUM2 exhibit different modes of regulation for SIAH1 that involve cooperativity with NANOS paralogues

Pumilio (PUM) proteins are RNA-binding proteins that posttranscriptionally regulate gene expression in many organisms. Their PUF domain recognizes specific PUM-binding elements (PBE) in the 3' untranslated region of target mRNAs while engaging protein cofactors such as NANOS that repress the expression of target mRNAs through the recruitment of effector complexes. Although the general process whereby PUM recognizes individual mRNAs has been studied extensively, the particulars of the mechanism underlying PUM-NANOS cooperation in mRNA regulation and the functional overlap among PUM and NANOS paralogues in mammals have not been elucidated. Here, using the novel PUM1 and PUM2 mRNA target SIAH1 as a model, we show mechanistic differences between PUM1 and PUM2 and between NANOS1, 2, and 3 paralogues in the regulation of SIAH1. Specifically, unlike PUM2, PUM1 exhibited PBE-independent repression of SIAH1 3'UTR-dependent luciferase expression. Concordantly, the PUF domains of PUM1 and PUM2 showed different EMSA complex formation patterns with SIAH1 3'UTRs. Importantly, we show direct binding of NANOS3, but not NANOS2, to SIAH1 3'UTR, which did not require PBEs or the PUF domain. To the best of our knowledge, this is the first report, showing that an NANOS protein directly binds RNA. Finally, using NANOS1 and NANOS3 constructs carrying mutations identified in infertile patients, we show that these mutations disrupt repression of the SIAH1-luciferase reporter and that the central region in NANOS1 appears to contribute to the regulation of SIAH1. Our findings highlight the mechanistic versatility of the PUM/NANOS machinery in mammalian posttranscriptional regulation.

Transcriptome Dynamics During Turbot Spermatogenesis Predicting the Potential Key Genes Regulating Male Germ Cell Proliferation and Maturation

Spermatogenesis is a dynamic developmental process in which spermatogonial stem cells proliferate, differentiate and mature into functional spermatozoa. These processes require an accurate gene regulation network. Here, we investigated the dynamic changes that occur during spermatogenesis through a combination of histological and transcriptome analyses of different developmental stages of the testis. We constructed 18 testis transcriptome libraries, and the average length, N50, and GC content of the unigenes were 1,795 bp; 3,240 bp and 49.25%, respectively. Differentially expressed genes (DEGs) that were related to germ cell proliferation and maturation, such as NANOS3, RARs, KIFs, steroid hormone synthesis-related genes and receptor genes, were identified between pairs of testis at different developmental stages. Gene ontology annotation and pathway analyses were conducted on DEGs with specific expression patterns involved in the regulation of spermatogenesis. Nine important pathways such as steroid hormone biosynthesis related to spermatogenesis were identified. A total of 21 modules that ranged from 49 to 7,448 genes were designed by a weighted gene co-expression network analysis. Furthermore, a total of 83 candidate miRNA were identified by computational methods. Our study provides the first transcriptomic evidence for differences in gene expression between different developmental stages of spermatogenesis in turbot (Scophthalmus maximus).

Post-transcriptional Regulatory Functions of Mammalian Pumilio Proteins

Mammalian Pumilio proteins, PUM1 and PUM2, are members of the PUF family of sequence-specific RNA-binding proteins. In this review, we explore their mechanisms, regulatory networks, biological functions, and relevance to diseases. Pumilio proteins bind an extensive network of mRNAs and repress protein expression by inhibiting translation and promoting mRNA decay. Opposingly, in certain contexts, they can activate protein expression. Pumilio proteins also regulate noncoding (nc)RNAs. The ncRNA, ncRNA activated by DNA damage (NORAD), can in turn modulate Pumilio activity. Genetic analysis provides new insights into Pumilio protein function. They are essential for growth and development. They control diverse processes, including stem cell fate, and neurological functions, such as behavior and memory formation. Novel findings show that their dysfunction contributes to neurodegeneration, epilepsy, movement disorders, intellectual disability, infertility, and cancer.

Nanos genes and their role in development and beyond

The hallmark of Nanos proteins is their typical (CCHC)2 zinc finger motif (zf-nanos). Animals have one to four nanos genes. For example, the fruit fly and demosponge have only one nanos gene, zebrafish and humans have three, and Fugu rubripes has four. Nanos genes are mainly known for their evolutionarily preserved role in germ cell survival and pluripotency. Nanos proteins have been reported to bind the C-terminal RNA-binding domain of Pumilio to form a post-transcriptional repressor complex. Several observations point to a link between the miRNA-mediated repression complex and the Nanos/Pumilio complex. Repression of the E2F3 oncogene product is, indeed, mediated by cooperation between the Nanos/Pumilio complex and miRNAs. Another important interaction partner of Nanos is the CCR4-NOT deadenylase complex. Besides the tissue-specific contribution of Nanos proteins to normal development, their ectopic expression has been observed in several cancer cell lines and various human cancers. An inverse correlation between the expression levels of human Nanos1 and Nanos3 and E-cadherin was observed in several cancer cell lines. Loss of E-cadherin, an important cell-cell adhesion protein, contributes to tumor invasion and metastasis. Overexpression of Nanos3 induces epithelial-mesenchymal transition in lung cancer cell lines partly by repressing E-cadherin. Other than some most interesting data from Nanos knockout mice, little is known about mammalian Nanos proteins, and further research is needed. In this review, we summarize the main roles of Nanos proteins and discuss the emerging concept of Nanos proteins as oncofetal antigens.

Human spermatogonial markers

In this review, we provide an up-to-date compilation of published human spermatogonial markers, with focus on the three nuclear subtypes A_dark, A_pale and B. In addition, we have extended our recently published list of putative spermatogonial markers with protein expression and RNA-sequencing data from the Human Protein Atlas and supported these by literature evidence. Most importantly, we have put substantial effort in acquiring a comprehensive list of new and potentially interesting markers by refiltering the raw data of 15 published germ cell expression datasets (four human, eleven rodent) and subsequent building of intersections to acquire a robust, cross-species set of spermatogonia-enriched or -specific transcripts.

Molecular Signatures of Primary Human Spermatogonial Progenitors and Its Neighboring Peritubular Stromal Compartment

In-depth understanding of human spermatogenesis requires studying specific molecular signatures and interactions of spermatogonia with other testicular cell populations, for which isolation of pure populations of different cell types is crucial. Here, we describe a technique to simultaneously enrich pure, multiple testicular cell populations, including spermatogonia, endothelial (TECs), and perivascular mesenchymal stem/stromal cells (TMSCs), from testicular tissue by flow cytometry using a combination of defined markers. Immunohistochemical studies, multicolor staining, and cell sorting followed by multiplex quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that spermatogonia were highly enriched in the CD49f⁺CD49a^-HLA-ABC^-SSEA-4⁺ fraction of primary testicular cells. In contrast to spermatogonia, TMSCs and TECs were highly enriched in the CD49f⁺CD49a⁺HLA-ABC⁺CD144^- and CD49f⁺CD49a⁺HLA-ABC⁺CD144⁺subsets, respectively. The delineation was confirmed by the expression of specific stromal and endothelial key markers as well as by the differentiation and angiogenic capacity of the sorted populations. In this article, for the first time, we performed transcriptome profiling of highly enriched, freshly isolated human spermatogonia and compared their expression profile with that of TMSCs. Our RNA sequencing data favor the hypothesis that TMSCs are candidate niche components for spermatogonia. The composite genotype and phenotype of defined testicular cell populations combined with a robust isolation procedure from small biopsies contributes to a better understanding of cellular interactions and for the establishment of efficient culture techniques to maintain spermatogonial progenitors.

Drosophila Nanos acts as a molecular clamp that modulates the RNA-binding and repression activities of Pumilio

Collaboration among the multitude of RNA-binding proteins (RBPs) is ubiquitous, yet our understanding of these key regulatory complexes has been limited to single RBPs. We investigated combinatorial translational regulation by Drosophila Pumilio (Pum) and Nanos (Nos), which control development, fertility, and neuronal functions. Our results show how the specificity of one RBP (Pum) is modulated by cooperative RNA recognition with a second RBP (Nos) to synergistically repress mRNAs. Crystal structures of Nos-Pum-RNA complexes reveal that Nos embraces Pum and RNA, contributes sequence-specific contacts, and increases Pum RNA-binding affinity. Nos shifts the recognition sequence and promotes repression complex formation on mRNAs that are not stably bound by Pum alone, explaining the preponderance of sub-optimal Pum sites regulated in vivo. Our results illuminate the molecular mechanism of a regulatory switch controlling crucial gene expression programs, and provide a framework for understanding how the partnering of RBPs evokes changes in binding specificity that underlie regulatory network dynamics.

DOI:http://dx.doi.org/10.7554/eLife.17096.001

Molecules of DNA contain the instructions needed to make proteins inside cells. Proteins perform many different roles and each needs to be produced at the right time and in the right amounts to enable the cells to survive. The DNA is first copied to make molecules of ribonucleic acid (RNA), which are then used as templates to make the proteins. One way to control protein production is to regulate the RNA molecules. A family of proteins called RNA-binding proteins can recognise and bind to specific RNA molecules and determine whether a RNA molecule is destroyed, used to produce proteins, or stored for later use. In effect, these RNA-binding proteins act as switches that turn protein production on or off.

Nanos and Pumilio are two RNA-binding proteins that are found in many organisms, including humans and other animals. Genetic studies in fruit flies show that these two proteins influence development, the nervous system and the behaviour of stem cells by switching off the production of certain proteins. To investigate how Nanos and Pumilio work together to regulate protein production, Weidmann, Qiu et al. used a variety of techniques to study the activity of these proteins in cells taken from fruit fly embryos.

The experiments reveal that Nanos acts like a clamp to hold Pumilio close to specific RNAs, which allows Pumilio to switch off the production of the corresponding proteins. The presence of Nanos allows Pumilio to regulate RNAs that it cannot bind to alone. Therefore, the experiments show that by working together with Nanos, Pumilio is able to regulate a wider variety of RNAs than it would otherwise be able to. These findings provide a molecular understanding for why fruit fly mutants that lack Nanos or Pumilio have severe body defects and reduced fertility. The next challenge is to identify the specific RNAs targeted by Nanos and Pumilio in stem cells, the nervous system and during development.

DOI:http://dx.doi.org/10.7554/eLife.17096.002

Transcription Factor GLIS3: A New and Critical Regulator of Postnatal Stages of Mouse Spermatogenesis

In this study, we identify a novel and essential role for the Krüppel-like zinc finger transcription factor GLI-similar 3 (GLIS3) in the regulation of postnatal spermatogenesis. We show that GLIS3 is expressed in gonocytes, spermatogonial stem cells (SSCs) and spermatogonial progenitors (SPCs), but not in differentiated spermatogonia and later stages of spermatogenesis or in somatic cells. Spermatogenesis is greatly impaired in GLIS3 knockout mice. Loss of GLIS3 function causes a moderate reduction in the number of gonocytes, but greatly affects the generation of SSCs/SPCs, and as a consequence the development of spermatocytes. Gene expression profiling demonstrated that the expression of genes associated with undifferentiated spermatogonia was dramatically decreased in GLIS3-deficient mice and that the cytoplasmic-to-nuclear translocation of FOXO1, which marks the gonocyte-to-SSC transition and is necessary for SSC self-renewal, is inhibited. These observations suggest that GLIS3 promotes the gonocyte-to-SSC transition and is a critical regulator of the dynamics of early postnatal spermatogenesis. Stem Cells 2016;34:2772-2783.

A Smaug2-Based Translational Repression Complex Determines the Balance between Precursor Maintenance versus Differentiation during Mammalian Neurogenesis

Here, we have asked about post-transcriptional mechanisms regulating murine developmental neurogenesis, focusing upon the RNA-binding proteins Smaug2 and Nanos1. We identify, in embryonic neural precursors of the murine cortex, a Smaug2 protein/nanos1 mRNA complex that is present in cytoplasmic granules with the translational repression proteins Dcp1 and 4E-T. We show that Smaug2 inhibits and Nanos1 promotes neurogenesis, with Smaug2 knockdown enhancing neurogenesis and depleting precursors, and Nanos1 knockdown inhibiting neurogenesis and maintaining precursors. Moreover, we show that Smaug2 likely regulates neurogenesis by silencing nanos1 mRNA. Specifically, Smaug2 knockdown inappropriately increases Nanos1 protein, and the Smaug2 knockdown-mediated neurogenesis is rescued by preventing this increase. Thus, Smaug2 and Nanos1 function as a bimodal translational repression switch to control neurogenesis, with Smaug2 acting in transcriptionally primed precursors to silence mRNAs important for neurogenesis, including nanos1 mRNA, and Nanos1 acting during the transition to neurons to repress the precursor state.

SIGNIFICANCE STATEMENT

The mechanisms instructing neural stem cells to generate the appropriate progeny are still poorly understood. Here, we show that the RNA-binding proteins Smaug2 and Nanos1 are critical regulators of this balance and provide evidence supporting the idea that neural precursors are transcriptionally primed to generate neurons but translational regulation maintains these precursors in a stem cell state until the appropriate developmental time.

Extrinsic and intrinsic factors controlling spermatogonial stem cell self-renewal and differentiation

Spermatogonial stem cells (SSCs), the stem cells responsible for male fertility, are one of a small number of cells with the abilities of both self-renewal and generation of large numbers of haploid cells. Technology improvements, most importantly, transplantation assays and in vitro culture systems have greatly expanded our understanding of SSC self-renewal and differentiation. Many important molecules crucial for the balance between self-renewal and differentiation have been recently identified although the exact mechanism(s) remain largely undefined. In this review, we give a brief introduction to SSCs, and then focus on extrinsic and intrinsic factors controlling SSCs self-renewal and differentiation.

Mechanisms Regulating Spermatogonial Differentiation

Mammalian spermatogenesis is a complex and highly ordered process by which male germ cells proceed through a series of differentiation steps to produce haploid flagellated spermatozoa. Underlying this process is a pool of adult stem cells, the spermatogonial stem cells (SSCs), which commence the spermatogenic lineage by undertaking a differentiation fate decision to become progenitor spermatogonia. Subsequently, progenitors acquire a differentiating spermatogonia phenotype and undergo a series of amplifying mitoses while becoming competent to enter meiosis. After spermatocytes complete meiosis, post-meiotic spermatids must then undergo a remarkable transformation from small round spermatids to a flagellated spermatozoa with extremely compacted nuclei. This chapter reviews the current literature pertaining to spermatogonial differentiation with an emphasis on the mechanisms controlling stem cell fate decisions and early differentiation events in the life of a spermatogonium.

Gonadotoxic effects of busulfan in two strains of mice

Busulfan is a chemotherapy drug that has side effects on spermatogonial stem cells (SSC). The effects of bulsufan treatment on male germ cells and fertility vary significantly between individuals. In this study, we have used molecular, cellular and histopathology approaches to investigate the effects of a single intraperitoneal dose of busulfan (40mgkg(-1)) in two mice strains, Balb/C and Swiss, at two different periods after treatment, 30 and 90 days. Testicular degeneration was observed in both Balb/C and Swiss mice after busulfan injection. Interestingly, testicular functions and fertility recovered spontaneously post busulfan treatment in Swiss mice, but not in Balb/C mice. Abnormal fertility induced by busulfan in Balb/C mice was associated with altered seminiferous tubules, sperm morphology and transcript levels of Nanos2, Nanos3, Gdnf and Plzf genes. These findings revealed that SSC of Balb/C mice are more sensitive to the toxic effects of busulfan then those of Swiss mice.

Sequencing and De Novo Assembly of the Gonadal Transcriptome of the Endangered Chinese Sturgeon (Acipenser sinensis)

Background

The Chinese sturgeon (Acipenser sinensis) is endangered through anthropogenic activities including over-fishing, damming, shipping, and pollution. Controlled reproduction has been adopted and successfully conducted for conservation. However, little information is available on the reproductive regulation of the species. In this study, we conducted de novo transcriptome assembly of the gonad tissue to create a comprehensive dataset for A. sinensis.

Results

The Illumina sequencing platform was adopted to obtain 47,333,701 and 47,229,705 high quality reads from testis and ovary cDNA libraries generated from three-year-old A. sinensis. We identified 86,027 unigenes of which 30,268 were annotated in the NCBI non-redundant protein database and 28,281 were annotated in the Swiss-prot database. Among the annotated unigenes, 26,152 and 7,734 unigenes, respectively, were assigned to gene ontology categories and clusters of orthologous groups. In addition, 12,557 unigenes were mapped to 231 pathways in the Kyoto Encyclopedia of Genes and Genomes Pathway database. A total of 1,896 unigenes, potentially differentially expressed between the two gonad types, were found, with 1,894 predicted to be up-regulated in ovary and only two in testis. Fifty-five potential gametogenesis-related genes were screened in the transcriptome and 34 genes with significant matches were found. Besides, more paralogs of 11 genes in three gene families (sox, apolipoprotein and cyclin) were found in A. sinensis compared to their orthologs in the diploid Danio rerio. In addition, 12,151 putative simple sequence repeats (SSRs) were detected.

Conclusions

This study provides the first de novo transcriptome analysis currently available for A. sinensis. The transcriptomic data represents the fundamental resource for future research on the mechanism of early gametogenesis in sturgeons. The SSRs identified in this work will be valuable for assessment of genetic diversity of wild fish and genealogy management of cultured fish.

Fgf9 inhibition of meiotic differentiation in spermatogonia is mediated by Erk-dependent activation of Nodal-Smad2/3 signaling and is antagonized by Kit Ligand

Both fibroblast growth factor 9 (Fgf9) and Kit Ligand (Kl) signal through tyrosine kinase receptors, yet they exert opposite effects on meiotic differentiation in postnatal spermatogonia, Fgf9 acting as a meiosis-inhibiting substance and Kl acting as a promoter of the differentiation process. To understand the molecular mechanisms that might underlie this difference, we tried to dissect the intracellular signaling elicited by these two growth factors. We found that both Fgf9 and Kl stimulate Erk1/2 activation in Kit+ (differentiating) spermatogonia, even though with different time courses, whereas Kl, but not Fgf9, elicits activation of the Pi3k-Akt pathway. Sustained Erk1/2 activity promoted by Fgf9 is required for induction of the autocrine Cripto-Nodal-Smad2/3 signaling loop in these cells. Nodal signaling, in turn, is essential to mediate Fgf9 suppression of the meiotic program, including inhibition of Stra8 and Scp3 expression and induction of the meiotic gatekeeper Nanos2. On the contrary, sustained activation of the Pi3k-Akt pathway is required for the induction of Stra8 expression elicited by Kl and retinoic acid. Moreover, we found that Kl treatment impairs Nodal mRNA expression and Fgf9-mediated Nanos2 induction, reinforcing the antagonistic effect of these two growth factors on the meiotic fate of male germ cells.

Fluorescence- and magnetic-activated cell sorting strategies to isolate and enrich human spermatogonial stem cells

OBJECTIVE

To determine the molecular characteristics of human spermatogonia and optimize methods to enrich spermatogonial stem cells (SSCs).

DESIGN

Laboratory study using human tissues.

SETTING

Research institute.

PATIENT(S)

Healthy adult human testicular tissue.

INTERVENTION(S)

Human testicular tissue was fixed or digested with enzymes to produce a cell suspension. Human testis cells were fractionated by fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS).

MAIN OUTCOME MEASURE(S)

Immunostaining for selected markers, human-to-nude mouse xenotransplantation assay.

RESULT(S)

Immunohistochemistry costaining revealed the relative expression patterns of SALL4, UTF1, ZBTB16, UCHL1, and ENO2 in human undifferentiated spermatogonia as well as the extent of overlap with the differentiation marker KIT. Whole mount analyses revealed that human undifferentiated spermatogonia (UCHL1+) were typically arranged in clones of one to four cells whereas differentiated spermatogonia (KIT+) were typically arranged in clones of eight or more cells. The ratio of undifferentiated-to-differentiated spermatogonia is greater in humans than in rodents. The SSC colonizing activity was enriched in the THY1dim and ITGA6+ fractions of human testes sorted by FACS. ITGA6 was effective for sorting human SSCs by MACS; THY1 and EPCAM were not.

CONCLUSION(S)

Human spermatogonial differentiation correlates with increased clone size and onset of KIT expression, similar to rodents. The undifferentiated-to-differentiated developmental dynamics in human spermatogonia is different than rodents. THY1, ITGA6, and EPCAM can be used to enrich human SSC colonizing activity by FACS, but only ITGA6 is amenable to high throughput sorting by MACS.

Maternal cypermethrin exposure during the perinatal period impairs testicular development in C57BL male offspring

Numerous studies have demonstrated that endocrine-disrupting compounds (EDC) are a possible cause of male reproductive organ malfunction and malformation. Cypermethrin (CYP) is a widely used synthetic pyrethroid and a potential EDC. This study aimed to examine the effects of perinatal exposure to low-dose CYP on the development and function of the offspring testes. Pregnant mice were intragastrically administered 0.12 to 12 mg/kg/day CYP from embryonic day 0.5 (E0.5) to weaning (PD21.5, postnatal day 21.5). Maternal exposure to 0.12, 1.2, and 12 mg/kg/day CYP affected the body and organ weight of the offspring. Exposure of CYP led to a dose-dependent decrease in the male-to-female sex ratio. A histopathological analysis revealed a thinner seminiferous epithelium layer at PD21.5, interstitial hyperplasia at PD45.5, and germ cell vacuolization at PD90.5 in the 12 mg/kg/day CYP group. The TUNEL assay results revealed increased germ cell apoptosis in the 12 mg/kg/day CYP group. The serum testosterone (T) level decreased, whereas the estradiol level increased with age in the 1.2 and 12 mg/kg/day CYP groups. The RT-PCR analysis demonstrated decreased expression of T production-related, mitosis-related, and meiosis-related genes in the 1.2 and 12 mg/kg/day CYP groups. The in vitro experimental results demonstrated reduced expression of steroidogenesis genes and decreased T levels. It is concluded that perinatal exposure to low-dose CYP affects testes development and function in adults.

Nanos3 gene targeting in medaka ES cells

Gene targeting (GT) by homologous recombination offers the best precision for genome editing in mice. nanos3 is a highly conserved gene and encodes a zinc-finger RNA binding protein essential for germ stem cell maintenance in Drosophila, zebrafish and mouse. Here we report nanos3 GT in embryonic stem (ES) cells of the fish medaka as a lower vertebrate model organism. A vector was designed for GT via homologous recombination on the basis of positive-negative selection (PNS). The ES cell line MES1 after gene transfer and PNS produced 56 colonies that were expanded into ES cell sublines. Nine sublines were GT-positive by PCR genotyping, 4 of which were homologous recombinants as revealed by Southern blot. We show that one of the 4, A15, contains a precisely targeted nanos3 allele without any random events, demonstrating the GT feasibility in medaka ES cells. Importantly, A15 retained all features of undifferentiated ES cells, including stable self-renewal, an undifferentiated phenotype, pluripotency gene expression and differentiation during chimeric embryogenesis. These results provide first evidence that the GT procedure and genuine GT on a chromosomal locus such as nanos3 do not compromise pluripotency in ES cells of a lower vertebrate.

Retinoic acid induces Sertoli cell paracrine signals for spermatogonia differentiation but cell autonomously drives spermatocyte meiosis

Direct evidence for a role of endogenous retinoic acid (RA), the active metabolite of vitamin A in the initial differentiation and meiotic entry of spermatogonia, and thus in the initiation of spermatogenesis is still lacking. RA is synthesized by dedicated enzymes, the retinaldehyde dehydrogenases (RALDH), and binds to and activates nuclear RA receptors (RARA, RARB, and RARG) either within the RA-synthesizing cells or in the neighboring cells. In the present study, we have used a combination of somatic genetic ablations and pharmacological approaches in vivo to show that during the first, prepubertal, spermatogenic cycle (i) RALDH-dependent synthesis of RA by Sertoli cells (SC), the supporting cells of the germ cell (GC) lineage, is indispensable to initiate differentiation of A aligned into A1 spermatogonia; (ii) RARA in SC mediates the effects of RA, possibly through activating Mafb expression, a gene whose Drosophila homolog is mandatory to GC differentiation; (iii) RA synthesized by premeiotic spermatocytes cell autonomously induces meiotic initiation through controlling the RAR-dependent expression of Stra8. Furthermore, we show that RA of SC origin is no longer necessary for the subsequent spermatogenic cycles but essential to spermiation. Altogether, our data establish that the effects of RA in vivo on spermatogonia differentiation are indirect, via SC, but direct on meiotic initiation in spermatocytes, supporting thereby the notion that, contrary to the situation in the female, RA is necessary to induce meiosis in the male.

Rhox13 is translated in premeiotic germ cells in male and female mice and is regulated by NANOS2 in the male

Male and female germ cells enter meiosis in response to an extrinsic cue by retinoic acid (RA), but the pathways downstream of RA signaling that regulate early gametogenesis remain uncertain. We identified a novel reproductive homeobox gene, Rhox13, transcribed in the prenatal ovary and testis beginning on Embryonic Day (E) 13.5. Translation of RHOX13 also begins in female germ cells on E13.5 but is suppressed in male germ cells until Postnatal Day 3. Translation of RHOX13 coincides with initiation of RA signaling in both male and female gonads in vivo but occurs precociously in neonatal testes exposed to RA in vitro or in fetal male germ cells when NANOS2 is absent in vivo. Conversely, RHOX13 translation in female germ cells is suppressed in the presence of ectopically induced NANOS2. These results strongly suggest that RHOX13 expression is regulated at a posttranscriptional step by direct interaction of NANOS2 with Rhox13 mRNA to suppress translation.

Dynamic changes in EPCAM expression during spermatogonial stem cell differentiation in the mouse testis

Background

Spermatogonial stem cells (SSCs) have the unique ability to undergo self-renewal division. However, these cells are morphologically indistinguishable from committed spermatogonia, which have limited mitotic activity. To establish a system for SSC purification, we analyzed the expression of SSC markers CD9 and epithelial cell adhesion molecule (EPCAM), both of which are also expressed on embryonic stem (ES) cells. We examined the correlation between their expression patterns and SSC activities.

Methodology and Principal Findings

By magnetic cell sorting, we found that EPCAM-selected mouse germ cells have limited clonogenic potential in vitro. Moreover, these cells showed stronger expression of progenitor markers than CD9-selected cells, which are significantly more enriched in SSCs. Fluorescence-activated cell sorting of CD9-selected cells indicated a significantly higher frequency of SSCs among the CD9⁺EPCAM^low/- population than among the CD9⁺EPCAM⁺ population. Overexpression of the active form of EPCAM in germline stem (GS) cell cultures did not significantly influence SSC activity, whereas EPCAM suppression by short hairpin RNA compromised GS cell proliferation and increased the concentration of SSCs, as revealed by germ cell transplantation.

Conclusions/Significance

These results show that SSCs are the most concentrated in CD9⁺EPCAM^low/- population and also suggest that EPCAM plays an important role in progenitor cell amplification in the mouse spermatogenic system. The establishment of a method to distinguish progenitor spermatogonia from SSCs will be useful for developing an improved purification strategy for SSCs from testis cells.

Inhibitor of DNA binding 4 is expressed selectively by single spermatogonia in the male germline and regulates the self-renewal of spermatogonial stem cells in mice

Continual spermatogenesis at a quantitatively normal level is required to sustain male fertility. The foundation of this process relies on maintenance of an undifferentiated spermatogonial population consisting of spermatogonial stem cells (SSCs) that self-renew as well as transient amplifying progenitors produced by differentiation. In mammals, type A(single) spermatogonia form the SSC population, but molecular markers distinguishing these from differentiating progenitors are undefined and knowledge of mechanisms regulating their functions is limited. We show that in the mouse male germline the transcriptional repressor ID4 is expressed by a subpopulation of undifferentiated spermatogonia and selectively marks A(single) spermatogonia. In addition, we found that ID4 expression is up-regulated in isolated SSC-enriched fractions by stimulation from GDNF, a key growth factor driving self-renewal. In mice lacking ID4 expression, quantitatively normal spermatogenesis was found to be impaired due to progressive loss of the undifferentiated spermatogonial population during adulthood. Moreover, reduction of ID4 expression by small interfering RNA treatment abolished the ability of wild-type SSCs to expand in vitro during long-term culture without affecting their survival. Collectively, these results indicate that ID4 is a distinguishing marker of SSCs in the mammalian germline and plays an important role in the regulation of self-renewal.

Translational control in germ cell development: A role for the RNA-binding proteins Musashi-1 and Musashi-2

Mammalian gametogenesis is a complex process involving specialised cell cycle progression and differentiation. As part of their differentiation, germ cells experience periods of transcriptional inactivation and chromatin inaccessibility whilst continuing to coordinate the correct temporal and spatial expression of genes required for continued development. To overcome these obstacles, mammalian germ cells express a wide variety of sequence-specific RNA-binding proteins, which assist in the translational control of many mRNA transcripts which are produced and stored during periods of high mRNA synthesis. In this review we focus on the Musashi family of RNA-binding proteins, a highly conserved family of translational regulatory proteins whose recent identification in germ cells of Drosophila and Xenopus, as well as their well described role in processes such as cell cycle progression and stem cell identity, has led us to investigate the role of these proteins in mammalian germ cell development.

Control of messenger RNA fate by RNA-binding proteins: an emphasis on mammalian spermatogenesis

Posttranscriptional status of messenger RNAs (mRNA) can be affected by many factors, most of which are RNA-binding proteins (RBP) that either bind mRNA in a nonspecific manner or through specific motifs, usually located in the 3' untranslated regions. RBPs can also be recruited by small noncoding RNAs (sncRNA), which have been shown to be involved in posttranscriptional regulations and transposon repression (eg, microRNAs or P-element-induced wimpy testis-interacting RNA) as components of the sncRNA effector complex. Non-sncRNA-binding RBPs have much more diverse effects on their target mRNAs. Some can cause degradation of their target transcripts and/or repression of translation, whereas others can stabilize and/or activate translation. The splicing and exportation of transcripts from the nucleus to the cytoplasm are often mediated by sequence-specific RBPs. The mechanisms by which RBPs regulate mRNA transcripts involve manipulating the 3' poly(A) tail, targeting the transcript to polysomes or to other ribonuclear protein particles, recruiting regulatory proteins, or competing with other RBPs. Here, we briefly review the known mechanisms of posttranscriptional regulation mediated by RBPs, with an emphasis on how these mechanisms might control spermatogenesis in general.

c-kit and its related genes in spermatogonial differentiation

Spermatogenesis is the process of production of male gametes from SSCs. The SSCs are the stem cells that differentiate into male gametes in the testis. in the mean time, the Spg are remarkable for their potential multiple trans-differentiations, which make them greatly invaluable for clinical applications. However, the molecular mechanism controlling differentiation of the Spg is still not clear. Among the discovered spermatogenesis-related genes, c-kit seems to be expressed first by the Spgs thus may play a central role in switching on the differentiation process. Expression of Kit and the activation of the Kit/Kitl pathway coincide with the start of differentiation of Spgs. Several genes have been discovered to be related to the Kit/Kitl pathway. in this review, we have summarized the recent discoveries of c-kit and the Kit/Kitl pathway-related genes in the spermatogenic cells during different stages of spermatogenesis.

Ontogenesis of Ap-2γ expression in rat testes

Searching for useful markers of spermatogonial stem cells and their differentiation, we used rat testes from ages representing different stages of testicular maturation to investigate the expression profile of transcription factor activation protein-2γ (Ap-2γ). The immunohistochemical and immunocytochemical evaluation using Ap-2γ and promyelocytic leukemia zinc finger in combination with sorting of CD9 and CD90 positive cells (undifferentiated spermatogonia) by fluorescence-activated cell sorting was performed. Our experiments revealed that Ap-2γ is detectable in testes of late fetal age and up to 60 days postnatally and is expressed in gonocytes and spermatogonia from late fetal age throughout all maturational stages. Restricted nuclear expression of Ap-2γ to undifferentiated male germ cells was verified by coexpression of Ap-2γ with promyelocytic leukemia zinc finger in sections of paraffin-embedded testes as well as in cells sorted positive for CD9 and CD90 expression. Our study demonstrated clearly that nuclear expression of Ap-2γ is a useful marker for identifying undifferentiated male germ cells, although its functional role is yet to be fully explored.

Spermatogonial stem cells, infertility and testicular cancer

The spermatogonial stem cells (SSCs) are responsible for the transmission of genetic information from an individual to the next generation. SSCs play critical roles in understanding the basic reproductive biology of gametes and treatments of human infertility. SSCs not only maintain normal spermatogenesis, but also sustain fertility by critically balancing both SSC self-renewal and differentiation. This self-renewal and differentiation in turn is tightly regulated by a combination of intrinsic gene expression within the SSC as well as the extrinsic gene signals from the niche. Increased SSCs self-renewal at the expense of differentiation result in germ cell tumours, on the other hand, higher differentiation at the expense of self-renewal can result in male sterility. Testicular germ cell cancers are the most frequent cancers among young men in industrialized countries. However, understanding the pathogenesis of testis cancer has been difficult because it is formed during foetal development. Recent studies suggest that SSCs can be reprogrammed to become embryonic stem (ES)-like cells to acquire pluripotency. In the present review, we summarize the recent developments in SSCs biology and role of SSC in testicular cancer. We believe that studying the biology of SSCs will not only provide better understanding of stem cell regulation in the testis, but eventually will also be a novel target for male infertility and testicular cancers.

In vivo and in vitro aging is detrimental to mouse spermatogonial stem cell function

The development of techniques to maintain the spermatogonial stem cell (SSC) in vivo and in vitro for extended periods essentially allows for the indefinite continuation of an individual germline. Recent evidence indicates that the aging of male reproductive function is due to failure of the SSC niche. SSCs are routinely cultured for 6 mo, and no apparent effect of culture over this period has been observed. To determine the effects of SSC aging, we utilized an in vitro culture system, followed by quantitative transplantation experiments. After culture for 6 mo, SSCs that had been aged in vivo for 1500 days had a slower proliferation rate than SSCs that were aged in vivo to 8 or 300 days. Examination of methylation patterns revealed no apparent difference in DNA methylation between SSCs that were aged 8, 300, or 1500 days before culture. Long-term culture periods resulted in a loss of stem cell potential without an obvious change in the visual appearance of the culture. DNA microarray analysis of in vivo- and in vitro-aged SSCs identified the differential expression of several genes important for SSC function, including B-cell CLL/lymphoma 6, member B (Bcl6b), Lim homeobox protein 1 (Lhx1), and thymus cell antigen 1, theta (Thy1). Collectively, these data indicate that, although both in vitro and in vivo aging are detrimental to SSC function, in vitro aging results in greater loss of function, potentially due to a decrease in core SSC self-renewal gene expression and an increase in germ cell differentiation gene expression.

Quantitative analysis of mRNA translation in mammalian spermatogenic cells with sucrose and Nycodenz gradients

BACKGROUND

Developmental and global regulation of mRNA translation plays a major role in regulating gene expression in mammalian spermatogenic cells. Sucrose gradients are widely used to analyze mRNA translation. Unfortunately, the information from sucrose gradient experiments is often compromised by the absence of quantification and absorbance tracings, and confusion about the basic properties of sucrose gradients.

METHODS

The Additional Materials contain detailed protocols for the preparation and analysis of sucrose and Nycodenz gradients, obtaining absorbance tracings of sucrose gradients, aligning tracings and fractions, and extraction of equal proportions of RNA from all fractions.

RESULTS

The techniques described here have produced consistent measurements despite changes in personnel and minor variations in RNA extraction, gradient analysis, and mRNA quantification, and describes for the first time potential problems in using gradients to analyze mRNA translation in purified spermatogenic cells.

CONCLUSIONS

Accurate quantification of the proportion of polysomal mRNA is useful in comparing translational activity at different developmental stages, different mRNAs, different techniques and different laboratories. The techniques described here are sufficiently accurate to elucidate the contributions of multiple regulatory elements of variable strength in regulating translation of the sperm mitochondria associated cysteine-rich protein (Smcp) mRNA in transgenic mice.

Function of Nanos2 in the male germ cell lineage in mice

Nanos is known as an evolutionarily conserved RNA-binding protein, the function of which is implicated in germ cell development. This includes the maintenance of both the primordial germ cells (PGCs) and germline stem cells. In mice, Nanos2 exhibits a unique feature in which its expression is induced only in the germ cells within the sexually determined male gonad. Nanos2 promotes male germ cell differentiation, while simultaneously suppressing a female program. In addition, Nanos2 is also expressed in the spermatogonial stem cells and functions as an intrinsic factor to maintain the stem cell population during spermatogenesis. Detailed cytological and biochemical analyses in embryonic male gonads in the mouse have revealed that Nanos2 localizes to the P-bodies, a center of RNA processing. It has also been shown that the Nanos2 interacts with protein components of the deadenylation complex involved in the initial step of the RNA degradation pathway.

Transforming growth factor beta1 induces osteogenic differentiation of murine bone marrow stromal cells

Bone marrow stromal cells (BMSCs) have been shown to contribute to regeneration of numerous mesodermal tissue types including adipose, bone, and cartilage. Recent studies have shown that BMSCs migrate into damaged bone and help facilitate effects such as fracture healing. Although bone morphogenic proteins have been shown to stimulate bone repair, their levels remain low postfracture. Peripheral blood levels of transforming growth factor beta1 (TGF-beta1), on the other hand, rise dramatically within 2 weeks postfracture. Therefore, we investigated the role of TGF-beta1 on BMSC osteogenic differentiation in vitro. Murine BMSCs were freshly isolated from femurs, fluorescence-activated cell sorted for Sca-1, cultured in Iscove's modified Dulbecco's medium, and exposed to TGF-beta1. After 14 days, real-time reverse transcriptase-polymerase chain reaction and immunohistochemical staining were performed to examine the expression of self-renewal and terminal differentiation markers. Results showed that the treatment with TGF-beta1 reduced mRNA levels of self-renewal markers (Oct4, Stella, Nanos3, and Abcg2) by twofold and increased osteoblast differentiation markers (Runx2, Opn, and Col1) up to sevenfold compared with controls. We also observed decreased mRNA levels of adipogenic markers (Pparg2 and Adn) and an increase in alkaline phosphatase activity. Transcriptional coactivator with PDZ-binding motif (TAZ) mRNA and protein levels were elevated up to threefold following TGF-beta1 stimulation. In conclusion, our findings revealed an unexpected osteogenic differentiation pathway in murine BMSCs under the control of TGF-beta that is mediated by TAZ, which is known to increase RUNX2-dependent gene transcription while repressing PPARgamma2-dependent transcription. This is the first report demonstrating the upregulation of TAZ activity in BMSCs by a physiological growth factor present during acute bone injury.

Spermatogonial stem cell regulation and spermatogenesis

This article will provide an updated review of spermatogonial stem cells and their role in maintaining the spermatogenic lineage. Experimental tools used to study spermatogonial stem cells (SSCs) will be described, along with research using these tools to enhance our understanding of stem cell biology and spermatogenesis. Increased knowledge about the biology of SSCs improves our capacity to manipulate these cells for practical application. The chapter concludes with a discussion of future directions for fundamental investigation and practical applications of SSCs.