TAF4b is required for mouse spermatogonial stem cell development

Tissue engineering studies in male infertility disorder

Infertility is an important issue among couples worldwide which is caused by a variety of complex diseases. Male infertility is a problem in 7% of all men. In vitro spermatogenesis (IVS) is the experimental approach that has been developed for mimicking seminiferous tubules-like functional structures in vitro. Currently, various researchers are interested in finding and developing a microenvironmental condition or a bioartificial testis applied for fertility restoration via gamete production in vitro. The tissue engineering (TE) has developed new approaches to treat male fertility preservation through development of functional male germ cells. This makes TE a possible future strategy for restoration of male fertility. Although 3D culture systems supply the perception of the effect of cellular interactions in the process of spermatogenesis, formation of a native gradient of autocrine/paracrine factors in 3D culture systems have not been considered. These results collectively suggest that maintaining the microenvironment of testicular cells even in the form of a 3D-culture system is crucial in achieving spermatogenesis ex vivo. It is also possible to engineer the testicular structures using biomaterials to provide a supporting scaffold for somatic and stem cells. The insemination of these cells with GFs is possible for temporally and spatially adjusted release to mimic the microenvironment of the in situ seminiferous epithelium. This review focuses on recent studies and advances in the application of TE strategies to cell-tissue culture on synthetic or natural scaffolds supplemented with growth factors.

Genome-Wide Association Studies and Runs of Homozygosity to Identify Reproduction-Related Genes in Yorkshire Pig Population

Reproductive traits hold considerable economic importance in pig breeding and production. However, candidate genes underpinning the reproductive traits are still poorly identified. In the present study, we executed a genome-wide association study (GWAS) and runs of homozygosity (ROH) analysis using the PorcineSNP50 BeadChip array for 585 Yorkshire pigs. Results from the GWAS identified two genome-wide significant and eighteen suggestive significant single nucleotide polymorphisms (SNPs) associated with seven reproductive traits. Furthermore, we identified candidate genes, including ELMO1, AOAH, INSIG2, NUP205, LYPLAL1, RPL34, LIPH, RNF7, GRK7, ETV5, FYN, and SLC30A5, which were chosen due to adjoining significant SNPs and their functions in immunity, fertilization, embryonic development, and sperm quality. Several genes were found in ROH islands associated with spermatozoa, development of the fetus, mature eggs, and litter size, including INSL6, TAF4B, E2F7, RTL1, CDKN1C, and GDF9. This study will provide insight into the genetic basis for pig reproductive traits, facilitating reproduction improvement using the marker-based selection methods.

Transcription and chromatin regulation by TAF4b during cellular quiescence of developing prospermatogonia

Prospermatogonia (ProSpg) link the embryonic development of male primordial germ cells to the healthy establishment of postnatal spermatogonia and spermatogonial stem cells. While these spermatogenic precursor cells undergo the characteristic transitions of cycling and quiescence, the transcriptional events underlying these developmental hallmarks remain unknown. Here, we investigated the expression and function of TBP-associated factor 4b (Taf4b) in the timely development of quiescent mouse ProSpg using an integration of gene expression profiling and chromatin mapping. We find that Taf4b mRNA expression is elevated during the transition of mitotic-to-quiescent ProSpg and Taf4b-deficient ProSpg are delayed in their entry into quiescence. Gene ontology, protein network analysis, and chromatin mapping demonstrate that TAF4b is a direct and indirect regulator of chromatin and cell cycle-related gene expression programs during ProSpg quiescence. Further validation of these cell cycle mRNA changes due to the loss of TAF4b was accomplished via immunostaining for proliferating cell nuclear antigen (PCNA). Together, these data indicate that TAF4b is a key transcriptional regulator of the chromatin and quiescent state of the developing mammalian spermatogenic precursor lineage.

Developmental regulators moonlighting as transposons defense factors

BACKGROUND

The germline perpetuates genetic information across generations. To maintain the integrity of the germline, transposable elements in the genome must be silenced, as these mobile elements would otherwise engender widespread mutations passed on to subsequent generations. There are several well-established mechanisms that are dedicated to providing defense against transposable elements, including DNA methylation, RNA interference, and the PIWI-interacting RNA pathway.

OBJECTIVES

Recently, several studies have provided evidence that transposon defense is not only provided by factors dedicated to this purpose but also factors with other roles, including in germline development. Many of these are transcription factors. Our objective is to summarize what is known about these "bi-functional" transcriptional regulators.

MATERIALS AND METHODS

Literature search.

RESULTS AND CONCLUSION

We summarize the evidence that six transcriptional regulators-GLIS3, MYBL1, RB1, RHOX10, SETDB1, and ZBTB16-are both developmental regulators and transposable element-defense factors. These factors act at different stages of germ cell development, including in pro-spermatogonia, spermatogonial stem cells, and spermatocytes. Collectively, the data suggest a model in which specific key transcriptional regulators have acquired multiple functions over evolutionary time to influence developmental decisions and safeguard transgenerational genetic information. It remains to be determined whether their developmental roles were primordial and their transposon defense roles were co-opted, or vice versa.

Cell type-specific role of CBX2 and its disordered region in spermatogenesis

Polycomb group (PcG) proteins maintain the repressed state of lineage-inappropriate genes and are therefore essential for embryonic development and adult tissue homeostasis. One critical function of PcG complexes is modulating chromatin structure. Canonical Polycomb repressive complex 1 (cPRC1), particularly its component CBX2, can compact chromatin and phase-separate in vitro. These activities are hypothesized to be critical for forming a repressed physical environment in cells. While much has been learned by studying these PcG activities in cell culture models, it is largely unexplored how cPRC1 regulates adult stem cells and their subsequent differentiation in living animals. Here, we show in vivo evidence of a critical nonenzymatic repressive function of cPRC1 component CBX2 in the male germline. CBX2 is up-regulated as spermatogonial stem cells differentiate and is required to repress genes that were active in stem cells. CBX2 forms condensates (similar to previously described Polycomb bodies) that colocalize with target genes bound by CBX2 in differentiating spermatogonia. Single-cell analyses of mosaic Cbx2 mutant testes show that CBX2 is specifically required to produce differentiating A1 spermatogonia. Furthermore, the region of CBX2 responsible for compaction and phase separation is needed for the long-term maintenance of male germ cells in the animal. These results emphasize that the regulation of chromatin structure by CBX2 at a specific stage of spermatogenesis is critical, which distinguishes this from a mechanism that is reliant on histone modification.

Single-cell transcriptome analysis and in vitro differentiation of testicular cells reveal novel insights into male sterility of the interspecific hybrid cattle-yak

BACKGROUND

Interspecific hybridization plays vital roles in enriching animal diversity, while male hybrid sterility (MHS) of the offspring commonly suffered from spermatogenic arrest constitutes the postzygotic reproductive isolation. Cattle-yak, the hybrid offspring of cattle (Bos taurus) and yak (Bos grunniens) can serve as an ideal MHS animal model. Although meiotic arrest was found to contribute to MHS of cattle-yak, yet the cellular characteristics and developmental potentials of male germline cell in pubertal cattle-yak remain to be systematically investigated.

RESULTS

Single-cell RNA-seq analysis of germline and niche cell types in pubertal testis of cattle-yak and yak indicated that dynamic gene expression of developmental germ cells was terminated at late primary spermatocyte (meiotic arrest) and abnormal components of niche cell in pubertal cattle-yak. Further in vitro proliferation and differentially expressed gene (DEG) analysis of specific type of cells revealed that undifferentiated spermatogonia of cattle-yak exhibited defects in viability and proliferation/differentiation potentials.

CONCLUSION

Comparative scRNA-seq and in vitro proliferation analysis of testicular cells indicated that not only meiotic arrest contributed to MHS of cattle-yak. Spermatogenic arrest of cattle-yak may originate from the differentiation stage of undifferentiated spermatogonia and niche cells of cattle-yak may provide an adverse microenvironment for spermatogenesis.

Sertoli cell-only syndrome: advances, challenges, and perspectives in genetics and mechanisms

Male infertility can be caused by quantitative and/or qualitative abnormalities in spermatogenesis, which affects men's physical and mental health. Sertoli cell-only syndrome (SCOS) is the most severe histological phenotype of male infertility characterized by the depletion of germ cells with only Sertoli cells remaining in the seminiferous tubules. Most SCOS cases cannot be explained by the already known genetic causes including karyotype abnormalities and microdeletions of the Y chromosome. With the development of sequencing technology, studies on screening new genetic causes for SCOS are growing in recent years. Directly sequencing of target genes in sporadic cases and whole-exome sequencing applied in familial cases have identified several genes associated with SCOS. Analyses of the testicular transcriptome, proteome, and epigenetics in SCOS patients provide explanations regarding the molecular mechanisms of SCOS. In this review, we discuss the possible relationship between defective germline development and SCOS based on mouse models with SCO phenotype. We also summarize the advances and challenges in the exploration of genetic causes and mechanisms of SCOS. Knowing the genetic factors of SCOS offers a better understanding of SCO and human spermatogenesis, and it also has practical significance for improving diagnosis, making appropriate medical decisions, and genetic counseling. For therapeutic implications, SCOS research, along with the achievements in stem cell technologies and gene therapy, build the foundation to develop novel therapies for SCOS patients to produce functional spermatozoa, giving them hope to father children.

TAF4b transcription networks regulating early oocyte differentiation

Establishment of a healthy ovarian reserve is contingent upon numerous regulatory pathways during embryogenesis. Previously, mice lacking TBP-associated factor 4b (Taf4b) were shown to exhibit a diminished ovarian reserve. However, potential oocyte-intrinsic functions of TAF4b have not been examined. Here, we use a combination of gene expression profiling and chromatin mapping to characterize TAF4b-dependent gene regulatory networks in mouse oocytes. We find that Taf4b-deficient oocytes display inappropriate expression of meiotic, chromatin modification/organization, and X-linked genes. Furthermore, dysregulated genes in Taf4b-deficient oocytes exhibit an unexpected amount of overlap with dysregulated genes in oocytes from XO female mice, a mouse model of Turner Syndrome. Using Cleavage Under Targets and Release Using Nuclease (CUT&RUN), we observed TAF4b enrichment at genes involved in chromatin remodeling and DNA repair, some of which are differentially expressed in Taf4b-deficient oocytes. Interestingly, TAF4b target genes were enriched for Sp/Klf family and NFY target motifs rather than TATA-box motifs, suggesting an alternative mode of promoter interaction. Together, our data connect several gene regulatory nodes that contribute to the precise development of the mammalian ovarian reserve.

A pathogenic DMC1 frameshift mutation causes nonobstructive azoospermia but not primary ovarian insufficiency in humans

Nonobstructive azoospermia (NOA) and diminished ovarian reserve (DOR) are two disorders that can lead to infertility in males and females. Genetic factors have been identified to contribute to NOA and DOR. However, the same genetic factor that can cause both NOA and DOR remains largely unknown. To explore the candidate pathogenic gene that causes both NOA and DOR, we conducted whole-exome sequencing (WES) in a non-consanguineous family with two daughters with DOR and a son with NOA. We detected one pathogenic frameshift variant (NM_007068:c.28delG, p. Glu10Asnfs*31) following a recessive inheritance mode in a meiosis gene DMC1 (DNA meiotic recombinase 1). Clinical analysis showed reduced antral follicle number in both daughters with DOR, but metaphase II oocytes could be retrieved from one of them. For the son with NOA, no spermatozoa were found after microsurgical testicular sperm extraction. A further homozygous Dmc1 knockout mice study demonstrated total failure of follicle development and spermatogenesis. These results revealed a discrepancy of DMC1 action between mice and humans. In humans, DMC1 is required for spermatogenesis but is dispensable for oogenesis, although the loss of function of this gene may lead to DOR. To our knowledge, this is the first report on the homozygous frameshift mutation as causative for both NOA and DOR and demonstrating that DMC1 is dispensable in human oogenesis.

RNA-binding protein ELAVL2 plays post-transcriptional roles in the regulation of spermatogonia proliferation and apoptosis

Objectives

RNA‐binding proteins (RBPs) play essential post‐transcriptional roles in regulating spermatogonial stem cells (SSCs) maintenance and differentiation. We identified a conserved and SSCs‐enriched RBP ELAVL2 from our single‐cell sequencing data, but its function and mechanism in SSCs were unclear.

Materials and methods

Expressions of ELAVL2 during human and mouse testis development were validated. Stable C18‐4 and TCam‐2 cell lines with overexpression and knockdown of ELAVL2 were established, which were applied to proliferation and apoptosis analysis. RNA immunoprecipitation and sequencing were used to identify ELAVL2 targets, and regulatory functions of ELAVL2 on target mRNAs were studied. Proteins interacting with ELAVL2 in human and mouse testes were identified using immunoprecipitation and mass spectrometric, which were validated by in vivo and in vitro experiments.

Results

ELAVL2 was testis‐enriched and preferentially expressed in human and mouse SSCs. ELAVL2 was down‐regulated in NOA patients. ELAVL2 promoted proliferation and inhibited apoptosis of C18‐4 and TCam‐2 cell lines via activating ERK and AKT pathways. ELAVL2 associated with mRNAs encoding essential regulators of SSCs proliferation and survival, and promoted their protein expression at post‐transcriptional level. ELAVL2 interacted with DAZL in vivo and in vitro in both human and mouse testes.

Conclusions

Taken together, these results indicate that ELAVL2 is a conserved SSCs‐enriched RBP that down‐regulated in NOA, which regulates spermatogonia proliferation and apoptosis by promoting protein expression of targets.

Targeted disruption of galectin 3 in mice delays the first wave of spermatogenesis and increases germ cell apoptosis

Galectin 3 is a multifunctional lectin implicated in cellular proliferation, differentiation, adhesion, and apoptosis. This lectin is broadly expressed in testicular somatic cells and germ cells, and is upregulated during testicular development. Since the role of galectin 3 in testicular function remains elusive, we aimed to characterize the role of galectin 3 in testicular physiology. We found that galectin 3 transgenic mice (Lgals3-/-) exhibited significantly decreased testicular weight in adulthood compared to controls. The transgenic mice also exhibited a delay to the first wave of spermatogenesis, a decrease in the number of germ cells at postnatal day 5 (P5) and P15, and defective Sertoli cell maturation. Mechanistically, we found that Insulin-like-3 (a Leydig cell marker) and enzymes involved in steroid biosynthesis were significantly upregulated in adult Lgals3-/- testes. These observations were accompanied by increased serum testosterone levels. To determine the underlying causes of the testicular atrophy, we monitored cellular apoptosis. Indeed, adult Lgals3-/- testicular cells exhibited an elevated apoptosis rate that is likely driven by downregulated Bcl-2 and upregulated Bax and Bak expression, molecules responsible for live/death cell balance. Moreover, the percentage of testicular macrophages within CD45+ cells was decreased in Lgals3-/- mice. These data suggest that galectin 3 regulates spermatogenesis initiation and Sertoli cell maturation in part, by preventing germ cells from undergoing apoptosis and regulating testosterone biosynthesis. Going forward, understanding the role of galectin 3 in testicular physiology will add important insights into the factors governing the development of germ cells and steroidogenesis and delineate novel biomarkers of testicular function.

Screening of Integrin Heterodimers Expressed Functionally on the Undifferentiated Spermatogonial Stem Cells in the Outbred ICR Mice

Background and Objectives

Outbred mice are widely used in toxicology, pharmacology, and fundamental biomedical research. However, there have been no reports of in vitro culture systems for spermatogonial stem cells (SSCs) derived from these mice.

Methods

As a step towards constructing a non-cellular niche supporting the in vitro maintenance of outbred mouse SSC self-renewal, we systematically investigated the types of integrin heterodimers that are expressed transcriptionally, translationally, and functionally in SSCs derived from Imprinting Control Region (ICR) mice.

Results

Among the genes encoding 25 integrin subunits, integrin α₁, α₅, α₆, α₉, α_V, and α_E, and integrin β₁ and β₅ had significantly higher transcriptional levels than the other subunits. Furthermore, at the translational level, integrin α₅, α₆, α₉, α_V, α_E, and β₁ were localized on the surface of SSCs, but integrin α₁ and β₅ not. Moreover, significantly stronger translational expression than integrin α₉ and α_E was observed in integrin α₅, α₆, α_V, and β₁. SSCs showed significantly increased adhesion to fibronectin, laminin, tenascin C and vitronectin, and functional blocking of integrin α₅β₁, α₆β₁, α₉β₁ or α_Vβ₁ significantly inhibited adhesion to these molecules.

Conclusions

We confirmed that integrin α₅β₁, α₆β₁, α₉β₁ and α_Vβ₁ actively function on the surface of undifferentiated SSCs derived from outbred ICR mice.

Intratesticular Peptidyl Prolyl Isomerase 1 Protein Delivery Using Cationic Lipid-Coated Fibroin Nanoparticle Complexes Rescues Male Infertility in Mice

Male infertility is a multifactorial condition. Unexplained male infertility is often caused by spermatogenesis dysfunction. Knockout of Pin1, an important regulator of cell proliferation and differentiation, produces male infertility phenotypes such as testicular immaturity and azoospermia with spermatogonia depletion and blood-testis barrier (BTB) dysfunction. Gene therapy has been clinically considered for the treatment of male infertility, but it is not preferred because of the risks of adverse effects in germ cells. Direct intracellular protein delivery using nanoparticles is considered an effective alternative to gene therapy; however, in vivo testicular protein delivery remains a pressing challenge. Here, we investigated the direct intracellular protein delivery strategy using a fibroin nanoparticle-encapsulated cationic lipid complex (Fibroplex) to restore intratesticular PIN1. Local intratesticular delivery of PIN1 via Fibroplex in Pin1 knockout testes produced fertile mice, achieving recovery from the infertile phenotypes. Mechanistically, PIN1-loaded Fibroplex was successfully delivered into testicular cells, including spermatogonial cells and Sertoli cells, and the sustained release of PIN1 restored the gene expression required for the proliferation of spermatogonial cells and BTB integrity in Pin1 knockout testes. Collectively, testicular PIN1 protein delivery using Fibroplex might be an effective strategy for treating male infertility.

Conversion from spermatogonia to spermatocytes: Extracellular cues and downstream transcription network

Spermatocyte (spc) formation from spermatogonia (spg) differentiation is the first step of spermatogenesis which produces prodigious spermatozoa for a lifetime. After decades of studies, several factors involved in the functioning of a mouse were discovered both inside and outside spg. Considering the peculiar expression and working pattern of each factor, this review divides the whole conversion of spg to spc into four consecutive development processes with a focus on extracellular cues and downstream transcription network in each one. Potential coordination among Dmrt1, Sohlh1/2 and BMP families mediates Ngn3 upregulation, which marks progenitor spg, with other changes. After that, retinoic acid (RA), as a master regulator, promotes A1 spg formation with its helpers and Sall4. A1-to-B spg transition is under the control of Kitl and impulsive RA signaling together with early and late transcription factors Stra8 and Dmrt6. Finally, RA and its responsive effectors conduct the entry into meiosis. The systematic transcription network from outside to inside still needs research to supplement or settle the controversials in each process. As a step further ahead, this review provides possible drug targets for infertility therapy by cross-linking humans and mouse model.

FIGLA, LHX8 and SOHLH1 transcription factor networks regulate mouse oocyte growth and differentiation

Germ-cell transcription factors control gene networks that regulate oocyte differentiation and primordial follicle formation during early, postnatal mouse oogenesis. Taking advantage of gene-edited mice lacking transcription factors expressed in female germ cells, we analyzed global gene expression profiles in perinatal ovaries from wildtype, FiglaNull, Lhx8Null and Sohlh1Null mice. Figla deficiency dysregulates expression of meiosis-related genes (e.g. Sycp3, Rad51, Ybx2) and a variety of genes (e.g. Nobox, Lhx8, Taf4b, Sohlh1, Sohlh2, Gdf9) associated with oocyte growth and differentiation. The absence of FIGLA significantly impedes meiotic progression, causes DNA damage and results in oocyte apoptosis. Moreover, we find that FIGLA and other transcriptional regulator proteins (e.g. NOBOX, LHX8, SOHLH1, SOHLH2) are co-expressed in the same subset of germ cells in perinatal ovaries and Figla ablation dramatically disrupts KIT, NOBOX, LHX8, SOHLH1 and SOHLH2 abundance. In addition, not only do FIGLA, LHX8 and SOHLH1 cross-regulate each other, they also cooperate by direct interaction with each during early oocyte development and share downstream gene targets. Thus, our findings substantiate a major role for FIGLA, LHX8 and SOHLH1 as multifunctional regulators of networks necessary for oocyte maintenance and differentiation during early folliculogenesis.

Analysis of TATA-box binding protein associated factor 4b gene mutations in a Chinese population with nonobstructive azoospermia

Nonobstructive azoospermia (NOA) is a severe form of male infertility. The molecular basis of NOA is still poorly understood. The aim of this study was to explore the associations between single nucleotide polymorphisms (SNPs) of the TATA-box binding protein associated factor 4b (TAF4B) gene and NOA. A total of 100 Han Chinese patients with NOA and 100 healthy men as controls were recruited. Targeted gene capture sequencing was performed. A total of 11 TAF4B SNPs were screened in the NOA and control subjects. Six synonymous and 4 nonsynonymous variants were detected. The c.11G>T (p.G4V) mutation was detected only in NOA patients. Polymorphism Phenotyping v2 and Sorting Intolerant From Tolerant analysis indicated that the p.G4V mutation influenced the protein structure of TAF4B. Haplotype analysis showed that the candidate SNPs did not independently associate with NOA and were found at extremely low frequencies in the subject population. Mutation Taster analysis indicated that the c.11G>T/p.G4V mutation was damaging. WebLogo analysis showed that the residue at amino acid 4 was relatively conserved. The p.Gly4Val substitution may affect the structure of the TAF4B protein. The c.11G>T mutation of the TAF4B gene may be associated with NOA in a Chinese population. Bioinformatics analysis indicated this variation may play an important role in the process of spermatogenesis.

ZFP628 Is a TAF4b-Interacting Transcription Factor Required for Mouse Spermiogenesis

TAF4b is a subunit of the TFIID complex that is highly expressed in the ovary and testis and required for mouse fertility. TAF4b-deficient male mice undergo a complex series of developmental defects that result in the inability to maintain long-term spermatogenesis. To decipher the transcriptional mechanisms upon which TAF4b functions in spermatogenesis, we used two-hybrid screening to identify a novel TAF4b-interacting transcriptional cofactor, ZFP628. Deletion analysis of both proteins reveals discrete and novel domains of ZFP628 and TAF4b protein that function to bridge their direct interaction in vitro Moreover, coimmunoprecipitation of ZFP628 and TAF4b proteins in testis-derived protein extracts supports their endogenous association. Using CRISPR-Cas9, we disrupted the expression of ZFP628 in the mouse and uncovered a postmeiotic germ cell arrest at the round spermatid stage in the seminiferous tubules of the testis in ZFP628-deficient mice that results in male infertility. Coincident with round spermatid arrest, we find reduced mRNA expression of transition protein (Tnp1 and Tnp2) and protamine (Prm1 and Prm2) genes, which are critical for the specialized maturation of haploid male germ cells called spermiogenesis. These data delineate a novel association of two transcription factors, TAF4b and ZFP628, and identify ZFP628 as a novel transcriptional regulator of stage-specific spermiogenesis.

Dynamic and regulated TAF gene expression during mouse embryonic germ cell development

Germ cells undergo many developmental transitions before ultimately becoming either eggs or sperm, and during embryonic development these transitions include epigenetic reprogramming, quiescence, and meiosis. To begin understanding the transcriptional regulation underlying these complex processes, we examined the spatial and temporal expression of TAF4b, a variant TFIID subunit required for fertility, during embryonic germ cell development. By analyzing published datasets and using our own experimental system to validate these expression studies, we determined that both Taf4b mRNA and protein are highly germ cell-enriched and that Taf4b mRNA levels dramatically increase from embryonic day 12.5–18.5. Surprisingly, additional mRNAs encoding other TFIID subunits are coordinately upregulated through this time course, including Taf7l and Taf9b. The expression of several of these germ cell-enriched TFIID genes is dependent upon Dazl and/or Stra8, known regulators of germ cell development and meiosis. Together, these data suggest that germ cells employ a highly specialized and dynamic form of TFIID to drive the transcriptional programs that underlie mammalian germ cell development.

Assisted reproductive therapy and fertility preservation are increasingly used to improve human reproduction across the world, yet there are still many unanswered questions regarding what factors govern the development of eggs and sperm and how these factors work together. We previously identified a subunit of the general transcription factor TFIID, TAF4b, that is essential for fertility. However, many basic characteristics of how Taf4b and its associated TFIID family members contribute to the formation of healthy sperm and eggs in mice and humans remain unknown. In this study, we find that mouse Taf4b and several closely related TFIID subunits become highly abundant during mouse embryonic gonad development, specifically in the cells that ultimately become eggs and sperm. Here, we analyzed data from public repositories and isolated these developing cells to examine their gene expression patterns throughout embryonic development. Together these data suggest that the dynamic expression of Taf4b and other TFIID family members are dependent on the well-established reproductive cell regulators Dazl and Stra8. This understanding of Taf4b gene expression and regulation in mouse reproductive cell development is likely conserved during development of human cells and offers novel insights into the interconnectedness of the factors that govern the formation of healthy eggs and sperm.

DAZL Regulates Germ Cell Survival through a Network of PolyA-Proximal mRNA Interactions

The RNA binding protein DAZL is essential for gametogenesis, but its direct in vivo functions, RNA targets, and the molecular basis for germ cell loss in Dazl-null mice are unknown. Here, we mapped transcriptome-wide DAZL-RNA interactions in vivo, revealing DAZL binding to thousands of mRNAs via polyA-proximal 3′ UTR interactions. In parallel, fluorescence-activated cell sorting and RNA-seq identified mRNAs sensitive to DAZL deletion in male germ cells. Despite binding a broad set of mRNAs, integrative analyses indicate that DAZL post-transcriptionally controls only a subset of its mRNA targets, namely those corresponding to a network of genes that are critical for germ cell proliferation and survival. In addition, we provide evidence that polyA sequences have key roles in specifying DAZL-RNA interactions across the transcriptome. Our results reveal a mechanism for DAZL-RNA binding and illustrate that DAZL functions as a master regulator of a post-transcriptional mRNA program essential for germ cell survival.

Combining transgenic mice, FACS, and multiple RNA-profiling methods, Zagore et al. show that DAZL binds thousands of mRNAs via GUU sites upstream of polyA tails. Loss of DAZL results in decreased mRNA levels for a network of genes that are essential for germ cell proliferation and differentiation.

The REGγ-Proteasome Regulates Spermatogenesis Partially by P53-PLZF Signaling

Development of spermatogonia and spermatocytes are the critical steps of spermatogenesis, impacting on male fertility. Investigation of the related regulators benefits the understanding of male reproduction. The proteasome system has been reported to regulate spermatogenesis, but the mechanisms and key contributing factors in vivo are poorly explored. Here we found that ablation of REGγ, a proteasome activator, resulted in male subfertility. Analysis of the mouse testes after birth showed there was a decreased number of PLZF⁺ spermatogonia and spermatocytes. Molecular analysis found that REGγ loss significantly increased the abundance of p53 protein in the testis, and directly repressed PLZF transcription in cell lines. Of note, allelic p53 haplodeficiency partially rescued the defects in spermatogenesis observed in REGγ-deficient mice. In summary, our results identify REGγ-p53-PLZF to be a critical pathway that regulates spermatogenesis and establishes a new molecular link between the proteasome system and male reproduction.

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REGγ loss results in male subfertility

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REGγ loss results in a decrease of spermatocytes and PLZF⁺ spermatogonial cells

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p53 protein, increased in REGγ^−/− mouse testes, represses PLZF expression

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Allelic p53 haplodeficiency partially rescues defects in REGγ^−/− mouse spermatogenesis

Cell-autonomous requirement for mammalian target of rapamycin (Mtor) in spermatogonial proliferation and differentiation in the mouse†

Spermatogonial stem cells must balance self-renewal with production of transit-amplifying progenitors that differentiate in response to retinoic acid (RA) before entering meiosis. This self-renewal vs. differentiation fate decision is critical for maintaining tissue homeostasis, as imbalances cause defects that can lead to human testicular cancer or infertility. Little is currently known about the program of differentiation initiated by RA, and the pathways and proteins involved are poorly defined. We recently found that RA stimulation of the Phosphatidylinositol 3-kinase (PI3K)/AKT/Mammalian target of rapamycin (mTOR) kinase signaling pathway is required for differentiation, and that short-term inhibition of mTOR complex 1 (mTORC1) by rapamycin blocked spermatogonial differentiation in vivo and prevented RA-induced translational activation. Since this phenotype resulted from global inhibition of mTORC1, we created conditional germ cell knockout mice to investigate the germ cell-autonomous role of MTOR in spermatogonial differentiation. MTOR germ cell KO mice were viable and healthy, but testes from neonatal (postnatal day (P)8), juvenile (P18), and adult (P > 60) KO mice were smaller than littermate controls, and no sperm were produced in adult testes. Histological and immunostaining analyses revealed that spermatogonial differentiation was blocked, and no spermatocytes were formed at any of the ages examined. Although spermatogonial proliferation was reduced in the neonatal testis, it was blocked altogether in the juvenile and adult testis. Importantly, a small population of self-renewing undifferentiated spermatogonia remained in adult testes. Taken together, these results reveal that MTOR is dispensable for the maintenance of undifferentiated spermatogonia, but is cell autonomously required for their proliferation and differentiation.

Spontaneous testicular atrophy occurs despite normal spermatogonial proliferation in a Tp53 knockout rat

The tumor suppressor protein p53 (TP53) has many functions in cell cycle regulation, apoptosis, and DNA damage repair and is also involved in spermatogenesis in the mouse. To evaluate the role of p53 in spermatogenesis in the rat, we characterized testis biology in adult males of a novel p53 knockout rat (SD-Tp53^tm1sage ). p53 knockout rats exhibited variable levels of testicular atrophy, including significantly decreased testis weights, atrophic seminiferous tubules, decreased seminiferous tubule diameter, and elevated spermatocyte TUNEL labeling rates, indicating a dysfunction in spermatogenesis. Phosphorylated histone H2AX protein levels and distribution were similar in the non-atrophic seminiferous tubules of both genotypes, showing evidence of pre-synaptic DNA double-strand breaks in leptotene and zygotene spermatocytes, preceding cell death in p53 knockout rat testes. Quantification of the spermatogonial stem cell (SSC) proliferation rate with bromodeoxyuridine (BrdU) labeling, in addition to staining with the undifferentiated type A spermatogonial marker GDNF family receptor alpha-1 (GFRA1), indicated that the undifferentiated spermatogonial population was normal in p53 knockout rats. Following exposure to 0.5 or 5 Gy X-ray, p53 knockout rats exhibited no germ cell apoptotic response beyond their unirradiated phenotype, while germ cell death in wild-type rat testes was elevated to a level similar to the unexposed p53 knockout rats. This study indicates that seminiferous tubule atrophy occurs following spontaneous, elevated levels of spermatocyte death in the p53 knockout rat. This phenomenon is variable across individual rats. These results indicate a critical role for p53 in rat germ cell survival and spermatogenesis.

The regulatory repertoire of PLZF and SALL4 in undifferentiated spermatogonia

Spermatogonial stem cells (SSCs) maintain spermatogenesis throughout adulthood through balanced self-renewal and differentiation, yet the regulatory logic of these fate decisions is poorly understood. The transcription factors Sal-like 4 (SALL4) and promyelocytic leukemia zinc finger (PLZF; also known as ZBTB16) are known to be required for normal SSC function, but their targets are largely unknown. ChIP-seq in mouse THY1(+) spermatogonia identified 4176 PLZF-bound and 2696 SALL4-bound genes, including 1149 and 515 that were unique to each factor, respectively, and 1295 that were bound by both factors. PLZF and SALL4 preferentially bound gene promoters and introns, respectively. Motif analyses identified putative PLZF and SALL4 binding sequences, but rarely both at shared sites, indicating significant non-autonomous binding in any given cell. Indeed, the majority of PLZF/SALL4 shared sites contained only PLZF motifs. SALL4 also bound gene introns at sites containing motifs for the differentiation factor DMRT1. Moreover, mRNA levels for both unique and shared target genes involved in both SSC self-renewal and differentiation were suppressed following SALL4 or PLZF knockdown. Together, these data reveal the full profile of PLZF and SALL4 regulatory targets in undifferentiated spermatogonia, including SSCs, which will help elucidate mechanisms controlling the earliest cell fate decisions in spermatogenesis.

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.