Expression profiles of Sox transcription factors within the postnatal rodent testes

Regulatory mechanisms of SoxD transcription factors and their influences on male fertility

Members of the SRY-related box (SOX) subfamily D (SoxD) of transcription factors are well conserved among vertebrate species and play important roles in different stages of male reproductive development. In mammals, the SoxD subfamily contains three members: SOX5, SOX6 and SOX13. Here, we describe their implications in testicular development and spermatogenesis, contributing to fertility. We also cover the mechanisms of action of SoxD transcription factors in gene regulation throughout male development. The specificity of activation of target genes by SoxD members depends, in part, on their post-translational modifications and interactions with other partners. Sperm production in adult males requires the coordination in the regulation of gene expression by different members of the SoxD subfamily of transcription factors in the testis. Specifically, the regulation of genes promoting adequate spermatogenesis by SoxD members is discussed in comparison between species.

Classical cadherins in the testis: how are they regulated?

Cadherins (CDH) are crucial intercellular adhesion molecules, contributing to morphogenesis and creating tissue barriers by regulating cells' movement, clustering and differentiation. In the testis, classical cadherins such as CDH1, CDH2 and CDH3 are critical to gonadogenesis by promoting the migration and the subsequent clustering of primordial germ cells with somatic cells. While CDH2 is present in both Sertoli and germ cells in rodents, CDH1 is primarily detected in undifferentiated spermatogonia. As for CDH3, its expression is mainly found in germ and pre-Sertoli cells in developing gonads until the establishment of the blood-testis barrier (BTB). This barrier is made of Sertoli cells forming intercellular junctional complexes. The restructuring of the BTB allows the movement of early spermatocytes toward the apical compartment as they differentiate during a process called spermatogenesis. CDH2 is among many junctional proteins participating in this process and is regulated by several pathways. While cytokines promote the disassembly of the BTB by enhancing junctional protein endocytosis for degradation, testosterone facilitates the assembly of the BTB by increasing the recycling of endocytosed junctional proteins. Mitogen-activated protein kinases (MAPKs) are also mediators of the BTB kinetics in many chemically induced damages in the testis. In addition to regulating Sertoli cell functions, follicle stimulating hormone can also regulate the expression of CDH2. In this review, we discuss the current knowledge on regulatory mechanisms of cadherin localisation and expression in the testis.

Single-cell transcriptomics reveals male germ cells and Sertoli cells developmental patterns in dairy goats

Spermatogenesis holds considerable promise for human-assisted reproduction and livestock breeding based on stem cells. It occurs in seminiferous tubules within the testis, which mainly comprise male germ cells and Sertoli cells. While the developmental progression of male germ cells and Sertoli cells has been widely reported in mice, much less is known in other large animal species, including dairy goats. In this study, we present the data of single cell RNA sequencing (scRNA-seq) for 25,373 cells from 45 (pre-puberty), 90 (puberty), and 180-day-old (post-puberty) dairy goat testes. We aimed to identify genes that are associated with key developmental events in male germ cells and Sertoli cells. We examined the development of spermatogenic cells and seminiferous tubules from 15, 30, 45, 60, 75, 90, 180, and 240-day-old buck goat testes. scRNA-seq clustering analysis of testicular cells from pre-puberty, puberty, and post-puberty goat testes revealed several cell types, including cell populations with characteristics of spermatogonia, early spermatocytes, spermatocytes, spermatids, Sertoli cells, Leydig cells, macrophages, and endothelial cells. We mapped the timeline for male germ cells development from spermatogonia to spermatids and identified gene signatures that define spermatogenic cell populations, such as AMH, SOHLH1, INHA, and ACTA2. Importantly, using immunofluorescence staining for different marker proteins (UCHL1, C-KIT, VASA, SOX9, AMH, and PCNA), we explored the proliferative activity and development of male germ cells and Sertoli cells. Moreover, we identified the expression patterns of potential key genes associated with the niche-related key pathways in male germ cells of dairy goats, including testosterone, retinoic acid, PDGF, FGF, and WNT pathways. In summary, our study systematically investigated the elaborate male germ cells and Sertoli cells developmental patterns in dairy goats that have so far remained largely unknown. This information represents a valuable resource for the establishment of goat male reproductive stem cells lines, induction of germ cell differentiation in vitro, and the exploration of sequential cell fate transition for spermatogenesis and testicular development at single-cell resolution.

Down Regulation of Catsper1 Expression by Calmodulin Inhibitor (Calmidazolium): Possible Implications for Fertility

The CatSper channel localizes exclusively in the flagella of sperm cells. The Catsper1 protein, together with three pore units, is essential for the CatSper Channel formation, which produces flagellum hyperactivation and confers sperm fertility. Catsper1 expression is dependent on Sox transcription factors, which can recognize in vitro at least three Sox binding sites on the promoter. Sox transcription factors have calmodulin-binding domains for nuclear importation. Calmodulin (CaM) is affected by the specific inhibitor calmidazolium (CMZ), which prevents the nuclear transport of Sox factors. In this work, we assess the regulation of the Catsper1 promoter in vivo by Sox factors in the murine testis and evaluate the effects of the inhibitor calmidazolium on the expression of the Casper genes, and the motility and fertility of the sperm. Catsper1 promoter has significant transcriptional activity in vivo; on the contrary, three Sox site mutants in the Catsper1 promoter reduced transcriptional activity in the testis. CaM inhibition affects Sox factor nuclear transport and has notable implications in the expression and production of Catsper1, as well as in the motility and fertility capability of sperm. The molecular mechanism described here might conform to the basis of a male contraceptive strategy acting at the transcriptional level by affecting the production of the CatSper channel, a fundamental piece of male fertility.

Identification of a novel Sox5 transcript in mouse testis

The transcription factor SOX5 is present in two distinct isoforms in both human and mouse, L-SOX5 and S-SOX5 (long and short isoforms of SOX5). Here, we identified and characterized a novel transcript of Sox5 (S-Sox5 variant) in mouse testis. eCLIP-based amplification of cDNA ends were performed to identify the potential Sox5 mRNA variant. This novel transcript shares a high similarity with the previously reported S-Sox5 in nucleotide sequence, but with a unique stretch of 5'UTR and an additional exon 9. Semi-quantitative PCR analysis revealed both S-Sox5 variant and S-Sox5 express specifically in mouse testis. Both transcripts increase significantly in mouse testis at postnatal day 21, when round spermatids appear. We further made a series of truncated Sox5 constructs and tagged them with eGFP in HeLa cells. In vitro transfection assay identified the N-terminus and the DNA-binding HMG domain are required for the nuclear localization of SOX5. Our results provides a basis for the future study to investigate the biological function of SOX5 in spermatogenesis.

Identification of SRY-box 30 as an age-related essential gatekeeper for male germ-cell meiosis and differentiation

Although important factors governing the meiosis have been reported in the embryonic ovary, meiosis in postnatal testis remains poorly understood. Herein, we first report that SRY‐box 30 (Sox30) is an age‐related and essential regulator of meiosis in the postnatal testis. Sox30‐null mice exhibited uniquely impaired testis, presenting the abnormal arrest of germ‐cell differentiation and irregular Leydig cell proliferation. In aged Sox30‐null mice, the observed testicular impairments were more severe. Furthermore, the germ‐cell arrest occurred at the stage of meiotic zygotene spermatocytes, which is strongly associated with critical regulators of meiosis (such as Cyp26b1, Stra8 and Rec8) and sex differentiation (such as Rspo1, Foxl2, Sox9, Wnt4 and Ctnnb1). Mechanistically, Sox30 can activate Stra8 and Rec8, and inhibit Cyp26b1 and Ctnnb1 by direct binding to their promoters. A different Sox30 domain required for regulating the activity of these gene promoters, providing a “fail‐safe” mechanism for Sox30 to facilitate germ‐cell differentiation. Indeed, retinoic acid levels were reduced owing to increased degradation following the elevation of Cyp26b1 in Sox30‐null testes. Re‐expression of Sox30 in Sox30‐null mice successfully restored germ‐cell meiosis, differentiation and Leydig cell proliferation. Moreover, the restoration of actual fertility appeared to improve over time. Consistently, Rec8 and Stra8 were reactivated, and Cyp26b1 and Ctnnb1 were reinhibited in the restored testes. In summary, Sox30 is necessary, sufficient and age‐associated for germ‐cell meiosis and differentiation in testes by direct regulating critical regulators. This study advances our understanding of the regulation of germ‐cell meiosis and differentiation in the postnatal testis.

SOX13 gene downregulation in peripheral blood mononuclear cells of patients with Klinefelter syndrome

Klinefelter syndrome (KS) is the most common sex chromosome disorder in men. It is characterized by germ cell loss and other variable clinical features, including autoimmunity. The sex-determining region of Y (SRY)-box 13 (Sox13) gene is expressed in mouse spermatogonia. In addition, it has been identified as islet cell autoantigen 12 (ICA12), which is involved in the pathogenesis of autoimmune diseases, including type 1 diabetes mellitus (DM) and primary biliary cirrhosis. Sox13 expression has never been investigated in patients with KS. In this age-matched, case-control study performed on ten patients with KS and ten controls, we found that SOX13 is significantly downregulated in peripheral blood mononuclear cells of patients with KS compared to controls. This finding might be consistent with the germ cell loss typical of patients with KS. However, the role of Sox13 in the pathogenesis of germ cell loss and humoral autoimmunity in patients with KS deserves to be further explored.

Characterization of sheep spermatogenesis through single-cell RNA sequencing

Spermatogenesis is an important biological process in male reproduction. The interaction between male germ cells and somatic cells during spermatogenesis, is necessary for male reproductive activities. This cellular heterogeneity has made it difficult to profile distinct cell types at different stages of development. Here, we present the first comprehensive, unbiased single-cell transcriptomic study of sheep spermatogenesis using 10× genomics single cell sequencing (scRNA-seq). We collected scRNA-seq data from 11 772 cells from the adult sheep testis and identified all known germ cells (including early primary spermatocytes, late primary spermatocytes, round spermatids, elongated spermatids, and sperm), and somatic cells (Sertoli cells and Leydig cells), as well as one somatic cell that unexpectedly contained leukocytes. The functional enrichment analysis indicated that several pathways of cell cycle, gamete generation, protein processing, and mRNA surveillance pathways were significantly enriched in testicular germ cell types, and ribosome pathway was significantly enriched in testicular somatic cell types. Further analysis identified several stage-specific marker genes of sheep germ cells, such as EZH2, SOX18, SCP2, PCNA, and PRKCD. Our research explored for the first time of the changes in the transcription level of various cell types during the process of sheep spermatogenesis, providing new insights for sheep spermatogenesis and spermatogenic cell development.

The transcription factors SF-1 and SOX8 cooperate to upregulate Cx43 expression in mouse TM4 sertoli cells

Gap junctions made by connexins within the adult testis are essential for communication between Sertoli cells and for spermatogenesis. Sertoli cells play an important role in supporting germ cells differentiation and maturation into spermatozoa. Connexin43 (Cx43) is the most abundant and important connexin of the testis. We have shown previously that the expression of Cx43 is being regulated by SOX and AP-1 transcription factors in Sertoli cells. However, additional regulatory elements being able to recruit orphan nuclear receptors may be involved. Since SOX and SF-1 transcription factors have been shown to cooperate to regulate gene expression in Sertoli cells, we wondered if such mechanism could be involved in the activation of Cx43 expression. Thus, the activity of the Cx43 promoter was measured by co-transfections of luciferase reporter plasmid constructs with different expression vectors for transcription factors in the TM4 Sertoli cell line. The recruitment of SF-1 to the proximal region of the Cx43 promoter was evaluated by chromatin immunoprecipitation. Our results indicate that SOX8 and SF-1, as well as SOX9 and Nur77, cooperate to activate the expression of Cx43 and that SF-1 is being recruited to the −132 to −26 bp region of the Cx43 promoter. These results allow us to have a better understanding of the mechanisms regulating Cx43 expression and could explain some disturbances in communication between Sertoli cells responsible for impaired fertility.

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SF-1 and SOX8 cooperate to activate Cx43 expression in TM4 Sertoli cells.

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SF-1 is being recruited to the proximal region of the Cx43 promoter.

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LRH-1 and Nur77 also cooperate with SOX factors to activate Cx43 expression.

Functional analysis of a SoxE gene in the oriental freshwater prawn, Macrobrachium nipponense by molecular cloning, expression pattern analysis, and in situ hybridization (de Haan, 1849)

In this study, a full-length cDNA sequence of SoxE (subgroup E within the Sox family of transcription factors) was cloned from Macrobrachium nipponense and named MnSoxE1. The full-length cDNA of MnSoxE1 is 1748 bp, consisting of a 110 bp 5' UTR, a 105 bp 3' UTR, and a 1533 bp ORF that encodes 510 amino acids. Conserved domains showed that MnSoxE1 has a high similarity to the SoxE gene of Penaeus vannamei. Phylogenetic tree analysis classified that MnSoxE1 with the SoxE gene of other arthropods into one clade. These results suggested that MnSoxE1 belongs to the SoxE subgroup. During embryonic development, MnSoxE1 was mainly expressed in the gastrula stage, implicating its involvement in tissue cell differentiation and formation. In the post-larval stages, the expression of MnSoxE1 continued to increase on days 1-10. The expression level in males was significantly higher than that in females. Males are clearly distinguishable from females on post-larval day 25, showing that MnSoxE1 may play a role in promoting early development and germ cell and gonadal differentiation, especially for males. qPCR analysis showed that MnSoxE1 may also be involved in oogonium proliferation during ovary development. Further in situ hybridization analysis revealed that MnSoxE1 was mainly located in oocytes and spermatocytes, especially in sertoli cells, and implies that it may be involved in the development of oocytes and spermatocytes, as well as the maintenance of testes in mature prawns. These results indicate that MnSoxE1 is involved in gonadal differentiation and development in M. nipponense, especially testis development.

A 50-bp enhancer of the mouse acrosomal vesicle protein 1 gene activates round spermatid-specific transcription in vivo†

Enhancers are cis-elements that activate transcription and play critical roles in tissue- and cell type-specific gene expression. During spermatogenesis, genes coding for specialized sperm structures are expressed in a developmental stage- and cell type-specific manner, but the enhancers responsible for their expression have not been identified. Using the mouse acrosomal vesicle protein (Acrv1) gene that codes for the acrosomal protein SP-10 as a model, our previous studies have shown that Acrv1 proximal promoter activates transcription in spermatids; and the goal of the present study was to separate the enhancer responsible. Transgenic mice showed that three copies of the -186/-135 fragment (50 bp enhancer) placed upstream of the Acrv1 core promoter (-91/+28) activated reporter expression in testis but not somatic tissues (n = 4). Immunohistochemistry showed that enhancer activity was restricted to the round spermatids. The Acrv1 enhancer failed to activate transcription in the context of a heterologous core promoter (n = 4), indicating a likely requirement for enhancer-core promoter compatibility. Chromatin accessibility assays showed that the Acrv1 enhancer assumes a nucleosome-free state in male germ cells (but not liver), indicating occupancy by transcription factors. Southwestern assays (SWA) identified specific binding of the enhancer to a testis nuclear protein of 47 kDa (TNP47). TNP47 was predominantly nuclear and becomes abundant during the haploid phase of spermatogenesis. Two-dimensional SWA revealed the isoelectric point of TNP47 to be 5.2. Taken together, this study delineated a 50-bp enhancer of the Acrv1 gene for round spermatid-specific transcription and identified a putative cognate factor. The 50-bp enhancer could become useful for delivery of proteins into spermatids.

Effects of long term antiprogestine mifepristone (RU486) exposure on sexually dimorphic lncRNA expression and gonadal masculinization in Nile tilapia (Oreochromis niloticus)

Mifepristone (RU486), a clinical abortion agent and potential endocrine disruptor, binds to progestin and glucocorticoid receptors and has multiple functional importance in reproductive physiology. A long-term exposure of RU486 resulted in masculinization of female fish, however, the epigenetic landscape remains elusive. Recent studies demonstrated that long non-coding RNAs (lncRNAs) might play potential roles in epigenetic modulation of sex differentiation, ovarian cancer and germline stem cell survival. To further understand the influence of RU486 exposure on epigenetic regulation, we performed a comparative investigation on sex-biased gonadal lncRNAs profiles using control XX/XY and RU486-induced sex reversed XX Nile tilapia (Oreochromis niloticus) by RNA-seq. In total, 962 sexually differentially expressed lncRNAs and their target genes were screened from the gonads of control and sex reversed fish. In comparison with the control XX group, sex reversal induced by RU486 treatment led to significant up-regulation of 757 lncRNAs and down-regulation of 221 lncRNAs. Hierarchical clustering analysis revealed that global lncRNA expression profiles in RU486-treated XX group clustered into the same branch with the control XY, whereas XX control group formed a separate branch. The KEGG pathway enrichment analysis showed that the cis-target genes between RU486-XX and control-XX were concentrated in NOD - like receptor signaling pathway, Cell adhesion molecules (CAMs) and Biosynthesis of amino acids. Real-time PCR and in situ hybridization experiments demonstrate that lncRNAs showing intense fluctuation during RU486 treatment are also sexually dimorphic during early sex differentiation, which further proves the intimate relationship between lncRNAs and sex differentiation and sexual transdifferentiation. Taken together, our data strongly indicates that a long-term exposure of RU486 resulted in sex reversal of XX female fish and the altered expression of sexually dimorphic lncRNAs might partially account for the sex reversal via epigenetic modification.

Transcriptomic analysis of overexpressed SOX4 and SOX8 in TM4 Sertoli cells with emphasis on cell-to-cell interactions

Sertoli cells are localized in seminiferous tubules within the testis. They are the first testicular cells to differentiate during male sex determination. In the adult, Sertoli cells provide nutrients to germ cells, control factors for spermatogenesis and protection by establishing the blood-testis barrier (BTB). This BTB is composed of tight junctions, basal ectoplasmic specializations, adherent junctions and gap junctions. The transcription factor SOX8 is necessary for the maintenance of spermatogenesis during adult life whereas SOX4 is involved in developmental processes. These factors are highly expressed in Sertoli cells. However, few of their target genes in adult Sertoli cells are known. Hence, we compared the transcriptomes of TM4 Sertoli cells overexpressing or not SOX4 or SOX8 using RNA-Seq followed by pathways and networks analyses. We found that SOX4 overexpression leads to downregulated genes enriched for cell junction organization and positive regulation of cell-to-cell adhesion. Upregulated genes in response to SOX8 overexpression were enriched for Sertoli cell development and differentiation. However, downregulated genes were enriched for cell-to-cell adhesion, tight junction interactions, gap junctions' assembly, as well as extracellular matrix binding. Hence, our results confirm that SOX8 is an important mediator of Sertoli cell maturation, whereas SOX4 and SOX8 influence gene expression related to regulation of blood-testis barrier assembly. In addition, TM4 cells can be considered as a useful model to better define the regulatory mechanisms of SOX4 or SOX8 on gene transcription in Sertoli cells.