Research resource: the dynamic transcriptional profile of sertoli cells during the progression of spermatogenesis

PTBP1 mediates Sertoli cell actin cytoskeleton organization by regulating alternative splicing of actin regulators

Spermatogenesis is a biological process within the testis that produces haploid spermatozoa for the continuity of species. Sertoli cells are somatic cells in the seminiferous epithelium that orchestrate spermatogenesis. Cyclic reorganization of Sertoli cell actin cytoskeleton is vital for spermatogenesis, but the underlying mechanism remains largely unclear. Here, we report that RNA-binding protein PTBP1 controls Sertoli cell actin cytoskeleton reorganization by programming alternative splicing of actin cytoskeleton regulators. This splicing control enables ectoplasmic specializations, the actin-based adhesion junctions, to maintain the blood-testis barrier and support spermatid transport and transformation. Particularly, we show that PTBP1 promotes actin bundle formation by repressing the inclusion of exon 14 of Tnik, a kinase present at the ectoplasmic specialization. Our results thus reveal a novel mechanism wherein Sertoli cell actin cytoskeleton dynamics is controlled post-transcriptionally by utilizing functionally distinct isoforms of actin regulatory proteins, and PTBP1 is a critical regulatory factor in generating such isoforms.

Etiology of Male Infertility: an Update

Spermatogenesis is a complex process of germ cell division and differentiation that involves extensive cross-talk between the developing germ cells and the somatic testicular cells. Defective endocrine signaling and/or intrinsic defects within the testes can adversely affect spermatogenic progression, leading to subfertility/infertility. In recent years, male infertility has been recognized as a global public health concern, and research over the last few decades has elucidated the complex etiology of male infertility. Congenital reproductive abnormalities, genetic mutations, and endocrine/metabolic dysfunction have been demonstrated to be involved in infertility/subfertility in males. Furthermore, acquired factors like exposure to environmental toxicants and lifestyle-related disorders such as illicit use of psychoactive drugs have been shown to adversely affect spermatogenesis. Despite the large body of available scientific literature on the etiology of male infertility, a substantial proportion of infertility cases are idiopathic in nature, with no known cause. The inability to treat such idiopathic cases stems from poor knowledge about the complex regulation of spermatogenesis. Emerging scientific evidence indicates that defective functioning of testicular Sertoli cells (Sc) may be an underlying cause of infertility/subfertility in males. Sc plays an indispensable role in regulating spermatogenesis, and impaired functional maturation of Sc has been shown to affect fertility in animal models as well as humans, suggesting abnormal Sc as a potential underlying cause of reproductive insufficiency/failure in such cases of unexplained infertility. This review summarizes the major causes of infertility/subfertility in males, with an emphasis on infertility due to dysregulated Sc function.

HDAC3 promotes Sertoli cell maturation and maintains the blood-testis barrier dynamics

Germ cell development depends on the capacity of somatic Sertoli cells to undergo differentiation into a mature state and establish a germ cell-specific blood-testis barrier (BTB). The BTB structure confers an immunological barrier for meiotic and postmeiotic germ cells, and its dynamic permeability facilitates a transient movement of preleptotene spermatocytes through BTB to enter meiosis. However, the regulatory factors involved in Sertoli cell maturation and how BTB dynamics coordinate germ cell development remain unclear. Here, we found a histone deacetylase HDAC3 abundantly expresses in Sertoli cells and localizes in both cytoplasm and nucleus. Sertoli cell-specific Hdac3 knockout in mice causes infertility with compromised integrity of blood-testis barrier, leading to germ cells unable to traverse through BTB and an accumulation of preleptotene spermatocytes in juvenile testis. Mechanistically, nuclear HDAC3 regulates the expression program of Sertoli cell maturation genes, and cytoplasmic HDAC3 forms a complex with the gap junction protein Connexin 43 to modulate the BTB integrity and dynamics through regulating the distribution of tight junction proteins. Our findings identify HDAC3 as a critical regulator in promoting Sertoli cell maturation and maintaining the homeostasis of the blood-testis barrier.

A comparative analysis of genes differentially expressed between rete testis cells and Sertoli cells of the mouse testis

The rete testis (RT) is a region of the mammalian testis that plays an important role in testicular physiology. The RT epithelium consists of cells sharing some well-known gene markers with supporting Sertoli cells (SCs). However, little is known about the differences in gene expression between these two cell populations. Here, we used fluorescence-activated cell sorting (FACS) to obtain pure cultures of neonatal RT cells and SCs and identified differentially expressed genes (DEGs) between these cell types using RNA sequencing (RNA-seq). We then compared our data with the RNA-seq data of other studies that examined RT cells and SCs of mice of different ages and generated a list of DEGs permanently upregulated in RT cells throughout testis development and in culture, which included 86 genes, and a list of 79 DEGs permanently upregulated in SCs. The analysis of studies on DMRT1 function revealed that nearly half of the permanent DEGs could be regulated by this SC upregulated transcription factor. We suggest that useful cell lineage markers and candidate genes for the specification of both RT cells and SCs may be present among these permanent DEGs.

Functions and mechanism of noncoding RNA in regulation and differentiation of male mammalian reproduction

Noncoding RNAs (ncRNAs) are active regulators of a wide range of biological and physiological processes, including the majority of mammalian reproductive events. Knowledge of the biological activities of ncRNAs in the context of mammalian reproduction will allow for a more comprehensive and comparative understanding of male sterility and fertility. In this review, we describe recent advances in ncRNA-mediated control of mammalian reproduction and emphasize the importance of ncRNAs in several aspects of mammalian reproduction, such as germ cell biogenesis and reproductive organ activity. Furthermore, we focus on gene expression regulatory feedback loops including hormones and ncRNA expression to better understand germ cell commitment and reproductive organ function. Finally, this study shows the role of ncRNAs in male reproductive failure and provides suggestions for further research.

Testis-specific serine kinase 3 is required for sperm morphogenesis and male fertility

BACKGROUND

The importance of phosphorylation in sperm during spermatogenesis has not been pursued extensively. Testis-specific serine kinase 3 (Tssk3) is a conserved gene, but TSSK3 kinase functions and phosphorylation substrates of TSSK3 are not known.

OBJECTIVE

The goals of our studies were to understand the mechanism of action of TSSK3.

MATERIALS AND METHODS

We analyzed the localization of TSSK3 in sperm, used CRISPR/Cas9 to generate Tssk3 knockout (KO) mice in which nearly all of the Tssk3 open reading frame was deleted (ensuring it is a null mutation), analyzed the fertility of Tssk3 KO mice by breeding mice for 4 months, and conducted phosphoproteomics analysis of male testicular germ cells.

RESULTS

TSSK3 is expressed in elongating sperm and localizes to the sperm tail. To define the essential roles of TSSK3 in vivo, heterozygous (HET) or homozygous KO male mice were mated with wild-type females, and fertility was assessed over 4 months; Tssk3 KO males are sterile, whereas HET males produced normal litter sizes. The absence of TSSK3 results in disorganization of all stages of testicular seminiferous epithelium and significantly increased vacuolization of germ cells, leading to dramatically reduced sperm counts and abnormal sperm morphology; despite these histologic changes, Tssk3 null mice have normal testis size. To elucidate the mechanisms causing the KO phenotype, we conducted phosphoproteomics using purified germ cells from Tssk3 HET and KO testes. We found that proteins implicated in male infertility, such as GAPDHS, ACTL7A, ACTL9, and REEP6, showed significantly reduced phosphorylation in KO testes compared to HET testes, despite unaltered total protein levels.

CONCLUSIONS

We demonstrated that TSSK3 is essential for male fertility and crucial for phosphorylation of multiple infertility-related proteins. These studies and the pathways in which TSSK3 functions have implications for human male infertility and nonhormonal contraception.

Single-cell transcriptomic profiling redefines the origin and specification of early adrenogonadal progenitors

Adrenal cortex and gonads represent the two major steroidogenic organs in mammals. Both tissues are considered to share a common developmental origin characterized by the expression of Nr5a1/Sf1. The precise origin of adrenogonadal progenitors and the processes driving differentiation toward the adrenal or gonadal fate remain, however, elusive. Here, we provide a comprehensive single-cell transcriptomic atlas of early mouse adrenogonadal development including 52 cell types belonging to twelve major cell lineages. Trajectory reconstruction reveals that adrenogonadal cells emerge from the lateral plate rather than the intermediate mesoderm. Surprisingly, we find that gonadal and adrenal fates have already diverged prior to Nr5a1 expression. Finally, lineage separation into gonadal and adrenal fates involves canonical versus non-canonical Wnt signaling and differential expression of Hox patterning genes. Thus, our study provides important insights into the molecular programs of adrenal and gonadal fate choice and will be a valuable resource for further research into adrenogonadal ontogenesis.

Human in vitro spermatogenesis as a regenerative therapy - where do we stand?

Spermatogenesis involves precise temporal and spatial gene expression and cell signalling to reach a coordinated balance between self-renewal and differentiation of spermatogonial stem cells through various germ cell states including mitosis, and meiosis I and II, which result in the generation of haploid cells with a unique genetic identity. Subsequently, these round spermatids undergo a series of morphological changes to shed excess cytoplast, develop a midpiece and tail, and undergo DNA repackaging to eventually form millions of spermatozoa. The goal of recreating this process in vitro has been pursued since the 1920s as a tool to treat male factor infertility in patients with azoospermia. Continued advances in reproductive bioengineering led to successful generation of mature, functional sperm in mice and, in the past 3 years, in humans. Multiple approaches to study human in vitro spermatogenesis have been proposed, but technical and ethical obstacles have limited the ability to complete spermiogenesis, and further work is needed to establish a robust culture system for clinical application.

The transcription factors Junb and Fosl2 cooperate to regulate Cdh3 expression in 15P-1 Sertoli cells

In Sertoli cells of the testis, cadherins (Cdh) are important cell-to-cell interaction proteins and contribute to the formation of the blood-testis barrier being essential for germ cells' protection. P-cadherin or Cdh3 is only expressed in Sertoli cells from embryonic to prepubertal development. Interestingly, the expression profile of Cdh3 correlates with that of activating protein-1 (AP-1) transcription factors during Sertoli cells development. To assess their potential implications in the regulation of Cdh3, different AP-1 transcription factors were overexpressed in 15P-1 Sertoli cells. We found that the overexpressions of Junb and Fosl2 activated Cdh3 promoter. ChIP-qPCR assay and luciferase reporter assay with 5' promoter deletions and site-directed mutagenesis confirmed the recruitment of Junb and Fosl2 to an AP-1 regulatory element at -47 bp in the proximal region of Cdh3 promoter in 15P-1 cells. These findings were further supported by histone modification markers and chromatin accessibility surrounding Cdh3 promoter in mouse testis. Moreover, the knockdowns of Junb and/or Fosl2 by siRNA decreased Cdh3 protein levels. Taken together, these data suggest that in 15P-1 Sertoli cells, the AP-1 family members Junb and Fosl2 are responsible for the regulation of Cdh3 expression, which requires the recruitment of both factors to the proximal region of the Cdh3 promoter.

Throughout in vitro first spermatogenic wave: Next-generation sequencing gene expression patterns of fresh and cryopreserved prepubertal mice testicular tissue explants

INTRODUCTION

Suitable cryopreservation procedures of pre-pubertal testicular tissue associated with efficient culture conditions are crucial in the fields of fertility preservation and restoration. In vitro spermatogenesis remains a challenging technical procedure to undergo a complete spermatogenesis.The number of haploid cells and more specifically the spermatic yield produced in vitro in mice is still extremely low compared to age-matched in vivo controls and this procedure has never yet been successfully transferred to humans.

METHODS

To evaluate the impact of in vitro culture and freezing procedure, pre-pubertal testicular mice testes were directly cultured until day 4 (D4), D16 and D30 or cryopreserved by controlled slow freezing then cultured until D30. Testes composed of a panel of 6.5 dpp (days postpartum), 10.5 dpp, 22.5 dpp, and 36.5 dpp mice were used as in vivo controls. Testicular tissues were assessed by histological (HES) and immunofluorescence (stimulated by retinoic acid gene 8, STRA8) analyses. Moreover, a detailed transcriptome evaluation study has been carried out to study the gene expression patterns throughout the first in vitro spermatogenic wave.

RESULTS

Transcriptomic analyses reveal that cultured tissues expression profiles are almost comparable between D16 and D30; highlighting an abnormal kinetic throughout the second half of the first spermatogenesis during in vitro cultures. In addition, testicular explants have shown dysregulation of their transcriptomic profile compared to controls with genes related to inflammation response, insulin-like growth factor and genes involved in steroidogenesis.

DISCUSSION

The present work first shows that cryopreservation had very little impact on gene expression in testicular tissue, either directly after thawing or after 30 days in culture. Transcriptomic analysis of testis tissue samples is highly informative due to the large number of expressed genes and identified isoforms. This study provides a very valuable basis for future studies concerning in vitro spermatogenesis in mice.

Disruption of male fertility-critical Dcaf17 dysregulates mouse testis transcriptome

During mammalian spermatogenesis, the ubiquitin proteasome system maintains protein homoeostasis (proteastasis) and spermatogenic cellular functions. DCAF17 is a substrate receptor in the ubiquitin CRL4 E3 Ligase complex, absence of which causes oligoasthenoteratozoospermia in mice resulting in male infertility. To determine the molecular phenomenon underlying the infertility phenotype caused by disrupting Dcaf17, we performed RNA-sequencing-based gene expression profiling of 3-weeks and 8-weeks old Dcaf17 wild type and Dcaf17 disrupted mutant mice testes. At three weeks, 44% and 56% differentially expressed genes (DEGs) were up- and down-regulated, respectively, with 32% and 68% DEGs were up- and down-regulated, respectively at 8 weeks. DEGs include protein coding genes and lncRNAs distributed across all autosomes and the X chromosome. Gene ontology analysis revealed major biological processes including proteolysis, regulation of transcription and chromatin remodelling are affected due to Dcaf17 disruption. We found that Dcaf17 disruption up-regulated several somatic genes, while germline-associated genes were down-regulated. Up to 10% of upregulated, and 12% of downregulated, genes were implicated in male reproductive phenotypes. Moreover, a large proportion of the up-regulated genes were highly expressed in spermatogonia and spermatocytes, while the majority of downregulated genes were predominantly expressed in round spermatids. Collectively, these data show that the Dcaf17 disruption affects directly or indirectly testicular proteastasis and transcriptional signature in mouse.

Decoding the Spermatogenesis Program: New Insights from Transcriptomic Analyses

Spermatogenesis is a complex differentiation process coordinated spatiotemporally across and along seminiferous tubules. Cellular heterogeneity has made it challenging to obtain stage-specific molecular profiles of germ and somatic cells using bulk transcriptomic analyses. This has limited our ability to understand regulation of spermatogenesis and to integrate knowledge from model organisms to humans. The recent advancement of single-cell RNA-sequencing (scRNA-seq) technologies provides insights into the cell type diversity and molecular signatures in the testis. Fine-grained cell atlases of the testis contain both known and novel cell types and define the functional states along the germ cell developmental trajectory in many species. These atlases provide a reference system for integrated interspecies comparisons to discover mechanistic parallels and to enable future studies. Despite recent advances, we currently lack high-resolution data to probe germ cell-somatic cell interactions in the tissue environment, but the use of highly multiplexed spatial analysis technologies has begun to resolve this problem. Taken together, recent single-cell studies provide an improvedunderstanding of gametogenesis to examine underlying causes of infertility and enable the development of new therapeutic interventions.

Long-term effects of early postnatal stress on Sertoli cells

Sertoli cells are somatic cells in testis essential for spermatogenesis, that support the development, maturation, and differentiation of germ cells. Sertoli cells are metabolically highly active and physiologically regulated by external signals, particularly factors in the blood stream. In disease conditions, circulating pathological signals may affect Sertoli cells and consequentially, alter germ cells and fertility. While the effects of stress on reproductive cells have been well studied, how Sertoli cells respond to stress remains poorly characterized. We used a mouse model of early postnatal stress to assess the effects of stress on Sertoli cells. We developed an improved strategy based on intracellular stainings and obtained enriched preparations of Sertoli cells from exposed males. We show that adult Sertoli cells have impaired electron transport chain (ETC) pathways and that several components of ETC complexes particularly complex I, III, and IV are persistently affected. We identify serum as potential mediator of the effects of stress on Sertoli cells by showing that it can recapitulate ETC alterations in primary cells. These results highlight Sertoli cells as cellular targets of stress in early life that can keep a trace of exposure until adulthood.

AIRE in Male Fertility: A New Hypothesis

Male infertility affects approximately 14% of all European men, of which ~44% are characterized as idiopathic. There is an urgency to identify the factors that affect male fertility. One such factor, Autoimmune Regulator (AIRE), a protein found in the thymus, has been studied in the context of central tolerance functioning as a nuclear transcription modulator, responsible for the expression of tissue-restricted antigens in specialized thymic cells that prevent autoimmunity. While its expression in the testes remains enigmatic, we recently observed that sterility in mice correlates with the absence of Aire in the testes, regardless of the deficient expression in medullary thymic epithelial cells or cells of the hematopoietic system. By assessing the Aire transcript levels, we discovered that Sertoli cells are the exclusive source of Aire in the testes, where it most likely plays a non-immune role, suggesting an unknown mechanism by which testicular Aire regulates fertility. Here, we discuss these results in the context of previous reports which have suggested that infertility observed in Aire deficient mice is of an autoimmune aetiology. We present an alternative point of view for the role of Aire in testes in respect to fertility altering the perspective of how Aire's function in the testes is currently perceived.

Two complementary approaches for efficient isolation of Sertoli cells for transcriptomic analysis

Sertoli cells (SCs) are the only somatic cells that reside in seminiferous tubules of testis. They directly interact with and support the development of germ cells, thus have an indispensable role in the process of spermatogenesis. SCs first appear in a proliferative state and then, with the initiation of the first wave of spermatogenesis, progress to a mature “nurturing” state which supports lifelong continuous sperm production. During this development, the SC transcriptome must adapt rapidly as obstacles in SC maturation often result in deficiencies in male fertility. Due to its importance in spermatogenesis, a reliable, rapid, and precise method for the isolation of high purity, viable and unadulterated SC has been largely missing. We have developed an improved method for the preparation of a testicular single cell suspension comprised of two alternative protocols to separate SCs from the rest of the testicular cells by FACS. The first sorting scheme is based on their co-expression of surface specific markers, FSHr and Occludin-1, while the second focuses on the co-staining of SCs with FSHr-specific antibody and Hoechst 33342, which discriminates DNA content of testicular cells. The entire procedure can be completed in less than 3 h which permits the analysis of the development-related transcriptional profile of these cells. Notably, our comparative study showed that this method resulted in a SC transcriptome that is largely comparable to SCs which were briskly isolated due to their cell-specific expression of fluorescent protein. Interestingly, we also show that SCs sorted as FSHr⁺Occludin⁺ cells contained a tangible portion of transcripts from all types of testicular germ cells. Sorting of SCs according to their 2C DNA content significantly reduced the presence of these transcripts, thus seems to be the most suitable approach for accurate determination of the SC transcriptome. We believe that these novel approaches for the isolation of SCs will assist researchers in the elucidation of their function as well as their role in spermatogenesis and disorders related to male infertility.

The testis-specific E3 ubiquitin ligase RNF133 is required for fecundity in mice

BACKGROUND

Ubiquitination is a post-translational modification required for a number of physiological functions regulating protein homeostasis, such as protein degradation. The endoplasmic reticulum (ER) quality control system recognizes and degrades proteins no longer needed in the ER through the ubiquitin-proteasome pathway. E2 and E3 enzymes containing a transmembrane domain have been shown to function in ER quality control. The ER transmembrane protein UBE2J1 is a E2 ubiquitin-conjugating enzyme reported to be essential for spermiogenesis at the elongating spermatid stage. Spermatids from Ube2j1 KO male mice are believed to have defects in the dislocation step of ER quality control. However, associated E3 ubiquitin-protein ligases that function during spermatogenesis remain unknown.

RESULTS

We identified four evolutionarily conserved testis-specific E3 ubiquitin-protein ligases [RING finger protein 133 (Rnf133); RING finger protein 148 (Rnf148); RING finger protein 151 (Rnf151); and Zinc finger SWIM-type containing 2 (Zswim2)]. Using the CRISPR/Cas9 system, we generated and analyzed the fertility of mutant mice with null alleles for each of these E3-encoding genes, as well as double and triple knockout (KO) mice. Male fertility, male reproductive organ, and sperm-associated parameters were analyzed in detail. Fecundity remained largely unaffected in Rnf148, Rnf151, and Zswim2 KO males; however, Rnf133 KO males displayed severe subfertility. Additionally, Rnf133 KO sperm exhibited abnormal morphology and reduced motility. Ultrastructural analysis demonstrated that cytoplasmic droplets were retained in Rnf133 KO spermatozoa. Although Rnf133 and Rnf148 encode paralogous genes that are chromosomally linked and encode putative ER transmembrane E3 ubiquitin-protein ligases based on their protein structures, there was limited functional redundancy of these proteins. In addition, we identified UBE2J1 as an E2 ubiquitin-conjugating protein that interacts with RNF133.

CONCLUSIONS

Our studies reveal that RNF133 is a testis-expressed E3 ubiquitin-protein ligase that plays a critical role for sperm function during spermiogenesis. Based on the presence of a transmembrane domain in RNF133 and its interaction with the ER containing E2 protein UBE2J1, we hypothesize that these ubiquitin-regulatory proteins function together in ER quality control during spermatogenesis.

Follicle-stimulating hormone signaling in Sertoli cells: a licence to the early stages of spermatogenesis

Follicle-stimulating hormone signaling is essential for the initiation and early stages of spermatogenesis. Follicle-stimulating hormone receptor is exclusively expressed in Sertoli cells. As the only type of somatic cell in the seminiferous tubule, Sertoli cells regulate spermatogenesis not only by controlling their own number and function but also through paracrine actions to nourish germ cells surrounded by Sertoli cells. After follicle-stimulating hormone binds to its receptor and activates the follicle-stimulating hormone signaling pathway, follicle-stimulating hormone signaling will establish a normal Sertoli cell number and promote their differentiation. Spermatogonia pool maintenance, spermatogonia differentiation and their entry into meiosis are also positively regulated by follicle-stimulating hormone signaling. In addition, follicle-stimulating hormone signaling regulates germ cell survival and limits their apoptosis. Our review summarizes the aforementioned functions of follicle-stimulating hormone signaling in Sertoli cells. We also describe the clinical potential of follicle-stimulating hormone treatment in male patients with infertility. Furthermore, our review may be helpful for developing better therapies for treating patients with dysfunctional follicle-stimulating hormone signaling in Sertoli cells.

FBXO38 Ubiquitin Ligase Controls Sertoli Cell Maturation

The ubiquitin ligase SCF^FBXO38 controls centromeric chromatin by promoting the degradation of the ZXDB protein. To determine the importance of this pathway during development, Fbxo38-deficient mice were generated. The loss of FBXO38 resulted in growth retardation affecting several organs, including the male reproductive system. A detailed analysis of the mutant testes revealed pathological changes in the seminiferous tubules, accompanied by a significant decrease in sperm production and reduced fertility. In adult testes, FBXO38 was specifically expressed in Sertoli cells, a somatic population essential for spermatogenesis initiation and progression. Sertoli cells lacking FBXO38 exhibited stabilized ZXDB protein and upregulated centromeric chromatin. Furthermore, the gene expression profile revealed that the absence of FBXO38 led to a defect in Sertoli cell maturation, specifically characterized by dysregulation in genes controlling retinoic acid metabolism and intercellular communication. Consequently, we documented significant changes in their ability to initiate spermatogonial differentiation. In conclusion, we show that FBXO38 acts as a Sertoli cell maturation factor, affecting the Sertoli cell transcription program, centromere integrity, and, subsequently, the ability to control spermatogenesis.

Understanding the Underlying Molecular Mechanisms of Meiotic Arrest during In Vitro Spermatogenesis in Rat Prepubertal Testicular Tissue

In vitro spermatogenesis appears to be a promising approach to restore the fertility of childhood cancer survivors. The rat model has proven to be challenging, since germ cell maturation is arrested in organotypic cultures. Here, we report that, despite a meiotic entry, abnormal synaptonemal complexes were found in spermatocytes, and in vitro matured rat prepubertal testicular tissues displayed an immature phenotype. RNA-sequencing analyses highlighted up to 600 differentially expressed genes between in vitro and in vivo conditions, including genes involved in blood-testis barrier (BTB) formation and steroidogenesis. BTB integrity, the expression of two steroidogenic enzymes, and androgen receptors were indeed altered in vitro. Moreover, most of the top 10 predicted upstream regulators of deregulated genes were involved in inflammatory processes or immune cell recruitment. However, none of the three anti-inflammatory molecules tested in this study promoted meiotic progression. By analysing for the first time in vitro matured rat prepubertal testicular tissues at the molecular level, we uncovered the deregulation of several genes and revealed that defective BTB function, altered steroidogenic pathway, and probably inflammation, could be at the origin of meiotic arrest.

Mapping Human Reproduction with Single-Cell Genomics

The trillions of cells in the human body develop as a result of the fusion of two extremely specialized cells: an oocyte and a sperm. This process is essential for the continuation of our species, as it ensures that parental genetic information is mixed and passed on from generation to generation. In addition to producing oocytes, the female reproductive system must provide the environment for the appropriate development of the fetus until birth. New genomic and computational tools offer unique opportunities to study the tight spatiotemporal regulatory mechanisms that are required for the cycle of human reproduction. This review explores how single-cell technologies have been used to build cellular atlases of the human reproductive system across the life span and how these maps have proven useful to better understand reproductive pathologies and dissect the heterogeneity of in vitro model systems. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

ESTABLISHMENT OF A PURE CULTURE OF IMMATURE SERTOLI CELLS BY PDGFRA STAINING AND CELL SORTING

Sertoli cells are key somatic cells in the testis that form seminiferous tubules and support spermatogenesis. The isolation of pure Sertoli cells is important for their study. However, it is a difficult effort because of the close association of Sertoli cells with peritubular myoid cells surrounding seminiferous tubules. Here we propose a novel approach to the establishment of a pure Sertoli cell culture from immature mouse testes. It is based on the staining of testicular cells for platelet-derived growth factor receptor alpha (PDGFRA) followed by fluorescence-activated cell sorting and culturing of a PDGFRA-negative cell population. Cells positive for a Sertoli cell marker WT1 accounted for more than 96% of cells in cultures from 6 and 12 dpp mice. The numbers of peritubular myoid cells identified by ACTA2 staining did not exceed 4%. Cells in the cultures were also positive for Sertoli cell proteins SOX9 and DMRT1. Amh and Hsd17b3 expression decreased and Ar and Gata1 expression increased in 12 dpp cultures compared to 6 dpp cultures, which suggests that cultured Sertoli cells at least partially retained their differentiation status. This method can be employed in various applications including the analysis of differential gene expression and functional studies. This article is protected by copyright. All rights reserved.

Follicle-stimulating hormone regulates Notch signalling in the seminiferous epithelium of continuously and seasonally breeding rodents

CONTEXT

Juxtacrine (contact-dependent) communication between the cells of seminiferous epithelium mediated by Notch signalling is of importance for the proper course of spermatogenesis in mammals.

AIMS

The present study was designed to evaluate the role of follicle-stimulating hormone (FSH) in the regulation of Notch signalling in rodent seminiferous epithelium.

METHODS

We explored the effects (1) of pharmacological inhibition of the hypothalamus-pituitary-gonadal (HPG) axis and FSH replacement in pubertal rats, and (2) of photoinhibition of HPG axis followed by FSH substitution in seasonally breeding rodents, bank voles, on Notch pathway activity. Experiments on isolated rat Sertoli cells exposed to FSH were also performed. Gene and protein expressions of Notch pathway components were analysed using RT-qPCR, western blot and immunohistochemistry/immunofluorescence.

KEY RESULTS

Distribution patterns of Notch pathway proteins in bank vole and rat seminiferous epithelium were comparable; however, levels of activated Notch1 and Notch3, hairy/enhancer of split 1 (HES1) and hairy/enhancer of split-related with YRPW motif 1 (HEY1) in bank voles were dependent on the length of the photoperiod. In response to FSH similar changes in these proteins were found in both species, indicating that FSH is a negative regulator of Notch pathway activity in seminiferous epithelium.

CONCLUSIONS

Our results support a common mechanism of FSH action on Notch pathway during onset and recrudescence of spermatogenesis in rodents.

IMPLICATIONS

Interaction between FSH signalling and Notch pathway in Sertoli cells may be involved in spermatogenic activity changes of the testes occurring during puberty or photoperiod shift in continuously and seasonally breeding rodents, respectively.

Lrh1 can help reprogram sexual cell fate and is required for Sertoli cell development and spermatogenesis in the mouse testis

The mammalian nuclear hormone receptors LRH1 (NR5A2) and SF1 (NR5A1) are close paralogs that can bind the same DNA motif and play crucial roles in gonadal development and function. Lrh1 is essential for follicle development in the ovary and has been proposed to regulate steroidogenesis in the testis. Lrh1 expression in the testis is highly elevated by loss of the sex regulator Dmrt1, which triggers male-to-female transdifferentiation of Sertoli cells. While Sf1 has a well-defined and crucial role in testis development, no function for Lrh1 in the male gonad has been reported. Here we use conditional genetics to examine Lrh1 requirements both in gonadal cell fate reprogramming and in normal development of the three major cell lineages of the mouse testis. We find that loss of Lrh1 suppresses sexual transdifferentiation, confirming that Lrh1 can act as a key driver in reprogramming sexual cell fate. In otherwise wild-type testes, we find that Lrh1 is dispensable in Leydig cells but is required in Sertoli cells for their proliferation, for seminiferous tubule morphogenesis, for maintenance of the blood-testis barrier, for feedback regulation of androgen production, and for support of spermatogenesis. Expression profiling identified misexpressed genes likely underlying most aspects of the Sertoli cell phenotype. In the germ line we found that Lrh1 is required for maintenance of functional spermatogonia, and hence mutants progressively lose spermatogenesis. Reduced expression of the RNA binding factor Nxf2 likely contributes to the SSC defect. Unexpectedly, however, over time the Lrh1 mutant germ line recovered abundant spermatogenesis and fertility. This finding indicates that severe germ line depletion triggers a response allowing mutant spermatogonia to recover the ability to undergo complete spermatogenesis. Our results demonstrate that Lrh1, like Sf1, is an essential regulator of testis development and function but has a very distinct repertoire of functions.

Follicle-stimulating hormone-mediated decline in miR-92a-3p expression in pubertal mice Sertoli cells is crucial for germ cell differentiation and fertility

Sertoli cells (Sc) are the sole target of follicle-stimulating hormone (FSH) in the testis and attain functional maturation post-birth to significantly augment germ cell (Gc) division and differentiation at puberty. Despite having an operational microRNA (miRNA) machinery, limited information is available on miRNA-mediated regulation of Sc maturation and male fertility. We have shown before that miR-92a-3p levels decline in pubertal rat Sc. In response to FSH treatment, the expressions of FSH Receptor, Claudin11 and Klf4 were found to be elevated in pubertal rat Sc coinciding with our finding of FSH-induced decline in miR-92a-3p levels. To investigate the association of miR-92a-3p and spermatogenesis, we generated transgenic mice where such pubertal decline of miR-92a-3p was prevented by its overexpression in pubertal Sc under proximal Rhox5 promoter, which is known to be activated specifically at puberty, in Sc. Our in vivo observations provided substantial evidence that FSH-induced decline in miR-92a-3p expression during Sc maturation acts as an essential prerequisite for the pubertal onset of spermatogenesis. Elevated expression of miR-92a-3p in post-pubertal testes results into functionally compromised Sc, leading to impairment of the blood-testis barrier formation and apoptosis of pre-meiotic Gc, ultimately culminating into infertility. Collectively, our data suggest that regulation of miR-92a-3p expression is crucial for Sc-mediated induction of active spermatogenesis at puberty and regulation of male fertility.

Updates in Sertoli Cell-Mediated Signaling During Spermatogenesis and Advances in Restoring Sertoli Cell Function

Since their initial description by Enrico Sertoli in 1865, Sertoli cells have continued to enchant testis biologists. Testis size and germ cell carrying capacity are intimately tied to Sertoli cell number and function. One critical Sertoli cell function is signaling from Sertoli cells to germ cells as part of regulation of the spermatogenic cycle. Sertoli cell signals can be endocrine or paracrine in nature. Here we review recent advances in understanding the interplay of Sertoli cell endocrine and paracrine signals that regulate germ cell state. Although these findings have long-term implications for treating male infertility, recent breakthroughs in Sertoli cell transplantation have more immediate implications. We summarize the surge of advances in Sertoli cell ablation and transplantation, both of which are wedded to a growing understanding of the unique Sertoli cell niche in the transitional zone of the testis.

Declining levels of miR-382-3p at puberty trigger the onset of spermatogenesis

A major change in the transcriptome of testicular Sertoli cells (Scs) at the onset of puberty enables them to induce robust spermatogenesis. Through comprehensive literature mining, we generated a list of genes crucial for Sc functioning and computationally predicted the microRNAs regulating them. Differential expression analysis of microRNAs in infant and pubertal rat Scs showed that miR-382-3p levels decline significantly in pubertal Scs. Interestingly, miR-382-3p was found to regulate genes like Ar and Wt1, which are crucial for functional competence of Scs. We generated a transgenic (Tg) mouse model in which pubertal decline of miR-382-3p was prevented by its overexpression in pubertal Scs. Elevated miR-382-3p restricted the functional maturation of Scs at puberty, leading to infertility. Prevention of decline in miR-382-3p expression in pubertal Scs was responsible for defective blood-testis barrier (BTB) formation, severe testicular defects, low epididymal sperm counts and loss of fertility in these mice. This provided substantial evidence that decline in levels of miR-382-3p at puberty is the essential trigger for onset of robust spermatogenesis at puberty. Hence, sustained high levels of miR-382-3p in pubertal Scs could be one of the underlying causes of idiopathic male infertility and should be considered for diagnosis and treatment of infertility.

Transcriptomic analysis of the seminal vesicle response to the reproductive toxicant acrylamide

BACKGROUND

The seminal vesicles synthesise bioactive factors that support gamete function, modulate the female reproductive tract to promote implantation, and influence developmental programming of offspring phenotype. Despite the significance of the seminal vesicles in reproduction, their biology remains poorly defined. Here, to advance understanding of seminal vesicle biology, we analyse the mouse seminal vesicle transcriptome under normal physiological conditions and in response to acute exposure to the reproductive toxicant acrylamide. Mice were administered acrylamide (25 mg/kg bw/day) or vehicle control daily for five consecutive days prior to collecting seminal vesicle tissue 72 h following the final injection.

RESULTS

A total of 15,304 genes were identified in the seminal vesicles with those encoding secreted proteins amongst the most abundant. In addition to reproductive hormone pathways, functional annotation of the seminal vesicle transcriptome identified cell proliferation, protein synthesis, and cellular death and survival pathways as prominent biological processes. Administration of acrylamide elicited 70 differentially regulated (fold-change ≥1.5 or ≤ 0.67) genes, several of which were orthogonally validated using quantitative PCR. Pathways that initiate gene and protein synthesis to promote cellular survival were prominent amongst the dysregulated pathways. Inflammation was also a key transcriptomic response to acrylamide, with the cytokine, Colony stimulating factor 2 (Csf2) identified as a top-ranked upstream driver and inflammatory mediator associated with recovery of homeostasis. Early growth response (Egr1), C-C motif chemokine ligand 8 (Ccl8), and Collagen, type V, alpha 1 (Col5a1) were also identified amongst the dysregulated genes. Additionally, acrylamide treatment led to subtle changes in the expression of genes that encode proteins secreted by the seminal vesicle, including the complement regulator, Complement factor b (Cfb).

CONCLUSIONS

These data add to emerging evidence demonstrating that the seminal vesicles, like other male reproductive tract tissues, are sensitive to environmental insults, and respond in a manner with potential to exert impact on fetal development and later offspring health.

Actions and Roles of FSH in Germinative Cells

Follicle stimulating hormone (FSH) is produced by the pituitary gland in a coordinated hypothalamic-pituitary-gonadal (HPG) axis event, plays important roles in reproduction and germ cell development during different phases of reproductive development (fetal, neonatal, puberty, and adult life), and is consequently essential for fertility. FSH is a heterodimeric glycoprotein hormone of two dissociable subunits, α and β. The FSH β-subunit (FSHβ) function starts upon coupling to its specific receptor: follicle-stimulating hormone receptor (FSHR). FSHRs are localized mainly on the surface of target cells on the testis and ovary (granulosa and Sertoli cells) and have recently been found in testicular stem cells and extra-gonadal tissue. Several reproduction disorders are associated with absent or low FSH secretion, with mutation of the FSH β-subunit or the FSH receptor, and/or its signaling pathways. However, the influence of FSH on germ cells is still poorly understood; some studies have suggested that this hormone also plays a determinant role in the self-renewal of germinative cells and acts to increase undifferentiated spermatogonia proliferation. In addition, in vitro, together with other factors, it assists the process of differentiation of primordial germ cells (PGCLCs) into gametes (oocyte-like and SSCLCs). In this review, we describe relevant research on the influence of FSH on spermatogenesis and folliculogenesis, mainly in the germ cell of humans and other species. The possible roles of FSH in germ cell generation in vitro are also presented.

Dynamics of the transcriptional landscape during human fetal testis and ovary development

STUDY QUESTION

Which transcriptional program triggers sex differentiation in bipotential gonads and downstream cellular events governing fetal testis and ovary development in humans?

SUMMARY ANSWER

The characterization of a dynamically regulated protein-coding and non-coding transcriptional landscape in developing human gonads of both sexes highlights a large number of potential key regulators that show an early sexually dimorphic expression pattern.

WHAT IS KNOWN ALREADY

Gonadal sex differentiation is orchestrated by a sexually dimorphic gene expression program in XX and XY developing fetal gonads. A comprehensive characterization of its non-coding counterpart offers promising perspectives for deciphering the molecular events underpinning gonad development and for a complete understanding of the etiology of disorders of sex development in humans.

STUDY DESIGN, SIZE, DURATION

To further investigate the protein-coding and non-coding transcriptional landscape during gonad differentiation, we used RNA-sequencing (RNA-seq) and characterized the RNA content of human fetal testis (N = 24) and ovaries (N = 24) from 6 to 17 postconceptional week (PCW), a key period in sex determination and gonad development.

PARTICIPANTS/MATERIALS, SETTING, METHODS

First trimester fetuses (6-12 PCW) and second trimester fetuses (13-14 and 17 PCW) were obtained from legally induced normally progressing terminations of pregnancy. Total RNA was extracted from whole human fetal gonads and sequenced as paired-end 2 × 50 base reads. Resulting sequences were mapped to the human genome, allowing for the assembly and quantification of corresponding transcripts.

MAIN RESULTS AND THE ROLE OF CHANCE

This RNA-seq analysis of human fetal testes and ovaries at seven key developmental stages led to the reconstruction of 22 080 transcripts differentially expressed during testicular and/or ovarian development. In addition to 8935 transcripts displaying sex-independent differential expression during gonad development, the comparison of testes and ovaries enabled the discrimination of 13 145 transcripts that show a sexually dimorphic expression profile. The latter include 1479 transcripts differentially expressed as early as 6 PCW, including 39 transcription factors, 40 long non-coding RNAs and 20 novel genes. Despite the use of stringent filtration criteria (expression cut-off of at least 1 fragment per kilobase of exon model per million reads mapped, fold change of at least 2 and false discovery rate adjusted P values of less than <1%), the possibility of assembly artifacts and of false-positive differentially expressed transcripts cannot be fully ruled out.

LARGE-SCALE DATA

Raw data files (fastq) and a searchable table (.xlss) containing information on genomic features and expression data for all refined transcripts have been submitted to the NCBI GEO under accession number GSE116278.

LIMITATIONS, REASONS FOR CAUTION

The intrinsic nature of this bulk analysis, i.e. the sequencing of transcripts from whole gonads, does not allow direct identification of the cellular origin(s) of the transcripts characterized. Potential cellular dilution effects (e.g. as a result of distinct proliferation rates in XX and XY gonads) may account for a few of the expression profiles identified as being sexually dimorphic. Finally, transcriptome alterations that would result from exposure to pre-abortive drugs cannot be completely excluded. Although we demonstrated the high quality of the sorted cell populations used for experimental validations using quantitative RT-PCR, it cannot be totally excluded that some germline expression may correspond to cell contamination by, for example, macrophages.

WIDER IMPLICATIONS OF THE FINDINGS

For the first time, this study has led to the identification of 1000 protein-coding and non-coding candidate genes showing an early, sexually dimorphic, expression pattern that have not previously been associated with sex differentiation. Collectively, these results increase our understanding of gonad development in humans, and contribute significantly to the identification of new candidate genes involved in fetal gonad differentiation. The results also provide a unique resource that may improve our understanding of the fetal origin of testicular and ovarian dysgenesis syndromes, including cryptorchidism and testicular cancers.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the French National Institute of Health and Medical Research (Inserm), the University of Rennes 1, the French School of Public Health (EHESP), the Swiss National Science Foundation [SNF n° CRS115_171007 to B.J.], the French National Research Agency [ANR n° 16-CE14-0017-02 and n° 18-CE14-0038-02 to F.C.], the Medical Research Council [MR/L010011/1 to P.A.F.] and the European Community's Seventh Framework Programme (FP7/2007-2013) [under grant agreement no 212885 to P.A.F.] and from the European Union's Horizon 2020 Research and Innovation Programme [under grant agreement no 825100 to P.A.F. and S.M.G.]. There are no competing interests related to this study.

Correlation Networks Provide New Insights into the Architecture of Testicular Steroid Pathways in Pigs

Steroid metabolism is a fundamental process in the porcine testis to provide testosterone but also estrogens and androstenone, which are essential for the physiology of the boar. This study concerns boars at an early stage of puberty. Using a RT-qPCR approach, we showed that the transcriptional activities of several genes providing key enzymes involved in this metabolism (such as CYP11A1) are correlated. Surprisingly, HSD17B3, a key gene for testosterone production, was absent from this group. An additional weighted gene co-expression network analysis was performed on two large sets of mRNA-seq to identify co-expression modules. Of these modules, two containing either CYP11A1 or HSD17B3 were further analyzed. This comprehensive correlation meta-analysis identified a group of 85 genes with CYP11A1 as hub gene, but did not allow the characterization of a robust correlation network around HSD17B3. As the CYP11A1-group includes most of the genes involved in steroid synthesis pathways (including LHCGR encoding for the LH receptor), it may control the synthesis of most of the testicular steroids. The independent expression of HSD17B3 probably allows part of the production of testosterone to escape this control. This CYP11A1-group contained also INSL3 and AGT genes encoding a peptide hormone and an angiotensin peptide precursor, respectively.

Novel Gene Regulation in Normal and Abnormal Spermatogenesis

Spermatogenesis is a complex and dynamic process which is precisely controlledby genetic and epigenetic factors. With the development of new technologies (e.g., single-cell RNA sequencing), increasingly more regulatory genes related to spermatogenesis have been identified. In this review, we address the roles and mechanisms of novel genes in regulating the normal and abnormal spermatogenesis. Specifically, we discussed the functions and signaling pathways of key new genes in mediating the proliferation, differentiation, and apoptosis of rodent and human spermatogonial stem cells (SSCs), as well as in controlling the meiosis of spermatocytes and other germ cells. Additionally, we summarized the gene regulation in the abnormal testicular microenvironment or the niche by Sertoli cells, peritubular myoid cells, and Leydig cells. Finally, we pointed out the future directions for investigating the molecular mechanisms underlying human spermatogenesis. This review could offer novel insights into genetic regulation in the normal and abnormal spermatogenesis, and it provides new molecular targets for gene therapy of male infertility.

The Role of Androgen Signaling in Male Sexual Development at Puberty

Puberty is characterized by major changes in the anatomy and function of reproductive organs. Androgen activity is low before puberty, but during pubertal development, the testes resume the production of androgens. Major physiological changes occur in the testicular cell compartments in response to the increase in intratesticular testosterone concentrations and androgen receptor expression. Androgen activity also impacts on the internal and external genitalia. In target cells, androgens signal through a classical and a nonclassical pathway. This review addresses the most recent advances in the knowledge of the role of androgen signaling in postnatal male sexual development, with a special emphasis on human puberty.

Contributions of Flow Cytometry to the Molecular Study of Spermatogenesis in Mammals

Mammalian testes are very heterogeneous organs, with a high number of different cell types. Testicular heterogeneity, together with the lack of reliable in vitro culture systems of spermatogenic cells, have been an obstacle for the characterization of the molecular bases of the unique events that take place along the different spermatogenic stages. In this context, flow cytometry has become an invaluable tool for the analysis of testicular heterogeneity, and for the purification of stage-specific spermatogenic cell populations, both for basic research and for clinical applications. In this review, we highlight the importance of flow cytometry for the advances on the knowledge of the molecular groundwork of spermatogenesis in mammals. Moreover, we provide examples of different approaches to the study of spermatogenesis that have benefited from flow cytometry, including the characterization of mutant phenotypes, transcriptomics, epigenetic and genome-wide chromatin studies, and the attempts to establish cell culture systems for research and/or clinical aims such as infertility treatment.

Low retinoic acid levels mediate regionalization of the Sertoli valve in the terminal segment of mouse seminiferous tubules

In mammalian testes, undifferentiated spermatogonia (A_undiff) undergo differentiation in response to retinoic acid (RA), while their progenitor states are partially maintained by fibroblast growth factors (FGFs). Sertoli valve (SV) is a region located at the terminal end of seminiferous tubule (ST) adjacent to the rete testis (RT), where the high density of A_undiff is constitutively maintained with the absence of active spermatogenesis. However, the molecular and cellular characteristics of SV epithelia still remain unclear. In this study, we first identified the region-specific AKT phosphorylation in the SV Sertoli cells and demonstrated non-cell autonomous specialization of Sertoli cells in the SV region by performing a Sertoli cell ablation/replacement experiment. The expression of Fgf9 was detected in the RT epithelia, while the exogenous administration of FGF9 caused ectopic AKT phosphorylation in the Sertoli cells of convoluted ST. Furthermore, we revealed the SV region-specific expression of Cyp26a1, which encodes an RA-degrading enzyme, and demonstrated that the increased RA levels in the SV region disrupt its pool of A_undiff by inducing their differentiation. Taken together, RT-derived FGFs and low levels of RA signaling contribute to the non-cell-autonomous regionalization of the SV epithelia and its local maintenance of A_undiff in the SV region.

Obesity-related genes are expressed in human Sertoli cells and modulated by energy homeostasis regulating hormones

The strong hormonal dysregulation associated with obesity is responsible for the disruption of several reproductive events. Sertoli cells (SCs) function is dependent on energetic homeostasis and thus, directly associated with energy homeostasis regulating hormones. To further understand the influence of those hormones with SCs function and obesity, we hypothesize that human SCs express obesity-related genes (ORG; MC4R, GNPDA2, TMEM18, and FTO) and that they respond to energy homeostasis regulating hormones (leptin, ghrelin, and glucagon-like protein 1 [GLP-1]) stimuli. To test our hypothesis, SCs were cultured with increasing doses of leptin (0, 5, 25, or 50 ng/ml, for 24 h), ghrelin (0, 20, 100, and 500 pM, for 24 h), and GLP-1 (10, 1000, or 1 × 105 pM, for 6 h). The presence and abundance of ORG transcripts and proteins in SCs were accessed by polymerase chain reaction techniques, Western blot analysis, and immunofluorescence staining. Our results show that human SCs express MC4R, GNPDA2, TMEM18, and FTO in specific cellular locations. MC4R and FTO expression in human SCs was not responsive to the treatments. However, GNPDA2 and TMEM18 expression increased after exposure to the highest concentration of leptin and ghrelin, respectively. We highlight for the first time that human SCs express ORG and that these are responsive to energy homeostasis hormonal stimuli. GNPDA2 and TMEM18 expression respond in opposite directions according to overall energy status, mediated by energy homeostasis regulating hormones. Leptin and ghrelin control of ORG expression by human SCs can be associated with overweight-related infertility and subfertility in males.

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.

Function and transcriptomic dynamics of Sertoli cells during prospermatogonia development in mouse testis

In mammals, spermatogonial stem cells (SSCs) arise from a subpopulation of prospermatogonia during neonatal testis development. Currently, molecular mechanisms directing the prospermatogonia to spermatogonial transition are not well understood. In the study, we found that reducing Sertoli cells number by Amh-cre mediated expression of diphtheria toxin (AC;DTA) in murine fetal testis caused defects in prospermatogonia fate decisions. Histological and immunohistochemical analyses confirmed that Sertoli cells loss occurred at embryonic day (E) 14.5. Prospermatogonia maintained mitotic arrest at E16.5 in control animals, in contrast, 13.4% of germ cells in AC;DTA testis reentered cell cycle and expressed gH2A.X and Sycp3, indicating the commitment to meiosis. After birth, the number of prospermatogonia resuming mitosis was significantly affected by Sertoli cell loss in AC;DTA animals. Lastly, we isolated primary Sertoli cells using a Sertoli cell specific GFP reporter line and showed dynamics of Sertoli cell transcriptomes at E12.5, E13.5, E16.5 and P1. By further analysis, we revealed unique gene expression patterns and potential candidate genes regulating Sertoli cell development and likely mediating interactions between Sertoli cells, prospermatogonia and other testicular cells.

Large-scale discovery of male reproductive tract-specific genes through analysis of RNA-seq datasets

Background

The development of a safe, effective, reversible, non-hormonal contraceptive method for men has been an ongoing effort for the past few decades. However, despite significant progress on elucidating the function of key proteins involved in reproduction, understanding male reproductive physiology is limited by incomplete information on the genes expressed in reproductive tissues, and no contraceptive targets have so far reached clinical trials. To advance product development, further identification of novel reproductive tract-specific genes leading to potentially druggable protein targets is imperative.

Results

In this study, we expand on previous single tissue, single species studies by integrating analysis of publicly available human and mouse RNA-seq datasets whose initial published purpose was not focused on identifying male reproductive tract-specific targets. We also incorporate analysis of additional newly acquired human and mouse testis and epididymis samples to increase the number of targets identified. We detected a combined total of 1178 genes for which no previous evidence of male reproductive tract-specific expression was annotated, many of which are potentially druggable targets. Through RT-PCR, we confirmed the reproductive tract-specific expression of 51 novel orthologous human and mouse genes without a reported mouse model. Of these, we ablated four epididymis-specific genes (Spint3, Spint4, Spint5, and Ces5a) and two testis-specific genes (Pp2d1 and Saxo1) in individual or double knockout mice generated through the CRISPR/Cas9 system. Our results validate a functional requirement for Spint4/5 and Ces5a in male mouse fertility, while demonstrating that Spint3, Pp2d1, and Saxo1 are each individually dispensable for male mouse fertility.

Conclusions

Our work provides a plethora of novel testis- and epididymis-specific genes and elucidates the functional requirement of several of these genes, which is essential towards understanding the etiology of male infertility and the development of male contraceptives.

Characterization of rodent Sertoli cell primary cultures

Sertoli cells play a vital role in spermatogenesis by offering physical and nutritional support to the differentiating male germ cells. They form the blood-testis barrier and secrete growth factors essential for germ cell differentiation. Sertoli cell primary cultures are critical for understanding the regulation of spermatogenesis; however, obtaining pure cultures has been a challenge. Rodent Sertoli cell isolation protocols do not rule out contamination by the interstitial or connective tissue cells. Sertoli cell-specific markers could be helpful, but there is no consensus. Vimentin, the most commonly used marker, is not specific for Sertoli cells since its expression has been reported in peritubular myoid cells, mesenchymal stem cells, fibroblasts, macrophages, and endothelial cells, which contaminate Sertoli cell preparations. Markers based on transcription and growth factors also have limitations. Thus, the impediment to obtaining pure Sertoli cell cultures pertains to both the method of isolation and marker usage. The aim of this review is to discuss improvements to current methods of rodent Sertoli cell primary cultures, assess the properties of prepubertal versus mature Sertoli cell cultures, and propose steps to improve cellular characterization. Potential benefits of using contemporary approaches, including lineage tracing, specific cell ablation, and RNA-seq for obtaining Sertoli-specific transcript markers are discussed. Evaluating the specificity and applicability of these markers at the protein level to characterize Sertoli cells in culture would be critical. This review is expected to positively impact future work using primary cultures of rodent Sertoli cells.

RNA profiling of human testicular cells identifies syntenic lncRNAs associated with spermatogenesis

STUDY QUESTION

Is the noncoding transcriptional landscape during spermatogenesis conserved between human and rodents?

SUMMARY ANSWER

We identified a core group of 113 long noncoding RNAs (lncRNAs) and 20 novel genes dynamically and syntenically transcribed during spermatogenesis.

WHAT IS KNOWN ALREADY

Spermatogenesis is a complex differentiation process driven by a tightly regulated and highly specific gene expression program. Recently, several studies in various species have established that a large proportion of known lncRNAs are preferentially expressed during meiosis and spermiogenesis in a testis-specific manner.

STUDY DESIGN, SIZE, DURATION

To further investigate lncRNA expression in human spermatogenesis, we carried out a cross-species RNA profiling study using isolated testicular cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human testes were obtained from post-mortem donors (N = 8, 51 years old on average) or from prostate cancer patients with no hormonal treatment (N = 9, 80 years old on average) and only patients with full spermatogenesis were used to prepare enriched populations of spermatocytes, spermatids, Leydig cells, peritubular cells and Sertoli cells. To minimize potential biases linked to inter-patient variations, RNAs from two or three donors were pooled prior to RNA-sequencing (paired-end, strand-specific). Resulting reads were mapped to the human genome, allowing for assembly and quantification of corresponding transcripts.

MAIN RESULTS AND THE ROLE OF CHANCE

Our RNA-sequencing analysis of pools of isolated human testicular cells enabled us to reconstruct over 25 000 transcripts. Among them we identified thousands of lncRNAs, as well as many previously unidentified genes (novel unannotated transcripts) that share many properties of lncRNAs. Of note is that although noncoding genes showed much lower synteny than protein-coding ones, a significant fraction of syntenic lncRNAs displayed conserved expression during spermatogenesis.

LARGE SCALE DATA

Raw data files (fastq) and a searchable table (.xlss) containing information on genomic features and expression data for all refined transcripts have been submitted to the NCBI Gene Expression Omnibus under accession number GSE74896.

LIMITATIONS, REASONS FOR CAUTION

Isolation procedures may alter the physiological state of testicular cells, especially for somatic cells, leading to substantial changes at the transcriptome level. We therefore cross-validated our findings with three previously published transcriptomic analyses of human spermatogenesis. Despite the use of stringent filtration criteria, i.e. expression cut-off of at least three fragments per kilobase of exon model per million reads mapped, fold-change of at least three and false discovery rate adjusted P-values of less than <1%, the possibility of assembly artifacts and false-positive transcripts cannot be fully ruled out.

WIDER IMPLICATIONS OF THE FINDINGS

For the first time, this study has led to the identification of a large number of conserved germline-associated lncRNAs that are potentially important for spermatogenesis and sexual reproduction. In addition to further substantiating the basis of the human testicular physiology, our study provides new candidate genes for male infertility of genetic origin. This is likely to be relevant for identifying interesting diagnostic and prognostic biomarkers and also potential novel therapeutic targets for male contraception.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by l'Institut national de la santé et de la recherche médicale (Inserm); l'Université de Rennes 1; l'Ecole des hautes études en santé publique (EHESP); INERIS-STORM to B.J. [N 10028NN]; Rennes Métropole 'Défis scientifiques émergents' to F.C (2011) and A.D.R (2013). The authors have no competing financial interests.

Follicle-stimulating Hormone (FSH) Action on Spermatogenesis: A Focus on Physiological and Therapeutic Roles

BACKGROUND

Human reproduction is regulated by the combined action of the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) on the gonads. Although FSH is largely used in female reproduction, in particular in women attending assisted reproductive techniques to stimulate multi-follicular growth, its efficacy in men with idiopathic infertility is not clearly demonstrated. Indeed, whether FSH administration improves fertility in patients with hypogonadotropic hypogonadism, the therapeutic benefit in men presenting alterations in sperm production despite normal FSH serum levels is still unclear. In the present review, we evaluate the potential pharmacological benefits of FSH administration in clinical practice.

METHODS

This is a narrative review, describing the FSH physiological role in spermatogenesis and its potential therapeutic action in men.

RESULTS

The FSH role on male fertility is reviewed starting from the physiological control of spermatogenesis, throughout its mechanism of action in Sertoli cells, the genetic regulation of its action on spermatogenesis, until the therapeutic options available to improve sperm production.

CONCLUSION

FSH administration in infertile men has potential benefits, although its action should be considered by evaluating its synergic action with testosterone, and well-controlled, powerful trials are required. Prospective studies and new compounds could be developed in the near future.

Discovery of a Vertebrate-Specific Factor that Processes Flagellar Glycolytic Enolase during Motile Ciliogenesis

Motile cilia and flagella require ATP for their formation and function. Although glycolytic enzymes are components of flagellar proteomes, how they translocate to flagella is unknown. Here we show that the expression pattern of the functionally nonannotated gene 4833427G06Rik (C11orf88), which is found only in vertebrates and is designated here as Hoatzin (Hoatz), suggests a functional association of its product with motile cilia and flagella. Hoatz knockout (KO) mice developed hydrocephalus and male infertility in an autosomal recessive manner, and the ependymal cilia frequently showed disorganized axonemes, reducing motility associated with collapsed spermatid flagella during cytodifferentiation. HOATZ was associated with certain proteins, including the flagellar glycolytic enzyme ENO4. In the testes of the Hoatz KO mice, the immature form of ENO4 accumulated in abnormal cytoplasmic puncta of developing spermatids. These data indicate that HOATZ is required for motile ciliogenesis and flagellar genesis in vertebrates by mediating the maturation of ENO4.

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Knockout of Hoatz causes hydrocephalus and oligo-astheno-terato-zoospermia

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Motile cilia are variably affected by the Hoatz mutation depending on tissue type

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Candidate HOATZ-interacting proteins including ENO4 are identified

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Knockout of Hoatz alters the western blot profile of ENO4

Characterisation and localisation of the endocannabinoid system components in the adult human testis

Heavy use of cannabis (marijuana) has been associated with decreased semen quality, which may reflect disruption of the endocannabinoid system (ECS) in the male reproductive tract by exogenous cannabinoids. Components of ECS have been previously described in human spermatozoa and in the rodent testis but there is little information on the ECS expression within the human testis. In this study we characterised the main components of the ECS by immunohistochemistry (IHC) on archived testis tissue samples from 15 patients, and by in silico analysis of existing transcriptome datasets from testicular cell populations. The presence of 2-arachidonoylglycerol (2-AG) in the human testis was confirmed by matrix-assisted laser desorption ionization imaging analysis. Endocannabinoid-synthesising enzymes; diacylglycerol lipase (DAGL) and N-acyl-phosphatidylethanolamine-specific phospholipase D (NAPE-PLD), were detected in germ cells and somatic cells, respectively. The cannabinoid receptors, CNR1 and CNR2 were detected at a low level in post-meiotic germ cells and Leydig- and peritubular cells. Different transcripts encoding distinct receptor isoforms (CB1, CB1A, CB1B and CB2A) were also differentially distributed, mainly in germ cells. The cannabinoid-metabolising enzymes were abundantly present; the α/β-hydrolase domain-containing protein 2 (ABHD2) in all germ cell types, except early spermatocytes, the monoacylglycerol lipase (MGLL) in Sertoli cells, and the fatty acid amide hydrolase (FAAH) in late spermatocytes and post-meiotic germ cells. Our findings are consistent with a direct involvement of the ECS in regulation of human testicular physiology, including spermatogenesis and Leydig cell function. The study provides new evidence supporting observations that recreational cannabis can have possible deleterious effects on human testicular function.

Retinoblastoma protein represses E2F3 to maintain Sertoli cell quiescence in mouse testis

Maintenance of the differentiated state and cell cycle exit in adult Sertoli cells depends on tumor suppressor retinoblastoma protein (RB, also known as RB1). We have previously shown that RB interacts with transcription factor E2F3 in the mouse testis. Here, we investigated how E2f3 contributes to adult Sertoli cell proliferation in a mouse model of Sertoli cell-specific knockout of Rb by crossing these mice with an E2f3 knockout mouse line. In the presence of intact RB, E2f3 was redundant in Sertoli cells. However, in the absence of RB, E2f3 is a key driver for cell cycle re-entry and loss of function in adult Sertoli cells. Knockout of E2f3 in Sertoli cells rescued the breakdown of Sertoli cell function associated with Rb loss, prevented proliferation of adult Sertoli cells and restored fertility of the mice. In summary, our results show that RB-mediated repression of E2F3 is critical for the maintenance of cell cycle exit and terminal differentiation in adult mouse Sertoli cells.

The roles of retinoic acid in the differentiation of spermatogonia and spermatogenic disorders

Male fertility depends on the regulatory balance between germ cell self-renewal and differentiation, and the spatial and temporal patterns of this balance must be maintained throughout the life cycle. Retinoic acid and its receptors are important factors in spermatogenesis. Spermatogonia cells can self-proliferate and differentiate and have unique meiotic capabilities; they halve their genetic material and produce monomorphic sperm to pass genetic material to the next generation. A number of studies have found that the spermatogenesis process is halted in animals with vitamin A deficiency and that most germ cells are degraded, but they tend to recover after treatment with RA or vitamin A. This literature review discusses our understanding of how RA regulates sperm cell differentiation and meiosis and also reviews the functional information and details of RA.