MAGE-B4, a binding partner of PRAMEF12, is dispensable for spermatogenesis and male fertility in mice.

Melanoma antigen (MAGE)-B4 belongs to the MAGE-B family genes, which are located on the X chromosome. The MAGE-B family genes are classified as cancer-testis antigens, as they are primarily expressed in the testis and are aberrantly expressed in most cancers. Although a no-stop mutation in MAGE-B4 causes rare X-linked azoospermia and oligozoospermia phenotype in humans, the specific function of MAGE-B4 on spermatogenesis in mice remains unclear. In this study, we identified MAGE-B4 as a binding partner of PRAME family member 12, which plays an important role in the maintenance of mouse spermatogenic lineage in juvenile testes. Additionally, we found that Mage-b4 transcripts were restricted to the testis and that Mage-b4 was specifically expressed in spermatogonia. To explore the function of MAGE-B4 in spermatogenesis, we generated a Mage-b4 knockout (KO) mouse model using CRISPR/Cas9 technology. However, we found that Mage-b4 KO males displayed normal testicular morphology and fertility. Further histological analysis revealed that all stages of spermatogenic cells were present in the seminiferous tubules of the Mage-b4 KO mice. Altogether, our data suggest that Mage-b4 is dispensable for mouse spermatogenesis and male fertility.

Transcriptome profiling of the initial segment and proximal caput of mouse epididymis.

Background: The proximal region of the mouse epididymis plays a pivotal role in sperm transport, sperm maturation, and male fertility. Several studies have focused on segment-dependent gene expression of the mouse epididymis through high-throughput sequencing without the precision of the microdissection. Methods and results: Herein, we isolated the initial segment (IS) and proximal caput (P-caput) by physical microdissection using an Lcn9-cre; Rosa26tdTomato mouse model. We defined the transcriptome changes of caput epididymis by RNA sequencing (RNA-seq), which identified 1,961 genes that were abundantly expressed in the IS and 1,739 genes that were prominently expressed in the P-caput. In addition, we found that many differentially expressed genes (DEGs) were predominantly or uniquely expressed in the epididymis and region-specific genes were highly associated with transport, secretion, sperm motility, fertilization, and male fertility. Conclusion: Thus, this study provides an RNA-seq resource to identify region-specific genes in the caput epididymis. The epididymal-selective/specific genes are potential targets for male contraception and may provide new insights into understanding segment-specific epididymal microenvironment-mediated sperm transport, maturation, and male fertility.

Epididymal DIS3 exosome ribonuclease is not necessary for mouse sperm maturation or fertility.

DIS3 is an RNA exosome associated ribonuclease that degrades a wide range of transcripts that can be essential for cell survival and development. The proximal region of the mouse epididymis (initial segment and caput) plays a pivotal role in sperm transport and maturation required for male fertility. However, whether DIS3 ribonuclease mediates RNA decay in proximal epididymides remains unclear. Herein, we established a conditional knockout mouse line by crossing a floxed Dis3 allele with Lcn9-cre mice in which the recombinase is expressed in the principal cells of initial segment as early as post-natal day 17. Morphological and histological analyses, immunofluorescence, computer-aided sperm analysis and fertility were used for functional analyses. We document that DIS3 deficiency in the initial segment had no effect on male fertility. Dis3 cKO males had normal spermatogenesis and initial segment development. In cauda epididymides of Dis3 cKO mice, sperm abundance, morphology, motility, and the frequency of acrosome exocytosis were comparable to controls. Collectively, our genetic model demonstrates that loss of DIS3 in the initial segment of the epididymis is not essential for sperm maturation, motility, or male fertility.

Sperm acrosome overgrowth and infertility in mice lacking chromosome 18 pachytene piRNA.

piRNAs are small non-coding RNAs required to maintain genome integrity and preserve RNA homeostasis during male gametogenesis. In murine adult testes, the highest levels of piRNAs are present in the pachytene stage of meiosis, but their mode of action and function remain incompletely understood. We previously reported that BTBD18 binds to 50 pachytene piRNA-producing loci. Here we show that spermatozoa in gene-edited mice lacking a BTBD18 targeted pachytene piRNA cluster on Chr18 have severe sperm head dysmorphology, poor motility, impaired acrosome exocytosis, zona pellucida penetration and are sterile. The mutant phenotype arises from aberrant formation of proacrosomal vesicles, distortion of the trans-Golgi network, and up-regulation of GOLGA2 transcripts and protein associated with acrosome dysgenesis. Collectively, our findings reveal central role of pachytene piRNAs in controlling spermiogenesis and male fertility.

scRNA-seq Profiling of Human Testes Reveals the Presence of the ACE2 Receptor, A Target for SARS-CoV-2 Infection in Spermatogonia, Leydig and Sertoli Cells.

In December 2019, a novel coronavirus (SARS-CoV-2) was identified in COVID-19 patients in Wuhan, Hubei Province, China. SARS-CoV-2 shares both high sequence similarity and the use of the same cell entry receptor, angiotensin-converting enzyme 2 (ACE2), with severe acute respiratory syndrome coronavirus (SARS-CoV). Several studies have provided bioinformatic evidence of potential routes of SARS-CoV-2 infection in respiratory, cardiovascular, digestive and urinary systems. However, whether the reproductive system is a potential target of SARS-CoV-2 infection has not yet been determined. Here, we investigate the expression pattern of ACE2 in adult human testes at the level of single-cell transcriptomes. The results indicate that ACE2 is predominantly enriched in spermatogonia and Leydig and Sertoli cells. Gene Set Enrichment Analysis (GSEA) indicates that Gene Ontology (GO) categories associated with viral reproduction and transmission are highly enriched in ACE2-positive spermatogonia, while male gamete generation related terms are downregulated. Cell-cell junction and immunity-related GO terms are increased in ACE2-positive Leydig and Sertoli cells, but mitochondria and reproduction-related GO terms are decreased. These findings provide evidence that the human testis is a potential target of SARS-CoV-2 infection, which may have significant impact on our understanding of the pathophysiology of this rapidly spreading disease.

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

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

Sertoli cell-only phenotype and scRNA-seq define PRAMEF12 as a factor essential for spermatogenesis in mice.

Spermatogonial stem cells (SSCs) have the dual capacity to self-renew and differentiate into progenitor spermatogonia that develop into mature spermatozoa. Here, we document that preferentially expressed antigen of melanoma family member 12 (PRAMEF12) plays a key role in maintenance of the spermatogenic lineage. In male mice, genetic ablation of Pramef12 arrests spermatogenesis and results in sterility which can be rescued by transgenic expression of Pramef12. Pramef12 deficiency globally decreases expression of spermatogenic-related genes, and single-cell transcriptional analysis of post-natal male germline cells identifies four spermatogonial states. In the absence of Pramef12 expression, there are fewer spermatogonial stem cells which exhibit lower expression of SSC maintenance-related genes and are defective in their ability to differentiate. The disruption of the first wave of spermatogenesis in juvenile mice results in agametic seminiferous tubules. These observations mimic a Sertoli cell-only syndrome in humans and may have translational implications for reproductive medicine.

Retinoic acid-induced CYP51 nuclear translocation promotes meiosis prophase I process and is correlated to the expression of REC8 and STAG3 in mice.

Lanosterol 14 α-demethylase (CYP51) plays a crucial role in cholesterol biosynthesis. In gamete development, CYP51 is involved in initiating meiosis resumption in oocytes through its product, meiosis activating sterol (MAS). In this study, CYP51 was observed to localize within the nucleus of germ cells undergoing meiotic prophase I. Following the addition of retinoic acid (RA) to induce meiosis or the RA receptor pan-antagonist AGN193109 to block meiosis in fetal ovaries, the translocation of CYP51 into the nucleus of oocytes was advanced or delayed, respectively. In addition, treatment with Cyp51-siRNA or RS21745, a specific CYP51 inhibitor, significantly delayed the meiotic progression of oocytes in the ovary, with most oocytes arresting at the zygotene stage, and likewise, significantly reduced perinatal primordial follicle formation. Furthermore, inhibition of CYP51 is correlated to significantly decreased expression of REC8 and STAG3, both of which are meiosis-specific cohesin subunits. To sum up, RA-induced CYP51 nuclear translocation is critical for oocytes meiotic progression, and consequently folliculogenesis, which might act through impacting the expression of meiosis-specific cohesins REC8 and STAG3.

Progesterone Receptor Membrane Component 1 Mediates Progesterone-Induced Suppression of Oocyte Meiotic Prophase I and Primordial Folliculogenesis.

Well-timed progression of primordial folliculogenesis is essential for mammalian female fertility. Progesterone (P4) inhibits primordial follicle formation under physiological conditions; however, P4 receptor that mediates this effect and its underlying mechanisms are unclear. In this study, we used an in vitro organ culture system to show that progesterone receptor membrane component 1 (PGRMC1) mediated P4-induced inhibition of oocyte meiotic prophase I and primordial follicle formation. We found that membrane-impermeable BSA-conjugated P4 inhibited primordial follicle formation similar to that by P4. Interestingly, PGRMC1 and its partner serpine1 mRNA-binding protein 1 were highly expressed in oocytes in perinatal ovaries. Inhibition or RNA interference of PGRMC1 abolished the suppressive effect of P4 on follicle formation. Furthermore, P4-PGRMC1 interaction blocked oocyte meiotic progression and decreased intra-oocyte cyclic AMP (cAMP) levels in perinatal ovaries. cAMP analog dibutyryl cAMP reversed P4-PGRMC1 interaction-induced inhibition of meiotic progression and follicle formation. Thus, our results indicated that PGRMC1 mediated P4-induced suppression of oocyte meiotic progression and primordial folliculogenesis by decreasing intra-oocyte cAMP levels.

JNK signaling regulates E-cadherin junctions in germline cysts and determines primordial follicle formation in mice.

Physiologically, the size of the primordial follicle pool determines the reproductive lifespan of female mammals, while its establishment largely depends on a process of germline cyst breakdown during the perinatal period. The mechanisms regulating this process are poorly understood. Here we demonstrate that c-Jun amino-terminal kinase (JNK) signaling is crucial for germline cyst breakdown and primordial follicle formation. JNK was specifically localized in oocytes and its activity increased as germline cyst breakdown progressed. Importantly, disruption of JNK signaling with a specific inhibitor (SP600125) or knockdown technology (Lenti-JNK-shRNAs) resulted in significantly suppressed cyst breakdown and primordial follicle formation in cultured mouse ovaries. Our results show that E-cadherin is intensely expressed in germline cysts, and that its decline is necessary for oocyte release from the cyst. However, inhibition of JNK signaling leads to aberrantly enhanced localization of E-cadherin at oocyte-oocyte contact sites. WNT4 expression is upregulated after SP600125 treatment. Additionally, similar to the effect of SP600125 treatment, WNT4 overexpression delays cyst breakdown and is accompanied by abnormal E-cadherin expression patterns. In conclusion, our results suggest that JNK signaling, which is inversely correlated with WNT4, plays an important role in perinatal germline cyst breakdown and primordial follicle formation by regulating E-cadherin junctions between oocytes in mouse ovaries.

Follistatin288 Regulates Germ Cell Cyst Breakdown and Primordial Follicle Assembly in the Mouse Ovary.

In mammals, the primordial follicle pool represents the entire reproductive potential of a female. The transforming growth factor-ß (TGF-ß) family member activin (ACT) contributes to folliculogenesis, although the exact mechanism is not known. The role of FST288, the strongest ACT-neutralizing isoform of follistatin (FST), during cyst breakdown and primordial follicle formation in the fetal mice ovary was assessed using an in vitro culture system. FST was continuously expressed in the oocytes as well as the cuboidal granulosa cells of growing follicles in perinatal mouse ovaries. Treatment with FST288 delayed germ cell nest breakdown, particularly near the periphery of the ovary, and dramatically decreased the percentage of primordial follicles. In addition, there was a dramatic decrease in proliferation of granulosa cells and somatic cell expression of Notch signaling was impaired. In conclusion, FST288 impacts germ cell nest breakdown and primordial follicle assembly by inhibiting somatic cell proliferation.

Cyclic AMP in oocytes controls meiotic prophase I and primordial folliculogenesis in the perinatal mouse ovary.

In mammalian ovaries, a fixed population of primordial follicles forms during the perinatal stage and the oocytes contained within are arrested at the dictyate stage of meiotic prophase I. In the current study, we provide evidence that the level of cyclic AMP (cAMP) in oocytes regulates oocyte meiotic prophase I and primordial folliculogenesis in the perinatal mouse ovary. Our results show that the early meiotic development of oocytes is closely correlated with increased levels of intra-oocyte cAMP. Inhibiting cAMP synthesis in fetal ovaries delayed oocyte meiotic progression and inhibited the disassembly and degradation of synaptonemal complex protein 1. In addition, inhibiting cAMP synthesis in in vitro cultured fetal ovaries prevented primordial follicle formation. Finally, using an in situ oocyte chromosome analysis approach, we found that the dictyate arrest of oocytes is essential for primordial follicle formation under physiological conditions. Taken together, these results suggest a role for cAMP in early meiotic development and primordial follicle formation in the mouse ovary.

Transforming growth factor-ß signaling participates in the maintenance of the primordial follicle pool in the mouse ovary.

Physiologically, only a few primordial follicles are activated to enter the growing follicle pool each wave. Recent studies in knock-out mice show that early follicular activation depends on signaling from the tuberous sclerosis complex, the mammalian target of rapamycin complex 1 (mTORC1), phosphatase and tensin homolog deleted on chromosome 10, and phosphatidylinositol 3-kinase (PI3K) pathways. However, the manner in which these pathways are normally regulated, and whether or not TGF-ß acts on them are poorly understood. So, this study aims to identify whether or not TGF-ß acts on the process. Ovary organ culture experiments showed that the culture of 18.5 days post-coitus (dpc) ovaries with TGF-ß1 reduced the total population of oocytes and activated follicles, accelerated oocyte growth was observed in ovaries treated with TGF-ßR1 inhibitor 2-(5-chloro-2-fluorophenyl)pteridin-4-yl]pyridin-4-yl-amine (SD208) compared with control ovaries, the down-regulation of TGF-ßR1 gene expression also activated early primordial follicle oocyte growth. We further showed that there was dramatically more proliferation of granulosa cells in SD208-treated ovaries and less proliferation in TGF-ß1-treated ovaries. Western blot and morphological analyses indicated that TGF-ß signaling manipulated primordial follicle growth through tuberous sclerosis complex/mTORC1 signaling in oocytes, and the mTORC1-specific inhibitor rapamycin could partially reverse the stimulated effect of SD208 on the oocyte growth and decreased the numbers of growing follicles. In conclusion, our results suggest that TGF-ß signaling plays an important physiological role in the maintenance of the dormant pool of primordial follicles, which functions through activation of p70 S6 kinase 1 (S6K1)/ribosomal protein S6 (rpS6) signaling in mouse ovaries.

Effect of different culture systems and 3, 5, 3'-triiodothyronine/follicle-stimulating hormone on preantral follicle development in mice.

The mechanical method to isolate preantral follicle has been reported for many years. However, the culture systems in vitro are still unstable. The aim of this study was to analyze the effect of the culture system of mice preantral follicles on the follicular development in vitro. The results showed that the 96-well plate system was the most effective method for mice follicle development in vitro (volume change: 51.71%; survival rate: 89%, at day 4). Follicle-stimulating hormone (FSH) and Thyroid hormone (TH) are important for normal follicular development and dysregulation of hormones are related with impaired follicular development. To determine the effect of hormone on preantral follicular development, we cultured follicle with hormones in the 96-well plate culture system and found that FSH significantly increased preantral follicular growth on day 4. The FSH-induced growth action was markedly enhanced by T3 although T3 was ineffective alone. We also demonstrated by QRT-PCR that T3 significantly enhanced FSH-induced up-regulation of Xiap mRNA level. Meanwhile, Bad, cell death inducer, was markedly down-regulated by the combination of hormones. Moreover, QRT-PCR results were also consistent with protein regulation which detected by Western Blotting analysis. Taken together, the findings of the present study demonstrate that 96-well plate system is an effective method for preantral follicle development in vitro. Moreover, these results provide insights on the role of thyroid hormone in increasing FSH-induced preantral follicular development, which mediated by up-regulating Xiap and down-regulating Bad.

Retinoic acid derived from the fetal ovary initiates meiosis in mouse germ cells.

Meiotic initiation of germ cells at 13.5 dpc (days post-coitus) indicates female sex determination in mice. Recent studies reveal that mesonephroi-derived retinoic acid (RA) is the key signal for induction of meiosis. However, whether the mesonephroi is dispensable for meiosis is unclear and the role of the ovary in this meiotic process remains to be clarified. This study provides data that RA derived from fetal ovaries is sufficient to induce germ cell meiosis in a fetal ovary culture system. When fetal ovaries were collected from 11.5 to 13.5 dpc fetuses, isolated and cultured in vitro, germ cells enter meiosis in the absence of mesonephroi. To exclude RA sourcing from mesonephroi, 11.5 dpc urogenital ridges (UGRs; mesonephroi and ovary complexes) were treated with diethylaminobenzaldehyde (DEAB) to block retinaldehyde dehydrogenase (RALDH) activity in the mesonephros and the ovary. Meiosis occurred when DEAB was withdrawn and the mesonephros was removed 2 days later. Furthermore, RALDH1, rather than RALDH2, serves as the major RA synthetase in UGRs from 12.5 to 15.5 dpc. DEAB treatment to the ovary alone was able to block germ cell meiotic entry. We also found that exogenously supplied RA dose-dependently reduced germ cell numbers in ovaries by accelerating the entry into meiosis. These results suggest that ovary-derived RA is responsible for meiosis initiation.

The effect of gonadotropin on glucose transport and apoptosis in rat ovary.

Although the effects of Gonadotropin on ovarian physiology have been known for many decades, its action on glucose uptake in the rat ovary remained poorly understood. Evidence also suggests that glucose uptake is mediated by a number of glucose transporter proteins (Glut). Therefore, we examined the rat ovary for the presence of Glut1-4 and blood glucose level after eCG (equine chorionic gonadotropin) and anti-eCG antiserum treatment. All of the glucose transports were present in the ovarian oocyte, granulosa cells and theca cells in different stage follicles. The expression of Glut in ovary was up-regulated by eCG, however, anti-eCG antiserum reversed eCG action. Western blot analysis also demonstrated the content of Glut1 was higher in eCG treatment group compared with anti-eCG antiserum and control group. The same tendency was shown in other glut isoforms. Moreover, there were no significant difference between the anti-eCG antiserum and control group. In additional, the level of serum glucose in eCG treatment group was significantly higher than others, which is similar with glut expression pattern. High glucose level in blood is correlated with increased expression of glucose transporter proteins in rat ovary. Meanwhile, anti-eCG antiserum increased granulosa cell apoptosis in antral follicle compared with those in eCG group. Our observations provide potential explanation for the effects of Glut on follicular development in rat ovary and a role for eCG in the regulation of ovarian glucose uptake.