Project description:In mammals, female, but not male, germ cells onset meiosis physiologically during embryonic stages. We examined whether germ cell-specific disruption of Max gene leads to the activation of meiosis-related genes in embryonic male germ cells by single cell RNA sequencing.
Project description:Meiosis is a specialized type of cell division that occurs physiologically only in germ cells. We previously demonstrated that MYC-associated factor X (MAX) blocks the ectopic onset of meiosis in embryonic and germline stem cells in culture systems. Here, we investigated the Max gene's role in mouse primordial germ cells. Although Max is generally ubiquitously expressed, we revealed that sexually undifferentiated male and female germ cells had abundant MAX protein because of their higher Max gene expression than somatic cells. Moreover, our data revealed that this high MAX protein level in female germ cells declined significantly around physiological meiotic onset. Max disruption in sexually undifferentiated germ cells led to ectopic and precocious expression of meiosis-related genes, including Meiosin, the gatekeeper of meiotic onset, in both male and female germ cells. However, Max-null male and female germ cells did not complete the entire meiotic process, but stalled during its early stages and were eventually eliminated by apoptosis. Additionally, our meta-analyses identified a regulatory region that supports the high Max expression in sexually undifferentiated male and female germ cells. These results indicate the strong connection between the Max gene and physiological onset of meiosis in vivo through dynamic alteration of its expression.
Project description:The switch from mitosis to meiosis is a major transition that takes place during germ cell development. The precise sequence and the different gene expression programs activated during this process are only partly known. Here, we applied single-cell mRNA sequencing to interrogate the transcriptional changes that occur during the early steps of male germ cell differentiation. We isolated single cells from testes using a Dazl-GFP reporter mouse, which allowed us to focus on germ cells undergoing the mitotic to meiotic transition. We identified 4 distinct meiotic stages with unique transcriptome profiles and reconstructed the timeline of the meiotic entry in silico, from spermatogonia up to the pachytene stage, identifying transcriptional changes with an unprecedented resolution. This allowed us to characterize 3 major transitions in the meiotic prophase 1 of the male germline: meiotic entry, the meiotic sex chromosome inactivation (MSCI), and concomitant pachytene transcriptional activation. Meiotic entry is initiated following the downregulation of a tightly connected set of pluripotency factors and accompanied by a global transcriptional silencing. In contrast, during subsequent sex chromosome inactivation at the zygotene stage, gene silencing proceeds in a defined order, related to gene function.
Project description:MAX (MYC Associated Factor X) is generally known as a mandatory partner for MYC transcription factor, which activates various genes involved in cell growth and metabolism. On the other hand, MAX, when interacting with MGA, forms the polycomb repressive complex (PRC) 1.6, one of the subtypes of PRC1, which directs the transcriptionally repressed chromatin state. Although physiological significance is not known at present, we have previously demonstrated that mouse embryonic stem cells (ESCs) bear a potential to onset meiosis, albeit not germ cells, and PRC1.6 prevent ESCs from their ectopic onset of meiosis (Suzuki et al., 2016, Nat. Commun. 7:11056 doi: 10.1038/ncomms11056). In this study, we aimed to investigate the role of Max in germ cells in vivo by performing the primordial germ cell-specific knockout of the Max gene.
Project description:Sex determination is distinct from development of other organs for its diversity among species. In zebrafish, the sex determination in juvenile stage could be hermaphroditic or gonochoristic. However, the detail mechanism is still unclear. Here in this study, we found that the transcription factor that belongs to forkhead box family, Foxl2l, is required for determination of female fate in zebrafish. Foxl2l was expressed from larva stage and became female bias in juvenile stage. The expression was restricted in pre-meiotic germ cells. Disruption of Foxl2l function by CRISPR/Cas9 system resulted in all-male phenotype in the mutant. Germ cells in foxl2l mutant were arrested in pre-meiotic stage at 21 dpf, the critical period for female meiotic entry. To further verify the downstream mechanism of Foxl2l on female sex determination, wildtype or foxl2l mutant germ cells labeled by foxl2l:egfp at 21 days post fertilization (dpf) and germ cells labeled by ziwi:egfp at 26 dpf were analyzed by RNA-seq and single-cell RNA-seq respectively
Project description:Meiotic prophase I characterized by homologous recombination and synapsis is an intricate step for spermatogenesis. This process entails extensive changes to chromatin and transcription. Recent studies have revealed that prior to prophase I, accessible chromatin bound by paused Pol II at meiotic gene promoters is essential for their timely activation during later stages of prophase I. However, the factor responsible for promoting accessible chromatin at meiotic gene promoters before entry into prophase I is unknown. Here, we discovered that NFYA expressed in pre-meiotic germ cells promotes accessible chromatin at meiotic gene promoters. Concordantly, conditional germline deletion of Nfya in male mice blocks meiotic entry. Functionally, our spatial and single-cell ATAC-seq data revealed that loss of NFYA in pre-meiotic cells disrupts accessible chromatin at meiotic gene promoters. Our study identifies a pioneer role for NFYA in facilitating permissive chromatin at meiotic gene promoters before meiosis, thereby controlling the timely activation of meiotic genetic program during later meiosis.
Project description:Meiotic prophase I characterized by homologous recombination and synapsis is an intricate step for spermatogenesis. This process entails extensive changes to chromatin and transcription. Recent studies have revealed that prior to prophase I, accessible chromatin bound by paused Pol II at meiotic gene promoters is essential for their timely activation during later stages of prophase I. However, the factor responsible for promoting accessible chromatin at meiotic gene promoters before entry into prophase I is unknown. Here, we discovered that NFYA expressed in pre-meiotic germ cells promotes accessible chromatin at meiotic gene promoters. Concordantly, conditional germline deletion of Nfya in male mice blocks meiotic entry. Functionally, our spatial and single-cell ATAC-seq data revealed that loss of NFYA in pre-meiotic cells disrupts accessible chromatin at meiotic gene promoters. Our study identifies a pioneer role for NFYA in facilitating permissive chromatin at meiotic gene promoters before meiosis, thereby controlling the timely activation of meiotic genetic program during later meiosis.
Project description:Male germ cells establish a unique heterochromatin domain, the XY-body, early in meiosis. How this domain is maintained through the end of meiosis and into post-meiotic germ cell differentiation is poorly understood. ADAD2 is a late meiotic male germ cell specific RNA binding protein, loss of which leads to post-meiotic germ cell defects. Analysis of ribosome association in Adad2 mutants revealed defective translation of Mdc1, a key regulator of XY-body formation, late in meiosis. As a result, Adad2 mutants show normal establishment but failed maintenance of the XY-body. Observed XY-body defects are concurrent with abnormal autosomal heterochromatin and ultimately lead to severely perturbed post-meiotic germ cell heterochromatin and cell death. These findings highlight the requirement of ADAD2 for Mdc1 translation, the role of MDC1 in maintaining meiotic male germ cell heterochromatin, and the importance of late meiotic heterochromatin for normal post-meiotic germ cell differentiation.
Project description:During spermatogenesis, mammalian spermatogonia undergo mitotic division, to maintain stem cell pool via self-renewal and generate differentiating progenitor cells for entry into meiotic prophase. During the perinatal stage, de novo DNA methylation occurring in pro-spermatogonia plays a key role to complete meiotic prophase and initiate meiotic division. In contrast, the role of the maintenance DNA methylation pathway for regulation of meiotic prophase, or meiotic division, in the adult is not well understood. Here, by using conditional mutants for Np95 (nuclear protein 95 kDa, also known as Uhrf1) or Dnmt1 [DNA (cytosine-5)-methyltransferase 1], two proteins that are essential for maintenance DNA methylation, we reveal that both NP95 and DNMT1 are co-expressed in spermatogonia and that these factors are necessary for meiosis in male germ cells. We found that Np95- or Dnmt1-deficient spermatocytes exhibited spermatogenic defects involving synaptic failure during meiotic prophase. In addition, assembly of pericentric heterochromatin clusters in early meiotic prophase, a phenomenon that is required for subsequent pairing of homologous chromosomes, is disrupted in Np95-deficient as well as Dnmt1-deficient spermatocytes. Based on these observations, we propose that DNA methylation established in pre-meiotic spermatogonia regulates synapsis of homologous chromosomes, and in turn quality control of male germ cells. Maintenance DNA methylation, therefore, plays a role to ensure faithful transmission of both genetic and epigenetic information to offspring.