The transition from mitotic to meiotic cell cycles is essential for haploid gamete formation and fertility. Stimulated by retinoic acid gene 8 ( Stra8 ) is an essential gatekeeper of meiotic initiation in vertebrates; yet, the molecular role of STRA8 remains principally unknown. Here we demonstrate that STRA8 functions as a suppressor of autophagy during spermatogenesis in mice. Stra8 -deficient germ cells fail to enter meiosis and present aberrant upregulation of autophagy-lysosome genes, commensurate with autophagy activation. Biochemical assays show that ectopic expression of STRA8 alone is sufficient to inhibit both autophagy induction and maturation. Studies also revealed that, Nr1d1 , a nuclear hormone receptor gene, is upregulated in Stra8 -deficient testes and that STRA8 binds to the Nr1d1 promoter, indicating that Nr1d1 is a direct target of STRA8 transcriptional repression. In addition, it was found that NR1D1 binds to the promoter of Ulk1 , a gene essential for autophagy initiation, and that Nr1d1 is required for the upregulated Ulk1 expression in Stra8 -deficient testes. Furthermore, both genetic deletion of Nr1d1 and pharmacologic inhibition of NR1D1 by its synthetic antagonist SR8278 exhibit rescuing effects on the meiotic initiation defects observed in Stra8 -deficient male germ cells. Together, the data suggest a novel link between STRA8-mediated autophagy suppression and meiotic initiation.

The molecular machinery and chromosome structures carrying out meiosis are frequently conserved from yeast to mammals. However, signals initiating meiosis appear divergent: while nutrient restriction induces meiosis in the yeast system, retinoic acid (RA) and its target Stra8 have been shown to be necessary but not sufficient to induce meiotic initiation in mammalian germ cells. Here, we use primary culture of mouse undifferentiated spermatogonia without the support of gonadal somatic cells to show that nutrient restriction in combination with RA is sufficient to induce Stra8- and Spo11-dependent meiotic gene and chromosome programs that recapitulate the transcriptomic and cytologic features of in vivo meiosis. We demonstrate that neither nutrient restriction nor RA alone exerts these effects. Moreover, we identify a distinctive network of 11 nutrient restriction-upregulated transcription factor genes, which are associated with early meiosis in vivo and whose expression does not require RA. Our study proposes a conserved model, in which nutrient restriction induces meiotic initiation by upregulating key transcription factor genes for the meiotic gene program and provides an in vitro platform for meiotic induction that could facilitate research and haploid gamete production.

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The transition from mitotic to meiotic cell cycles is a transcriptional event that entails the activation of genes important for meiosis and requires germline-specific retinoic acid (RA) signaling target, Stra8. To identify novel transcription factors underlying mammalian meiotic initiation, we conducted integrative snATAC-seq and scRNA-seq analysis using wild-type and Stra8-deficient mouse testicular cells to map the chromatin accessibility and gene expression landscapes of normal and genetically arrested meiotic initiation. Our results identified a cluster of putative inhibitory transcription factors for meiotic initiation, which we consider meiotic inhibitors. STRA8 binds to the regulatory sequences of these meiotic inhibitors and represses their expression upon meiotic initiation. In Stra8-deficient cells that suffer meiotic initiation arrest, the chromatin accessibility of these meiotic inhibitors is increased, concurrent with their uncontrolled and sustained expression. Among these meiotic inhibitors include KLF4, MAX, and MAZ. Importantly, by analyzing the single cell transcriptomes of human testes, our data show that these putative meiotic inhibitor genes are upregulated in early germ cells from patients with spermatogenic failure. Our study suggests that proper repression of meiotic inhibitors is essential for both mouse and human spermatogenesis.

The molecular machinery of ovarian aging and female age-related pathway remain unclear. Here, we utilized single-cell RNA-seq to profile over 9815 cells from both young and old female mouse and identified age-related alterations in the female somatic microenvironment. Interestingly, by aging-related signature calculation, we examined HIF1A in mouse ovarian cell aging regulated roles which effect pathways included glycolysis, TCA, OXPHOS and fatty acid metabolism. Additionally, inactivated HIF1A, decreased glycolysis was observed. Comparison analysis reveals the aging related regulon; metabolic and nutrient absorption changes provides a comprehensive understanding of the cell-type-specific mechanisms underlying mouse ovarian aging at single-cell resolution. This study, revealing new potential candidate biomarkers for the diagnosis of aging-associated ovary pathology.