5-methylcytosine (m⁵C) is a post-transcriptional RNA modification identified in both stable and highly abundant tRNAs and rRNAs, and in mRNAs. However, its regulatory role in mRNA metabolism is still largely unknown. Here, we reveal that m⁵C modification is enriched in CG-rich regions and in regions immediately downstream of translation initiation sites and has conserved, tissue-specific and dynamic features across mammalian transcriptomes. Moreover, m⁵C formation in mRNAs is mainly catalyzed by the RNA methyltransferase NSUN2, and m⁵C is specifically recognized by the mRNA export adaptor ALYREF as shown by in vitro and in vivo studies. NSUN2 modulates ALYREF's nuclear-cytoplasmic shuttling, RNA-binding affinity and associated mRNA export. Dysregulation of ALYREF-mediated mRNA export upon NSUN2 depletion could be restored by reconstitution of wild-type but not methyltransferase-defective NSUN2. Our study provides comprehensive m⁵C profiles of mammalian transcriptomes and suggests an essential role for m⁵C modification in mRNA export and post-transcriptional regulation.

Epigenetics of human embryonic development: Substantial epigenetic reprogramming occurs in mammalian early development. Xia et al. investigated the reprogramming dynamics of three key histone modifications in human early embryonic development. The reprogramming in humans is highly species-specific and different than that in mice. A globally permissive chromatin state connects parental and zygotic epigenomes during maternal-to-zygotic transition. Inner-cell mass-specific, but not trophectoderm-specific, genes are asymmetrically patterned by a histone mark during early lineage segregation. Science , this issue p. 353

Background: This article aims to reveal the therapeutic effects and potential mechanisms of bone mesenchymal stem cell (BMSC)-derived exosomes on premature ovarian failure (POF). Methods: Exosomes were collected from BMSCs and were used to treat cisplatin-induced POF mouse models. Pathological changes of ovarian tissue were detected by using HE staining and by Western blot that detected the expression of apoptosis-related proteins. In cisplatin-induced primary granulosa cell injury, exosomes were co-cultured with the granulosa cells. The apoptosis or viability of granulosa cells was analyzed by flow cytometry or MTT, respectively. In Target scan and microT-CDS databases, an intersection of miRNAs targeting to p53 was found. The expressions of miRNAs in BMSC-derived exosomes were detected by qRT-PCR. Besides, miR-664-5p targeted to p53 of cells was verified by dual-luciferase reporter assay. Results: BMSC-derived exosomes improved the follicular morphology of POF mice and inhibited the expression of apoptosis-related protein. By co-culture of exosomes and primary granulosa cells, BMSC-derived exosomes repressed cisplatin-induced granulosa cells apoptosis and increased cells viability, while these effects were abrogated after the exosome-containing RNA was degraded by RNase. By Target scan, microT-CDS and qRT-PCR, miR-664-5p was regarded as the dominated RNA in BMSC-derived exosomes. By dual-luciferase reporter assay, miR-664-5p negatively regulated p53 luciferase activity. After shRNA interfering miR-664-5p of BMSC, BMSC-derived exosomes exerted no protective effect on cisplatin-induced granulosa cell apoptosis. Conclusion: Our results indicated that miR-644-5p carried by BMSC-derived exosomes inhibited the apoptosis of ovarian granulosa cell by targeting p53 of cells, suggesting that miR-644-5p had the potential to treat POF and restore ovarian function.

Context: Recently, two patients with primary ovarian insufficiency (POI) delivered healthy babies after in vitro activation (IVA) treatment followed by auto-transplantation of frozen-thawed ovarian tissues. Objective: This study sought to report the first case of live birth after IVA treatment following fresh ovarian tissue grafting in patients with POI, together with monitoring of follicle development and serum hormonal changes. Design: This was a prospective observational cohort study. Setting: We performed IVA treatment in 14 patients with POI with mean age of 29 years, mean duration since last menses of 3.8 years, and average basal FSH level of 94.5 mIU/mL. Interventions: Prior to IVA treatment, all patients received routine hormonal treatments with no follicle development. We removed one ovary from patients with POI and treated them with Akt stimulators. We improved upon early procedures by grafting back fresh tissues using a simplified protocol. Main Outcome Measures: In six of the 14 patients (43%), a total of 15 follicle development waves were detected, and four patients had successful oocyte retrieval to yield six oocytes. For two patients showing no spontaneous follicle growth, human menopausal gonadotropin treatment induced follicle growth at 6–8 months after grafting. After vitro fertilization of oocyte retrieved, four early embryos were derived. Following embryo transfer, one patient became pregnant and delivered a healthy baby boy, with three other embryos under cryopreservation. Conclusion: IVA technology can effectively activate residual follicles in some patients with POI and allow them to conceive their own genetic offspring. IVA may also be useful for treating patients with ovarian dysfunction including aging women and cancer survivors.

Our previous studies have shown that microRNA-320 (miR-320) is one of the most down-regulated microRNAs (miRNA) in mouse ovarian granulosa cells (GCs) after TGF-β1 treatment. However, the underlying mechanisms of miR-320 involved in GC function during follicular development remain unknown. In this study, we found that pregnant mare serum gonadotropin treatment resulted in the suppression of miR-320 expression in a time-dependent manner. miR-320 was mainly expressed in GCs and oocytes of mouse ovarian follicles in follicular development. Overexpression of miR-320 inhibited estradiol synthesis and proliferation of GCs through targeting E2F1 and SF-1. E2F1/SF-1 mediated miR-320-induced suppression of GC proliferation and of GC steroidogenesis. FSH down-regulated the expression of miR-320 and regulated the function of miR-320 in mouse GCs. miR-383 promoted the expression of miR-320 and enhanced miR-320-mediated suppression of GC proliferation. Injection of miR-320 into the ovaries of mice partially promoted the production of testosterone and progesterone but inhibited estradiol release in vivo. Moreover, the expression of miR-320 and miR-383 was up-regulated in the follicular fluid of polycystic ovarian syndrome patients, although the expression of E2F1 and SF-1 was down-regulated in GCs. These data demonstrated that miR-320 regulates the proliferation and steroid production by targeting E2F1 and SF-1 in the follicular development. Understanding the regulation of miRNA biogenesis and function in the follicular development will potentiate the usefulness of miRNA in the treatment of reproduction and some steroid-related disorders.