The Study Of Epigenetic Profiling And Its Biological Implications In Mouse Female Germline Stem Cells

Because germline stem cells(GSCs)are the sources of mature male and female gametes,which play a key role in genome transmission to the next generation,it is quite necessary to understand the molecular mechanisms of regulating GSCs self-renewal and differentiation.Additionally,the studies of GSCs behavior and gametogenesis in vitro could be very important for clinical application in the field of reproductive medicine.For decades,a widely accepted view in reproductive biology is that germline stem cells exist in adult males and spermatogenesis occurs in the entire adult life.However,the production of oocyte in most female mammals is considered to cease before birth.This doctrine was challenged recent years by studies showing that a population of female germline stem cells(FGSC)exist in adult mouse,rat and human ovaries,which has been detected at cell biology,biological chemistry and molecular biology levels.However,the molecular regulation mechanisms involved in basic biological characteristics of FGSC are unclear.Cell fate determination requires the close coordination between genetic(e.g.,cis-regulatory elements promoters and enhancers)and epigenetic(e.g.,DNA methylation and histone modifications)regulations.Recent reports demonstrated that epigenetic modification play a key role in regulating gene expression and detecting regulatory sequences.FGSCs are unipotent adult stem cells that possess the ability to self-renew while remain capable of giving rise to specialized ovum.However,the underlying molecular mechanisms for the specification of FGSC are not clear.With the aim to address this question,this study performed ChIP-Seq,MethylCap-Seq and RNA-Seq to detect the profiling of histone modifications(H3K4me3,H3K27me3,H3K4me1,H3K27ac),RNA polymerase II,DNA methylation and gene expression using mouse FGSC cultured in vitro.Through comparisons to primordial germ cells(PGC)and embryonic stem cells(ESC),this work revealed that FGSC characterized with an unique chromatin signature at distal regulatory elements,which distinguishes FGSC from PGC and ESC.Gene functional annotation reveals that genes related with FGSC-specific regulatory elements are highly involved in maintaining reproductive system phenotypes.Moreover,gene expression analysis and the test of Dnmt1 knockdown showed that DNA methylation play an important role in repressing somatic programme and maintaining unipotency of FGSC by inhibiting the activities of development related genes.When compared with male germline stem cells(MGSC)this study revealed that DNA methylation is potentially involved in maintaining sexual identity of FGSC.Additionally,the results of RNA interference showed that Prmt5 and Max are implicated in FGSC identity by repressing expression of genes linked to differentiation.Together,this study reveals that the molecular chromatin signatures of FGSC play a key role in maintaining FGSC-specific biological characteristics.Moreover,this work provides resources for further analysis of generation and differentiation of FGSC and establishes a preliminary foundation for clinical application of FGSC.