The Function And Mechanism Of UHRF1 In Mouse Germ Cells Development

Part 1 The function of UHRF1 in male germ cells[Purpose] Retrotransposon silencing is critical for the maintenance of genomic integrity in the germline.DNA methylation,repressive histone marks and PIWI proteins are essential for controlling retrotransposon silencing in mammalian germline.However,it remains unknown how these repressive epigenetic pathways crosstalk to ensure retrotransposon silencing in the male germline.UHRF1 has been demonstrated to play important roles in DNA methylation and histone modifications.In this study,we aim to know UHRF1 whether plays a role in retrotransposon silencing by DNA methylation,repressive histone marks and PIWI proteins.[Methods] We construct conditional deletion of Uhrf1(Stra8-cre;Uhrf1_lox/lox)mouse model.[Results] We show that UHRF1 is responsible for retrotransposon silencing by synergizing the repressive epigenetic pathways in postnatal male germ cells.Conditional loss of Uhrf1 in postnatal germ cells causes complete male sterility,preceded by germ cells depletion in adulthood,the upregulation of retrotransposon,activation of a DNA damage response as well as hypo-methylation of global DNA.Meanwhile,a chromatin status switch from repressive H3K9me2/3 marks to active H3K4me3 marks was revealed in Uhrf1 deficient testes.Furthermore,we show that UHRF1 interplays with PRMT5,an arginine methyltransferase,to regulate the repressive histone arginine modifications?H4R3me2s and H3R2me2s?,and cooperates with PIWI proteins during spermatogenesis.[Conclusions] Collectively,UHRF1 is essential for spermatogenesis and regulates retrotransposon silencing in male germ cells and provides a molecular link among DNA methylation,histone modification and PIWI pathway in the germline.Part 2 The function of UHRF1 in female germ cell and early embryo development[Purpose] Epigenetic reprogramming is thought to be crucial for early embryo development.During the oocyte maturation,epigenetic modification changes dramatically.Early embryo development exibits active cell division and differentiation,and zygotic genome activation also occurs in this period with dynamic changes of DNA methylation and histone modifications.Therefore,investigating maternal factors that modulate epigenetic modification is of great significance to determine how the epigenetic reprogramming is performed during the transition from specialized oocytes to totipotent embryos.[Methods] Here,we explore the function of UHRF1 in oocyte and early embryo by conditional deletion of Uhrf1 in mouse dormant and growing oocytes.We generate conditional deletion of Uhrf1(Zp3-cre;Uhrf1_lox/lox and Gdf9-cre;Uhrf1_lox/lox)mouse model.[Results] UHRF1 deficiency in oocyte leads to female completely infertility.The morphology and histology of ovaries were not affected in c KO mice,and oocyte-specific deletion of Uhrf1 may not affect folliculogenesis and MII oocyte maturation.UHRF1 deficiency mediated by Zp3-cre leads to developmental arrest at morula stage and UHRF1 deficiency mediated by Gdf9-cre leads to developmental arrest at two-cell stage,accompanied by dramatic and stepwise alterations in DNA methylation and histome modifications.[Conclusions] UHRF1 is not essential for the oocyte maturation,but it exhibits its crucial roles in supporting the correct epigenetic chromatin reprogramming during early embryo development.