Role of the Dnmt3 family in de novo methylation of imprinted and repetitive sequences during male germ cell development in the mouse

Abstract

DNA methylation is an important epigenetic modification regulating various biological phenomena, including genomic imprinting and transposon silencing. It is known that methylation of the differentially methylated regions (DMRs) associated with paternally imprinted genes and of some repetitive elements occurs during male germ cell development in the mouse. We have performed a detailed methylation analysis of the paternally methylated DMRs (H19, Dlk1/Gtl2 and Rasgrf1), interspersed repeats [SineB1, intracisternal A particle (IAP) and Line1] and satellite repeats (major and minor) to determine the timing of this de novo methylation in male germ cells. Furthermore, we have examined the roles of the de novo methyltransferases (Dnmt3a and Dnmt3b) and related protein (Dnmt3L) in this process. We found that methylation of all DMRs and repeats occurred progressively in fetal prospermatogonia and was completed by the newborn stage. Analysis of newborn prospermatogonia from germline-specific Dnmt3a and Dnmt3b knockout mice revealed that Dnmt3a mainly methylates the H19 and Dlk1/Gtl2 DMRs and a short interspersed repeat SineB1. Both Dnmt3a and Dnmt3b were involved in the methylation of Rasgrf1 DMR and long interspersed repeats IAP and Line1. Only Dnmt3b was required for the methylation of the satellite repeats. These results indicate both common and differential target specificities of Dnmt3a and Dnmt3b in vivo. Finally, all these sequences showed moderate to severe hypomethylation in Dnmt3L-deficient prospermatogonia, indicating the critical function and broad specificity of this factor in de novo methylation.

microRNA-29b is a novel mediator of Sox2 function in the regulation of somatic cell reprogramming

“…Dnmt3a and Dnmt3b are de novo methyltransferases that are critically important for the establishment of DNA methylation patterns during cell differentiation and reprogramming [37]. Treatment with AZA facilitates iPSC induction by three factors (Oct4, Sox2, and Klf4) or only two factors (Oct4 and Klf4) [14][15][16].…”

Genomic imprinting and its relevance to congenital disease, infertility, molar pregnancy and induced pluripotent stem cell

“…[20][21][22] This enzyme forms a complex with the structurally related, germ-cell-specific cofactor Dnmt3L, which enhances the catalytic activity of Dnmt3a and is important for imprint establishment (Figure 1). 21,[23][24][25] The other de novo methyltransferase Dnmt3b is not involved, except at one particular ICR (see later). Thus, the key proteins in the imprint establishment machinery have been identified, but how they are recruited to specific targets is less clear.…”

“…So far, this is the only ICR involving the PIWI-interacting RNA pathway, and it is interesting that the involvement of Dnmt3b is also unique to this ICR. 21 At the H19 ICR, CTCFL (also known as BORIS) and a protein arginine methyltransferase Prmt7 appear to have roles in methylation imprint establishment in prospermatogonia (Figure 1). 33 CTCFL is a paralog of the insulator protein CTCF and highly expressed in the male germline.…”

Genomic imprinting and mammalian reproduction

“…DNMT3A mediates de 113" novo methylation in both male and female gametes, although in males a second 114" methyltransferase, DNMT3B, is also involved in methylation at the Rasgrf1 imprinted locus 115" (Kato et al, 2007). Furthermore, the methylation of all imprinted DMRs is dependent on 116" DNMT3L, which is non-enzymatic but plays a crucial role in methylation at imprinted loci 117" (Kaneda et al, 2004).…”