Bovine DNA Methylation Imprints Are Established in an Oocyte Size-Specific Manner, Which Are Coordinated with the Expression of the DNMT3 Family Proteins1

Abstract

A subset of genes, known as imprinted genes, is present in the mammalian genome. Genomic imprinting governs the monoallelic expression of these genes, depending on whether the gene was inherited from the sperm or the egg. This parent-of-origin specific gene expression is generally dependent on the epigenetic modification, DNA methylation, and the DNA methylation status of CpG dinucleotides residing in loci known as differentially methylated regions (DMRs). The enzymatic machinery responsible for the addition of methyl (-CH(3)) groups to the cytosine residue in the CpG dinucleotides are known as DNA methyltransferases (DNMTs). Correct establishment and maintenance of methylation patterns at imprinted genes has been associated with placental function and regulation of embryonic/fetal development. Much work has been carried out on imprinted genes in mouse and human; however, little is known about the methylation dynamics in the bovine oocyte. The primary objective of the present study was to characterize the establishment of methylation at maternally imprinted genes in bovine growing oocytes and to determine if the expression of the bovine DNMTs-DNMT3A, DNMT3B, and DNMT3L-was coordinated with DNA methylation during oocyte development. To this end, a panel of maternally imprinted genes was selected (SNRPN, MEST, IGF2R, PEG10, and PLAGL1) and putative DMRs for MEST, IGF2R, PEG10, and PLAGL1 were identified within the 5' regions for each gene; the SNRPN DMR has been reported previously. Conventional bisulfite sequencing revealed that methylation marks were acquired at all five DMRs investigated in an oocyte size-dependent fashion. This was confirmed for a selection of genes using pyrosequencing analysis. Furthermore, mRNA expression and protein analysis revealed that DNMT3A, DNMT3B, and DNMT3L are also present in the bovine oocyte during its growth phase. This study demonstrates for the first time that an increase in bovine imprinted gene DMR methylation occurs during oocyte growth, as is observed in mouse.

Angelman syndrome imprinting center encodes a transcriptional promoter

“…S2). Similar to the mouse, exon 1 of the bovine SNRPN gene is hypermethylated on the maternal allele, with methylation acquisition in the oocyte being related to oocyte size (24,25). To date, no bovine SNRPN upstream exons appear in the UCSC Genome Browser, and application of 5′ RACE to bovine oocyte or hypothalamus RNA identified 5′ ends only in the vicinity of body exon 1 (Fig.…”

“…Although maintained during somatic development, differential methylation at gDMRs is erased during fetal germ-cell development, particularly as primordial germ cells complete their migration to the fetal gonad (27). In female embryos, DMR methylation first appears shortly after birth in a DNMT3A-and DNMT3L-dependent process that is tied to oocyte growth (25,28,29). How specific regions are selected for methylation in oocytes is poorly understood, but substantial recent work indicates the essential role of transcription in setting methylation imprints in the female germline.…”

DNA methylation and mRNA expression profiles in bovine oocytes derived from prepubertal and adult donors

“…This suggests that the treatment of calves with FSH and IGF1 prior to OPU renders the epigenetic status of the oocyte closer to that of the adult untreated oocyte. Recently, O'Doherty et al (2012) reported size-dependent methylation dynamics in growing bovine oocytes, possibly linking the acquisition of developmental competence with the acquisition of specific methylation.…”

DNA methylation dynamics during oocyte and embryo development and its associationwith environmental induced alterations

“…During spermatogenesis and oogenesis, epigenetic modifications are established which are required for normal embryonic progression (Bourc'his et al, 2001;Rideout et al, 2001;O'Doherty et al, 2012). Reprogramming the maternal genome, through appropriate DNA methylation of differentially methylated regions (DMRs), is central in regulating genomic imprinting (Li et al, 1993), a process in which a small cohort of genes are exclusively expressed from a single allele, according to parent-of-origin (Preece and Moore, 2000).…”