Epigenetic reprogramming in the porcine germ line

Abstract

BackgroundEpigenetic reprogramming is critical for genome regulation during germ line development. Genome-wide demethylation in mouse primordial germ cells (PGC) is a unique reprogramming event essential for erasing epigenetic memory and preventing the transmission of epimutations to the next generation. In addition to DNA demethylation, PGC are subject to a major reprogramming of histone marks, and many of these changes are concurrent with a cell cycle arrest in the G2 phase. There is limited information on how well conserved these events are in mammals. Here we report on the dynamic reprogramming of DNA methylation at CpGs of imprinted loci and DNA repeats, and the global changes in H3K27me3 and H3K9me2 in the developing germ line of the domestic pig.ResultsOur results show loss of DNA methylation in PGC colonizing the genital ridges. Analysis of IGF2-H19 regulatory region showed a gradual demethylation between E22-E42. In contrast, DMR2 of IGF2R was already demethylated in male PGC by E22. In females, IGF2R demethylation was delayed until E29-31, and was de novo methylated by E42. DNA repeats were gradually demethylated from E25 to E29-31, and became de novo methylated by E42. Analysis of histone marks showed strong H3K27me3 staining in migratory PGC between E15 and E21. In contrast, H3K9me2 signal was low in PGC by E15 and completely erased by E21. Cell cycle analysis of gonadal PGC (E22-31) showed a typical pattern of cycling cells, however, migrating PGC (E17) showed an increased proportion of cells in G2.ConclusionsOur study demonstrates that epigenetic reprogramming occurs in pig migratory and gonadal PGC, and establishes the window of time for the occurrence of these events. Reprogramming of histone H3K9me2 and H3K27me3 detected between E15-E21 precedes the dynamic DNA demethylation at imprinted loci and DNA repeats between E22-E42. Our findings demonstrate that major epigenetic reprogramming in the pig germ line follows the overall dynamics shown in mice, suggesting that epigenetic reprogramming of germ cells is conserved in mammals. A better understanding of the sequential reprogramming of PGC in the pig will facilitate the derivation of embryonic germ cells in this species.

Biallelic transcription of the porcine IGF2R gene

“…This is in agreement with a previous study in pigs reporting also hypomethylation for this CpG island (named DMR1 in their study) in liver and heart of E45 embryos and E31 brains Hyldig et al (2011). This region, recently named CpG 1, was completely unmethylated on both human chromosomes (Riesewijk et al, 1996).…”

Dietary betaine supplementation to gestational sows enhances hippocampal IGF2 expression in newborn piglets with modified DNA methylation of the differentially methylated regions

“…(AY044827); the arrow above the light gray box indicates the transcription start site of H19; the white box represents the ICR containing three DMRs; open circles indicate individual CpG dinucleotides within the amplified region, b a fragment genomic structure of porcine IGF2R locus. The schematic diagram of the IGF2R construct is as described in Hyldig et al [38]. The arrow in the exon1 indicates the transcription direction of IGF2R; the white box represents the DMR.…”

“…The mRNA abundances were expressed as the fold change relative to the mean value of control group. [38], as well as the proximal promoter sequences of other genes, respectively, by real-time PCR. A pair of primers was used to amplify a fragment of FBP1 promoter absent of CpG sites.…”

Epigenetics and developmental programming of welfare and production traits in farm animals

“…The mechanisms of germline reprogramming have been characterised primarily in rodents, but studies in large mammals (i.e. human and pig) show that the overall equivalent kinetics are similar, although some of the changes occur in a more protracted manner, consistent with slower development compared with rodents (Hyldig et al 2011;Gkountela et al 2013).…”