Impact of FecB Mutation on Ovarian DNA Methylome in Small-Tail Han Sheep

Booroola fecundity (FecB) gene, a mutant of bone morphogenetic protein 1B (BMPR-1B) that was discovered in Booroola Merino, was the first prolificacy gene identified in sheep related to increased ovulation rate and litter size. The mechanism of FecB impact on reproduction is unclear. Methods: In this study, adult Han ewes with homozygous FecB(B)/FecB(B) mutations (Han BB group) and ewes with FecB(+)/FecB(+) wildtype (Han ++ group) were selected. Methylated DNA immunoprecipitation and high-throughput sequencing (MeDIP-seq) was used to identify differences in methylated genes in ovary tissue. Results: We examined differences in DNA methylation patterns between HanBB and Han ++ sheep. In both sheep, methylated reads were mainly distributed at the gene body regions, CpG islands and introns. The differentially methylated genes were enriched in neurotrophy in signaling pathway, Gonadotropin Releasing Hormone (GnRH) signaling pathway, Wnt signaling pathway, oocyte meiosis, vascular endothelial growth factor (VEGF) signaling pathway, etc. Differentially-methylated genes were co-analyzed with differentially-expressed mRNAs. Several genes which could be associated with female reproduction were identified, such as FOXP3 (forkhead box P3), TMEFF2 (Transmembrane Protein with EGF Like and Two Follistatin Like Domains 2) and ADAT2 (Adenosine Deaminase TRNA Specific 2). Conclusions: We constructed a MeDIP-seq based methylomic study to investigate the ovarian DNA methylation differences between Small-Tail Han sheep with homozygous FecB mutant and wildtype, and successfully identified FecB gene-associated differentially-methylated genes. This study has provided information with which to understand the mechanisms of FecB gene-induced hyperprolificacy in sheep.