2023 Articles

Imprinting at the 𝘒𝘉𝘛𝘉𝘋6 locus involves species-specific maternal methylation and monoallelic expression in livestock animals

Ahn, Jinsoo; Hwang, In-Sul; Park, Mi-Ryung; Hwang, Seongsoo; Lee, Kichoon

Background
The primary differentially methylated regions (DMRs) which are maternally hypermethylated serve as imprinting control regions (ICRs) that drive monoallelic gene expression, and these ICRs have been investigated due to their implications in mammalian development. Although a subset of genes has been identified as imprinted, in-depth comparative approach needs to be developed for identification of species-specific imprinted genes. Here, we examined DNA methylation status and allelic expression at the 𝘒𝘉𝘛𝘉𝘋6 locus across species and tissues and explored potential mechanisms of imprinting.

Results
Using whole-genome bisulfite sequencing and RNA-sequencing on parthenogenetic and normal porcine embryos, we identified a maternally hypermethylated DMR between the embryos at the 𝘒𝘉𝘛𝘉𝘋6 promoter CpG island and paternal monoallelic expression of 𝘒𝘉𝘛𝘉𝘋6. Also, in analyzed domesticated mammals but not in humans, non-human primates and mice, the 𝘒𝘉𝘛𝘉𝘋6 promoter CpG islands were methylated in oocytes and/or allelically methylated in tissues, and monoallelic 𝘒𝘉𝘛𝘉𝘋6expression was observed, indicating livestock-specific imprinting. Further analysis revealed that these CpG islands were embedded within transcripts in porcine and bovine oocytes which coexisted with an active transcription mark and DNA methylation, implying the presence of transcription-dependent imprinting.

Conclusions
In this study, our comparative approach revealed an imprinted expression of the 𝘒𝘉𝘛𝘉𝘋6 gene in domesticated mammals, but not in humans, non-human primates, and mice which implicates species-specific evolution of genomic imprinting.