IMPACT and OSBPL1A are two isoform-specific imprinted genes in bovines

Abstract

The epigenetic process of genomic imprinting results in the monoallelic expression of genes based on their parental origin. Comparative analysis of imprinted genes between species is useful for investigating the biological significance and regulatory mechanisms of genomic imprinting. Mouse Impact is an imprinted gene, but its human ortholog IMPACT escapes genomic imprinting. Hrh4 and Osbpl1a are the two nearest neighbors of the Impact located in distal and proximal regions, respectively. This study aims to assess the allelic expression of bovine IMPACT, OSBPL1A and HRH4 genes and examine the differentially methylated regions (DMRs) associated with these three genes. Based on an expressed single-nucleotide polymorphism (SNP) approach, we found that both the IMPACT and OSBPL1A genes exhibit isoform-specific monoallelic expression in bovine adult tissues. In the seven detected bovine IMPACT transcripts, only one transcript variant (X6) is monoallelically expressed in bovine adult tissues and paternally expressed in the placenta. However, no DMR was found in the promoter region of the IMPACT gene. We obtained five transcript variants (V1–V5) of the bovine OSBPL1A gene of different lengths that start transcription from distinct alternative promoters by RT–PCR. Only the longest variant V1 was found to be expressed monoallelically in bovine adult tissues and a DMR was identified in its promoter region using the bisulfite sequencing method. Thus, the DMR in OSBPL1A V1 promoter region may contribute to its isoform-specific monoallelic expression. The bovine HRH4 gene is expressed biallelically. Hypermethylation was observed in brains without HRH4 expression, while hypomethylation was found in the spleens with HRH4 expression, so and the level of DNA methylation in the promoter seemed to be related to its expression in tissues.