Analyses of Allele Expression and DNA Methylation Status of Yak (Bos grunniens) PMM2 Gene in Tissues

Imprinted genes are closely related to mammalian development, growth and behavior. To date more than 150 imprinted genes have been identified in human and mice but only a very limited number of imprinted genes have been reported in bovine. A novel gene PMM2 was identified as paternally imprinted in cattle (Bos taurus), but little is known about its expression pattern in yak (Bos grunniens). The aim of the present study was to investigate the imprinting status as well as expression levels of PMM2 gene in yak tissues and to determine whether DNA methylation would play a role in its expression.

The exonic SNPs of yak PMM2 gene were discovered by direct sequencing of PCR amplicons from genomic DNA, by which the allelic expression was confirmed with reverse transcription PCR. Moreover, RT-qPCR was used to derive the expression levels of this gene in various tissues, and the DNA methylation status in the promoter was finally analyzed by bisulfite sequencing.

A total of four SNPs were screened out through direct sequencing of PCR amplicons in exon 9, based on these SNPs, we found that only one allele of the PMM2 gene was expressed in tissues of heart, lung, kidney, testis and muscle. Moreover, RT-qPCR revealed that the PMM2 gene was highly expressed in testis but at extremely low levels in lung. Finally, the DNA methylation status of a CpG enriched region in promoter was analyzed by using bisulfite sequencing and a hypermethylated status was found in all the tissues in 18 CpG sites, indicating that the DNA methylation modification of promoter region may not be involved in the regulation of PMM2 expression in yak. This study provides a reference for further exploring the molecular mechanisms of PMM2 gene function and imprinting in yak.