Comparative genomic imprinting and expression analysis of six cattle genes

Imprinted genes are monoallelically expressed in a parent-of-origin-specific manner under epigenetic regulation. Although it is generally believed that genomic imprinting is conserved among mammalian species, there is accumulating evidence that suggests such an assumption is false. Identification of species-specific imprinted genes is necessary to understand the evolution of genomic imprinting and to elucidate mechanisms leading to allele-specific expression. In this study, we analyzed the imprinting status of the CD81, target of antiproliferation antibody 1 (TSSC4), and oxysterol-binding protein homologue 1 (OBPH1) genes clustered on bovine chromosome 29; the paternally expressed gene 10 and ankyrin repeat and suppressor of cytokine signaling box-containing protein 4 genes clustered on bovine chromosome 4; and the 5-hydroxytryptamine (serotonin) 2A receptor microdomain gene on bovine chromosome 12 using a sequencing-based approach. It was found that CD81 and OBPH1 showed biallelic expression in all cattle tissues examined, whereas TSSC4 showed monoallelic expression in placental tissues, like its mouse ortholog. Comparative expression analysis showed that the imprinting pattern of the CD81, TSSC4, and OBPH1 cluster was not conserved among mouse, human, and cattle. None of these genes were imprinted in all 3 species. The the paternally expressed gene 10 gene was imprinted in all 3 species, whereas ankyrin repeat and suppressor of cytokine signaling box-containing protein 4 gene, reported to be imprinted in mouse, was not imprinted in cattle. The the 5-hydroxytryptamine (serotonin) 2A receptor gene was not imprinted in cattle, and human imprinting data has shown conflicting results. It is more likely that imprinting in the genes examined in this study is species-specific. In addition, we studied the expression and tissue distribution of transcripts of these genes in 174 fetal and adult cattle tissues.