The COPG2, DCN, and SDHD genes are biallelically expressed in cattle

Imprinted genes are preferentially expressed from either the maternally inherited allele or the paternally inherited allele. Most genes known to be imprinted have been identified and studied in the human and the mouse. There is only a small number of reported imprinted genes in cattle, which is probably because of the limited sequence and polymorphism information available for bovine genes. To study the imprinting status of cattle genes and assess their conservation among mammalian species, the expression patterns of COPG2, DCN, and SDHD genes were examined in a total of 128 fetal and adult tissues. Two single nucleotide polymorphisms (SNPs) were identified in COPG2, three SNPs in DCN, and one SNP in SDHD. These polymorphisms were used to distinguish between monoallelic and biallelic expression using a primer extension method and a sequencing-based approach. In all 128 tissues, COPG2, DCN, and SDHD transcripts showed biallelic expression. Other cattle genes examined to date have been found to be imprinted like their known counterparts in human and mouse. This is the first report of genes that are not imprinted in cattle while the corresponding genes in human or mouse are imprinted. Lack of conservation of imprinting among mammals suggests important biological, developmental, and regulatory consequences.