Molecular cloning, mRNA expression and imprinting status of PEG3, NAP1L5 and PPP1R9A genes in pig

Imprinted genes are expressed monoallelically depending on their parental origin, and play important roles in the regulation of fetal growth, development, and postnatal behavior. Most genes known to be imprinted have been identified and studied in the human and the mouse. However, there are only a small number of reported imprinted genes in pigs. Therefore, identification and characterization of more imprinted genes in pigs is useful for comparative analysis of genomic imprinting across species. In this study, we cloned the porcine PEG3, NAP1L5 and PPP1R9A genes. The imprinting status of these genes was determined using sequencing directly and single nucleotide polymorphisms (SNPs) identified in individuals from reciprocal cross of Meishan and Large White pigs. Imprinting analysis was carried out in 13 different tissues (skeletal muscle, fat, pituitary gland, heart, lung, liver, kidney, spleen, stomach, small intestine, uterus, ovary and testis) from twelve 2-month-old piglets. Imprinting analysis showed that PEG3 and NAP1L5 were exclusively expressed from the paternal allele whereas PPP1R9A was biallelically expressed in all tissues tested where the genes were expressed. The study is of interest to understand the conservation of genomic imprinting among mammals at the 3 loci.