Short Communication: The AIRN lncRNA is imprinted and paternally expressed in pigs

Genomic imprinting plays critical roles during the development of mammalian species and underlying epigenetic mechanisms frequently involve long non-coding RNAs (lncRNAs). The paternal transcription of the antisense Igf2r RNA noncoding (Airn) is responsible for paternal silencing of the mouse insulin-like growth factor 2 receptor (Igf2r) gene and maternal Igf2r expression. Although the corresponding maternal DNA methylation imprint is conserved in humans and pigs, the orthologous AIRN lncRNA has been identified in humans but not in pigs. Here, we aimed to examine imprinted allelic expression of the porcine AIRN lncRNA along with a corresponding differentially methylated region (DMR) and to analyze allelic expression of AIRN and IGF2R in pigs. By comparing parthenogenetic and control porcine embryos, we identified a maternally methylated DMR and a significantly higher expression of AIRN lncRNA in control embryos (P < 0.05) indicating its paternal expression. Further analyses revealed that the expression of AIRN lncRNA was enriched in the pig brain and its subregions, and it was monoallelically expressed; whereas, IGF2R was expressed biallelically suggesting an absence of allele-specific transcriptional regulation. Our findings will lead to further investigations into the role of the imprinted porcine AIRN lncRNA during pig development.Genomic imprinting is important for the development of mammals and long non-coding RNAs are often involved in the imprinting process. In mice, Airn encodes a long non-coding RNA that is imprinted, and therefore, transcribed only from the paternal allele. This paternal transcription of Airn interferes with the adjacent Igf2r promoter, leading to maternal expression of Igf2r. In pigs, the orthologous AIRN has not been identified as well as its imprinting. In the current study, we report porcine AIRN and allelic expression of both AIRN and IGF2R using our parthenogenetic embryo models and various normal pig tissues.