DNA methylation-mediated silencing of neuronatin (NNAT) in pig parthenogenetic fetuses

• NNAT was loss of expression in pig PA samples.
• NNAT was hypermethylated in PA fetuses.
• NNAT was hypomethylated in sperms and hypermethylated in MII oocytes, respectively.
• Promoter methylation may mediate silencing of NNAT.
• Aberrant NNAT may contribute to the defective development of pig PA fetuses.

It is generally believed that aberrant expression of imprinted genes participates in growth retardation of mammalian parthenogenesis. Neuronatin (NNAT), a paternally expressed gene, plays important roles in neuronal growth and metabolic regulation. Here we have compared the gene expression and promoter methylation pattern of NNAT between pig normally fertilized (Con) and parthenogenetic (PA) embryos. The results showed loss of NNAT expression (p < 0.001) and hypermethylation of NNAT promoter in PA samples. Additionally, partial methylation was observed in Con fetuses, while almost full methylation and unmethylation of NNAT promoter were apparent in Metaphase II (MII) oocytes and mature sperms, respectively, which identified the CpG promoter region as a putative differentially methylated region (DMR) of NNAT. The data demonstrate that promoter hypermethylation is associated with the silencing of NNAT in pig PA fetuses, which may be related to developmental failure of pig parthenogenesis at early stages.