Abstract
It has been proposed that imprints in uniparental mouse embryos, for some genes, can be appropriately adjusted by dosage compensation or counting mechanisms. We were interested to investigate a possible relationship between imprint expression and ploidy in pig embryos. To gain insight into this phenomenon, we compared the expression patterns of eight imprinted genes and the methylation status of IGF2/H19 DMR3 between haploid and diploid porcine parthenogenetic (PG) blastocysts. The results demonstrated that IGF2, NNAT and PEG10 did not display detectable levels of expression in haploid PG blastocysts while GRB10, H19, IGF2R, PEG1 and XIST were expressed at lower levels in haploid PG blastocysts in comparison to diploid their counterparts. These results indicate that the paternally expressed genes, with the exception of PEG1, were activated in diploid PG blastocysts, but not in haploid PG blastocysts. Moreover, the methylation status of IGF2/H19 DMR3 in haploid and diploid PG blastocysts was investigated using the COBRA assay. The results showed that the IGF2/H19 DMR3 was partially digested in diploid PG blastocysts but this region in haploid PG blastocysts remained undigested. Moreover, the observed digestion pattern in diploid PG blastocysts was somewhat different from that of the IVF blastocysts, indicating that the methylation status of this region in diploid PG blastocysts was partly altered. These findings appear to be evidence that there exists a process to adjust imprinted expression of certain genes, even in diploid PG embryos. This phenomenon may be associated with altered methylation at an imprinting control region.
