Yy1 gene dosage effect and bi-allelic expression of Peg3

In the current study, we tested the in vivo effects of Yy1 gene dosage on the Peg3 imprinted domain with various breeding schemes utilizing two sets of mutant alleles. The results indicated that a half dosage of Yy1 coincides with the up-regulation of Peg3 and Zim1, suggesting a repressor role of Yy1 in this imprinted domain. This repressor role of Yy1 is consistent with the observations derived from previous in vitro studies. The current study also provided an unexpected observation that the maternal allele of Peg3 is also normally expressed, and thus the expression of Peg3 is bi-allelic in the specific areas of the brain, including the choroid plexus, the PVN (Paraventricular Nucleus) and the SON (Supraoptic Nucleus) of the hypothalamus. The exact roles of the maternal allele of Peg3 in these cell types are currently unknown, but this new finding confirms the previous prediction that the maternal allele may be functional in specific cell types based on the lethality associated with the homozygotes for several mutant alleles of the Peg3 locus. Overall, these results confirm the repressor role of Yy1 in the Peg3 domain and also provide a new insight regarding the bi-allelic expression of Peg3 in mouse brain.