Complementary roles of genes regulated by two paternally methylated imprinted regions on chromosomes 7 and 12 in mouse placentation.

Imprinted genes have prominent effects on placentation; however, there is limited knowledge about the manner in which the genes controlled by two paternally methylated regions on chromosomes 7 and 12 contribute to placentation. In order to clarify the functions of these genes in mouse placentation, we examined transcription levels of the paternally methylated genes, tissue differentiation and development and the circulatory system in placentae derived from three types of bi-maternal conceptuses that contained genomes of non-growing (ng) and fully grown (fg) oocytes. The genetic backgrounds of the ng oocytes were as follows: one was derived from the wild-type (ngWT) and another from mutant mice carrying a 13 kb deletion in the H19 transcription unit including the germline-derived differentially methylated region (H19-DMR) on chromosome 7 (ngDeltach7). Another set of oocytes was derived from mutant mice carrying a 4.15 kb deletion in the intergenic germline-derived DMR (IG-DMR) on chromosome 12 (ngDeltach12). Although placental mass was lower in the ngWT/fg placentae compared with that in the WT placentae, it was recovered in the ngDeltach7/fg placentae, but not in the ngDeltach12/fg placentae. The ngDeltach7/fg placental growth improvement was associated with severe dysplasia such as an expanded spongiotrophoblast layer and a malformed labyrinthine zone. In contrast, the ngDeltach12/fg placentae retained the layer structures with expanded giant cells, but their total masses were smaller with a normal circulatory system in order. Our findings demonstrate that the genes controlled by the two paternally methylated regions, H19-DMR and IG-DMR, complementarily organize placentation.