MOUSE EMBRYOS WITH PATERNAL DUPLICATION OF AN IMPRINTED CHROMOSOME-7 REGION DIE AT MIDGESTATION AND LACK PLACENTAL SPONGIOTROPHOBLAST

Imprinted genomic regions have been defined by the production of mice with uniparental inheritance or duplication of homologous chromosome r egions, With most of the genome investigated, paternal duplication of only distal chromosomes 7 and 12 results in the lack of offspring, and prenatal lethality is presumed, Aberrant expression of imprinted gene s in these two autosomal regions is therefore strongly implicated in t he periimplantation lethality of androgenetic embryos. We report that mouse embryos with paternal duplication of distal chromosome 7 (PatDup .d7) die at midgestation and lack placental spongiotrophoblast, Thus, the much earlier death of androgenones must involve paternal duplicati on of other autosomal regions, acting independently of or synergistica lly with PatDup.d7. The phenotype observed is similar, if not identica l to, that resulting from mutation of the imprinted distal chromosome 7 gene, Mash2, which in normal midgestation embryos exhibits spongiotr ophoblast-specific maternally active/paternally inactive (m(+)/p(-)) a llelic expression, Thus, the simplest explanation for the PatDup.d7 ph enotype is p(-)/p(-) expression of this gene. We also confirm that Pat Dup.d7 embryos lack H19 RNA and possess excess Igf2 RNA as might be ex pected from the parental-specific activities of these genes in normal embryos.