Genomic imprinting of Mash2, a mouse gene required for trophoblast development

The mouse gene Mash2 encodes a transcription factor required for development of trophoblast progenitors. Mash2- homozygous mutant embryos die at 10 days post−coitum from placental failure. Here we show that Mash2 is genomically imprinted. First, Mash2+/- embryos inheriting a wild−type allele from their father die at the same stage as -/- embryos, with a similar placental phenotype. Second, the Mash2 paternal allele is initially expressed by groups of trophoblast cells at 6.5 and 7.5 days post−coitum, but appears almost completely repressed by 8.5 days post−coitum. Finally, we have genetically and physically mapped Mash2 to the distal region of chromosome 7, within a cluster of imprinted genes, including insulin−2, insulin−like growth factor−2 and H19