The mouse cornichon gene family

As part of a large scale mouse Expressed Sequence Tag (EST) project to iden tify molecules involved in the initiation of mammalian development, a homol og of the Drosophila cornichon gene was detected as a mouse maternal transc ript present in the two-cell embryo. Cornichon is a multigene family in the mouse: the new gene, Cnih, maps to mouse chromosome 10, another cornichon homolog, Cnil, maps to chromosome 14 and two additional cornichon-related l oci, possibly pseudogenes, localize to chromosomes 3 and 10, respectively. Cnih encodes an open reading frame (ORF) of 144 amino acids that is 93% hom ologous (68% identical) to the Drosophila protein, whereas the ORF of Cnil contains two extra polypeptide regions not found in these other proteins. T ranscripts of Cnih are highly abundant in the full grown oocyte and the ovu lated unfertilized egg, while Cnil message is only detectable after activat ion of the embryonic genome at the eight-cell stage. In situ hybridization shows specific localization of Cnih transcripts to ovarian oocytes. The lac k of cytoplasmic poly-adenylation of the maternally inherited Cnih transcri pt suggests chat Cnih mRNA Is translated in the full grown oocyte before, b ut not after, ovulation. In Drosophila, cornichon is involved in the establ ishment of both anterior-posterior and dorso-ventral polarity via the epide rmal growth factor (EGF)-receptor signaling pathway. Finding Cnih in the ma mmalian oocyte opens a new perspective on the investigation of EGF-signalin g in the oocyte.