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General Comment |
Hwang SY et al found a homolog of the Drosophila cornichon gene as a
mouse maternal transcript 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 loci, possibly pseudogenes, localize to
chromosomes 3 and 10, respectively. Cnih encodes an open reading frame (ORF) of 144 amino acids that
is 93% homologous (68% identical) to the Drosophila protein, whereas the ORF of Cnil contains two
extra polypeptide regions not found in these other proteins. Transcripts of Cnih are highly abundant in the
full grown oocyte and the ovulated unfertilized egg, while Cnil message is only detectable after
activation of the embryonic genome at the eight-cell stage. In situ hybridization shows specific
localization of Cnih transcripts to ovarian oocytes. The lack of cytoplasmic polyadenylation of the
maternally inherited Cnih transcript suggests that Cnih mRNA is translated in the full grown oocyte
before, but not after, ovulation. In Drosophila, cornichon is involved in the establishment of both
anterior-posterior and dorso-ventral polarity via the epidermal growth factor (EGF)-receptor signaling
pathway. Finding Cnih in the mammalian oocyte opens a new perspective on the investigation of
EGF-signaling in the oocyte.
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