As part of a large scale mouse Expressed Sequence Tag (EST) project to identifymolecules involved in the initiation of mammalian development, a homolog of theDrosophila cornichon gene was detected 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 tochromosome 14 and two additional cornichon-related loci, possibly pseudogenes,localize to chromosomes 3 and 10, respectively. Cnih encodes an open readingframe (ORF) of 144 amino acids that is 93% homologous (68% identical) to theDrosophila protein, whereas the ORF of Cnil contains two extra polypeptideregions not found in these other proteins. Transcripts of Cnih are highlyabundant in the full grown oocyte and the ovulated unfertilized egg, while Cnilmessage is only detectable after activation of the embryonic genome at theeight-cell stage. In situ hybridization shows specific localization of Cnihtranscripts to ovarian oocytes. The lack of cytoplasmic polyadenylation of thematernally inherited Cnih transcript suggests that Cnih mRNA is translated in thefull grown oocyte before, but not after, ovulation. In Drosophila, cornichon isinvolved in the establishment of both anterior-posterior and dorso-ventralpolarity via the epidermal growth factor (EGF)-receptor signaling pathway.Finding Cnih in the mammalian oocyte opens a new perspective on the investigationof EGF-signaling in the oocyte.

To identify novel genes induced in the early stage of T-cell activation, mRNAexpression in alloactivated human lymphocytes was examined. Differentialdisplay-reverse transcription PCR analysis revealed a 207-bp cDNA fragment which was upregulated 24 h after allostimulation of a human T-cell line. Thecorresponding complete 1396 bp cDNA, named TGAM77, encodes a predicted 134 amino acid protein which shares 63% homology with the cornichon (cni) protein ofDrosophila melanogaster. Upregulation of TGAM77 mRNA in the early phase of T-cellactivation was confirmed by Northern blot and RT-PCR analysis of activated human lymphocytes. TGAM77 mRNA is expressed in a variety of human tissues with various expression levels. In analogy to cni which is involved in an epidermal growthfactor-like signaling pathway inducing cellular asymmetry in Drosophilaoogenesis, TGAM77 might function in similar signaling establishing vectorialre-localization and concentration of signaling events in T-cell activation.

Dorsoventral polarity in the egg chamber of Drosophila involves the localization of maternal gurken RNA to the dorsal side of the oocyte. The gurken protein hashomology to secreted growth factors and may bind to the torpedo/DER receptortyrosine kinase present on the adjacent follicle cells. This localized signalfrom the oocyte to the follicle cells appears to initiate a cascade of eventsleading to dorsal follicle cell differentiation, and delimiting and orienting thefuture dorsoventral axis of the embryo.