| Research Abstract |
We have identified argos gene through the screening of mutants affecting the development of Drosophila compound eyes.argosencodes asecreted protein with an EGF motif which acts as an inhibitor of cellular differentiation during mutiple developmental process including those of compound eye, embryonic PNS and wing vein. Genetic analyses revealed that argos diminished the signal transduction via EGF-R activation and the subsequent Ras/MAPK pathway. in the eye, Argos overexpression caused a decrease of the retinal cell number by induction of ectopic cell deaths, an opposite phenotype to that of the loss of function of argos. This "gain-of-function" phenotype was considerably suppressed by the overexpression of baculovirus P35 protein, suggesting that the inhibition of Ras/MAPK signaling by Argos activated the cell death machinery mediated by member(s) of the caspase family. Correspondingly, gain of function mutations of the genes encoding Drosophila MEK and MAPKwere shown to supress the apoptosis which was induced by the overexpression of Drosophila cell death gene, hid. To better understand the molecular mechanisms of the Argos actions, we are performing genetic screening for modifiers of the "gain-of-function" phenotype of argos (GMR-argos)to identify novel loci involved in regulation of the Ras signaling and apoptosis. Interestingly, the heterozygotes of H99 deletion, lacking three of the Drosophilacell death genes, significantly supressed the gain-of-function phenotype of argus in the eye. These results led us to propose that inhibition of Ras/MAPK-signalling by Argos can induce apoptosis at the upstream level to the activation of some of the Drosophilacell death genes, reaper, hid and grim (deleted in H99), which finally activates members of the caspase family. Here, we will also present biochemical characterizations of Argos upon the Ras/MAPK pathway by using the recombinant Argos protein and stable transformants of Drosophila S2 cells expressing Drosophila EGF-R.
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