MULTIPLE FUNCTIONS OF THE EGF RECEPTOR IN DROSOPHILA EYE DEVELOPMENT

Background: During animal development, cells need to make spatially an d temporally regulated fate decisions. These decisions are largely con trolled by intercellular signalling, often through receptor tyrosine k inases, One of these, the epidermal growth factor receptor (EGFR), reg ulates multiple cell fate decisions. Its importance in the recruitment of photoreceptors in the developing fly eye, a useful model for neura l development, has already been reported. Other EGFR functions in the eye have not been characterised. Results: We have examined the consequ ences of removing or activating the EGFR at different stages of eye de velopment. The earliest stages of assembly occurred normally within EG FR(-) clones - the morphogenetic furrow was unimpeded and the R8 photo receptor was specified, All subsequent photoreceptor recruitment was b locked, EGFR- clones had a characteristic shape indicating that they h ad undergone substantial cell death posterior to the furrow, where the differentiation program is normally activated; consistent with this, excess apoptosis was detected. We found that the receptor also regulat es cell proliferation in the disc, has an early function at the disc m argin (where the morphogenetic furrow initiates) and contributes to th e regulation of spacing of the R8 precursors. Finally, we found that a ctivation of the receptor is sufficient to trigger non-R8 photorecepto r development, even in cells in front of the furrow or in the absence of the proneural gene atonal. Conclusion: Al: least five distinct func tions of EGFR signalling need to be integrated during fly eye developm ent. These include roles in cell proliferation, survival and different iation.