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.