DIFFERENTIAL-EFFECTS OF EGF RECEPTOR SIGNALING ON NEUROBLAST LINEAGESALONG THE DORSOVENTRAL AXIS OF THE DROSOPHILA CNS

The Drosophila ventral nerve cord derives from a stereotype population of about 30 neural stem cells, the neuroblasts, per hemineuromere. Pr evious experiments provided indications for inductive signals at ventr al sites of the neuroectoderm that confer neuroblast identities. Using cell lineage analysis, molecular markers and cell transplantation, me show here that EGF receptor signalling plays an instructive role in C NS patterning and exerts differential effects on dorsoventral subpopul ations of neuroblasts, The Drosophila EGF receptor (DER) is capable of cell autonomously specifiying medial and intermediate neuroblast cell fates. DER signalling appears to be most critical for proper developm ent of intermediate neuroblasts and less important for medial neurobla sts, It is not required for lateral neuroblast lineages or for cells t o adopt CNS midline cell fate, Thus, dorsoventral patterning of the CN S involves both DER-dependent and -independent regulatory pathways, Fu rthermore, we discuss the possibility that different phases of DER act ivation exist during neuroectodermal patterning with an early phase in dependent of midline-derived signals.