REQUIREMENT FOR ENGRAILED AND INVECTED GENES REVEALS NOVEL REGULATORYINTERACTIONS BETWEEN ENGRAILED INVECTED, PATCHED, GOOSEBERRY AND WINGLESS DURING DROSOPHILA NEUROGENESIS/

During neurogenesis, the transmembrane protein Patched (Ptc) promotes a wingless (wg)-mediated specification of a neuronal precursor cell, N B4-2, by repressing gooseberry (gsb). In this study, novel interaction s of these genes with engrailed (en) and invected (inv) during neuroge nesis have been uncovered, While in row 4 cells Ptc represses gsb and ntg, in row 5 cells en/inv relieve Ptc repression of gsb by a non-auto nomous mechanism that does not involve hedgehog (hh). This differentia l regulation of gsb leads to the specification of NB5-3 and NB4-2 iden tities to two distinct neuroblasts. The uncoupling of the ptc-gsb regu latory circuit also enables gsb to promote Wg expression in row 5 cell s. Our results suggest that the en/inv-->ptc-->gsb-->wg pathway uncove red here and the hh-->wg are distinct pathways that function to mainta in wild-type level of Wg. Our results also indicate that Hh is not the only ligand for Ptc and similarly Ptc is not the only receptor for Hh .