phyllopod, downstream of the proneural genes, is the key component in promoting the external sensory (ES) organ formation in Drosophila. S.K. Huang , H.W. Pi , C.T Chien. Academic Sinica, Institute of Molecular Biology, Taipei, Taiwan.

   During ES organ development, phyllopod (phyl) expression is required for sensory organ precursor (SOP) formation. SOPs are lost in phyl mutants. We showed that overexpression of phyl can rescue the proneural gene achaete (ac) and scute(sc) mutant balding phenotype. Ectopic expression of sc induces phyl expression while phyl does not affect ac and sc expression. Notch (N) signaling is also involved in phyl regulation. In N mutants, phyl was strongly expressed. We identified that 3.4kb sequence upstream of phyl is sufficient to drive reporter gene expression in SOP and proneural cluster of ES organs in wing imaginal disks and pupa notum in a pattern similar to those of ac and sc expression. This 3.4kb promoter region fused with phyl cDNA can rescue phyl strong allele bristle- missing phenotype. This region contains four high affinity binding sites (E-box) for Ac and Sc and three binding sites for Senseless. We suggest that phyl expression is directly regulated by Ac, Sc and Senseless.