THE COLD-SENSITIVE PERIOD FOR FRIZZLED IN THE DEVELOPMENT OF WING HAIR POLARITY ENDS PRIOR TO THE START OF HAIR MORPHOGENESIS

The function of the frizzled (fz) gene is essential for the developmen t of the normal pattern of hairs on the Drosophila wing. In the absenc e of fz function hairs develop, but they display an abnormal polarity. Mutations in fi result in an altered subcellular location for the ass embly of the F-actin filled prehair that becomes the adult cuticular h air. This observation led to the suggestion that fz and other tissue p olarity genes form a regulatory pathway that controls the initiation o f prehairs. We have isolated a cold-sensitive fi allele and found that the cold-sensitive period for fz in the pupal wing starts in the earl y pupae and ends prior to the first sign of prehair morphogenesis. Thi s cold-sensitive mutation is due to a missense mutation in a putative transmembrane domain. Western blot analysis shows that the accumulatio n of the mutant protein is not cold sensitive, consistent with the sup position that it is the activity of the mutant protein that is cold se nsitive. Our data argue that fi has a regulatory function in specifyin g where the prehair forms, but no role in the actual morphogenesis of the prehair.