Cell size and the morphogenesis of wing hairs in Drosophila

Almost all epidermal cells on the Drosophila wing produce a single cuticula r hair. This is formed in the pupae from a microvillus-like cell projection called the prehair. Previous experiments have shown the existence of two m echanisms that ensure that only a single hair is made, One is the restricti on of prehair initiation to a small subregion of the cell by the action of the frizzled tissue polarity pathway. The second is a system that ensures t he integrity of the prehair. Mutations and drugs that inhibit the actin cyt oskeleton lead to the splitting of a single prehair into multiple smaller h airs. We report that large polyploid cells produce multiple hairs both beca use they form multiple independent prehair initiation centers and because t he larger than normal hairs these cells produce have a tendency to split. W e show that reducing cell sire by starvation partially suppresses the pheno type seen in polyploid cells and that increasing apical cell surface area b y mechanical stretching also results in the formation of multiple prehair i nitiation centers. We also show that the frizzled tissue polarity pathway i s functional in large polyploid cells even if it is unable to restrict preh air initiation to a small region of the cell, We conclude that both of thes e cellular systems are limited in their ability to scale to accommodate lar ger cell size, (C) 2000 Wiley-Liss, Inc.