The dominant mutation glazed is a gain-of-function allele of wingless that, similar to loss of APC, interferes with normal eye development

Dominant mutations have served as invaluable tools for Drosophila geneticis ts. Here we analyze the dominant eye mutation Glazed (Gla) that was describ ed by T. H. Morgan more than 50 years ago. We show that Gla causes the loss of photoreceptor cells during pupal stages, in a process reminiscent of ap optosis, with a concomitant overproduction of eye pigment. This phenotype i s very similar to that caused by the loss of D-APC, a negative regulator of Wingless (Wg) signal transduction. Genetic analyses reveal however that th e Gla gain-of-function phenotype can be reverted to wild-type. By generatin g a P-element-induced revertant of Gla we demonstrate that Gla is allelic t o wg. The molecular lesion in Gla indicates that the insertion of a roo ret rotransposon leads to ectopic expression of wg during pupal stages. We show that the Gla phenotype is similar to that caused by ectopic expression of Wg driven by the sevenless (sev) enhancer. In both cases Wg exerts its effe ct, at least in part, by negatively regulating the expression of the Pax2 h omolog sparkling (spa). Gla represents not only the first dominant allele o f wg, but it may also be the first allele ever described for wg. (C) 1999 A cademic Press.