The grainy head transcription factor is essential for the function of the frizzled pathway in the Drosophila wing.

The Drosophila wing is covered by an array of distally pointing hairs. This tissue planar polarity is regulated by the frizzled pathway. We have found that the function of the grainy head transcription factor is essential for the function of the frizzled pathway. grainy head mutant cells fail to localize planar polarity proteins at either the proximal or distal sides of wing cells and produce multiple hairs of abnormal polarity. Levels of the Starry night protein are strongly reduced in grainy head mutants in both larval wing discs and pupal wings, which is sufficient to account for much of the polarity phenotype. In addition, we found that grh has frizzled pathway independent functions during the development of the adult cuticle.