DAUGHTERLESS IS REQUIRED FOR DROSOPHILA PHOTORECEPTOR CELL DETERMINATION, EYE MORPHOGENESIS, AND CELL-CYCLE PROGRESSION

Initiation of Drosophila peripheral nervous system (PNS) development r equires the achaete-scute complex (AS-C) and the atonal (ato) genes. T he AS-C and ato encode basic helix-loop-helix (bHLH) transcription fac tors that dimerize in vitro with another bHLH protein, daughterless (d a). da has many functions during Drosophila embryonic development, as it is required for proper sex determination, oogenesis, and neurogenes is. Here, we examine the expression and function of da within the deve loping Drosophila eye. The use of a monoclonal antibody to the Da prot ein revealed that Da levels are modulated across the developing eye di sc. Within the morphogenetic furrow (ME) and photoreceptor cell R8, th ere is a cell-by-cell correspondence between high levels of Da protein expression and Ato protein expression. Mosaic analysis of adult tissu e demonstrates that da function is cell autonomous and required within R2, R3, R4, R5, and R8. Examination of gene expression in da- imagina l disc clones reveals that da regulates Ato expression in the MF, affe cts the progression of the MF, and is necessary for the reestablishmen t of the G(2) and M phases of the synchronized cell cycle posterior to the MF. (C) 1996 Academic Press, Inc.