CELL-CYCLE PROGRESSION IN THE DEVELOPING DROSOPHILA EYE - ROUGHEX ENCODES A NOVEL PROTEIN REQUIRED FOR THE ESTABLISHMENT OF G1

The onset of pattern formation in the developing Drosophila eye is mar ked by the simultaneous synchronization of all cells in the G1 phase o f the cell cycle. These cells will then either commit to another round of cell division or differentiate into neurons. Although cell cycle s ynchronization occurs in rougher (rux) mutants, cells circumvent G1 an d all cells enter S phase, including cells that would normally differe ntiate. This leads to defects in early steps of pattern formation and cell fate determination. rux is suppressed by mutations in genes that promote cell cycle progression (i.e., cyclin A and string) and enhance d by mutations in genes that promote differentiation (i.e., Ras1 and S tar). rux encodes a novel protein of 335 amino acids. We propose that rux functions as a negative regulator of G1 progression in the develop ing eye.