Using fly eye development as a model system the research focuses on understanding the mechanisms that regulate the cell cycle. Photoreceptor cell precursors in the eye imaginal disc differentiate in the wake of the morphogenetic furrow. The anterior to posterior movement of the furrow across the disc and the differentiation event is coupled with striking control of the cell cycle. Mitosis occurs in a random pattern ahead of the furrow, ceases within the furrow and resumes in some, but not other cells posterior to the furrow. Thus, one population of precursors makes a final division after entering the furrow while a second population is inhibited from entering the cycle in order to follow a differentiation pathway. Starting from a dominant small eye mutation, a novel eye specific cell cycle regulatory gene has been cloned. The predicted protein structure suggest that this gene is related to a yeast cell cycle inhibitor. The phenotype of mutants in the gene and its role in cell cycle inhibition are being investigated.