CONTROL OF G(1) IN THE DEVELOPING DROSOPHILA EYE - RCA1 REGULATES CYCLIN-A

In the developing eye of Drosophila melanogaster, cells become synchro nized in the G(1) phase of the cell cycle just prior to the onset of c ellular differentiation and morphogenesis. In rougher (rux) mutants, c ells enter S phase precociously because of ectopic activation of a Cyc lin A/Cdk complex in early G(1). This leads to defects in cell fate an d pattern formation, and results in abnormalities in the morphology of the adult eye. A screen for dominant suppressors of the rux eye pheno type led to the identification of mutations in cyclin A, string (cdc25 ), and new cell cycle genes. One of these genes, regulator of cyclin A (real), encodes a novel protein required for both mitotic and meiotic cell cycle progression. rca1 mutants arrest in G(2) of embryonic cell cycle 16 with a phenotype very similar to cyclin A loss of function m utants. Expression of real transgenes in G(1) or in postmitotic neuron s promotes Cyclin A protein accumulation and drives cells into S phase in a Cyclin A-dependent fashion.