REQUIREMENTS FOR DE2F FUNCTION IN PROLIFERATING CELLS AND IN POSTMITOTIC DIFFERENTIATING CELLS

The transcription factor E2F is a target of the retino-blastoma tumor suppressor protein (pRB) and may mediate pRB regulation of S phase ent ry in mammalian cells, The recent identification of mutant alleles of the Drosophila E2F gene (dE2F) has shown that dE2F is required for emb ryogenesis. dE2F-mutant embryos lack a co-ordinated program of gene ex pression which accompanies S phase entry and DNA synthesis declines to levels that are barely detectable. We have investigated the role of t he dE2F gene at later stages of development, dE2F is expressed in seve ral larval tissues and is required for cell proliferation in the eye i maginal disc, Surprisingly, dE2F expression persists in post-mitotic c ells of the eye disc of third-instar larvae. The loss of dE2F function in these cells causes a novel phenotype, characterized by loss of pho toreceptors and abnormal rhabdomere cell morphology. These results sho w that dE2F is required at multiple stages of development and suggest that E2F may have an important function in post-mitotic cells in addit ion to its role during cell proliferation.