NUCLEAR-FALLOUT, A DROSOPHILA PROTEIN THAT CYCLES FROM THE CYTOPLASM TO THE CENTROSOMES, REGULATES CORTICAL MICROFILAMENT ORGANIZATION

nuclear fallout (nuf) is a maternal effect mutation that specifically disrupts the cortical syncytial divisions during Drosophila embryogene sis. We show that the nuf gene encodes a highly phosphorylated novel p rotein of 502 amino acids with C-terminal regions predicted to form co iled-coils. During prophase of the late syncytial divisions, Nuf conce ntrates at the centrosomes and is generally cytoplasmic throughout the rest of the nuclear cycle. In nuf-derived embryos, the recruitment of actin from caps to furrows during prophase is disrupted. This results in incomplete metaphase furrows specifically in regions distant from the centrosomes, The nuf mutation does not disrupt anillin or peanut r ecruitment to the metaphase furrows indicating that Nuf is not involve d in the signaling of metaphase furrow formation. These results also s uggest that anillin and peanut localization are independent of actin l ocalization to the metaphase furrows. nuf also disrupts the initial st ages of cellularization and produces disruptions in cellularization fu rrows similar to those observed in the metaphase furrows. The localiza tion of Nuf to centrosomal regions throughout cellularization suggests that it plays a similar role in the initial formation of both metapha se and cellularization furrows. A model is presented in which Nuf prov ides a functional link between centrosomes and microfilaments.