A Diaphanous and Enabled-dependent asymmetric actin cable array repositions nuclei during Drosophila oogenesis.

Abstract

Cells reposition their nuclei for diverse specialized functions through a wide variety of cytoskeletal mechanisms. During Drosophila oogenesis, 15 nurse cells connected by ring canals to each other and the oocyte contract, 'dumping' their cytoplasm into the oocyte. Prior to dumping, actin cables initiate from the nurse cell cortex and elongate toward their nuclei, pushing them away from ring canals to prevent obstruction. How the cable arrays reposition nuclei is unknown. We found that these arrays are asymmetric, with regional differences in actin cable growth rate dependent on the differential localization of the actin assembly factors Enabled and Diaphanous. Enabled mislocalization produces a uniform growth rate. In oocyte-contacting nurse cells with asymmetric cable arrays, nuclei move away from ring canals. With uniform arrays, these nuclei move toward the adjacent ring canal instead. This correlated with ring canal nuclear blockage and incomplete dumping. Our data suggest that nuclear repositioning relies on the regulated cortical localization of Diaphanous and Enabled to produce actin cable arrays with asymmetric growth that push nuclei away from ring canals, enabling successful oogenesis.