Asymmetric cell division in the drosophila embryonic neuroblast

Abstract

A novel coiled-coil protein, Spindle Miranda (Spim) or Drosophila CG9646 protein, was isolated from a microarray screen for potential effectors of telophase rescue in the insc mutant background. Both Spim and Insc are positively regulated by the Snail family of transcription factors. Single mutants of spim do not exhibit any defects in development or asymmetric division. Only spim insc double mutant embryos manifest abnormalities like delayed development and severe mislocalization of Mira/Pros to the mitotic spindle in mitotic metaphase NBs. These findings strongly support the existence of a genetic interaction between Spim and Insc in the NB, as Insc is specifically expressed in NBs. The genetic interaction between Spim and Insc is involved in targeting Mira/Pros to the basal cortex in mitotic NBs, possibly by stabilizing the actin cytoskeleton and interacting with Lgl and Non-muscle myosin II. The Spim-Insc genetic interaction is required for Pins expression and may also have role in cell cycle regulation and development.