Cortical aPKC kinase activity distinguishes neural stem cells from progenitor cells by ensuring asymmetric segregation of Numb

► Progenitor cells revert back to form ectopic neuroblasts in lgl mutant brains. ► Lgl and aPKC together ensure asymmetric segregation of Numb in mitotic neuroblasts. ► aPKC regulates asymmetric localization of Numb via the ACBD3 binding region. ► Serines 48/52 are necessary for localization but dispensable for function of Numb. ► The ACBD3 binding region of Numb exerts neuroblast-specific suppression of Notch.