INVESTIGATING THE ROLE OF NORA IN ASYMMETRIC DIVISION OF DROSOPHILA NEURAL STEM CELLS

Abstract

During development, neuroblasts undergo asymmetric division to give rise to a self-renewing neuroblast and a differentiating ganglion mother cell. Central to this process is atypical protein kinase C (aPKC), which mediates localized phosphorylation events to bring about cortical exclusion of cell fate determinants from the apical side of neuroblasts, facilitating their ultimate partitioning into the ganglion mother cell. Given the importance of aPKC in asymmetric division, this study aims to identify novel regulators of aPKC by a proteomic approach. Through tandem affinity purification coupled to mass spectrometry, we identified a previously uncharacterized protein, which we named Novel regulator of aPKC (Nora), as a potential aPKC-interacting partner. Here, we show that Nora forms a protein complex with aPKC in vivo, and that the two proteins are also found to interact directly in vitro. In addition, we observed co-expression of Nora and aPKC in neuroblasts, which suggests Nora can interact with and regulate aPKC in these cells. Indeed, we establish that Nora is required for proper localization and activity of aPKC, and that it promotes the basal targeting of cell fate determinant adaptor protein Miranda in an aPKC-dependent manner. Moreover, further investigation in this study reveals that the interaction of Nora with the N-terminus of aPKC is necessary for apical restriction, as well as nuclear exclusion, of aPKC in neuroblasts.