Bazooka/Par3 cooperates with Sanpodo for the assembly of Notch signaling clusters following asymmetric division ofDrosophilasensory organ precursor cells

In multiple cell lineages, Delta-Notch signaling regulates cell fate decisions owing to unidirectional signaling between daughter cells. InDrosophilapupal sensory organ lineage, Notch regulates pIIa/pIIb fate decision at cytokinesis. Notch and Delta that localize apically and basally at the pIIa-pIIb interface, are expressed at low levels and their residence time at the plasma membrane is in the order of the minute. How Delta can effectively interact with Notch to trigger signaling from a large plasma membrane remains poorly understood. Here, we report that the signaling interface possesses a unique apicobasal polarity with Par3/Bazooka localizing in the form of nano-clusters at the apical and basal level. Notch is preferentially targeted to the pIIa-pIIb interface where it co-clusters with Bazooka and the Notch cofactor Sanpodo. Clusters whose assembly relies on Bazooka and Sanpodo activities, are also positive for Neuralized, the E3 ligase required for Delta-activity. We propose that the nano-clusters act as snap buttons at the new pIIa-pIIb interface to allow efficient intra-lineage signaling.