The Clathrin adaptor AP-1 and the Rab-stabilizing chaperone Stratum act in two parallel pathways to control the activation of the Notch pathway in Drosophila
Drosophila sensory organ precursors divide asymmetrically to generate pIIa/pIIb cells whose identity relies on the differential activation of Notch during cytokinesis. While Notch is present apically and basally relative to the midbody at the pIIa-pIIb interface, only the basal pool of Notch is reported to contribute to Notch activation in the pIIa cell. Such proper intra-lineage signalling therefore requires appropriate apico-basal targeting of Notch, its ligand Delta and its trafficking partner Sanpodo. We previously reported that AP-1 and Stratum regulate the intracellular trafficking of Notch and Sanpodo from the trans-Golgi network to basolateral membrane. Loss of AP-1 or of Stratum caused mild Notch phenotype. Here, we report that the concomitant loss of AP-1 and Stratum result in the stabilization of the apical pool of Notch, Delta and Spdo, the loss of the basal pool of Notch at the pIIa-pIIb interface, and is associated with activation of Notch in the two SOP daughters. We propose that AP-1 and Stratum control two parallel pathways towards plasma membrane and that Notch intra-lineage signalling could also occur at the apical pIIa-pIIb interface.