During development, neuroepithelial cells from the Drosophila optic lobe proliferate by dividing symmetrically until a proneural wave triggers a switch to asymmetric divisions that generate neuroblasts. A number of signalling pathways, such as the Notch and epidermal growth factor receptor (EGFR)–Ras pathways, have been shown to be essential for regulating the development of the Drosophila optic lobe in a tissue-autonomous manner. Ana Carmena and colleagues (p. 4873), however, investigate non-autonomous regulatory mechanisms that might modulate this process. They find that the Notch ligand Serrate is expressed in the glia and forms a complex in vivo with Notch and the PDZ protein Canoe, which are expressed in the neuroepithelium, at the interface between the glia and the neuroepithelial cells. Moreover, the Canoe–Notch–Serrate complex is required for interactions between the neuroepithelial cells and the glia during optic lobe development. The authors next show that Serrate has both tissue-autonomous and non-autonomous effects in the glia and in the neuroepithelium, activating different E(spl) Notch target genes in each tissue. Serrate activates Notch in the glia to regulate its proliferation and, by triggering Notch signalling in neuroepithelial cells, Serrate non-autonomously restricts the activation of the EGFR–Ras pathway to the transition zone between symmetric and asymmetric cell divisions. The authors therefore propose a model in which a complex between Notch and Canoe is required in the neuroepithelium to receive and transduce the Serrate signal from the glia.

• © 2013. Published by The Company of Biologists Ltd