Local N-cadherin interactions mediate distinct steps in the targeting of lamina neurons

The organization of neuronal processes into a series of layers is a hallmark of many brain regions. Homophilic cell adhesion molecules of the cadherin family have been implicated in layer choice. How they contribute to the targeting of neurons to distinct layers remains unclear. Here we systematically explore the role of a classical cadherin, Drosophila N-cadherin (CadN), in the targeting of five classes of related neurons to a series of consecutive layers in the fly visual system. We show that CadN is required in lamina neurons at discrete developmental steps but not used in a layer-specific fashion. Local CadN expression patterns correlate with specific growth cone movements, and CadN expression on one growth cone in a specific layer is essential for the targeting of processes of another neuron to this layer. We propose that dynamic regulation of CadN enables this widely expressed protein to mediate specific local interactions during neural circuit assembly.