Cell adhesion molecules CadN, DIP-α and klg regulate axon targeting and dendritic elaboration through synergistic and opposing effects.

Cell adhesion molecules (CAMs) are critical regulators of neural wiring that guide axon targeting, dendritic arborization and synaptic connections. Although individual neurons express diverse CAMs, the integrated regulatory roles of these molecules remain largely unclear. We identified three CAMs, N-Cadherin (CadN), immunoglobulin superfamily members DIP-α and Klingon (Klg), which are co-expressed in Drosophila amacrine neuron Dm12 in the visual system, exploring how they synergistically regulate the precise wiring of Dm12 neurons. Using single-cell MARCM clones and developmental time-course analyses, we showed that CadN and DIP-α cooperate in parallel pathways to promote layer-specific axon targeting and dendritic elaboration. Simultaneous loss of both CAMs yielded more severe defects of axon mistargeting and dendritic field size reduction compared to single mutants. Conversely, loss of klg triggered expansion of the dendritic field, which caused a proportional scaling of total synapse number while maintaining normal synaptic density. Both loss and overexpression of klg caused an expansion of dendritic coverage, indicating that Dm12 dendritic arborization was highly sensitive to homeostatic Klg levels. Finally, we found that dendritic expansion via klg manipulation significantly suppressed the axon mistargeting ratio of DIP-α mutants and alleviated the severity of targeting defects in CadN mutants. Furthermore, loss of either DIP-α or CadN significantly reduced the expansion of dendritic coverage in klg mutant Dm12, resulting in intermediate dendritic field sizes. In summary, our work highlighted how multiple CAMs with opposing regulatory roles functioned synergistically to fine-tune neurite morphogenesis during neural circuits assembly.