Nectin-like molecules/SynCAMs are required for post-crossing commissural axon guidance

The Necl/SynCAM subgroup of immunoglobulin superfamily cell adhesion molecules has been implicated in late stages of neural circuit formation. They were shown to be sufficient for synaptogenesis by their trans-synaptic interactions. Additionally, they are involved in myelination, both in the central and the peripheral nervous system, by mediating adhesion between glia cells and axons. Here, we show that Necls/SynCAMs are also required for early stages of neural circuit formation. We demonstrate a role for Necls/SynCAMs in post-crossing commissural axon guidance in the developing spinal cord in vivo. Necl3/SynCAM2, the family member that has not been characterized functionally so far, plays a crucial role in this process. It is expressed by floorplate cells and interacts with Necls/SynCAMs expressed by commissural axons to mediate a turning response in post-crossing commissural axons.