Opposites attract

The nectin family's preference for heterophilic interactions prevents one dendrite from forming an attachment to another and leads to proper wiring in the nervous system, according to Togashi et al. (page 141).

During embryonic development, neurons send out axons and dendrites. And though dendrites bump into other dendrites, only connections between axons and dendrites mature into synapses.

Cadherin and catenin proteins are found on both sides of a neuronal synapse and are required for synapse formation but do not appear to control the selective attachment between axons and dendrites. Members of the nectin subfamily of immunoglobulin proteins, however, are distributed asymmetrically at mature synapses with nectin-1 (N1) on the axonal side and nectin-3 (N3) on the dendritic side.

Looking at hippocampal neurons in culture, Togashi et al. found that N1 expression was restricted to...