Interneurite affinity is regulated by heterophilic nectin interactions in concert with the cadherin machinery

Neurites recognize their specific partners during the formation of interneuronal connections. In hippocampal pyramidal neurons, axons attach to dendrites for their synaptogenesis, but the dendrites do not form stable contacts with each other, suggesting the presence of a mechanism to allow their selective associations. Nectin-1 (N1), an immunoglobulin domain adhesive protein, is preferentially localized in axons, and its heterophilic partner, N3, is present in both axons and dendrites; we tested their potential roles in interneurite recognition. The overexpression of N1, causing its mislocalization to dendrites, induced atypical dendrodendritic as well as excessive axodendritic associations. On the contrary, the genetic deletion of N1 loosened the contacts between axons and dendritic spines. Those actions of nectins required cadherin-catenin activities, but the overexpression of cadherin itself could not accelerate neurite attachment. These results suggest that the axon-biased localization of N1 and its transinteraction with N3 in cooperation with the cadherin machinery is critical for the ordered association of axons and dendrites.