The catenin/cadherin adhesion system is localized in synaptic junctions bordering transmitter release zones.

TLDR

Little is known about the molecular mechanisms linking pre‑ and postsynaptic membranes, but cadherin/catenin complexes are thought to be critical for synaptic junction formation and maintenance. The authors aimed to determine whether the cadherin adhesion system localizes to synapses in mouse and chick brains. They examined cadherin adhesion system localization by immunolabeling mouse and chick brain synapses. Alpha‑N and beta‑catenin, together with N‑cadherin, are broadly distributed in adult and developing synapses, forming symmetrical adhesion structures that border transmitter release sites and define a catenin‑based adherens junction subdomain.

Abstract

Molecular mechanisms linking pre- and postsynaptic membranes at the interneuronal synapses are little known. We tested the cadherin adhesion system for its localization in synapses of mouse and chick brains. We found that two classes of cadherin-associated proteins, alpha N- and beta-catenin, are broadly distributed in adult brains, colocalizing with a synaptic marker, synaptophysin. At the ultrastructural level, these proteins were localized in synaptic junctions of various types, forming a symmetrical adhesion structure. These structures sharply bordered the transmitter release sites associated with synaptic vesicles, although their segregation was less clear in certain types of synapses. N-cadherin was also localized at a similar site of synaptic junctions but in restricted brain nuclei. In developing synapses, the catenin-bearing contacts dominated their junctional structures. These findings demonstrate that interneuronal synaptic junctions comprise two subdomains, transmitter release zone and catenin-based adherens junction. The catenins localized in these junctions are likely associated with certain cadherin molecules including N-cadherin, and the cadherin/ catenin complex may play a critical role in the formation or maintenance of synaptic junctions.