Calsyntenin-3 (Clstn3) is a postsynaptic adhesion molecule that induces presynaptic differentiation via presynaptic neurexins (Nrxns), but whether Nrxns directly bind to Clstn3 has been a matter of debate. Here, using LC–MS/MS–based protein analysis, confocal microscopy, RNAscope assays, and electrophysiological recordings, we show that β-Nrxns directly interact via their LNS domain with Clstn3 and Clstn3 cadherin domains. Expression of splice site 4 (SS4) insert–positive β-Nrxn variants, but not insert–negative variants, reversed the impaired Clstn3 synaptogenic activity observed in Nrxn-deficient neurons. Consistently, Clstn3 selectively formed complexes with SS4–positive Nrxns in vivo. Neuron-specific Clstn3 deletion caused significant reductions in number of excitatory synaptic inputs. Moreover, expression of Clstn3 cadherin domains in CA1 neurons of Clstn3 conditional knockout mice rescued structural deficits in excitatory synapses, especially within the stratum radiatum layer. Collectively, our results suggest that Clstn3 links to SS4–positive Nrxns to induce presynaptic differentiation and orchestrate excitatory synapse development in specific hippocampal neural circuits, including Schaffer collateral afferents.

中文翻译：

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Calsyntenin-3 与 α- 和 β-neurexins 相互作用，调节特定 Schaffer 侧支通路中的兴奋性突触神经支配。

Calsyntenin-3 (Clstn3) 是一种突触后粘附分子，可通过突触前神经毒素 (Nrxns) 诱导突触前分化，但 Nrxns 是否直接与 Clstn3 结合一直存在争议。在这里，使用基于 LC-MS/MS 的蛋白质分析、共聚焦显微镜、RNAscope 测定和电生理记录，我们表明 β-Nrxns 通过其 LNS 结构域与 Clstn3 和 Clstn3 钙粘蛋白结构域直接相互作用。剪接位点 4 (SS4) 插入阳性 β-Nrxn 变体（而非插入阴性变体）的表达逆转了 Nrxn 缺陷神经元中观察到的受损的 Clstn3 突触活性。一致地，Clstn3 在体内选择性地与 SS4 阳性 Nrxns 形成复合物。神经元特异性 Clstn3 缺失导致兴奋性突触输入数量显着减少。而且，Clstn3 条件敲除小鼠的 CA1 神经元中 Clstn3 钙粘蛋白结构域的表达可挽救兴奋性突触的结构缺陷，特别是在辐射层内。总的来说，我们的结果表明，Clstn3 与 SS4 阳性 Nrxns 相关，可诱导突触前分化并协调特定海马神经回路（包括 Schaffer 侧支传入）中的兴奋性突触发育。