Neurexins (Nrxns) and LAR-RPTPs (leukocyte common antigen-related protein tyrosine phosphatases) are presynaptic adhesion proteins responsible for organizing presynaptic machineries through interactions with nonoverlapping extracellular ligands. Here, we report that two members of the LAR-RPTP family, PTP and PTP, are required for the presynaptogenic activity of Nrxns. Intriguingly, Nrxn1 and PTP require distinct sets of intracellular proteins for the assembly of specific presynaptic terminals. In addition, Nrxn1α showed robust heparan sulfate (HS)-dependent, high-affinity interactions with Ig domains of PTP that were regulated by the splicing status of PTP. Furthermore, Nrxn1α WT, but not a Nrxn1α mutant lacking HS moieties (Nrxn1α HS), inhibited postsynapse-inducing activity of PTP at excitatory, but not inhibitory, synapses. Similarly, cis expression of Nrxn1α WT, but not Nrxn1α HS, suppressed the PTP-mediated maintenance of excitatory postsynaptic specializations in mouse cultured hippocampal neurons. Lastly, genetics analyses using male or female Drosophila Dlar and Dnrx mutant larvae identified epistatic interactions that control synapse formation and synaptic transmission at neuromuscular junctions. Our results suggest a novel synaptogenesis model whereby different presynaptic adhesion molecules combine with distinct regulatory codes to orchestrate specific synaptic adhesion pathways.

SIGNIFICANCE STATEMENT We provide evidence supporting the physical interactions of neurexins with leukocyte common-antigen related receptor tyrosine phosphatases (LAR-RPTPs). The availability of heparan sulfates and alternative splicing of LAR-RPTPs regulate the binding affinity of these interactions. A set of intracellular presynaptic proteins is involved in common for Nrxn- and LAR-RPTP-mediated presynaptic assembly. PTP triggers glutamatergic and GABAergic postsynaptic differentiation in an alternative splicing-dependent manner, whereas Nrxn1α induces GABAergic postsynaptic differentiation in an alternative splicing-independent manner. Strikingly, Nrxn1α inhibits the glutamatergic postsynapse-inducing activity of PTP, suggesting that PTP and Nrxn1α might control recruitment of a different pool of postsynaptic machinery. Drosophila orthologs of Nrxns and LAR-RPTPs mediate epistatic interactions in controlling synapse structure and strength at neuromuscular junctions, underscoring the physiological significance in vivo.

Neurexins（Nrxns）和LAR-RPTPs（白细胞常见抗原相关蛋白酪氨酸磷酸酶）是突触前粘附蛋白，负责通过与非重叠细胞外配体的相互作用来组织突触前机器。在这里，我们报告LAR-RPTP家族的两个成员，PTP和PTP，对于Nrxns的突触前活性是必需的。有趣的是，Nrxn1和PTP需要不同的细胞内蛋白集才能装配特定的突触前末端。此外，Nrxn1α显示出与硫酸乙酰肝素（HS）密切相关的，与PTP Ig结构域的高亲和力相互作用，该相互作用受PTP的剪接状态所调节。此外，Nrxn1αWT，但不是缺少HS部分的Nrxn1α突变体（Nrxn1αHS），在兴奋性但非抑制性突触中抑制PTP的突触后诱导活性。同样，Nrxn1αWT的顺式表达，而不是Nrxn1αHS的顺式表达，抑制了小鼠培养的海马神经元中PTP介导的兴奋性突触后特化的维持。最后，使用果蝇Dlar和Dnrx突变幼虫的雌性或果蝇的遗传学分析确定了上位性相互作用，该相互作用控制着神经肌肉接头处的突触形成和突触传递。我们的结果提出了一种新颖的突触形成模型，其中不同的突触前粘附分子与不同的调控代码结合，以编排特定的突触粘附途径。

重要性声明我们提供证据支持神经毒素与白细胞共同抗原相关受体酪氨酸磷酸酶（LAR-RPTPs）的物理相互作用。硫酸乙酰肝素的可用性和LAR-RPTP的可变剪接调节了这些相互作用的结合亲和力。Nrxn和LAR-RPTP介导的突触前组装共同涉及一组细胞内突触前蛋白质。PTP以另一种剪接依赖性方式触发谷氨酸能和GABA能突触后分化，而Nrxn1α以另一种剪接无关方式诱导GABA能突触后分化。引人注目的是，Nrxn1α抑制了PTP的谷氨酸能突触后诱导活性，这表明PTP和Nrxn1α可能控制了突触后机制池的募集。果蝇Nrxns和LAR-RPTPs的直系同源物介导上位性相互作用，控制神经肌肉接头的突触结构和强度，强调了体内的生理学意义。