Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, Utah 84112.
Service of Genetic Medicine, Geneva University Hospitals, 1211 Geneva 14, Switzerland.
J Neurosci. 2020 Jul 8;40(28):5376-5388. doi: 10.1523/JNEUROSCI.3058-19.2020. Epub 2020 Jun 5.
Missense variants in Kirrel3 are repeatedly identified as risk factors for autism spectrum disorder and intellectual disability, but it has not been reported if or how these variants disrupt Kirrel3 function. Previously, we studied Kirrel3 loss of function using KO mice and showed that Kirrel3 is a synaptic adhesion molecule necessary to form one specific type of hippocampal synapse Here, we developed an , gain-of-function assay for Kirrel3 using neuron cultures prepared from male and female mice and rats. We find that WT Kirrel3 induces synapse formation selectively between Kirrel3-expressing neurons via homophilic, transcellular binding. We tested six disease-associated Kirrel3 missense variants and found that five attenuate this synaptogenic function. All variants tested traffic to the cell surface and localize to synapses similar to WT Kirrel3. Two tested variants lack homophilic transcellular binding, which likely accounts for their reduced synaptogenic function. Interestingly, we also identified variants that bind in trans but cannot induce synapses, indicating that Kirrel3 transcellular binding is necessary but not sufficient for its synaptogenic function. Collectively, these results suggest Kirrel3 functions as a synaptogenic, cell-recognition molecule, and this function is attenuated by missense variants associated with autism spectrum disorder and intellectual disability. Thus, we provide critical insight to the mechanism of Kirrel3 function and the consequences of missense variants associated with autism and intellectual disability. Here, we advance our understanding of mechanisms mediating target-specific synapse formation by providing evidence that Kirrel3 transcellular interactions mediate target recognition and signaling to promote synapse development. Moreover, this study tests the effects of disease-associated Kirrel3 missense variants on synapse formation, and thereby, increases understanding of the complex etiology of neurodevelopmental disorders arising from rare missense variants in synaptic genes.
错义变异在 Kirrel3 中被反复鉴定为自闭症谱系障碍和智力障碍的风险因素，但尚未报道这些变异是否以及如何破坏 Kirrel3 功能。此前，我们使用 KO 小鼠研究了 Kirrel3 的功能丧失，并表明 Kirrel3 是一种突触粘附分子，对于形成特定类型的海马突触是必需的。在这里，我们使用来自雄性和雌性小鼠和大鼠的神经元培养物开发了 Kirrel3 的功能获得性测定法。我们发现，WT Kirrel3 通过同种型、细胞间结合选择性地诱导 Kirrel3 表达神经元之间的突触形成。我们测试了六种与疾病相关的 Kirrel3 错义变异体，发现其中五种减弱了这种突触形成功能。所有测试的变异体都能够转运到细胞表面，并定位于与 WT Kirrel3 相似的突触。两种测试的变异体缺乏同种型细胞间结合，这可能是其突触形成功能减弱的原因。有趣的是，我们还鉴定了能够结合但不能诱导突触形成的变异体，表明 Kirrel3 细胞间结合对于其突触形成功能是必要的，但不是充分的。总的来说，这些结果表明 Kirrel3 作为一种突触形成、细胞识别分子发挥作用，并且与自闭症谱系障碍和智力障碍相关的错义变异体削弱了其功能。因此，我们为 Kirrel3 功能的机制以及与自闭症和智力障碍相关的错义变异体的后果提供了关键的见解。在这里，我们通过提供证据表明 Kirrel3 细胞间相互作用介导靶标识别和信号转导以促进突触发育，从而推进了对介导靶标特异性突触形成的机制的理解。此外，这项研究测试了与疾病相关的 Kirrel3 错义变异体对突触形成的影响，从而增加了对源自突触基因中罕见错义变异体的神经发育障碍的复杂病因的理解。
