Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305.
Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305
J Neurosci. 2018 May 16;38(20):4774-4790. doi: 10.1523/JNEUROSCI.0360-18.2018. Epub 2018 Apr 24.
Cerebellins are synaptic organizer molecules that bind to presynaptic neurexins and postsynaptic receptors. They are well studied in the cerebellum, but three of the four cerebellins (Cbln1, Cbln2, and Cbln4) are also broadly expressed outside of the cerebellum, suggesting that they perform general functions throughout the brain. Here, we generated male and female constitutive single (KO), double KO (dKO), and triple KO (tKO) mice of Cbln1, Cbln2, and Cbln4. We found that all constitutive cerebellin-deficient mice were viable and fertile, suggesting that cerebellins are not essential for survival. Cbln1/2 dKO mice exhibited salience-induced seizures that were aggravated in Cbln1/2/4 tKO mice, suggesting that all cerebellins contribute to brain function. As described previously, Cbln1 KO mice displayed major motor impairments that were aggravated by additional KO of Cbln2. Strikingly, the Cbln1/2 dKO did not cause alterations in synapse density in the hippocampus of young adult (1- and 2-month-old) mice, but produced a selective ∼50% decrease in hippocampal synapse density in the stratum lacunosum moleculare of the CA1 region and in the dentate gyrus of aging, 6-month-old mice. A similar decrease in excitatory synapse density was observed in the striatum and retrosplenial cortex. Behaviorally, the Cbln1 KO produced dramatic changes in motor behaviors that were partly aggravated by additional deletion of Cbln2 and/or Cbln4. Our results show that cerebellins are not essential for survival and do not contribute to initial synapse formation, but perform multiple functions throughout the brain; as a consequence, their ablation results in a delayed loss of synapses and in behavioral impairments. Cerebellins (Cbln1-4) are -synaptic cell adhesion molecules. In the cerebellum, Cbln1 functions as a bidirectional organizer of parallel fiber-Purkinje cell synapses by binding to presynaptic neurexins and postsynaptic GluRδ2. Little is known about the function of cerebellins outside of the cerebellum; therefore, the present study used single, double, and triple constitutive KO mice of Cbln1, Cbln2, and Cbln4 to analyze the overall function of cerebellins. We show that cerebellins act as important synaptic organizers in specific subsets of neurons and likely contribute to many different brain functions. We also show that cerebellins are not initially required for synapse formation, but rather for specification and long-term synapse maintenance and demonstrate that all cerebellins, not just Cbln1, contribute to brain function.
小脑肽是一种突触组织分子，与突触前神经连接蛋白和突触后受体结合。它们在小脑内研究得比较透彻，但四种小脑肽中的三种（Cbln1、Cbln2 和 Cbln4）在小脑外也广泛表达，这表明它们在大脑中具有普遍的功能。在这里，我们生成了 Cbln1、Cbln2 和 Cbln4 的雄性和雌性组成型单（KO）、双 KO（dKO）和三 KO（tKO）小鼠。我们发现所有组成型小脑肽缺陷小鼠均存活且可育，表明小脑肽不是生存所必需的。Cbln1/2 dKO 小鼠表现出显著诱导的癫痫发作，而在 Cbln1/2/4 tKO 小鼠中则加重，表明所有小脑肽都有助于大脑功能。如前所述，Cbln1 KO 小鼠表现出严重的运动障碍，而 Cbln2 的额外 KO 则加重了这种障碍。引人注目的是，Cbln1/2 dKO 小鼠在年轻成年（1-和 2 个月大）小鼠的海马体中并没有导致突触密度的改变，但在 6 个月大的衰老小鼠的 CA1 区的腔隙状分子层和齿状回中导致了约 50%的突触密度选择性减少。在纹状体和后顶叶皮层中也观察到兴奋性突触密度的类似减少。行为上，Cbln1 KO 小鼠的运动行为发生了显著变化，而 Cbln2 和/或 Cbln4 的额外缺失部分加重了这种变化。我们的结果表明，小脑肽不是生存所必需的，也不参与初始突触形成，但在整个大脑中发挥多种功能；因此，它们的缺失导致突触的延迟丢失和行为障碍。小脑肽（Cbln1-4）是 -突触细胞粘附分子。在小脑内，Cbln1 通过与突触前神经连接蛋白和突触后 GluRδ2 结合，作为平行纤维-浦肯野细胞突触的双向组织者。小脑肽在小脑外的功能知之甚少；因此，本研究使用 Cbln1、Cbln2 和 Cbln4 的单、双和三组成型 KO 小鼠来分析小脑肽的整体功能。我们表明，小脑肽在特定神经元亚群中作为重要的突触组织者发挥作用，可能有助于许多不同的大脑功能。我们还表明，小脑肽最初不是用于突触形成，而是用于特定和长期的突触维持，并表明所有小脑肽，而不仅仅是 Cbln1，都有助于大脑功能。
