Clustered Protocadherins Are Required for Building Functional Neural Circuits.
Clustered Protocadherins Are Required for Building Functional Neural Circuits.
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DOI：
10.3389/fnmol.2017.00114
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发表时间：
2017
影响因子：
4.8
通讯作者：
Yagi T
中科院分区：
文献类型：
--
作者：
Hasegawa S;Kobayashi H;Kumagai M;Nishimaru H;Tarusawa E;Kanda H;Sanbo M;Yoshimura Y;Hirabayashi M;Hirabayashi T;Yagi T
神经元的同一性是由聚集性原钙粘蛋白(PcdH)亚型在细胞表面的表达产生的。在小鼠中，来自三个基因簇Pcdhα、Pcdhβ和Pcdhγ的58个亚型在神经元中差异表达。由于细胞表面的顺式异构体Pcdh寡聚体与其他神经元中的Pcdh低聚体同源同源相互作用，所以一直认为Pcdh异构体决定突触的结合特异性。我们先前描述了所有三个Pcdh基因簇的异构体在脊髓神经元存活和突触形成中的协同作用。然而，神经元的丢失和随后的新生儿死亡阻碍了对簇状Pcdh-空(Δαβγ)神经回路的出生后发育和特征的分析。在这里，我们使用了两种方法，一种是产生将Δαβγ神经元移植到小鼠胚胎中的嵌合小鼠，另一种是产生双突变小鼠，这些小鼠同时含有Pcdh基因和促凋亡基因bax的零等位基因，以防止神经元丢失。首先，我们的结果显示，存活的Δαβγ细胞贡献较高的嵌合体小鼠出现瘫痪，并在出生后死亡。对嵌合小鼠出生后发育脑区神经元存活的分析表明，与脑干网状结构中的神经元不同，前脑中的许多Δαβγ神经元没有凋亡。第二，在Δαβγ/bax缺失双突变体中，即使在没有神经退行性变的情况下，运动中枢模式生成器也不能产生左右交替的模式。第三，培养的海马神经元的钙成像显示，Δαβγ神经元的网络活动趋于同步化，并且失去了对照网络中观察到的同时活动的神经元数量的变异性。最后，对外源引入的单个Pcdh-γA3亚型在对照神经元和Δαβγ神经元之间的跨同亲性相互作用进行了比较分析，结果表明，异构体特异性的跨同亲性相互作用需要在相互作用的神经元之间的接触部位表达的同型异构体完全匹配。这些结果表明，聚集性PcdH亚型的组合是建立适当的神经回路所必需的。
Neuronal identity is generated by the cell-surface expression of clustered protocadherin (Pcdh) isoforms. In mice, 58 isoforms from three gene clusters, Pcdhα, Pcdhβ, and Pcdhγ, are differentially expressed in neurons. Since cis-heteromeric Pcdh oligomers on the cell surface interact homophilically with that in other neurons in trans, it has been thought that the Pcdh isoform repertoire determines the binding specificity of synapses. We previously described the cooperative functions of isoforms from all three Pcdh gene clusters in neuronal survival and synapse formation in the spinal cord. However, the neuronal loss and the following neonatal lethality prevented an analysis of the postnatal development and characteristics of the clustered-Pcdh-null (Δαβγ) neural circuits. Here, we used two methods, one to generate the chimeric mice that have transplanted Δαβγ neurons into mouse embryos, and the other to generate double mutant mice harboring null alleles of both the Pcdh gene and the proapoptotic gene Bax to prevent neuronal loss. First, our results showed that the surviving chimeric mice that had a high contribution of Δαβγ cells exhibited paralysis and died in the postnatal period. An analysis of neuronal survival in postnatally developing brain regions of chimeric mice clarified that many Δαβγ neurons in the forebrain were spared from apoptosis, unlike those in the reticular formation of the brainstem. Second, in Δαβγ/Bax null double mutants, the central pattern generator (CPG) for locomotion failed to create a left-right alternating pattern even in the absence of neurodegeneraton. Third, calcium imaging of cultured hippocampal neurons showed that the network activity of Δαβγ neurons tended to be more synchronized and lost the variability in the number of simultaneously active neurons observed in the control network. Lastly, a comparative analysis for trans-homophilic interactions of the exogenously introduced single Pcdh-γA3 isoforms between the control and the Δαβγ neurons suggested that the isoform-specific trans-homophilic interactions require a complete match of the expressed isoform repertoire at the contacting sites between interactive neurons. These results suggested that combinations of clustered Pcdh isoforms are required for building appropriate neural circuits.