Analysis of Clustered Protocadherin Function in Mammalian Neurodevelopment

描述（由申请人提供）：对于成熟神经系统的正常功能，神经元在发育过程中发出过程，必须从大量细胞中选择正确的突触伴侣。这一过程在哺乳动物大脑中的重要性得到了越来越多的认识，即许多神经发育障碍，如自闭症和癫痫，以及成人疾病，如双相情感障碍和精神分裂症，可能是由于神经元回路的不当形成。因此，充分了解介导突触伴侣选择的分子对于我们理解和治疗这些疾病的进展至关重要。虽然已经确定了许多指导线索，帮助长出的轴突到达大脑的一个区域，但轴突如何选择确切的突触伙伴还不太清楚。成簇的原钙粘蛋白基因家族（Pcdhs）在哺乳动物脑发育中显示出很大的潜力来填补这一角色。Pcdh基因家族由三个基因簇（1、2和3）中的58个基因组成，每个基因簇编码独特的粘附跨膜蛋白。已经表明，单个神经元表达广泛多样的Pcdh同种型，并且研究已经表明它们对于突触形成和轴突靶向某些类别的神经元的重要性。此外，精神分裂症和双相情感障碍患者的连锁分析揭示了这两种疾病的易感基因位点在人类基因组中的聚集原钙粘蛋白基因家族附近。然而，Pcdh-3基因敲除动物的致死性限制了对Pcdh功能的理解，而对其他簇的研究很少（Pcdh-1）或不存在（Pcdh-2）。然而，通过使用双标记镶嵌分析（MADM），应该可以获得新的见解Pcdhs有助于神经发育的机制。简言之，MADM允许在单个细胞中同时标记和基因敲除。通过将合适的标记盒插入18号染色体并繁殖这些小鼠（称为MADM 18小鼠）与各种Pcdh杂合突变小鼠（1、2和3个突变体，或其中所有三个簇都已缺失的突变小鼠），将有可能分析轴突投射，树突分支，以及在已知表达这些蛋白质的各种脑区域中，缺乏Pcdh的神经元与野生型标记的神经元相邻的突触形成。与以前的Pcdh敲除研究相比，这种策略有几个好处：它避免了与Pcdh-3完全丢失相关的致命性，并且应该通过单细胞敲除基因提供更准确的Pcdh功能评估。表征成簇的原钙粘蛋白在神经元发育中的作用也可能对理解几种神经系统疾病的分子机制有价值，例如自闭症和精神分裂症，其中认为可能涉及不适当的突触形成。最后，为这项研究生产的MADM小鼠可以在未来用于分析18号染色体上MADM盒远端的任何基因，这可能是各种科学领域研究人员的有用工具。

DESCRIPTION (provided by applicant): For proper function of the mature nervous system, neurons send processes out during development that must choose their correct synaptic partners from an enormous population of cells. The importance of this process in the mammalian brain is underscored by the growing knowledge that many neurodevelopmental disorders, such as autism and epilepsy, as well as adult disorders like bipolar disorder and schizophrenia, may result from improper formation of neuronal circuits. Therefore, a full understanding of the molecules mediating synaptic partner choice is crucial for make advancements in our comprehension and treatment of these diseases. While many guidance cues have been identified that assist outgrowing axons to reach an area of the brain, it's less clear how an axon chooses its exact synaptic partner. The clustered protocadherin family of genes (Pcdhs) show great potential to fill this role in mammalian brain development. The Pcdh gene family consists of 58 genes in three gene clusters (1, 2, and 3), each encoding for a unique adhesive transmembrane protein. It has been shown that individual neurons express a wide diversity of Pcdh isoforms, and studies have suggested their importance for synapse formation and axon targeting in certain classes of neurons. Furthermore, linkage analyses of schizophrenia and bipolar disorder patients have uncovered susceptibility loci for both disorders in the human genome near the clustered protocadherin gene family. Yet progress in understanding the function of Pcdhs has been limited by lethality in Pcdh-3 knockout animals, while studies of the other clusters are few (for Pcdh-1) or non-existent (for Pcdh-2). However, by using Mosaic Analysis with Double Markers (MADM), it should be possible to gain novel insight into the mechanisms by which Pcdhs contribute to neural development. Briefly, MADM allows for simultaneous labeling and gene knockout in individual cells. By inserting the appropriate labeling cassettes into chromosome 18 and breeding these mice (called MADM18 mice) with various Pcdh heterozygous mutant mice (1, 2, and 3 mutants, or a mutant mouse where all three clusters have been deleted), it will be possible to analyze axonal projections, dendritic arborizations, and synapse formation of Pcdh-lacking neurons next to wildtype-labeled neurons in a variety of brain regions where these proteins are known to be expressed. Compared to previous Pcdh-knockout studies, this strategy has several benefits: it avoids the lethality associated with complete loss of Pcdh-3, and should provide a more accurate assessment of Pcdh function through single cell knockout of the genes. Characterizing the role of the clustered protocadherins in neuronal development may also have value for understanding the molecular mechanisms of several neurological diseases, such as autism and schizophrenia, where it's thought that improper synapse formation may be involved. Finally, the MADM mouse produced for this study could be used in the future to analyze any gene distal to the MADM cassettes on the chromosome 18, which may be a useful tool for researchers in a variety of scientific fields.