Functional analyses of the constant region of CNR/protocadherin-a of the dustered protocadherins

钙粘蛋白超家族中最大的一个亚类是前钙粘蛋白（Protocadherins，Pcdhs）。聚簇的Pcdhs的大约60个成员产生自独特的基因簇。根据在该基因簇中的位置，成簇的原钙粘蛋白进一步分为三个亚家族，CNR/原钙粘蛋白-α（Pcdha）、Pcdh-β和Pcdh-γ。由于已报道成簇的Pcdhs定位于突触和发育中的轴突，因此它们被认为在神经回路形成和/或选择性突触形成中起重要作用。然而，集群Pcdhs的功能作用仍有待澄清。在这个项目中，我们专注于恒定区的功能，这是在所有Pcdha蛋白中发现的共同胞质区域。Pcdha突变小鼠的表型分析Pcdha蛋白在嗅觉感觉神经元（OSNs）中的强烈表达促使我们在Pcdha突变小鼠中检测这些神经元向嗅球的轴突投射，其中恒定区外显子已通过基因打靶被删除。在野生型小鼠中，表达特定气味受体基因的OSN将其轴突投射到嗅球两半中的每一个肾小球。然而，在Pcdha突变小鼠中，OSN轴突进入肾小球的轴突分选受到干扰，并且气味受体的多个小的外来肾小球被破坏。恒定区在Pcdha蛋白亚细胞定位中的作用Pcdha蛋白有两个交替的恒定区，A型和B型。过表达的具有A型恒定区的Pcdha蛋白很少被转运到质膜。在这个项目中，我们研究了A型恒定区的哪个结构域负责Pcdha-A型蛋白的亚细胞定位。我们的研究结果表明，赖氨酸丰富的结构域附近的羧基端的A型恒定区干扰运输到质膜的细胞系和神经元。

Clustered protocadherins (Pcdhs) constitute the largest subgroup in the cadherin superfamily. About sixty members of clustered Pcdhs are produced from a unique gene cluster. According to the positions in this gene cluster, clustered protocadherins are further classified into three subfamilies, CNR/protocadherin-alpha (Pcdha), Pcdh-beta and Pcdh-gamma. Since clustered Pcdhs have been reported to localize at synapses and in developing axons, they have been assumed to play important roles in neural circuit formation and/or selective synapse formation. However, the functional roles of clustered Pcdhs have remained to be clarified. In this project, we focused on functions of the constant region, a common cytoplasmic region found in all Pcdha proteins.1. Phenotype analyses of Pcdha mutant miceIntense expression of Pcdha proteins in the olfactory sensory neurons (OSNs) prompted us to examine axonal projection of these neurons to the olfactory glomeruli in Pcdha mutant mice, in which the constant region exons had been deleted by gene targeting. In wild-type mice, OSNs that express a given odorant receptor gene project their axons to one glomerulus in each of the two halves of an olfactory bulb. In the Pcdha mutant mice, however, axonal sorting of OSN axons into glomeruli were perturbed, and multiple, small, extraneous glomeruli for the odorant receptors were observed.2. Roles of the constant region in subcellular localization of Pcdha proteins.Pcdha proteins have two alternative constant regions, A- and B-type. Overexpressed Pcdha proteins with A-type constant region are rarely transported to the plasma membrane. In this project, we examined which domain of the A-type constant region is responsible for the subcellular localization of Pcdha-A type proteins. Our results indicate that a lysine-rich domain near the carboxyl-terminus of A-type constant region interferes transport to the plasma membrane in cell lines and neurons.