Rahman Z, Gold S J, Potenza M N, Cowan C W, Ni Y G, He W, Wensel T G, Nestler E J
Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06508, USA.
J Neurosci. 1999 Mar 15;19(6):2016-26. doi: 10.1523/JNEUROSCI.19-06-02016.1999.
Regulators of G-protein signaling (RGS) proteins act as GTPase-activating proteins (GAPs) for alpha subunits of heterotrimeric G-proteins. Previous in situ hybridization analysis of mRNAs encoding RGS3-RGS11 revealed region-specific expression patterns in rat brain. RGS9 showed a particularly striking pattern of almost exclusive enrichment in striatum. In a parallel study, RGS9 cDNA, here referred to as RGS9-1, was cloned from retinal cDNA libraries, and the encoded protein was identified as a GAP for transducin (Galphat) in rod outer segments. In the present study we identify a novel splice variant of RGS9, RGS9-2, cloned from a mouse forebrain cDNA library, which encodes a striatal-specific isoform of the protein. RGS9-2 is 191 amino acids longer than the retinal isoform, has a unique 3' untranslated region, and is highly enriched in striatum, with much lower levels seen in other brain regions and no expression detectable in retina. Immunohistochemistry showed that RGS9-2 protein is restricted to striatal neuropil and absent in striatal terminal fields. The functional activity of RGS9-2 is supported by the finding that it, but not RGS9-1, dampens the Gi/o-coupled mu-opioid receptor response in vitro. Characterization of a bacterial artificial chromosome genomic clone of approximately 200 kb indicates that these isoforms represent alternatively spliced mRNAs from a single gene and that the RGS domain, conserved among all known RGS members, is encoded over three distinct exons. The distinct C-terminal domains of RGS9-2 and RGS9-1 presumably contribute to unique regulatory properties in the neural and retinal cells in which these proteins are selectively expressed.
G蛋白信号调节（RGS）蛋白作为异源三聚体G蛋白α亚基的GTP酶激活蛋白（GAP）发挥作用。先前对编码RGS3 - RGS11的mRNA进行的原位杂交分析揭示了大鼠脑中区域特异性的表达模式。RGS9显示出一种特别显著的模式，几乎只在纹状体中高度富集。在一项平行研究中，从视网膜cDNA文库中克隆了RGS9 cDNA，此处称为RGS9 - 1，其编码的蛋白被鉴定为视杆细胞外段中传导素（Galphat）的GAP。在本研究中，我们从一个小鼠前脑cDNA文库中鉴定出一种新的RGS9剪接变体RGS9 - 2，它编码一种纹状体特异性的蛋白异构体。RGS9 - 2比视网膜异构体长191个氨基酸，有一个独特的3'非翻译区，并且在纹状体中高度富集，在其他脑区水平低得多，在视网膜中未检测到表达。免疫组织化学显示，RGS9 - 2蛋白局限于纹状体神经毡，在纹状体终末区域不存在。RGS9 - 2的功能活性得到以下发现的支持：在体外，它而非RGS9 - 1能减弱Gi/o偶联的μ - 阿片受体反应。对一个约200 kb的细菌人工染色体基因组克隆的表征表明，这些异构体代表来自单个基因的选择性剪接的mRNA，并且在所有已知RGS成员中保守的RGS结构域由三个不同的外显子编码。RGS9 - 2和RGS9 - 1不同的C末端结构域可能导致这些蛋白选择性表达的神经和视网膜细胞中具有独特的调节特性。
