PROJ 5: ID & FUNCTIONAL CHARACTERIZATION OF SNPS INRXRA GENE

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。该项目的总体目标是：确定类维甲酸x受体a （RXRa）基因的遗传多态性，确定美国人群中的主要单倍型，并表征所定义的单倍型对RXRa靶基因表达转录调控的功能影响。主要假设是RXRa基因的遗传多态性存在于美国人群中；这些多态性在不同的种族群体中被组织成特定的单倍型；可能导致rxrcc基因表达个体间变异的单倍型尚未确定；这些变异可能通过改变转录调控导致rxra靶基因表达的差异。RXRa是9-顺式维甲酸的核受体，在基因转录调控中起核心作用。RXRa与其他视黄酸受体（RARa、p和y）形成异源二聚体，激活各种类视黄酸介导的信号通路，控制正常细胞的分化和增殖。RXRa在肝脏中高表达，肝脏中含有不同RXRa的异源二聚体（FXR、PXR、CAR、PPARa、PPARy等）与靶基因启动子中特定的DNA应答元件结合，调节其转录并控制其重要功能，如维持糖脂稳态、胆汁酸合成、药物代谢等。该项目将解决三个具体目标：(1)通过对100名受试者进行测序，确定RXRa基因外显子、内含子/外显子边界、3'-未翻译区和5'-启动子区域的遗传多态性（主要是单核苷酸多态性，snp），这些受试者来自美国四个主要种族：高加索人、非洲裔美国人、东亚人和墨西哥裔美国人；(2)通过对美国4个主要族群（各100个）400份样本中平均分布在RXRa基因上的12-15个已鉴定snp进行基因分型，确定主要单倍型模式；(3)通过体外和体内两种方法来表征所定义的单倍型对rxra靶基因表达的功能影响。在这个项目完成后，我们希望了解我们的人群中存在哪些遗传多态性，它们在不同的单倍型中是如何组织的，以及它们如何影响rxra -靶基因的表达。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goals of this project are to: identify genetic polymorphisms in the retinoid-X-receptor a (RXRa) gene, determine major haplotypes in American populations, and characterize functional effects of the defined haplotypes on the transcriptional regulation of RXRa-target-gene expression. The main hypothesis is that genetic polymorphisms in the RXRa gene exist in American populations; these polymorphisms are organized in specific haplotypes in different ethnic groups; that the haplotypes, which may contribute to inter-individual variations of RXRcc-gene expression, have not yet been defined; and that such variations may cause differences of RXRa-target-gene expression by altering transcriptional regulation. RXRa is a nuclear receptor for 9-cis-retinoic acid and plays a central role for gene transcriptional regulation. RXRa forms heterodimers with the other retinoic-acid receptors (RARa, p, and y) resulting in activation of various retinoid-mediated-signal pathways for controlling normal cell differentiation and proliferation. RXRa is highly expressed in liver, where different RXRa-containing heterodimers (FXR, PXR, CAR, PPARa, PPARy, etc.) bind to specific DNA- response elements in the promoters of target genes, to regulate their transcription and to control important functions, such as the maintenance of glucose and lipid homeostasis, synthesis of bile acids, and the metabolism of drugs. Three specific aims will be addressed in this project: (1) to identify genetic polymorphisms (mostly single nucleotide polymorphisms, SNPs) in exons, intron/exon boundaries, 3'-untranslated region, and 5'-promoter region of the RXRa gene by sequencing 100 human subjects from the four major American ethnic groups: Caucasian, African-American, East-Asian and Mexican-American; (2) To determine major haplotype patterns by genotyping 12-15 identified SNPs evenly distributed in the RXRa gene in 400 samples from the 4 major American ethnic groups (100 from each); (3) to characterize functional effects of the defined haplotypes on RXRa-target-gene expression by using both in vitro and in vivo approaches. After completion of this project, we expect to learn what genetic polymorphisms exist in our population, how they are organized in different haplotypes, and how they affect RXRa-target-gene expression.