Deciphering the Evolution of the Opioid/Orphanin Gene Family

有颌脊椎动物（颌口动物）大脑中化学通讯系统的一个显著特征是产生有用神经肽化合物的基因的明显复制。例如，在哺乳动物中，有四种神经肽前体（前脑啡肽、前啡肽、原黑素皮质素和原孤儿蛋白）产生阿片样肽（阿片样肽）或伤害样肽（孤儿蛋白）。这四种前体是一个基因家族的成员，阿片/孤儿蛋白家族，这个家族中明显的基因冗余实际上反映了脊椎动物的进化史。脊椎动物进化中离散点的基因复制事件使得神经肽网络随着时间的推移而分层，并导致这些肽产物功能的多样化，包括在镇痛、伤害感觉、运动控制和摄食中的作用。该项目将分子生物学方法与比较方法相结合，以确定啮齿动物中孤儿素/阿片基因家族的进化辐射趋势。cdna的克隆和测序，加上通过实时PCR测量基因表达，将生成该家族中每个基因的序列数据库，该数据库将用于进行分支分析和鉴定新的阿片类药物序列。通过检查选定的脊椎动物谱系，其中该基因家族的进化速度比哺乳动物或硬骨鱼慢，可以推断出该基因家族在顺序进化中的起源和转变。这些数据将检验“前脑啡肽假说”，即阿片样蛋白/孤儿蛋白基因家族中的祖先基因是编码脑啡肽样产物的基因。研究结果将为了解这一重要神经肽家族功能多样性的进化机制提供一个新的水平。这个项目的影响将从神经内分泌学扩展到一般的分子神经生物学，以及关于促进物种多样性趋势的进化生物学。多学科的本科生和研究生培养也是该项目的重要组成部分。

A striking feature of chemical communication systems in the brains of jawed vertebrates (gnathostomes) is the apparent duplication of genes that produce useful neuropeptide compounds. For example, in mammals there are four neuropeptide precursors (proenkephalin, prodynorphin, proopiomelanocortin, and proorphanin) that produce opiate-like peptides (opioids) or nociceptic-like peptides (orphanins). These four precursors are members of a gene family, the opioid/orphanin family, and the apparent redundancy of genes in this family in fact reflects the evolutionary history of the vertebrates. Gene duplication events at discrete points in vertebrate evolution have allowed for the layering of neuropeptide networks over time, and have led to a diversification in function of these peptide products, including roles in analgesia, nociception, motor control, and feeding. This project combines molecular biology procedures with a comparative approach to define trends in the evolutionary radiation of the orphanin/opioid gene family in gnathostomes. The cloning and sequencing of cDNAs, coupled with the measurement of gene expression by real-time PCR, will generate a database of sequences for each gene in the family that will be used to perform cladistic analyses and to identify novel opioid sequences. By examining selected vertebrate lineages where the evolution of this gene family has been slower than in mammals or teleost fish, it is possible to make inferences about the origin and transitions in the sequential evolution of this gene family. These data will test the 'proenkephalin hypothesis' that the ancestral gene in the opioid/orphanin gene family was a gene that coded for the enkephalin-like product. Results will provide a new level of understanding of the evolutionary mechanisms underlying the functional diversity in this important family of neuropeptides. The impact of this project will extend beyond neuroendocrinology to molecular neurobiology in general, and to evolutionary biology with respect to the trends that promote species diversity. Multi-disciplinary undergraduate and graduate training also is an important component of this project.