Opioid-coding Genes: Evolution in Lungfish and Amphibians

项目概要Robert Dores 基因复制是脊椎动物多肽、激素和神经肽进化过程中反复出现的主题。这些重复事件导致基因家族的形成，其中功能分歧是通常的结果。在阿片编码基因的情况下，复制事件沿着两条路径进行：a）明显的功能复制（脑啡肽原和强啡肽原回路都是中枢神经系统中的抑制网络）;或B）如在脑啡肽原和强啡肽原产物的镇痛活性中所见的功能分歧，与原阿片黑皮质素产物的提高的疼痛反应性（伤害感受性）活性或原阿片黑皮质素产物的黑皮质素（颜色变化和慢性应激调节）活性相比。这些复制事件是完全随机的，还是与脊椎动物的离散辐射点相对应？这一提议发展了一种假设，即阿片样物质编码基因家族（脑啡肽原、强啡肽原、前感受肽和阿黑皮素原）的复制驱动的扩张对应于多倍化（整个基因组的复制）改变脊椎动物进化过程的时期。为了确定这些“爆发”期，Dores博士和他的同事将比较方法与分子方法相结合。 本分析所选的物种（肺鱼、有尾目两栖动物和一个古老的无尾两栖动物谱系）代表了一个预测的基因组复制事件（泥盆纪有鳍鱼类和四足动物的兴起）的谱系。因此，通过采取比较的方法，有可能根据化石记录选择符合逻辑系统发育假设的分类群。通过采用分子方法，有可能检验这一假设。在这项研究中，阿片类药物编码基因家族将被用作模型来分析自然选择如何作用于重复的基因以改变序列，并潜在地改变功能。分子方法的关键是关注该基因家族所有成员共有的祖先特征-阿片样物质核心序列YGGF（M/L）。通过采用这种方法，我们已经检测到基因的射线鳍鱼和叶鳍鱼（前一阶段的支持），这是以前没有怀疑。此外，新的阿片肽已被发现，其阿片激动剂的潜力尚未进行评估。虽然可以理解的是，在这项研究中使用的分类群都不是“活化石”，通过采取比较/分子方法，有可能重建，通过分支范例（最大简约），最有可能的途径，导致现存的阿片样物质编码基因，以及这些基因的潜在分支相对于脊椎动物中枢神经系统中神经元回路的进化。

PROJECT SUMMARY Robert Dores Gene duplication is a recurring theme in the evolution of vertebrate polypeptide hormones and neuropeptides. These duplication events lead to the formation of gene families in which divergence of function is the usual outcome. In the case of the opioid-coding genes, duplication events have proceeded along two paths: a) an apparent duplication of function (both Proenkephalin and Prodynorphin circuits function as inhibitory networks in the central nervous system); or b) divergence of function as seen in analgesic activity of Proenkephalin and Prodynorphin products, as compared to the heightened pain responsiveness (nociceptic) activity of Pronociceptin products, or the melanocortin (color change and chronic stress regulation) activity of Proopiomelanocortin products. Are these duplication events entirely random, or do they correspond to discrete points of radiation of the vertebrates? This proposal develops the hypothesis that the duplication-driven expansion of the opioid-coding gene family (Proenkephalin, Prodynorphin, Pronociceptin, and Proopiomelanocortin) corresponds to periods when polyploidization (replication of the entire genome) altered the course of vertebrate evolution. To identify these "burst" periods, Dr Dores and colleagues have combined a comparative approach with a molecular approach. The species selected for this analysis (lungfish, urodele amphibians, and a ancient lineage of anuran amphibians) represent lineages that bracketed one of the predicted genome duplication events (the rise of the lobed finned fish and tetrapods in the Devonian). Thus, by taking a comparative approach it is possible to select taxa that fit into a logical phylogenetic hypothesis based on the fossil record. By employing the molecular approach, it is possible to test that hypothesis. In this study, the opioid-coding gene family will be used as a model to analyze how natural selection acts on duplicated genes to alter sequence, and potenti ally alter function. The key to the molecular approach is to focus on an ancestral character common to all members of this gene family - the opioid core sequence YGGF(M/L). By taking this approach, we have already detected genes in ray-finned fish and lobe finned fish (previous period of support) which were previously unsuspected. In addition, novel opioid peptides have been revealed whose opiate agonist potential has not been evaluated. While it is appreciated that none of the taxa used in this study are a "living fossil," by taking a comparative/molecular approach it is possible to reconstruct, through cladistic paradigms (maximum parsimony), the most likely pathways which have lead to the extant opioid-coding genes, and the potential ramifications of these genes with respect to evolution of neuronal circuits in the vertebrate central nervous system.