Molecular evolution of the opioid/orphanin gene family

Gene duplication is a recurring theme in the evolution of vertebrate polype ptide hormones and neuropeptides. These duplication events can lead to the formation of gene families in which divergence of function is the usual out come. In the case of the opioid/orphanin family of genes, duplication event s have proceeded along two paths: (a) an apparent duplication of function a s seen in the analgesic activity of Proenkephalin and Prodynorphin end-prod ucts; and (b) divergence of function as seen in the nociceptic activity of Proorphanin endproducts or the melanocortin (color change and chronic stres s regulation) activity of Proopiomelanocortin endproducts. Although genes c oding for Proopiomelanocortin, Proenkephalin, Prodynorphin, and Proorphanin have been extensively studied in mammals, the distribution and radiation o f these genes in nonmammalian vertebrates is less well understood. This rev iew will present the hypothesis that the radiation of the opioid/orphanin g ene family is the result of the duplication and divergence of the Proenkeph alin gene during the radiation of the chordates. To evaluate the Proenkepha lin gene duplication hypothesis, a 3'RACE procedure was used to screen for the presence of Prodynorphin-related, Proenkephalin-related, and Proorphani n-related cDNAs expressed in the brains of nonmammalian vertebrates. (C) 19 99 Academic Press.