Characterization of Y and dopamine receptors in lampreys by using "in situ" hybridizationan evolutionary approach"

Resumo

Neuropeptide Y (NPY) and dopamine systems are involved in numerous and important functions in all vertebrates. Three different subfamilies of G-protein-coupled receptors (Y1, Y2 and Y5), named Y receptors, are included within the NPY system, whereas the effects of dopamine are mediated by two evolutionary convergent classes of G-protein-coupled receptors: D1 and D2 classes. A critical evolutionary period for both groups of receptors is thought to be happened during the early vertebrate evolution (500-800 Ma ago), when the two whole genome duplications (WGDs) proposed by the 2R hypothesis occurred. The lineage leading to lampreys is thought to have diverged from the common trunk of vertebrates about 560 Ma ago. The aim of the present study was to complete the repertory of genes belonging to Y and dopamine receptor families in the sea lamprey Petromyzon marinus by using available genome databases, studying their phylogenies, and comparing their brain expression patterns by in situ hybridization with the distributions reported for the Y and dopamine receptors in other vertebrates. Four genes were cloned in P. marinus belonging to the Y system: Y1 and Y8, from the Y1 subfamily, one Y2, and one Y5 receptor. Both, phylogenetic studies and the comparison of the expression patterns in the lamprey brain and in other vertebrates, saved Y2 that is not expressed in lamprey, showed that they are homologue to their counterparts in other vertebrates. Concerning dopamine receptors, D2 and D4 were cloned in lampreys, where D1 had been previously cloned by other group. The expression pattern of these three receptors in lampreys was similar to that of D1, D2 and D4 receptors in other vertebrates. The results show that lampreys carry at least one member per family of receptors, in both Y and dopamine systems. This receptor, in every family, is widely expressed in the brain and shows a conserved expression pattern when compared with other vertebrates. We suggest that in every family they have preserved the roles of the ancestral gen. Furthermore, the gene repertory, the phylogenetic studies, and the expression patterns support that lampreys lineage branched between the two WGDs.