Evolution of the Neuropeptide Y and Opioid Systems and their Genomic Regions

Two whole genome duplications (2R) occurred early in vertebrate evolution. By using combined information from phylogenetic analyses and chromosomal location of genes, this thesis delineates the evolutionary history of two receptor-ligand systems that expanded by these large scale events. A third whole genome duplication (3R) took place in the teleost fish lineage and has also contributed to the complexity of the gene families. New members of neuropeptide Y (NPY) peptide and receptor families were generated in 2R and 3R. Evolutionary comparisons show that the ancestral teleost fish had four peptides; subsequently, differential losses of the peptide genes occurred. In zebrafish the peptides and receptors display differences in tissue distribution and have evolved binding preferences. In the frog Silurana tropicalis three peptides and six receptors werev identified, also displaying some differences in tissue distribution and receptor-ligand preferences. The findings in these experimental animals highlight both evolutionary conservation and lineage-specific features of the NPY system. The opioid system consists of four receptors and several peptides originating from four precursors. These results show that the receptor family was formed in 2R and 3R and that 2R together with one local duplication gave rise to the peptide family. The ancestral receptor and peptide genes were located on the same chromosome, suggesting coevolution. The Hox gene clusters, important in early development, provided the first strong evidence for 2R. Several neighboring gene families were analyzed and found to have expanded in 2R and 3R. In depth analyses of insulin-like growth factor binding protein (IGFBP) and voltage-gated sodium channel (SCN) gene families illustrates the importance of local duplications in combination with whole genome duplications in the formation of gene families. These findings provide additional strong evidence for two genome duplications in early vertebrate evolution and show that these events generated many new genes that could evolve new or more specialized functions