Functional Evolution of Primate Odorant Receptors

The olfactory system provides excellent models for evaluating primate adaptation to diverse and changing environments because the olfactory receptors are imperative in determining odor perception and in modulating species-specific behaviors. Consistent with this, chemosensory receptors including the odorant receptors (OR) are among the fastest evolving genes in animals. Although extensive bioinformatic analyses of OR sequences in primates have been conducted, little is known about the functional changes of individual receptors during evolution. Using heterologous cell systems, functional evaluation of ORs in primate evolution has become increasingly feasible. Orthologues of ORs can be cloned from different species, and functional analysis of these orthologues and their nonsynonymous changes should reveal OR responses to the cognate ligands and sites causing increases or decreases in sensitivity, as well as changes in ligand selectivity of the ORs. Functionally important residues can be used to evaluate sites with evidence of natural selection as predicted by existing computational analyses.