Evolution of vomeronasal-type odorant receptor genes in the zebrafish genome

Teleost fishes have two distinct families of odorant receptors, main odorant receptors (MORs) and vomeronasal receptors family 2 (V2Rs), both of which are expressed in the olfactory epithelium where they detect soluble chemicals. To obtain an insight into the evolution of the fish V2R gene family, V2R genes and their chromosomal locations were identified from zebrafish genome sequences. Eighty-eight putative V2R genes and pseudogenes were identified, most being tightly clustered into two chromosomal regions. The phylogenetic analysis revealed that V2R genes belonging to the same phylogenetic clade were located close to one another on the same chromosome. However, some V2R genes were also found in several different chromosome regions, either as singletons or small gene clusters. Recent large-scale duplications of V2R-containing chromosomal regions were detected in two V2R gene clusters. The evolution of the zebrafish V2R gene family can be explained by repeated tandem gene duplications within gene clusters and large-scale duplications among chromosomes.