Abstract
The survival of vertebrate species is dependent on the ability of individuals to adequately interact with each other, a function often mediated by the olfactory system. Diverse olfactory receptor repertoires are used by this system to recognize chemicals. Among these receptors, the V1rs, encoded by a very large gene family in most mammals, are able to detect pheromones. Teleosts, which also express V1r receptors, possess a very limited V1r repertoire. Here, taking advantage of the possibility to unequivocally identify V1r orthologs in teleosts, we analyzed the olfactory expression and evolutionary constraints of a pair of clustered fish V1r receptor genes, V1r1 and V1r2. Orthologs of the two genes were found in zebrafish, medaka, and threespine stickleback, but a single representative was observed in tetraodontidae species. Analysis of V1r1 and V1r2 sequences from 12 different euteleost species indicate different evolutionary rates between the two paralogous genes, leading to a highly conserved V1r2 gene and a V1r1 gene under more relaxed selective constraint. Moreover, positively-selected sites were detected in specific branches of the V1r1 clade. Our results suggest a conserved agonist specificity of the V1R2 receptor between euteleost species, its loss in the tetraodontidae lineage, and the acquisition of different chemosensory characteristics for the V1R1 receptor.
Highlights
In vertebrates, interindividual interactions related to reproduction are largely dependent on pheromonal communication
Taking advantage of the newly released zebrafish (Zv6, 2006), medaka (Medaka 1, 2006) and threespine stickleback (Gasterosteus aculeatus, Ga) (BROAD S1, 2006) assemblies, and including the fugu (Fugu 4.0, 2005) and tetraodon databases, we performed a search for potential novel V1r sequences
Using PCR primers specific for Dr V1r1 and V1r2 sequences, we investigated the presence of the two genes in the following species: D. albolineatus (Da), D. choprae (Dc), D. dangila (Dd), D. kerri (Dk), D. kyathit (Dky), D. malabaricus (Dm), D. nigrofasciatus (Dn), D. pantheri (Dp) and D. yoma (Dy) (Table 1).V1r1 and V1r2 sequences were found in all tested Danio species
Summary
Interindividual interactions related to reproduction are largely dependent on pheromonal communication. Chemosensory structures located in mammals in the nasal cavity and in teleosts in the olfactory rosette represent the major tools used for such exchanges. These structures contain thousands of olfactory sensory neurons, organized in pseudostratified neuroepithelia. Each olfactory sensory neuron extends a single dendrite towards the outside world and an axon which directly connects to the olfactory bulb, in the brain. A single or a few members of a remarkably large olfactory receptor gene repertoire are expressed by each olfactory sensory neuron. Chemical information from the outside world is transported by multiple parallel lines to the olfactory bulb, where it is processed, directed towards various brain areas, and translated into a conscious or unconscious perception
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