TRP2: A candidate transduction channel for mammalian pheromone sensory signaling

The vomeronasal organ (VNO) of terrestrial vertebrates plays a key role in the detection of pheromones, chemicals released by animals that elicit ster eotyped sexual and aggressive behaviors among conspecifics, Sensory transdu ction in the VNO appears unrelated to that in the vertebrate olfactory and visual systems: the putative pheromone receptors of the VNO are evolutionar ily independent from the odorant receptors and, in contrast to vertebrate v isual and olfactory transduction, vomeronasal transduction is unlikely to b e mediated by cyclic-nucleotide-gated channels. We hypothesized that sensor y transduction in the VNO might instead involve an ion channel of the trans ient receptor potential (TRP) family, members of which mediate cyclic-nucle otide-independent sensory responses in Drosophila melanogaster and Caenorha bditis elegans and play unknown functions in mammals. We have isolated a cD NA (rTRP2) from rat VNO encoding a protein of 885 amino acids that is equal ly distant from vertebrate and invertebrate TRP channels (10-30% amino acid identity). rTRP2 mRNA is exclusively expressed in VNO neurons, and the pro tein is highly localized to VNO sensory microvilli, the proposed site of ph eromone sensory transduction, The absence of Ca2+ stores in sensory microvi lli suggests that, in contrast to a proposed mechanism of activation of mam malian TRP channels, but in accord with analysis of TRP function in Drosoph ila phototransduction, the gating of TRP2 is independent from the depletion of internal Ca2+ stores. Thus, TRP2 is likely to participate in vomeronasa l sensory transduction, which may share additional similarities with light- induced signaling in the Drosophila eye.