The sensory neurone membrane protein SNMP1 contributes to the sensitivity of a pheromone detection system.

Male moths detect female-released sex pheromones with extraordinary sensitivity. The remarkable sensory ability is based on a cooperative interplay of pheromone binding proteins in the lymph of hair-like sensilla trichodea and pheromone receptors in the dendrites of sensory neurones. Here we examined whether in Heliothis virescens the so-called 'sensory neurone membrane protein 1' (SNMP1) may contribute to responsiveness to the pheromone component, (Z)-11-hexadecenal (Z11-16:Ald). By means of immunohistochemistry and in situ hybridization we demonstrated that SNMP1 is in fact present in cells expressing the Z11-16:Ald receptor HR13 and the dendrites of sensory neurones. To assess a possible function of SNMP1 we monitored the responsiveness of cell lines that expressed HR13 alone or the combination SNMP1/HR13 to stimulation with Z11-16:Ald by calcium imaging. It was found that SNMP1/HR13 cells were 1000-fold more sensitive to pheromone stimulation compared with HR13 cells. In contrast, cells that expressed HR13 and the non-neuronal SNMP2-type showed no change in pheromone sensitivity. Overall, our reconstitution experiments demonstrate that the presence of SNMP1 significantly increases the HR13-based responsiveness of cells to Z11-16:Ald, suggesting that SNMP1 also contributes to the response of the antennal neurones and thus to the remarkable sensitivity of the pheromone detection system.