Aplysia seductin is a water-borne protein pheromone that acts in concert with attractin to stimulate mate attraction

Mate attraction in Aplysia involves the long-distance water-borne protein pheromones attractin, enticin, and temptin which are released during egg-laying. Other water-borne pheromones are predicted to act in concert with attractin, enticin, and temptin, but their identities were unknown. We recently identified a highly expressed Aplysiacalifornica albumen gland gene (Alb-23) that encoded a novel protein by differential library screening of an albumen gland cDNA library. To determine whether Alb-23 ('seductin') was a water-borne pheromone, we employed Western blot analysis, purification and expression of albumen gland proteins, immunolocalization studies, pheromone secretion assays, comparative genomics, and behavioral bioassays. Immunoreactive seductin was detected in eluates of egg cordons, indicating that seductin was secreted onto the cordon during egg laying. Aplysiabrasiliana seductin was 94% identical to its A.californica homolog. In T-maze attraction assays, the combination of attractin and seductin was significantly attractive to potential mates, whereas either protein alone was not. Data from this and previous studies support the hypothesis that seductin is a water-borne protein pheromone that acts in concert with attractin, enticin, and temptin to attract Aplysia to form and maintain mating aggregations.