Characterization of a Family of Pheromonal Attractants

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Animals use a variety of signals to coordinate their activity with that of other members of their species. Some of these signals are visual (e.g., bright colors or posturing), others are verbal (e.g., singing, growling, or whimpering), and still others are chemical (e.g., marking territories or inducing spawning). The chemical signals are known as pheromones, which to date have been most thoroughly investigated in insects. Pheromones are involved in coordinating the activities of aquatic animals, yet little is known about the chemical identities or specific activities of these substances. This is particularly true of water-borne peptide pheromones, which are difficult to isolate and characterize because: (a) only small numbers of animals secrete pheromones at any one time; (b) little is known about the stimulus that induces pheromone secretion; (c) relatively small amounts of pheromones are secreted; (d) secretion occurs into large volumes of water that has contacted a variety of animals and their products; and (e) there is a strong possibility that the pheromone is rapidly degraded.Two characteristics of the reproductive system in Aplysia, a marine mollusk, make it possible to address some of these problems. For example, injection of egg laying hormone causes Aplysia to lay a long string of eggs (an egg cordon), which is the source of pheromones that attract other animals to the area and induce them to lay eggs and/or mate. This useful tool to induce egg laying makes it possible to control the number of animals laying eggs, the timing and synchronization of egg laying, the general area where eggs are deposited, and the relative purity of the surrounding seawater. Using Aplysia, a water-borne peptide pheromone ("attractin") has been isolated and chemically characterized. This pheromone has multiple activities in laboratory bioassays and belongs to a family of attractin-related peptides in different species of Aplysia and perhaps other aquatic gastropods.The experiments in this proposal will use molecular, biochemical and behavioral techniques to test three hypotheses: (1) There are attractin-related peptide pheromones in other species of Aplysia, in other opisthobranchs (Bursatella), and in aquatic pulomonates (Lymnaea). (2) Egg cordons are a source of multiple pheromonal attractants. (3) There is a family of peptide pheromones that trigger mass spawning in oysters.Biochemical and behavioral characterization of Aplysia attractin and related peptides will contribute to understanding of pheromonal regulation of reproductive behavior in mollusks; of peptide pheromones and their function(s); of attractin's active site; and the nature and mechanism of action of the attractin receptor.