CHARACTERIZATION OF APLYSIA ATTRACTIN, THE FIRST WATER-BORNE PEPTIDE PHEROMONE IN INVERTEBRATES

Although animals in the genus Aplysia are solitary during most of the year, they form breeding aggregations during the reproductive season. The aggregations contain both mating and egg-laying animals and are as sociated with masses of egg cordons. The egg cordons are a source of p heromones that establish and maintain the aggregation, but none of the pheromonal factors have been chemically characterized. In these studi es, specimens of Aplysia were induced to lay eggs, the egg cordons col lected and eluted, and the eluates fractionated by C18 reversed-phase HPLC. Four peak fractions were bioassayed in a T-maze. All four increa sed the number of animals attracted to a nonlaying conspecific and wer e thus subjected to compositional and microsequence analysis. Each con tained the same NH2-terminal peptide sequence. The full-length peptide (''attractin'') was isolated from the albumen gland, a large exocrine organ that packages the eggs into a cordon. The complete 58-residue s equence was obtained, and it matched that predicted by an albumen glan d cDNA. Mass spectrometry showed that attractin is 21 wt.% carbohydrat e as the result of N-linked glycosylation. T-maze bioassays confirmed that the full-length peptide is attractive. Attractin is the first wat er-borne peptide pheromone characterized in molluscs, and the first in invertebrates.