title: Revisiting fifty years of research on pheromone signaling in ciliates.
abstract: Among protists, pheromones have been identified in a great variety of algal species for their activity in driving gamete-gamete interactions for fertilization. Analogously in ciliates, pheromones have been identified for their activity in inducing the sexual phenomenon of conjugation. Although this identification was pioneered by Kimball more than fifty years ago, an effective isolation and chemical characterization of ciliate pheromones has remained confined to species of Blepharisma, Dileptus and Euplotes. In Euplotes species, in which the molecular structures have been determined, pheromones form species-specific families of structurally homologous helical, cysteine-rich, highly-stable proteins. Being structurally homologous, they can bind cells in competition with one another, raising interesting functional analogies with the families of growth factors and cytokines that regulate cell differentiation and development in higher organisms. In addition to inducing conjugation by binding cells in heterologous fashion, Euplotes pheromones act also as autocrine growth factors by binding to, and promoting the vegetative reproduction of the same cells from which they originate. This autocrine activity is most likely primary, providing a concrete example of how the original function of a molecule can be obscured during evolution by the acquisition of a new one.
authors.affiliation: Laboratory of Eukaryotic Microbiology and Animal Biology, School of Biosciences and Veterinary Medicine, University of Camerino, 62032 Camerino, MC, Italy. Electronic address: piero.luporini@unicam.it.
authors.forename: Pierangelo
authors.initials: P
authors.lastname: Luporini
authors.affiliation: Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
authors.forename: Bill
authors.initials: B
authors.lastname: Pedrini
authors.affiliation: Laboratory of Eukaryotic Microbiology and Animal Biology, School of Biosciences and Veterinary Medicine, University of Camerino, 62032 Camerino, MC, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Alimenti
authors.affiliation: Laboratory of Eukaryotic Microbiology and Animal Biology, School of Biosciences and Veterinary Medicine, University of Camerino, 62032 Camerino, MC, Italy.
authors.forename: Adriana
authors.initials: A
authors.lastname: Vallesi
mesh_terms: D016798:Ciliophora / Q000502:physiology*; D010675:Pheromones / Q000502:physiology*; D012106:Research
chemical_list: D010675:Pheromones
keywords: Cell–cell communication; Chemical signaling; Conjugation; Pheromones; Protein structure; Self/non-self recognition