Molecular basis of self/nonself recognition in ciliate mating type systems. REPORT of the XIIIth scientific meeting of the Italian Association of Developmental and Comparative Immunobiology (IADCI), Camerino MC.

Like numerous other organisms, ciliates alternate their life cycles between vegetative (mitotic) growth and sex. However, ciliate sex is unique for at least two major aspects: (i) it becomes manifest as temporary cytoplasmic fusion between cells that carry diploid sets of genes and may equally be identical or different in their genotypes, and (ii) is under the control of a genetic mechanism of mating-types which may either be only two as is the case in various species of Paramecium and Blepharisma, or multiple as is the case in various species of Tetrahymena, Euplotes, Stylonychia and the hypotrichs in general. While the mating type binary systems recall the duality of the sex of the multi-cellular organisms, the multiple systems find much closer counterparts with the self/non-self recognition mechanisms that permit animals to react immunologically against invaders, and fungi and flowering plants to decide their evolution between self-sterility and self-fertility strategies. A persevering research interest on the multiple mating type systems of different species of Euplotes lead us to obtain relevant information on the genes and the cell type-specific diffusible signal proteins (pheromones) that interplay in the control of these systems. Functionally most relevant was the finding that, in full accord with their genetic determination provided by multiple sets of single-locus genes, these Euplotes pheromones are represented by species-specific family of structurally homologous proteins which, as such, can compete with one another for binding to their cell receptors in either autocrine (self), or paracrine-like (non-self) fashion. Cells grow in response to the pheromone binding that signals self, and temporarily shift to the sexual stage in response to the pheromone binding that signals non-self.