PHEROMONES OF THE CILIATE EUPLOTES-OCTOCARINATUS NOT ONLY INDUCE CONJUGATION BUT ALSO FUNCTION AS CHEMOATTRACTANTS

Cells of the ten mating types of the ciliate Euplotes octocarinatus co mmunicate by pheromones before they enter conjugation. The pheromones induce homotypic pairing when applied to mating types that do not secr ete the same pheromone(s). Heterotypic pairs (i.e., those between cell s of different mating types) are formed only when both mating types in a mixture secrete a pheromone that the other does not. The genetics o f mating types is based on four codominant mating type alleles, each a llele determining production of a different pheromone. Here we report that the pheromones not only induce pair formation but also attract ce lls. This was shown by placing cells of various mating types in neighb oring agar wells so that the pheromones could diffuse from one well to the next. We found that the cells accumulated on the side of the well where a pheromone entered by diffusion. This response was observed on ly if the pheromone had the capacity to induce the cells to conjugate. That the pheromones and not some other substances attract the cells w as shown by placing pheromone 3, expressed in Escherichia coli, in wel ls next to tester strains. Mating types known to respond to pheromone 3 by pair formation also showed accumulation on the side of the well a t which the pheromone entered by diffusion. Since the pattern of cell attraction corresponds with the pattern of conjugation induction, we s uggest that not only conjugation induction but also cell attraction is governed by pheromone-specific receptors. In addition, we describe a succession of changes in the behavior of cells affected by the pheromo nes. (C) 1997 Wiley-Liss, Inc.