Developmental analysis of the cell recognition mechanism in the ciliate Euplotes raikovi

Abstract

Euplotes raikovi, like other ciliates, passes through a postconjugal immaturity, operatively identified by an apparent cell inability to form mating pairs under experimental conditions that are the same as those used for inducing mating at maturity. In cells homozygous for the gene mat-2, which controls the pheromone Er-2, Er-2 mRNA synthesis and mature Er-2 secretion were shown to start from the very beginning of the life cycle and continue throughout immaturity, although to extents estimated to be 5- to 10-fold lower than at maturity. In addition, experiments of 125I-Er-2 binding and crosslinking provided evidence that autocrine pheromone-binding sites, showing values of the dissociation constant of the order of 10(-9) M, are on the surface of immature cells. The number of these sites per cell was estimated to increase from less than 10(6) per cell of 5-7 fissions of age, to about 16 x 10(6) at maturity. These results were taken to suggest that a pheromone-receptor production is stimulated during immaturity by autocrine pheromone binding to cells and that this production might be essential for the development of a pheromone-receptor density high enough to transform the cell from "immature" to "adult," that is competent to respond as well to pheromones of conspecific, genetically different cells.

Developmentally and environmentally regulated expression of gamone 1: the trigger molecule for sexual reproduction inBlepharisma japonicum

“…In the ciliate Euplotes raikovi, mating pheromones (euplomones) are synthesized constitutively throughout the entire clonal life cycle and in growing cells (Miceli et al, 1989;Luporini et al, 1992;Miceli et al, 1992;Vallesi et al, 1995;Luporini et al, 1995;Ortenzi et al, 2000). The gene encoding each pheromone generates at least two distinct molecules by alternative splicing, one of which is the soluble pheromone and the other a membrane-bound pheromone isoform.…”

How often does conjugation in ciliates occur? Clues from a seven-year study on marine sandy shores

“…Thus, it seems reasonable to suppose that ciliates mate under similar conditions in the field as well: when and were crowding occurs, ciliates may consume the food patch quickly and then conjugate. A high density of sexually complementary conspecifics greatly increases the probability of mating, by increasing both the frequency of encounters between sexually complementary partners and the intensity of pre-conjugative interactions (Luporini et al 1992, Doerder et al 1996, Miyake 1996. Such interactions may thus be more effective in crowded patches of conspecifics.…”

“…The possibility of easily inducing conjugation by favouring pre-conjugative interactions and synchronising complementary cells (e.g. Fujishima 1988, Luporini et al 1992, Miyake 1996, Santangelo & Bruno 2001 suggested that this process could also occur frequently in nature, though both the instability of the natural environment and the basically clonal population structure of protists (Kusch & Heckmann 1996) could greatly reduce its frequency. As these studies were based on labcultured strains, they cannot provide any information about the actual incidence of conjugation in nature.…”

Receptor Oligomerization as a Process Modulating Cellular Semiotics

“…Euplotes raikovi are unicellular ciliate organisms that synthesize and secrete constitutively their pheromones (Luporini et al 1992). Pheromones are cell typespecific and structurally homologous proteins that may act as mitogenic signals when bound to the cell from which they originate-autocrine processing-or as mating signals inducing sexual reproduction when bound to other neighboring cellsparacrine processing (Vallesi et al 1995).…”