Rapid response to nutrient depletion on the expression of mating pheromone, gamone 1, in Blepharisma japonicum

抄録

Ciliate conjugation usually occurs when cells are moderately starved after rapid proliferation. In Blepharisma japonicum, at the stationary phase, a mating pheromone (gamone 1) is secreted by mating type I cells and stimulates mating type II cells to secrete another mating pheromone (gamone 2), which stimulates mating type I cells. Both stimulated cells are transformed to be able to form pairs. We showed previously that the gamone 1 transcription occurs only in the stationary-phase cells, not in logarithmic-phase cells. However, it is still unknown how rapidly cells response to starvation and express gamone 1. Here we show that gamone 1 expression is initiated by sudden artificial starvation, and we determined the time required for the initiation of transcription and secretion of gamone 1 in B. japonicum. Proliferating cells rapidly responded to artificial starvation, approx. 1.5 h at most was necessary for the initiation of the transcription of gamone 1 gene, and approx. 3 h was needed for the secretion of gamone 1. Gamone 1 expression tested in single cells suggests that gamone 1 expression may be correlated with the cell-cycle, most probably with the certain stage of G1 phase in B. japonicum. Our present findings provide an experimental system to investigate the environmental factors involved in the initiation of conjugation.