AUTOCRINE MITOGENIC ACTIVITY OF PHEROMONES PRODUCED BY THE PROTOZOAN CILIATE EUPLOTES-RAIKOVI

DIFFUSIBLE polypeptide pheromones (formerly referred to as mating-type factors, sex factors or gamones), which distinguish otherwise morphol ogically identical vegetative cell (mating) types from one another, ar e produced by some species of ciliates(1,2), Their most striking effec t can be observed by exposing cells of one type to a pheromone secrete d by another co-specific cell type(3). In the presence of this 'non-se lf' signal, these cells interrupt their vegetative life to unite tempo rarily in mating pairs, Thus ciliate pheromones have traditionally bee n associated only with mating induction(2,4), However, the identificat ion of autocrine pheromone receptors(5,6) suggests a broader role, whi ch is supported by the hypothesis that ciliates evolved their mating-t ype mechanism for pursuing self-recognition(1). We now report studies, in the cosmopolitan marine sand-dwelling protozoan ciliate Euplotes r aikovi, demonstrating that these molecules promote the vegetative repr oduction (mitogenic proliferation or growth) of the same cells from wh ich they originate, As, understandably, such autocrine pheromone activ ity is primary to that of targeting and inducing a foreign cell to mat e (paracrine functions), this finding provides an example of how the o riginal function of a molecule can be obscured during evolution by the acquisition of a new one.