This family consists of several Euplotes raikovi mating pheromone proteins. Diffusible polypeptide pheromones, which distinguish otherwise morphologically identical vegetative cell types from one another, are produced by some species of ciliates. In the marine sand-dwelling protozoan ciliate Euplotes raikovi, pheromone molecules promote the vegetative reproduction (mitogenic proliferation or growth) of the same cells from which they originate. As, understandably, such autocrine pheromone activity is primary to that of targeting and inducing a foreign cell to mate (paracrine functions), this finding provides an example of how the original function of a molecule can be obscured during evolution by the acquisition of a new one [1].

1: Autocrine mitogenic activity of pheromones produced by the protozoan ciliate Euplotes raikovi. Vallesi A, Giuli G, Bradshaw RA, Luporini P; Nature 1995;376:522-524. PMID:7637785

2: Structural characterization of mating pheromone precursors of the ciliate protozoan Euplotes raikovi. High conservation of pre and pro regions versus high variability of secreted regions. Miceli C, La Terza A, Bradshaw RA, Luporini P; Eur J Biochem 1991;202:759-764. PMID:1722455

3: A cooperative model for receptor recognition and cell adhesion: evidence from the molecular packing in the 1.6-A crystal structure of the pheromone Er-1 from the ciliated protozoan Euplotes raikovi. Weiss MS, Anderson DH, Raffioni S, Bradshaw RA, Ortenzi C, Luporini P, Eisenberg D; Proc Natl Acad Sci U S A 1995;92:10172-10176. PMID:7479748