Isolation of the Lembadion‐factor, A morphogenetically active signal, that induces Euplotes cells to change from their ovoid form into a larger lateral winged morph

A morphogenetically active substance released by the predatory ciliate Lem‐badion bullinum is recognized by ciliates of the genus Euplotes, which are potential prey organisms of Lembadion. The substance (L‐factor) induces cells of the genus Euplotes to become less compact, which reduces their likelihood of becoming engulfed. Under the influence of this Lembadion‐ derived signal, E. octocarinatus develops extended wings and dorsal and ventral ridges and transforms within a few hours from its typical ovoid morph into an enlarged circular morph. This takes place without cell division. We have isolated the L‐factor and report that it is a protein with a mass of 31,500 Da. The factor has been purified to chromatographic and electrophoretic homogeneity and was found to be active at concentrations as low as 10−12 mol/L.