Propagation of meiosis and other nuclear changes in multicellular complexes of Blepharisma

Meiosis and other nuclear changes in conjugation of Blepharisma japonicum regularly occur when cells of complementary mating types I and II unite (heterotypic union). But no nuclear changes occur if unions are induced between cells of the same mating type (homotypic union). Similarly, chains of homotypically united cells, induced by treating type II cells of a doublet strain (mutant with two attachment points) with gamone of mating type I, do not undergo nuclear changes. However, if a type I cell unites at one end of such a chain, the nuclear changes of conjugation occur not only in the doublet to which the type I cell unites but also in other doublets in the same chain. We examined the mode of propagation of nuclear activation by surgically separating all cells in the chain and observing the subsequent occurrence of nuclear changes in these isolated cells. The nuclear activation began at the site of heterotypic union and propagated from cell-to-cell without skipping. In chains of a given length, the propagation slowed down as it proceeded in the chain. If compared at the corresponding site of the chain, the propagation was slower in longer chains. We conclude that meiosis and other nuclear changes in conjugation are initiated by a substance originating at the site of heterotypic union and transferable to other cells through the united regions of the cells.