Cell surface interactions in conjugation: Tetrahymena ciliary membrane vesicles.

Tetrahymena ciliary membrane vesicles are shown to interact with preconjugant cells in a mating type-specific way. When cells are treated with vesicles of a different mating type before mixing for conjugation, cell pairing is enhanced, and the normal prepairing period is partially eliminated. This enhancement is mating type specific since it is not observed after pretreatment of cells with vesicles of their own mating type. In contrast, when vesicles are added at the time of mixing of two starved cultures, cell pairing is delayed in a concentration-dependent manner. By varying the conditions, we demonstrated enhancement or inhibition, or both. These results are interpreted in terms of two independent interactions of cells with vesicles. We suggest that first, vesicles substitute for another cell in cell-cell prepairing interaction and second, vesicles compete for adhesion sites produced during the prepairing period. Finally, the data presented are summarized within a speculative framework that calls attention to potential analogies with hormone-receptor signaling in mammalian cells.