Pronuclear fusion failure: an alternate conjugational pathway in Tetrahymena thermophila, induced by vinblastine.

Vinblastine is shown to induce pronuclear fusion failure in conjugating Tetrahymena thermophila. In this alternate conjugational pathway gametic pronuclei are exchanged between conjugants but do not fuse. Each pronucleus undergoes one mitotic division to produce a new macro- and micronucleus. Genetic consequences of pronuclear fusion failure include the following: (1) the progeny are whole genome homozygotes with nuclei derived from single meiotic products, and (2) half of the progeny are heterokaryons with micro- and macronuclei of different genetic origins. These facts make this process extremely useful in strain construction and mutant isolation. The induction of pronuclear fusion failure by vinblastine suggests that microtubules play an essential role in pronuclear fusion.