Evidence for kinesin- and dynein-like protein function in circular nuclear migration in the green alga Pleurenterium tumidum:: Digital time lapse analysis of inhibitor effects

The unicellular green alga Pleurenterium tumidum Breb. performs a unique type of circular nuclear migration, wherein the nucleus leaves its central position and starts revolutions in the cortical isthmus area about 10 h after mitosis. This motion lasts for at least 12 h with an average velocity of about 1 h per revolution. Possible force generation modes during circular nuclear migration of Pleurenterium were investigated by application of inhibitors and the use of digital time-lapse video microscopy. 5'-Adenylylimidodiphosphate, a nonhydrolyzable nucleotide analogue, retarded or inhibited circular nuclear migration, suggesting that ATPase dependent motor proteins are involved. Ado- ciasulfate-2, a kinesin specific inhibitor, caused displacement of the nucleus, suggesting that the linkage between the microtubule track and the nucleus is lost. The nucleus was still able to move for short distances, but no normal revolutions took place. Erythro-9-[3-(2-hydroxynonyl)] adenine, a dynein ATPase inhibitor, led to complete inhibition of nuclear revolutions, suggesting a function in force generation also for this molecular motor. In addition, kinesin- and dynein-like proteins were detected in Pleurenterium extracts by Western blotting. The myosin specific inhibitor 2,3-butanedione 2-monoxime did not influence circular nuclear migration in Pleurenterium. This result and the absence of actin filaments around the migrating nucleus as depicted by means of microinjection of Alexa phalloidin in the present study indicate that the actin-myosin system can be excluded from force generation.