THE EFFECTS OF DIAZEPAM ON MITOSIS AND THE MICROTUBULE CYTOSKELETON .1. OBSERVATIONS ON THE DIATOMS HANTZSCHIA-AMPHIOXYS AND SURIRELLA-ROBUSTA

The effects of diazepam (DZP) on mitosis and the microtubule (MT) cyto skeleton in the live diatoms Hantzschia amphioxys and Surirella robust a were followed using time-lapse video microscopy. Similarly treated c ells were fixed and later examined for immunoflouresence staining of M Ts or for transmission electron microscopy. DZP treatment (250 mu M) h ad no effect on interphase cells but affected mitosis, resulting in th e majority of prometaphase and metaphase chromosomes releasing from on e or both spindle poles and collecting irregularly along the central s pindle. Chromosomes remaining attached to one pole continued to displa y slight prometaphase oscillations; however, this activity was never o bserved in metaphase spindles. Following removal of DZP, some chromoso mes still bipolarly attached, immediately released elastically from on e pole. Within the first 2 minutes of recovery, all chromosomes recomm enced spindle attachment, exhibiting normal prometaphase oscillations and proceeded through mitosis. DZP treatment during anaphase had no de tectable effect on chromosome motion or cell cleavage.These results su ggest that DZP acts as an anti-MT agent, selectively affecting polar M Ts at prophase, prometaphase and metaphase, and thereby weakening kine tochore connection to the poles. From these and other results (unpubli shed), its mode of action is different to that of most anti-MT agents.