Effects of cytochalasin B on steroid-induced oocyte meiosis and centrifugally induced nuclear movement in the goldfish Carassius auratus.

In goldfish, 17 alpha, 20 beta-dihydroxyprogesterone (DHP) induced oocyte nucleus or germinal vesicle migration (GVM) and dissolution (GVD) in a dose-related fashion. Administration of cytochalasin B (CB) in the presence of DHP inhibited the steroid-induced GVM and GVD after 24 and 48 h of incubation. The presence of CB alone, at concentrations below 25 micrograms/mL, had no effect on GVM or GVD. Furthermore, CB, either alone or in combination with DHP, elicited significant increases in follicular diameter after 24 and 48 h of incubation. To test the effect of CB on ooplasmic viscoelasticity, fully grown follicles were centrifuged and the centrifugally induced germinal vesicle (GV) displacement was determined. Pretreatment (24 h) of follicles with high doses of CB (25 and 50 micrograms/mL) increased the movement of GV in a centripetal direction. However, at lower concentrations (0.005-5 micrograms/mL), CB treatment was without an effect on the centrifugally induced GV movement in the oocyte. The present study suggests involvement of microfilaments or other cytoskeletal components, sensitive to CB, in the mechanisms of GVM and GVD in goldfish oocytes. In addition, a simple technique has been described for testing ooplasmic viscoelasticity determined by movement of the GV under a centrifugal force.