Unique effects of spindle inhibitors on mammalian oocyte meiosis.

The effects of Nocodazole, reported to be a rapidly reversible inhibitor of microtubules in somatic cells (1), and Colcemid, a classic microtubule inhibitor, were studied for their effects on mouse and cow oocyte in vitro meiotic resumption. When present throughout the maturation period to Metaphase II/Polar Body I, both compounds predictably inhibited progression at Metaphase I (MI). An unexpected effect was seen on mouse germinal vesicle breakdown (GVB) with both inhibitors, but not in cow oocytes tested with Nocodazole. Recovery from Nocodazole was notably retarded in mouse oocytes even with brief exposure times. Addition of 1 microgram/ml of Nocodazole 10 min after commencement of mouse and cow oocyte incubation was sufficient time to allow normal GVB, while inhibition at MI still took place suggesting that the critical events of GVB occur very quickly in vitro.