Estramustine phosphate inhibits germinal vesicle breakdown and induces depolymerization of microtubules in mouse oocyte.

The first meiotic cell division (meiotic maturation) of the dictyate stage of mouse oocytes, removed from the follicle, resumes spontaneously in vitro. This study indicates that estramustine phosphate reversibly blocks meiotic maturation by inhibiting germinal vesicle breakdown. Oocyte cryostat sections were stained with anti-tubulin and two antibodies (anti-MAP1: JA2 and 5051) which decorated the metaphase spindle during meiotic maturation. It was found that (1) estramustine phosphate depolymerized microtubules in ovo and dispersed non-tubulin antigens associated with microtubules of the metaphase spindle at various stages of maturation, and (2) estramustine phosphate decreased the ability of taxol to induce cytoplasmic asters. These results suggest that germinal vesicle breakdown and microtubule polymerization may be linked.