Action of phorbol myristate acetate (PMA) at fertilization of mouse oocytes in vitro.

Phorbol ester (PMA) in concentration 5 and 10 ng ml-1 blocks cytokinesis of the second maturation division in mouse oocytes. Karyokinesis is not impaired and digynic triploid oocytes are obtained which undergo first cleavage division. Effectiveness of blocking cytokinesis is dependent on the timing of exposure of oocytes to PMA action. When oocytes are subjected to PMA at the onset of the second maturation division only 14.5% of eggs are triploid. PMA present during fertilization in vitro (about 1 h exposure to PMA) induces triploidy in 40% eggs. Extending the time of exposure of oocytes to 2 h produces 76% tripronucleate eggs. Applicability of PMA is compared with the use of cytochalasin B to induce triploidy in the mouse.