Demecolcine effects on microtubule kinetics and on chemically assisted enucleation of bovine oocytes.

This study aimed to evaluate the effect of demecolcine, a microtubule-depolymerizing agent, on microtubule kinetics; to determine the best concentration of demecolcine as a chemically assisted enucleation agent in metaphase I (MI) and metaphase II (MII) bovine oocytes, and to evaluate the embryonic development after nuclear transfer (NT) using chemically assisted enucleation of recipient oocytes. Oocytes in vitro matured for 12 h (MI) and 21 h (MII) were exposed to several concentrations of demecolcine and evaluated for enucleation or membrane protrusion formation. Demecolcine concentration of 0.05 microg/mL produced the highest rates of enucleation in group MI (15.2%) and protrusion formation in group MII (55.1%), and was employed in the following experiments. Demecolcine effect was seen as early as 0.5 h after treatment, with a significant increase in the frequency of oocytes with complete microtubule depletion in MI (58.9%) and MII (21.8%) compared to initial averages at 0 h (27.4% and 1.9%, respectively). Microtubule repolymerization was observed when MII-treated oocytes were cultured in demecolcine-free medium for 6 h (42.4% oocytes with two evident sets of microtubules). Chemically assisted enucleated oocytes were used as recipient cytoplasts in NT procedures to assess embryonic development. For NT, 219 of 515 oocytes (42.5%) formed protrusions and were enucleated, and reconstructed, resulting in 58 nuclear-transferred one-cell embryos. Cleavage (84.5%) and blastocyst development (27.6%) rates were assessed. In conclusion, demecolcine can be used at lower concentrations than routinely employed, and the chemically assisted enucleation technique was proven to be highly efficient allowing embryonic development in bovine.