Cell cycle-dependent behavior of microtubules in hybrids of mouse oocytes and blastomeres.

The behavior of microtubules was studied in hybrids formed between mouse oocytes arrested in metaphase II or activated parthenogenetically and mouse embryo interphase blastomeres. In all cases the interphase blastomere's network of microtubules disassembles rapidly after fusion with oocytes. Introduction of interphase cytoplasm and nuclei to metaphase oocytes during fusion induces the polymerization of new microtubules in the cytoplasm and in the meiotic spindle. The degree and the duration of this facilitated polymerization of microtubules was positively correlated with the volume of blastomeres used for fusion. The blastomere nuclei induce the formation of microtubular frames, which become more evident when the chromatin undergoes premature condensation. Finally, spindle-like structures are formed around the prematurely condensed chromosomes. In hybrids activated around the time of fusion, the blastomere nuclei undergo pronuclear-like transformation. These hybrids develop an interphase network of microtubules typical for activated oocytes. These results are discussed with regards to the cell cycle control of microtubule behavior.