CHROMOSOME CONDENSATION ACTIVITY (CCA) IN BISECTED C57BL 6JXCBA MOUSEOOCYTES/

Chromosome condensation activity (CCA) has been analysed in C57BL/6JxC BA mouse oocytes bisected (i) shortly after germinal vesicle breakdown (GVBD), (ii) in metaphase I (MI) and (iii) in metaphase II (MII) into two equal halves (nucleated, enucleated) which were thereafter fused to S- or G2-phase 4-cell-stage mouse blastomeres. In nucleated halves, premature chromosome condensation (PCC) in transplanted nuclei was al ways induced irrespective of the cell cycle stage of the blastomere, w hereas in enucleated halves only G2 nuclei underwent PCC after transpl antation. Premature chromosome condensation in S-phase nuclei was indu ced only in enucleated halves produced shortly after GVBD. Although S- phase nuclei transplanted to MI or MII enucleated halves remained inta ct, their capacity to synthesize DNA was invariably suppressed. When s pindles were destroyed by preincubation of the oocytes in colcemid bef ore bisection, both nucleated and enucleated halves produced at MI or MII induced PCC of both G2- or S-phase nuclei. These results demonstra te that chromosome condensation activity in mammalian oocytes is compa rtmentalized rather than uniformly distributed across the cell, and th at the enucleation of mammalian oocytes before nuclear transplantation may, under some conditions, influence the levels of CCA and subsequen t response of introduced nuclei to cytoplasmic factors.