RESPONSE OF AVIAN NUCLEI TO MAMMALIAN MATURATION PROMOTING FACTOR (MPF)

Chicken blastodermal cells (stage X) were fused to mouse enucleated oo cytes with either no or high maturation promoting factor (MPF) activit y. High MPF levels always induced premature chromosome condensation (P CC) irrespective of the number of nuclei fused to a single oocyte. Whe n a single blastodermal cell was fused to a single oocyte without MPF activity the nucleus remained intact for up to 3 h and thereafter unde rwent PCC. A quite different situation was observed after multiple fus ion of several blastodermal cells to a single oocyte without MPF activ ity. Here, the transplanted nuclei remained intact even after prolonge d culture but underwent extensive swelling. DNA synthesis was detected in almost all unfused blastodermal cells. However, after the fusion o f several blastodermal cells to a single oocyte no DNA synthesis could be detected. These results provide further evidence that MPF is the u niversal cell-cycle regulator in the animal kingdom. Its activity is b locked (or neutralised) after fusion to several S-phase cells. Interes tingly, our results further suggest that DNA synthesis is suppressed i n meiotic cytoplasm even in the presence of an intact nuclear envelope .