Excessive centrosomes often lead to multipolar spindles, and thus probably to multipolar mitosis and aneuploidy. In Caenorhabditis elegans, approximately 70% of the paternal emb-27APC6 mutant embryonic cells contained more than two centrosomes and formed multipolar spindles. However, only 30% of the cells with tripolar spindles formed two cytokinetic furrows (Figure A, right). The rest formed one furrow, like normal cells (Figure A, left). To investigate the mechanism underlying this inconsistency, we conducted live-cell imaging in emb-27APC6 mutant cells. We observed that the chromatids were aligned only on two of the three sides of the tripolar spindle, and the angle of the tripolar spindle relative to the long axis of the cell correlated with the number of cytokinetic furrows (Figure B). Our numerical modeling showed that the combination of cell shape, cortical pulling forces, and heterogeneity of centrosome size determines whether cells with tripolar spindle form one or two cytokinetic furrows.

Figure:
(A) Images of a living C. elegans embryo with three centrosomes (arrows). In 1-furrow cytokinesis (left), a cleavage furrow (arrowheads) was observed between separated chromatids. In 2-furrow cytokinesis (right), two cleavage furrows (arrowheads) were observed.
(B) The proposed model showing how 1-furrow and 2-furrow cytokinesis are determined depending on the angle of tripolar spindle.