Choice between 1- and 2-furrow cytokinesis inCaenorhabditis elegansembryos with tripolar spindles

Abstract

Excessive centrosomes often lead to multipolar spindles, and thus probably to multipolar mitosis and aneuploidy. In Caenorhabditis elegans, ∼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. The rest formed one furrow, similar to normal cells. To investigate the mechanism via which cells avoid forming two cytokinetic furrows even with a tripolar spindle, we conducted live-cell imaging in emb-27APC6 mutant cells. We observed that the chromatids were aligned on only 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. Our numerical modeling showed that the combination of cell shape, cortical pulling forces, and heterogeneity of centrosome size determines whether cells with a tripolar spindle form one or two cytokinetic furrows.

Enucleation of theC. elegansembryo revealed dynein-dependent spacing between microtubule asters

“…The centrosomes migrate toward the cell center and meet the oocyte pronucleus. The emb-27 mutants affected the number of centrosomes supplied by the sperm ( Kondo & Kimura, 2018 Preprint , 2019 ). Consequently, the presence of 1–4 centrosomes was observed in the one-cell stage emb-27 mutant and in the enucleated embryo.…”

Cytoplasmic streaming drifts the polarity cue and specifies the cell polarity inCaenorhabditis eleganszygotes

“…(carrying fem-1(hc17)) hermaphrodites 30 were grown at restrictive temperature (25 °C) and were mated to CAL0841 (carrying him-5(e1490)) males. CAL1041 hermaphrodites were mated to CAL1651 (carrying him-5(e1490)) males at 22 °C.…”

Enucleation of theC. elegansembryo revealed the mechanism of dynein-dependent spacing between microtubule asters

“…In the 3-dimensional space (ellipsoid), we placed force generators in the cytoplasm and in a thin layer of the cortex uniformly (Fig. 5B), similar to our previous simulation (Kondo and Kimura, 2019). The centrosomes were positioned corresponding to their initial positions in representative experiments (Table S3).…”

“…The settings of our previous simulation (Kondo and Kimura, 2019) were modified to model the embryo as a 3D ellipsoid with the long axis of 46.0 μm and the two short axes of 27.6 μm based on the size of a representative enucleated (control) embryo. For the simulation of gene knockdown conditions, we modified the sizes based on the sizes of each condition (Table S3).…”

“…The parameter values used for the numerical simulations are summarized in Supplemental Tables S2 and S3. We followed the embryo geometry based on the experimental measurements and the simulation setup in our previous study (Kondo and Kimura, 2019). The parameters for force generation are basically the same as those of Farhadifar et al (2020).…”