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

Abstract

The intracellular positioning of the centrosome, a major microtubule-organizing center, is important for cellular functions. One of the features of centrosome positioning is the spacing between centrosomes; however, the underlying mechanisms are not fully understood. To characterize the spacing activity inCaenorhabditis elegansembryos, a genetic setup was developed to produce enucleated embryos. The centrosome was duplicated multiple times in the enucleated embryo, which enabled us to characterize the chromosome-independent spacing activity between sister and non-sister centrosome pairs. We found that the timely spacing depended on cytoplasmic dynein, and we propose a stoichiometric model of cortical and cytoplasmic pulling forces for the spacing between centrosomes. We also observed dynein-independent but non-muscle myosin II-dependent movement of centrosomes in the later cell cycle phase. The spacing mechanisms revealed in this study are expected to function between centrosomes in general, regardless of the presence of a chromosome/nucleus between them, including centrosome separation and spindle elongation.

Live-cell imaging under centrifugation characterized the cellular force for nuclear centration in theCaenorhabditis elegansembryo

“…A simple explanation for this discrepancy is the difference in cell size (an ellipsoid with a long axis of 50 μm and short axes of 30 μm for the C. elegans embryo and a sphere with a diameter of 90 μm for the sea urchin egg). If the driving forces are produced throughout the cytoplasm and thus are dependent on the length of the microtubule, as proposed in these organisms 6,[9][10][11][12]38 , it is reasonable for the generated force to depend on the cell size. However, the force-producing mechanism for centration is currently under debate and may involve microtubule pushing against the cell cortex 14,16 or microtubule pulling from the cell cortex 37,39 .…”