Cell Architecture Laboratory / Kimura Group

A joint group of Drs. Nicolas Minc at Institut Jacques Monod (France) and Akatsuki Kimura at National Institute of Genetics/SOKENDAI analyzed the centering of microtubule asters in the sea urchin egg, and constructed a quantitative model that dictates the speed and trajectory of the centering in normal cell as well as shape-manipulated cells. The study was initiated when Prof. Kimura was a visiting researcher at the Minc lab through the SOKENDAI Young Faculty Overseas Visit Program.

In this study, Dr. Hirokazu Tanimoto et al. utilized multiple approaches such as laser ablation and pharmacological assays to demonstrate that the centering is accomplished by the forces pulling on asters from the cytoplasm. An interesting feature of the centering was to find that asters moved at a constant speed. Considering the speed was comparable to that of the growth speed of the aster, Tanimoto et al. proposed a theoretical model for the centering that explains the constant speed independent on the actual size of the aster. The model predicts well the change of the speed and trajectory of asters when the shape of the cells was manipulated in micro-chambers. Overall, this study advanced our understanding on the long-standing debate on the mechanism of the centering of microtubule asters and their associating nucleus.

See also: Ben Short “How asters find their center” J Cell Biol 212, 743 (2016) DOI: 10.1083/jcb.2127if

(A) The centering of microtubule asters (green) in the sea urchin embryo. The size of the embryo is large compared to C. elegans. The aster does not cover the entire cell during the centering, and the center of the aster (red) approaches the cell center with a speed comparable to the growth speed of the aster.
(B) Examples of shape manipulation using micro-chambers. The sperm pronucleus (i.e. the center of the aster, green) moves toward the center. (The entire trajectories are shown on the rightmost panels.) The theoretical model constructed in the study reproduces the speed and trajectory of aster movements even in the shape-manipulated embryos.