Pushing the spindle upwards with a needle (dotted lines, top) moves the RhoA zone (white) upwards (bottom).
Evidence that the cytokinetic apparatus is dependent on spindle microtubules comes primarily from classical experiments in which the spindle was manually moved or disrupted. On
page 91, Bement et al. reveal the physiology that underlies these findings. Active RhoA localizes to a narrow zone at the site of future furrow formation in a microtubule-dependent manner, and the RhoA zone moves in response to spindle movement.RhoA, a GTPase that positively regulates actin–myosin contraction, has been detected before at the site of furrow formation. However, it wasn't clear if or how RhoA functioned in furrow formation, especially because both guanine nucleotide exchange factors, which activate RhoA, and GTPase-activating proteins, which inhibit are also in the furrow region.
Bement et al. injected sea urchin and Xenopus embryos with a GFP...
