RhoA activation is autocatalytic. (A) The time derivative of normalized RhoA activity (GFP::AHPH) plotted versus normalized activity during the early phase of pulse initiation in the P0 (top: n = 40 pulses in four embryos) and AB (bottom: n = 41 pulses in seven embryos). Error bars indicate 95% confidence interval. (B and C) Analysis of pulse dynamics in embryos progressively depleted of RHO-1 by RNAi. (B) Top panels show GFP::AHPH distributions in interphase embryos from mothers subjected to no (wild-type), 10 h, and 13 h of rho-1(RNAi). Middle panels show kymographs from the same embryos illustrating spatiotemporal dynamics of GFP::AHPH from interphase through cytokinesis. Dashed yellow lines indicate approximate pattern of cortical flow. Cyan arrowheads indicate accumulation of GFP::AHPH just before cytokinesis. (C) Timeline indicating the presence (magenta circles) or absence (cyan circles) of pulsing in embryos treated with rho-1(RNAi) for the indicated times, revealing an abrupt transition from pulsing to no pulsing at ∼12 h after treatment. Bars, 5 µm.