Fig. 1.

PIV analysis of the flow velocity distribution in the C. elegans embryo. (A) Both cortical flow and cytoplasmic flow of GFP-labeled yolk granules were observed in embryos of the RT130 strain. We observed migration of yolk granules toward the posterior (P) pole in the central region (left) and toward the anterior (A) pole near the periphery of the cell (right). The black dots denote the position of a single granule over time. t (s) is the time after beginning observation. The black line indicates the initial position (at t = 0) of the black dot granule. (Scale bar, 10 μm.) (B) The flow velocity distribution determined by PIV represented as color maps [representative records: upper, a wild-type embryo; lower, an nmy-2(RNAi) embryo]. Red and blue denote posterior-directed and anterior-directed flow, respectively. The outline of the cell is shown as a black line. (Scale bar, 5 μm.) (C) Quantification of the flow velocity component along the AP axis (//AP) in the posterior half for wild-type and nmy-2(RNAi) embryos. Positive and negative values correspond to posterior-directed and anterior-directed velocities, respectively. White bars, flow velocities in the cytoplasmic region; gray bars, flow velocities in the cortical region. Data are means ± standard deviations (SD). Control (“WT”): n = 6 embryos; nmy-2(RNAi): n = 6 embryos. (D) The definition of x, y coordinates used in this study. x-axis is parallel to the anterior-posterior axis, and y-axis is the axis perpendicular to x-axis on the confocal plane. x = 0 at the posterior pole. y = 0 at the cortex of the middle of the cell, and maximum (y =  ∼ 13 μm) at the cell center. (E) The velocity components at the cell periphery parallel to the cell cortex (//cortex) at position x were plotted (dots). Positive and negative values correspond to posterior-directed and anterior-directed velocities, respectively. Data were fitted with a 3-segment connected line using the least-squares method.