Figure 3.

(A, B) Posteriorly tilted rotation of nodal cilia. (A) Definition of the analysis parameters. The conic rotation of the nodal cilium was parameterized with the following parameters: tilt of axis, Θ; direction of the axis, Φ; slant height, ρ; and apex angle, Ψ̃. (B) Distributions of the parameters in mouse, rabbit, and medaka embryos. (C, D) Posterior bias in the positions of the roots of the nodal cilia. (C) Fluorescent micrograph of a rabbit node. Green dots show the roots of the nodal cilia, whereas red staining shows the cells' boundaries. The orientation is indicated in the panels as anterior (A), posterior (P), left (L), and right (R). Most of the green dots are located on the posterior side. Scale bar = 10 µm. (D) High-magnification scanning electron micrograph of rabbit nodal ciliated cells. Note the domelike curvature of the apical plasma membrane and posteriorly tilted projection of the monocilia nearly perpendicular to the plasma membrane. Scale bar = 5 µm. (E) Model of the generation of nodal flow. The orientation is indicated as anterior (A), posterior (P), left (L), and right (R). The conic rotation of the nodal cilia is posteriorly tilted. Therefore, the cilia move in a nearly perpendicular manner from right to left. The return movement from left to right occurs just above the cell surface. The viscous drag thus dumps the movement of the fluid to the right (purple). As a result, unidirectional leftward flow (blue) is generated. (Figure modified from Okada et al. 2005 and Hirokawa et al. 2006 with permission.)