Absence of leftward flow and altered gastrocoel roof plate (GRP) morphology in PACRG morphants. (A,B) Loss of leftward flow in PACRG morphant GRPs. Gradient time trail (GTT) projection of directed bead trajectories (25 s, indicated in color bar). (A’,B’) Circular histograms of mean angles of trajectories. (C) Quality of flow, as depicted by the dimensionless number rho. (D,E) SEM analysis of wild-type (D) and PACRG morphant (E) dorsal explants. GRP area indicated by dashed line. Note the loss of posterior polarization of cilia in enlargements of characteristic cells in (D’,E’), and the marked increase in non-ciliated cells (D”,E”). (F) Altered ciliation rates, mean cilia lengths, polarization of residual cilia and mean apical cell surface areas, as assessed in standardized central GRP areas of 86 μm2 each .