Fig. 4. Defects in cilia beat of the Tg737^orpk mutant result in impaired fluid flow over the ependymal cells. Red and yellow arrowheads label the ependyma and ependymal apical cilia, respectively. (A,B) DIC (A) and fluorescence (B) images of wild-type and mutant ependyma. Fluorescence images were overlaid with the movement of the fluorescently labeled beads, as recorded by motion tracking (yellow lines, see Movie 1 in the supplementary material). Movement of the beads propelled by wild-type cilia beating was rapid and directional, whereas movement of the beads in the mutant samples was random. Scale bar: 20 µm. (C) Graph showing quantitative analysis of the flow generated by the cilia in the left (LV) and fourth (4V) ventricles from mutant and wild-type samples (n=6; ^*P<0.005).