Beating of Cilia of Sea Urchin Embryos: A Critical Comparison of the Normal and Reversed Beating of Cilia of Isolated Cells

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Abstract
Two different types of ciliary beating, normal and reversed, were analyzed on the same cilia on cells isolated from echinoplutei. Bends on the cilium in reversed beating were observed to increase in curvature during propagation in the effective stroke of the beat, whereas in normal beating, bends propagate with a constant curvature in both effective and recovery strokes. The proximal region of the cilium showed an almost identical oscillation of shear angle in both normal and reversed beating with respect to the time normalized to the average beat period, which was determined by the rotational movement of the cell body. In reversed beating, a common temporal profile generated at the proximal region was preserved in the oscillation over the length of the cilium. The local oscillations in normal beating, however, changed in temporal profile as seen from base to tip. The conversion of the temporal oscillatory profile from normal to reversed beating occurred in association with changes in the centre of the oscillation (static bias), whose difference increased with the distance from the base. The data indicate that the changes in bending pattern between normal and reversed beating of sea urchin embryo cilia are not due to changes in the initiation of the oscillation at the base, but largely to temporal and static changes in the pattern of propagation of the oscillatory activity.