New evidence for a "biased baseline" mechanism for calcium-regulated asymmetry of flagellar bending.

Time-averaged data covering six to ten beat cycles for ATP-reactivated spermatozoa of a sea urchin and Ciona, and from a uniflagellate mutant of Chlamydomonas, were analyzed to obtain parameters of oscillation and mean shear angle at each point along the flagellum. The mean shear angles usually show a sharp change near the base of the flagellum. This sharp basal change in angle is correlated with perceived asymmetry in the development times of principal and reverse bends when these bends are measured directly from the asymmetric bending patterns, without subtracting out the mean shear angle. The asymmetry in development times was previously considered to be evidence against a "biased baseline" mechanism for asymmetric bending waves, in which completely symmetric bending waves develop and propagate on a curved flagellum. Our analysis now shows that the asymmetry in development times can be fully explained by the presence of a sharp static bend near the base of the flagellum, which can confuse the determination of the times of initiation of new bends at the base of the flagellum. Our reinterpretation of these data removes previous objections to the "biased baseline" mechanism for the regulation of bending wave asymmetry by calcium, and supports other evidence favoring a biased baseline mechanism, rather than a "biased switching" mechanism.