INDUCTION OF TEMPORARY BEATING IN PARALYZED FLAGELLA OF CHLAMYDOMONASMUTANTS BY APPLICATION OF EXTERNAL FORCE

To help understand the mechanism by which the sliding movement of oute r-doublet microtubules in cilia and flagella is converted into bending waves, we examined the effect of mechanical force imposed on the flag ella of Chlamydomonas mutants lacking the central pair or multiple dyn eins. These mutants were almost completely nonmotile under normal cond itions. A bend was produced in a flagellum either by holding a cell wi th a micropipette and quickly moving it with a piezoelectric actuator, or by pushing a flagellum with a microneedle. After removal of the ex ternal force, mutants lacking the central pair (pf18 and pf19) display ed beating at irregular intervals of >1 second for one to several cycl es. Similarly, a double mutant (ida2ida4) lacking four species of inne r-arm dynein displayed beating at intervals of >0.1 second for up to 8 0 cycles. However, paralyzed flagella of double mutants that lack the outer dynein arm in addition to the central pair or the inner dynein a rm did not show cyclical movements upon application of external force, These results indicate that the central pair and the inner dynein arm are important fur both stable bend formation at the base and efficien t bend propagation along the flagellar length, They also suggest that the outer dynein arm, and not the inner dynein arm, enables the flagel lar axoneme to propagate bends independently of the central pair. We p ropose that the axoneme is equipped with two independent motor systems for oscillatory movements: an outer-arm system controlled by the axon emal mechanical state independently of the central pair/radial spoke s ystem, and an inner-arm system controlled by both the axonemal mechani cal state and the central pair/radial spokes. (C) 1997 Wiley-Liss, Inc .