Regulation of outer-arm-dynein activity by phosphorylation and control of ciliary beat frequency

Abstract

Summary. Ciliary beating is empowered by a mechanochemical enzyme, dynein, which appears as two rows of projections on doublet microtubules. While inner-arm dyneins modulate beat form, outer-arm dynein empowers ciliary beat and sets beat frequency. Beat frequency is controlled via phosphorylation of outer-arm dynein. Using Paramecium tetraurelia as model system, we have previously identified a regulatory light chain of outer-arm dynein (22S dynein), Mr29 (p29), whose phosphorylation is cAMP-dependent. The phosphorylation state of the p29 in 22 S dynein determines in vitro microtubule translocation velocity. Although in vitro phosphorylation of p29 takes place in a short time, the percent change ist significantly less than the percent change in dynein activation, or in ciliary beat frequency. A potential mechanism that explains how a few activated dyneins can change ciliary beating is discussed.

Dephosphorylation of inner arm 1 is associated with ciliary reversals in Tetrahymena thermophila

“…Hyperpolarizing stimuli, such as chemoattractants [Van Houten, 1979], posterior mechanical stimulation [Naitoh and Eckert, 1969], or the overall ionic concentration of the bathing medium [Bonini et al, 1986], increase ciliary beat frequency and result in fast forward swimming. Hyperpolarization is thought to lead to phosphorylation of an outer dynein arm subunit and increased beat frequency and faster swimming [Bonini et al, 1986;Hamasaki et al, 1991Hamasaki et al, , 1998Barkalow et al, 1994;Hamasaki, 1999;Christensen et al, 2001]. Conversely, depolarizing stimuli, such as chemorepellants [Clark et al, 1993;Hennessey et al, 1995;Kim et al, 1999], anterior mechanical stimulation [Naitoh and Eckert, 1969], or ionic stimuli [Machemer et al, 1988a], cause temporary ciliary reversal and backward swimming or an avoidance response (repetitive bouts of forward and backward swimming).…”