The effects of Ca²⁺and ADP on dynein switching during the beat cycle of reactivated bull sperm models

Abstract

Calcium regulation of flagellar motility is the basis for chemotaxis, phototaxis, and hyperactivation responses in eukaryotic flagellates and spermatozoa. Ca2+ is the internal messenger for these responses, but the coupling between Ca2+ and the motor mechanism that generates the flagellar beat is incompletely understood. We examined the effects of Ca2+ on the flagellar curvature at the switch-points of the beat cycle in bull sperm. The sperm were detergent extracted and reactivated with 0.1 mM adenosine triphosphate (ATP). With their heads immobilized and their tails beating freely it is possible to calculate the bending torque and the transverse force acting on the flagellum at the switch-points. An increase in the free Ca2+ concentration (pCa 8 to pCa 4) significantly decreased the development of torque and t-force in the principal bending direction, while having negligible effect on the reverse bend. The action of Ca2+ was more pronounced when the sperm were also treated with 4 mM adenosine diphosphate (ADP); it was sufficient to change the direction of bending that reaches the greater curvature. We also observed that the curvature of the distal half of the flagellum became locked in one direction in the presence of Ca2+ . This indicates that a subset of the dynein becomes continuously activated by Ca2+ and fails to switch with the beat cycle. Our evidence suggests this subset of dyneins is localized to doublets #1-4 of the axoneme.

Intracellular Ca2+ threshold reversibly switches flagellar beat off and on†

“…Ca 2+ appears to disproportionately influence dynein motors situated on one side of the ring of dynein doublets [3,25,32]. It is suspected that high [Ca 2+ ] i levels may lock certain dyneins into a sustained activation state which impedes switching with the period of the beat cycle [32,33,34], due to the production of force and bending torque acting to bend the flagellum in one direction. This would explain why high [Ca 2+ ] i arrests many types of cilia and flagella [35].…”

Dynein‐deficient flagella respond to increased viscosity with contrasting changes in power and recovery strokes

“…This could be due to early termination of activity on the set of doublets (6-7-8) responsible for the recovery stroke, or early initiation of dynein activity on the doublets (2-3-4) responsible for the power stroke, or both (Lesich et al, 2014). In contrast, oda2 cells are able to maintain a large amplitude waveform despite lower average curvature values (Figure 8) by completing a longer power stroke before the recovery stroke begins (Figure 12).…”

“…King (King, 2010) has proposed a mechanism for force feedback in the outer dynein arms based on tension sensing by the γHC-LC1-LC4- microtubule complex (King, 2010). Lindemann and co-authors (Lindemann, 2002, 1994c, Lesich et al, 2014; Lindemann and Lesich, 2010) have presented a large body of evidence in support of a relationship between inter-doublet-spacing, transverse force, and dynein activity: the “geometric clutch” hypothesis (Figure 14). Since the transverse force is roughly proportional to the product of cumulative dynein force and curvature (Bayly and Wilson, 2014; Lindemann, 1994a), it is plausible that at high viscosity the threshold levels of transverse force required for switching are reached earlier in the stroke.…”

“…King [2010] has proposed a mechanism for force feedback in the outer dynein arms based on tension sensing by the cHC-LC1-LC4-microtubule complex. Lindemann and coworkers [Lindemann, 1994b,;Lindemann and Lesich, 2010;Lesich et al, 2014] have presented a large body of evidence in support of a relationship between interdoublet-spacing, transverse force, and dynein activity: the "geometric clutch" hypothesis ( Fig. 14).…”

The axoneme: the propulsive engine of spermatozoa and cilia and associated ciliopathies leading to infertility

“…The rate of increase in intracellular calcium (from pCa 8 to pCa4) is followed by a G-protein signaling cascade in conjunction with a brief depolarization of the sperm membrane and a rise in cAMP levels. These signals are transmitted to, and stimulate the axoneme, and evidence implicates phosphorylation of radial spoke/CPMA interactions that relay to the phosphorylation of inner dyneins and nexin-DRC, which according to Lindemann and colleagues [ 117 ] may determine which doublet microtubules on which side of the axoneme will slide in a given sequence (Fig. 6 ); dephosphorylation presumably returns the axoneme to it prestimulated state.…”