Mechanism of flagellar oscillation–bending-induced switching of dynein activity in elastase-treated axonemes of sea urchin sperm

Abstract

Oscillatory movement of eukaryotic flagella is caused by dynein-driven microtubule sliding in the axoneme. The mechanical feedback from the bending itself is involved in the regulation of dynein activity, the main mechanism of which is thought to be switching of the activity of dynein between the two sides of the central pair microtubules. To test this, we developed an experimental system using elastase-treated axonemes of sperm flagella, which have a large Ca2+-induced principal bend (P-bend) at the base. On photoreleasing ATP from caged ATP, they slid apart into two bundles of doublets. When the distal overlap region of the slid bundles was bent in the direction opposite to the basal P-bend, backward sliding of the thinner bundle was induced along the flagellum including the bent region. The velocity of the backward sliding was significantly lower than that of the forward sliding, supporting the idea that the dynein activity alternated between the two sides of the central pair on bending. Our results show that the combination of the direction of bending and the conformational state of dynein-microtubule interaction induce the switching of the dynein activity in flagella, thus providing the basis for flagellar oscillation.

Ttll9 −/− mice sperm flagella show shortening of doublet 7, reduction of doublet 5 polyglutamylation and a stall in beating

“…4F), its deficiency could impair the initiation of pro-hook bend. A shortened doublet 7 would perturb any feedback system from distal to proximal flagellum (Hayashi and Shingyoji, 2008).…”

Flagellar and ciliary beating: the proven and the possible

“…By looking at individual doublet pairs sticking out from the frayed end of a Chlamydomonas flagellum, they showed that the pairs of doublets set up a limited beat of their own by sliding and bending to a critical bend angle and then separating near the base where the t-force is greatest. Recent important studies have demonstrated that imposed bending can initiate and reverse episodes of sliding in sea urchin sperm flagella when the doublets have been freed to slide by enzymatically cutting the nexin links with elastase (Morita and Shingyoji, 2004;Hayashi and Shingyoji, 2008); moreover, imposed bending can initiate beating at very low ATP concentrations (Ishikawa and Shingyoji, 2007). These results demonstrated that the curvature imposed on the partially digested structure controls the direction of dynein-driven sliding as the axoneme disintegrates.…”

“…It is equally possible that the action of the bending is mediated through a mechanism that senses the direction and degree of spoke tilting and relays an activating signal to the dyneins on one side, Recent reports (Morita and Shingyoji, 2004;Hayashi and Shingyoji, 2008) have shown that bending can initiate microtubule sliding and can determine which doublets are activated. The illustration shows a mechanism that might be responsible for the selection, but does not invoke CP-or spoke-dependent regulation.…”

Effects of external strain on the regulation of microtubule sliding induced by outer arm dynein of sea urchin sperm flagella

“…There has been a report on using axonemal tubulin (95%)-derived microtubules for the in vitro motility assay of axonemal dynein, but it only shows higher velocity in short (<6 µm) conspecific microtubules than those polymerized from porcine brain tubulin (100%), and does not show any significant difference in longer microtubules (Alper et al, 2013; see the next section for the description of the lengths of the microtubules used in the present study). Micromanipulation was carried out according to our previously developed method (Morita and Shingyoji, 2004;Hayashi and Shingyoji, 2008) with some modifications. In our open-surface chamber, sliding velocity of the microtubules was 4.6±1.1 µm s −1 (mean±s.d.…”

“…How are the dynein activities regulated and coordinated in flagella? Studies using intact sperm or demembranated flagellar axonemes have revealed that the sliding activities of dynein can be modulated by external strain or bending imposed to the axoneme when dynein is within the 9+2 structure of a flagellum (Gibbons et al, 1987;Shingyoji et al, 1991;Morita and Shingyoji, 2004;Hayashi and Shingyoji, 2008). This leads to an idea of the 'feedback regulation' of dynein in the axoneme, in which the inter-doublet sliding induced by dynein results in the bending of the axoneme, and the bending regulates the dynein activities in turn.…”