Rotation and twist of the central-pair microtubules in the cilia of Paramecium.

Abstract

The orientation and configuration of the central-pair microtubules in cilia were studied by serial thin-section analysis of "instantaneously fixed" paramecia. Cilia were frozen in various positions in metachronal waves by such a fixation . The spatial sequence of these positions across the wave represents the temporal sequence of the positions during the active beat cycle of a cilium . Systematic shifts of central-pair orientation across the wave indicate that the central pair rotates 360°counterclockwise (viewed from outside) with each ciliary beat cycle (C . K. Omoto, 1979, Thesis, University of Wisconsin, Madison; C. K. Omoto and C. Kung, 1979, Nature [Lond .] 279:532-534) . This is true even for paramecia with different directions of effective stroke as in forward-or backward-swimming cells. The systematic shifts of centralpair orientation cannot be seen in Ni"-paralyzed cells or sluggish mutants which do not have metachronal waves. Both serial thin-section and thick-section high-voltage electron microscopy show that whenever a twist in the central pair is seen, it is always left-handed . This twist is consistent with the hypothesis that the central pair continuously rotates counterclockwise with the rotation originating at the base of the cilium . That the rotation of the central pair is most likely with respect to the peripheral tubules as well as the cell surface is discussed . These results are incorporated into a model in which the central-pair complex is a component in the regulation of the mechanism needed for three-dimensional ciliary movement .Cilia (eucaryotic flagella and sperm tails) have been studied to determine the function of the components responsible for generating motion (reviewed in references 4, 14, and 40) . The sliding-microtubule model is now accepted as the fundamental motile mechanism for cilia . In the late 1960's Satir (39) produced the first evidence for sliding rather than contraction as the basis for ciliary motion. The sliding-microtubule hypothesis was given support by the direct demonstration of sliding disintegration in trypsin-treated axonemes by Summers and Gibbons (46) . The force that causes the ciliary microtubules to slide is generated by the pair of dynein arms that project out periodically along the length of each peripheral microtubule doublet (11). Sliding was shown to be unipolar by Sale and Satir (37) in Tetrahymena cilia .Studies indicate some interaction between the radial spokes of the peripheral doublets and the projections from the central pair (47,51) . It is suggested that such an interaction converts sliding to bending, but how sliding of the peripheral doublets is transduced into active coordinated beating of cilia is not known . The functions in motility of such components as the radial spokes and the central-tubule complex are largely un-

Asymmetry of the central apparatus defines the location of active microtubule sliding in Chlamydomonas flagella

“…Our data do not address the role of central apparatus twist during beating. Most likely, twist allows for regulation of dynein activity along the length of the axoneme as predicted by Omoto and Kung (18).…”

“…The central apparatus in Chlamydomonas, as well as in other organisms, is reported to twist (9,18,55). In each case, the twist is left-handed, though the pitch of the twist is variable.…”

“…In these organisms, the central pair projections may periodically interact with subsets of radial spokes, distributing an ordered and sequential signal to the dynein arms (17,18). We hypothesized that if the asymmetry of the central apparatus specifies dynein activity on subsets of doublet microtubules, then the orientation of the central apparatus would correlate with the location of dynein-driven microtubule sliding.…”

Immunogold method evidences that kinesin and myosin bind to and couple microtubules and actin filaments in lipotubuloids of Ornithogalum umbellatum ovary epidermis

“…Our earlier studies on lipotubuloid movement in O. umbellatum revealed that in a vigorously rotating lipotubuloid microtubules exhibited different widths or diameters on longitudinal (Kwiatkowska 1972) or cross (Kwiatkowska et al 2009) sections, respectively. The use of OsO 4 for direct fixation of microtubules, due to its quick penetration, allowed to maintain their structure identical to that observed in vivo (Omoto and Kung 1980). Differences in size were even visible in the microtubules consisting of the same number of protofilaments (Kwiatkowska et al 2009).…”

The Evolution of Eukaryotic Cilia and Flagella as Motile and Sensory Organelles

“…The geometry of this regulatory mechanism presumably favors an outer cylinder of precisely nine doublet microtubules, with the distance between doublets determined by the reach of dyneins that must span each interdoublet gap. Whether central pair regulation was based on a fixed central pair orientation, as found today in metazoans such as bivalves 48 , sea urchins 49 , and ctenophores 50 and possibly in excavates such as euglenids 51 , or a rotating central pair 52 , as commonly found in green algae such as Chlamydomonas 53 and Micromonas 54 , and chromalveolates such as Paramecium 55 and Synura 56 , remains to be determined. Central pair rotation may allow regulation of bends in different beat planes, and therefore be a more flexible regulatory system for organisms whose survival is most highly dependent on rapid changes in flagellar beat parameters 47,53 .…”