Metachronal wave and hydrodynamic interaction for deterministic switching rowers

We employ a model system, called rowers, as a generic physical framework to define the problem of the coordinated motion of cilia (the metachronal wave) as a far from equilibrium process. Rowers are active (two-state) oscillators interacting solely through forces of hydrodynamic origin. In this work, we consider the case of fully deterministic dynamics, find analytical solutions of the equation of motion in the long wavelength (continuum) limit, and investigate numerically the short wavelength limit. We prove the existence of metachronal waves below a characteristic wavelength. Such waves are unstable and become stable only if the sign of the coupling is reversed. We also find that with normal hydrodynamic interaction the metachronal pattern has the form of stable trains of traveling wave packets sustained by the onset of anti-coordinated beating of consecutive rowers.Comment: 11 pages, 7 figure

Hydrodynamic flow patterns and synchronization of beating cilia

We calculate the hydrodynamic flow field generated far from a cilium which is attached to a surface and beats periodically. In the case of two beating cilia, hydrodynamic interactions can lead to synchronization of the cilia, which are nonlinear oscillators. We present a state diagram where synchronized states occur as a function of distance of cilia and the relative orientation of their beat. Synchronized states occur with different relative phases. In addition, asynchronous solutions exist. Our work could be relevant for the synchronized motion of cilia generating hydrodynamic flows on the surface of cells.Comment: 5 pages, 4 figures, v2: minor correction

Non-equilibrium raft-like membrane domains under continuous recycling

We present a model for the kinetics of spontaneous membrane domain (raft) assembly that includes the effect of membrane recycling ubiquitous in living cells. We show that the domains have a broad power-law distribution with an average radius that scales with the 1/4 power of the domain lifetime when the line tension at the domain edges is large. For biologically reasonable recycling and diffusion rates the average domain radius is in the tens of nm range, consistent with observations. This represents one possible link between signaling (involving rafts) and traffic (recycling) in cells. Finally, we present evidence that suggests that the average raft size may be the same for all scale-free recycling schemes.Comment: 8 pages, 5 figure

An Outer Arm Dynein Conformational Switch Is Required for Metachronal Synchrony of Motile Cilia in Planaria

Here we use the motile ventral cilia of the planarian S. mediterranea to examine the role of outer arm dynein in the generation and maintenance of metachronal synchrony. We demonstrate that a single dynein light chain plays a mechanosensory role necessary to entrain and maintain the metachronal synchrony of motile cilia

B-Cyclin/CDKs Regulate Mitotic Spindle Assembly by Phosphorylating Kinesins-5 in Budding Yeast

Although it has been known for many years that B-cyclin/CDK complexes regulate the assembly of the mitotic spindle and entry into mitosis, the full complement of relevant CDK targets has not been identified. It has previously been shown in a variety of model systems that B-type cyclin/CDK complexes, kinesin-5 motors, and the SCFCdc4 ubiquitin ligase are required for the separation of spindle poles and assembly of a bipolar spindle. It has been suggested that, in budding yeast, B-type cyclin/CDK (Clb/Cdc28) complexes promote spindle pole separation by inhibiting the degradation of the kinesins-5 Kip1 and Cin8 by the anaphase-promoting complex (APCCdh1). We have determined, however, that the Kip1 and Cin8 proteins are present at wild-type levels in the absence of Clb/Cdc28 kinase activity. Here, we show that Kip1 and Cin8 are in vitro targets of Clb2/Cdc28 and that the mutation of conserved CDK phosphorylation sites on Kip1 inhibits spindle pole separation without affecting the protein's in vivo localization or abundance. Mass spectrometry analysis confirms that two CDK sites in the tail domain of Kip1 are phosphorylated in vivo. In addition, we have determined that Sic1, a Clb/Cdc28-specific inhibitor, is the SCFCdc4 target that inhibits spindle pole separation in cells lacking functional Cdc4. Based on these findings, we propose that Clb/Cdc28 drives spindle pole separation by direct phosphorylation of kinesin-5 motors

Extraction of cilium beat parameters by the combined application of photoelectric measurements and computer simulation.

Photoelectric signals were created and used to investigate the features of the signals as a function of the ciliary beat parameters. Moreover, correlation between the simulated and the measured signals permitted measurement of the cilium beat parameters. The simulations of the signals were based on generation of a series of time-frozen top-view frames of an active ciliary area and determination of the amount of light passing through an observation area in each of these frames. All the factors that might contribute to the shape of the signals, namely, partial ciliary transmittance of light, three-dimensional ciliary beat (composed of recovery, effective, and pause parts), phase distribution on the ciliary surface, and the large number of cilia that contribute to the photoelectric signal, were taken into account in generation of the signals. Changes in the ciliary parameters influenced the shape of the photoelectric signals, and the different phases of the beat could not be directly and unequivocally identified in the signals. The degree of temporal asymmetry of the beat and the portion of the cycle occupied by the pause significantly influenced the shapes of both the lower and the upper parts of the signal and the slopes of the signal. Increases in the angle of the arc swept by the cilium during the effective stroke smoothed the signals and increased the duration of the upper part of the signal. The angle of the arc projected by the cilium onto the cell surface during the recovery stroke had minor effects on the signal's shape. Characteristics of the metachronal wave also influenced the signal's shape markedly. Decreases in ciliary spacing smoothed the signals, whereas ciliary length had a minor influence on the simulated photoelectric signals. Comparison of the simulated and the measured signals showed that the beat parameters of the best-fitting simulated signals converged to values that agree well with the accepted range of beat parameters in mucociliary systems