Nonlinear amplitude dynamics in flagellar beating

TL;DR

This paper explores the nonlinear dynamics of flagellar beating by modeling dynein motor activity, revealing how nonlinear amplitude selection and mode saturation occur without nonlinear axonemal responses.

Contribution

It introduces a new axonemal sliding control model for dynein activity, demonstrating nonlinear amplitude selection and mode saturation mechanisms in flagellar beating.

Findings

Nonlinear amplitude selection occurs naturally in the model.

Unstable modes saturate through dynein-flagellum coupling.

The model explains flagellar dynamics without nonlinear axonemal responses.

Abstract

The physical basis of flagellar and ciliary beating is a major problem in biology which is still far from completely understood. The fundamental cytoskeleton structure of cilia and flagella is the axoneme, a cylindrical array of microtubule doublets connected by passive crosslinkers and dynein motor proteins. The complex interplay of these elements leads to the generation of self-organized bending waves. Although many mathematical models have been proposed to understand this process, few attempts have been made to assess the role of dyneins on the nonlinear nature of the axoneme. Here, we investigate the nonlinear dynamics of flagella by considering an axonemal sliding control mechanism for dynein activity. This approach unveils the nonlinear selection of the oscillation amplitudes, which are typically either missed or prescribed in mathematical models. The explicit set of nonlinear equations are derived and solved numerically. Our analysis reveals the spatiotemporal dynamics of dynein populations and flagellum shape for different regimes of motor activity, medium viscosity and flagellum elasticity. Unstable modes saturate via the coupling of dynein kinetics and flagellum shape without the need of invoking a nonlinear axonemal response. Hence, our work reveals a novel mechanism for the saturation of unstable modes in axonemal beating.