A preliminary study of dynein-driven ciliary motility: a computational model

The movement of embryonic cilia presents a crucial function in specifying the left-right axis for vertebrates. Those mono-cilia are primary (9+0) cilia, whose characteristic architecture is based on a cylindrical arrangement of 9 microtubule doublets. Dynein motors located between adjacent doublets convert the chemical energy of ATP hydrolysis into mechanical work that induces doublet sliding. Passive components, such as the mediated cytoplasm, the ciliary membrane, and other possibly-existent structures constraint the ciliary motion and maintain the cilia structural integrity, thus resulting in the axonemal bending. Dynein motors located along microtubule doublets of a motile nodal cilium activate in a sequential manner. However, due to inherent difficulties, the dynein activation patterns in moving cilia can hardly be directly observed. The exact mechanism that controls ciliary motion is still unrevealed. In this work, we present a protein-structure model to simulate the ultrastructure of embryonic cilia and to study the dynein-dependent ciliary motility. This model includes time accurate three-dimensional solid mechanical analysis of the sliding between adjacent microtubule doublets and their induced ciliary bending. As a conceptual test, the mathematical model provides a platform to investigate various assumptions of dynein activity, which facilitates us to evaluate their rationality and to propose the most possible dynein activation pattern. The proposed protein-trigger pattern can reproduce the rotation-like ciliary motion as observed by experiments. This computational model may improve our understandings regarding the protein-beating problems of cilia, and may guide and inspire further experimental investigations on this topic.