An Investigation of the Mechanism Producing Rhythmic Beating in Cilia and Flagella

Oakland University, Rochester MI

Investigators

Abstract

Flagella and cilia are self-contained biological machines (micro in scale in the aggregate but consisting of nanoscale mechanical parts) that convert chemical energy from ATP into useful mechanical work. These are highly conserved eukaryotic organelles that are found in plants, protistans, and animals (including humans). The general function of flagella and cilia is nearly always to move in a rhythmic fashion (although the nonmotile "sensory cilia" represent a notable exception). These rhythmic movements play important roles in various life processes such as reproduction, embryonic development, and movement of fluids across cell surfaces in contexts as varied as protozoan feeding and mucus clearing in the trachea and bronchi of lungs. We still do not fully understand how this basic component of a living eukaryotic cell works. This project is directed at understanding, at a precise molecular and physical level, how cilia and flagella work. The major goal is to experimentally gather critical physical information about the flagellum and to incorporate it into a theoretical and computational model of flagellar mechanics. To accomplish this goal, Dr. Lindemann has developed a unique set of tools that will aid him in this endeavor. One such tool is a novel method, based on force-calibrated glass microprobes, for measuring small forces, which enables the measurement of force actively produced by flagella and the passive mechanical stiffness of a flagellum. This novel methodology permits the acquisition of new and useful information that can be used to describe the mechanical behavior of flagella. Another tool is a detailed computational model of the mechanics of the axoneme (the mechanostructural component of the flagellum or cilium) that Dr. Lindemann has developed, termed The Geometric Clutch model. This simulation model has successfully duplicated, and even predicted, the behavior of cilia and flagella. The computer model provides a framework that can be used to build toward a more complete picture of the mechanics of the axoneme. Dr. Lindemann will use the data from his force measurement experiments to improve the computer model. When experimental results and computed simulation are in agreement, the model often provides a means to understand the mechanism behind the observed result; in other words, the combination of experimentation and modelling can help us learn how the flagellum works. Intellectual Merit: The goal of the project is to understand how flagella and cilia work. Therefore, the project will contribute basic scientific knowledge about the living eukaryotic cell. There are very few research programs that are combining computer modeling with laboratory experiments to study the mechanical workings of flagella. The mechanical and physical information obtained from these studies complement the remarkable advances in understanding the flagellum at the molecular level. The Geometric Clutch model allows the physical properties of many specific axoneme structures to be identified with the appropriate molecular components. This has already yielded concrete predictions about properties that the various molecular components, including spokes, the dynein heads and the nexin links, must have in order to be functional in a flagellum. Dr. Lindemann's research program has a well-established base of experience with mammalian sperm. He is now developing a computer model specific to the mouse sperm flagellum. The mouse is one of the primary research model systems and, as such, a large data base is available on the genome and molecular biology of this animal. A working model of the mouse sperm axoneme will position Dr. Lindemann's laboratory as the only research program that can do experimental measurements on mouse sperm and also examine the results in a theoretical framework. Dr. Lindemann is also embarking on a collaboration with Dr. David Mitchell that will involve the analysis of Dr. Mitchell's remarkable transmission electron micrographs of Chlamydomonas flagella, obtained by Dr. Mitchell through the use of his innovative methods of rapid fixation and orientation of samples for sectioning. Again, the large data base of molecular and genetic information about the structure and properties of the flagella of this model unicellular organism will assist in the analysis and interpretation of the images in terms of mechanism. Broader impacts: Dr. Lindemann's work applies physics and computational modeling to a biological system. It has drawn the interest of people in the mathematics, physics and engineering communities because it is a successful melding of ideas from different disciplines. The flagellum is nature's own micro-machine, built of nanoscale parts. Despite the extensive knowledge of the biochemistry of the flagellum that is available, it is only by understanding the mechanical properties that we can reach a full understanding of how it works. This understanding is crucial to the development of biomimetic devices that harness molecular motors to create new functional and useful nano- and micro-machines. We must observe and learn from nature to build tomorrow's nanotechnology. Dr. Lindemann has an extensive record of mentoring undergraduate students and introducing them to the principles and practice of laboratory research, and many of the undergraduates are co-authors on scientific reports and upon graduation, advance into careers in science, teaching and medicine. This project will continue to be a vehicle for this integration of research with teaching and training .