RUI: 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 that convert chemical energy from ATP into useful mechanical work. If biologists are to understand how a flagellum works, they must have reliable information about the mechanical properties of a flagellum, and the forces that it produces. The goal of this project is to gather some of this vital information and incorporate it into a model of flagellar mechanics that can be described computationally. To accomplish this goal, Dr. Lindemann has developed a unique set of tools that will aid him in this endeavor. He can measure small forces using a method based on force-calibrated glass microprobes. The technique has allowed him to measure the stall-force produced by a beating bull sperm flagellum. The stall force is valuable information because it tells us a great deal about how dynein works while it is harnessed in the confines of the intact axoneme. He has also measured the torque generated by a rat sperm flagellum in response to calcium, and the passive stiffness of both rat and bull sperm flagella. All of these are new and useful pieces of information that help to describe the mechanical behavior of flagella. Much of the planned activity in this project is directed at collecting needed information by applying the force measurement technique to novel experimental protocols. In addition, adaptations will be incorporated into an Atomic Force Microscope to improve the sensitivity of the technique. This will allow the PI to make finer measurements than heretofore possible. The P. I. has developed a detailed computational model of the mechanics of the axoneme, called the Geometric Clutch model. The Geometric Clutch model is the only computational model to be specifically and successfully adapted to simulate the mammalian sperm axoneme. The Geometric Clutch model has so far been very effective at simulating, and even predicting, the behavior of bull sperm flagella. The computer model provides a framework that can be used to build a more complete representation of the mechanics of the axoneme. The data from force measurement experiments will be used to incorporate more accurate values for the active and passive elastic forces into the computer model. In turn, the model will be used to simulate the behavior of a flagellum. When experimental results and computed simulation are in agreement, the model often provides a means to understand the mechanism behind the observed result. The computed model provides the ability to compare experimental data and theory; this is a valuable tool in the process of understanding how the axoneme works. Experimental model systems have assumed immense importance in biological research. The Chlamydomonas model system, with its large collection of mutant strains, has provided a priceless resource for studying the flagellum. Because of this there has been a remarkable period of growth in our knowledge of the molecular components of cilia and flagella. The mouse model is rapidly becoming a second resource for mutations affecting flagellar function, especially for mammalian sperm studies. Dr. Lindemann's research program has a well-established base of experience with mammalian sperm. He will develop a computer model specific to the mouse sperm axoneme as has been done with bull sperm and Chlamydomonas. A working model of the mouse sperm axoneme will position Dr. Lindemann's laboratory as the only research program that can both do experimental measurements on mouse sperm and also examine the results in a theoretical framework. Molecular discoveries are latent opportunities for understanding the axoneme, but only if there is a way to quantitate their effect on function. This project provides the tools to do this, in both of the prevailing experimental model systems. The work will be done in the context of a predominantly undergraduate university environment. Undergraduates will be actively involved in the research, and will receive interdisciplinary training in physics, biomechanics, molecular biology, cell biology, and computational modeling.