9707268 Mitchell This is a Career Advancement Award for Women Scientists and Engineers. Eukaryotic flagella are complex organelles whose regulation is still only minimally understood. Flagellar bending is based on the sliding of doublet microtubules driven by multiple dynein ATPase isozymes. The radial spokes and central pair microtubules are axonemal structures which have been implicated in the regulation of flagellar beat. This project is directed at extending ongoing studies on the regulation of dynein arm activity by axonemal protein kinases and phosphatases that are in turn controlled by the radial spoke - central pair complex. The biflagellate alga Chlamydomonas reinhardtii is an excellent model system for studies on flagellar function, in part because it is well-suited for genetic analysis. Extragenic suppressor mutations have been isolated which bypass the paralysis normally associated with the absence of the radial spokes or central pair microtubules. Some of these suppressor mutations, which code for altered forms of outer arm dynein heavy chains, also result in a defect in a signal transduction pathway leading to flagellar quiescence. The goal of this research is to begin analysis of the role of these outer arm dyneins in the regulation of flagellar beat and quiescence. It is expected that this signal transduction pathway involves protein kinase/phosphatase activity, and the proposed experiments are designed to explore this possibility. This award involves a one-year sabbatical leave during which experiments will be conducted in the laboratory of Dr. Winfield Sale at Emory University School of Medicine. This collaborative effort will utilize previously isolated suppressor mutants in combination with techniques currently in use in Dr. Sale's lab, including videomicroscopic analysis of microtubule sliding rates and phosphoprotein characterization. Increased understanding of regulatory cascades important in Chlamydomonas flagellar motility will also contribute to better u nderstanding of motility regulation in cilia and flagella of other organisms, and perhaps in cytoplasmic dynein motility systems as well. A sabbatical leave will provide the PI with exposure to a dynamic research environment, including several individuals focusing on different aspects of flagellar regulation in Chlamydomonas. In addition, the opportunity to attend research seminars on a regular basis, as well as to attend professional meetings will enhance the career advancement aspect of this award. Flagella are whip-like appendages that propel motile eukaryotic cells as diverse as unicellular algae and mammalian spermatozoa. The ability of these cells to swim smoothly and in appropriate response to environmental cues is critical to their survival and function. The experiments to be performed during Dr. Mitchell's sabbatical will further our understanding of the mechanism whereby flagella beat with a regular motion that results in smooth swimming. ***
