Flagellar Length Control in Chlamydomonas: The Role of Intraflagellar Transport and Turnover

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How cells regulate organelle size is a fundamental question in cell biology. In this project the eukaryotic flagellum will be used as a model system for studies of organelle size regulation, by reducing the problem of measuring size to a single dimension: length. Flagella undergo continuous turnover, and the length control mechanism must balance the rates of assembly and disassembly to maintain a steady-state length. Several models have been proposed to explain this balance. One model relies on the inherent length-dependence of intraflagellar transport (IFT), an active transport process that occurs within flagella. Based on prior studies of IFT, it is predicted that the efficiency of transport will decrease as flagellar length increases, leading to a balance-point between assembly and disassembly occurring at a unique length. An alternative model proposes that length is regulated by a length-sensor coupled to a feedback control system. This project will test these models by examining the mechanistic basis of flagellar length mutants. The balance point model predicts that such mutants must affect either transport or turnover. A combination of genetics and microscopy will be used to test whether length-altering mutants can be entirely explained by changes in the rates of turnover or transport. This project will provide research training for undergraduate and graduate students.