How cells measure length: clocks, rulers, and diffusion

The mechanisms by which living cells are able to build structures of defined size and geometry remain poorly understood, despite extensive knowledge of the molecular building blocks. We are using the flagellum of the model organism Chlamydomonas as a test-bed to explore possible mechanisms by which cells can measure the length of a simple organelle. Our approach is to formulate simple physical models and then test them them by taking advantage of the powerful genetics of this model system, in combination with quantitative microscopy and mathematical modeling. We are currently exploring length-measurement schemes based on molecular timers, ion channels, and diffusion of motors. The approaches used to formulate and test these models for flagella should be generally applicable to probing size control mechanisms of other organelles.