Book Description

Microtubules are highly dynamic structural filaments that spatially and temporally organize the cytoplasm of nearly all Eukaryotic cells. To adopt different spatial arrangements in functionally diverse and morphologically disparate cells, microtubule polymerization dynamics are subject to poorly understood physiological regulation based on external and internal cellular cues. In this study, we have designed a microfluidic approach capable of isolating biologically relevant volumes of Xenopus laevis cell-free extract. This approach allowed us to identify and characterize the relationship between the dynamic instability factor, microtubule polymerization rate, and the number of actively growing microtubule plus-ends in the cytoplasm. One function of this relationship might be to determine steady-state mass of the microtubule assembly, or to prevent sub-regions of microtubules from depleting limited precursor molecules. Our studies show a length scale for this relationship, with microtubules only a few microns apart exerting negative feedback on one another, which provides the first direct experimental evidence for a local component-limitation mechanism in regulating microtubule polymerization dynamics. Lastly, we have identified a role for component limitation in determining the microtubule mass of the interphase aster, as the addition of tubulin to our cell-free extracts was sufficient to drive changes in microtubule mass and microtubule polymerization rates.