Centrosomal Control of Microtubule Dynamics. V. I. Rodionov, E. Nadezhdina and G.G. Borisy PNAS, 96: 115-120, 1999

In many animal cells, minus ends of microtubules (MTs) are thought to be capped by the centrosome while plus ends are free and display dynamic instability. We tested the role of the centrosome by examining MT behavior in cytoplasts from which the centrosome was removed. Cells were injected with Cy3-tubulin to fluorescently label MTs and were enucleated by a centrifugation procedure. Enucleation resulted in a mixture of cytoplasts containing or lacking the centrosome. Fibroblast (CHO-K1) and epithelial (BSC-1) cells were investigated. In fibroblast type cytoplasts containing the centrosome, MTs showed dynamic instability indistinguishable from that in intact cells. In contrast, in cytoplasts lacking the centrosome, microtubules treadmilled,--shortened at the minus end at about 12 µm/min while growing at the plus end at the same rate. The change in behavior of the plus end from dynamic instability to persistent growth correlated with an elevated level of free tubulin subunits (78% in centrosome-free cytoplasts vs 44% in intact cells) generated by minus-end depolymerization. In contrast to fibroblast type cells, in centrosome-free cytoplasts prepared from epithelial type cells, MTs displayed dynamic instability at plus ends and relative stability at minus ends presumably because of specific minus-end stability factors distributed throughout the cytoplasm. We suggest that, in fibroblast type cells, a minus-end depolymerization mechanism functions to eliminate errors in microtubule organization and that dynamic instability of microtubule plus ends is a result of capping of minus ends by the centrosome.

	Figure 1 (143 K) - Distribution of MTs in intact cells and cytoplasts
	Figure 2 (86 K) - Fluorescence imaging of MTs in living cytoplasts
	Figure 3 (114 K) - Quantitation of MT dynamics in cytoplasts
	Figure 4 (86 K) - Proportion of polymerized tubulin in cytoplasts
	Figure 5 (143 K) - Hypothesis for MT treadmilling

	Microtubule dynamics (859 K) - Black and white
	Minus-end release (866 K) - Released microtubules shown in red

	Treadmilling (904 K) - Black and white
	Treadmilling (815 K) - Three of the microtubules shown in red
	Speckles (1.8 M)