Effects of colcemid and taxol on microtubules and intermediate filaments in chick embryo fibroblasts

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Abstract
Reports on how changes in microtubule (MT) distribution or polymerization affect the distribution of intermediate filaments (IFs) differ. Therefore, we have used cytoimmunofluorescence techniques and electron microscopy to systematically examine and compare the arrangements of MTs and IFs in cultures of chick embryo fibroblasts under the following conditions: at different times during the cell cycle, in the presence of Colcemid or of taxol, in the presence of both drugs in succession or simultaneously in varying ratios, and during recovery from treatment with Colcemid or taxol.We have found that depolymerization of MTs by 1 μM Colcemid resulted in the rapid formation of massive IF‐cables, structures distinct from “collapsed IFs” or “juxtanuclear coils.” Neither the rapid formation of IF‐cables nor their dispersion during recovery required protein synthesis. Cells treated with 10 μM taxol rapidly formed MT‐bundles, as well as aggregates of intertwining IFs, termed “IF‐skeins.” MT‐bundles and IF‐skeins displayed strikingly complementary distributions. This reciprocal distribution of packed MTs and IFs was also obvious in untreated anaphase and telophase cells. When 10 μM taxol and 1 μM Colcemid were applied simultaneously, the complementary distributions of MT‐bundles and IF‐skeins mimicked those in taxol alone. This ability of taxol to block Colcemid's effects was concentration dependent Decreasing the taxol:Colcemid ratio allowed the depolymerization of MTs, which correlated with the formation of IF‐cables.

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