In L-cells thin bundles of vimentin filaments occupy 80% of cell body and the density of filament distribution on cell periphery is larger than in the perinuclear region. The radial distribution of filament bundles is predominant at cell periphery. In order to characterize filament bundles we use the following parameters: 1) "apparent thickness of the bundle", which is calculated by the multiplication of average intensity of fluorescence of the bundle (over the background) by its apparent diameter; 2) the ratio between the area occupied by vimentin filaments and total cell area (%). Intermediate filaments undergo gradual collapse when RNA synthesis was inhibited by addition of the actinomicyn D and after enucleation of cells. Collapse takes place in the presence of microtubule system and without inhibition of microtubule-associate transport. The process of collapse undergo subsequent stages: on the first stage the twisting of thin bundles of filaments occur, the bundles become curved and form loops. The density of filaments in the center of the cell or the cytoplast became higher than at the periphery. The apparent thickness of bundles increased 2.4-4 times, and the area occupied by them decreased up to 24%. This stage lasts for 8-10 h. On the second stage the apparent thickness of bundles increased more than 10 times and the area occupied by them decreased up to 9%. The ring-like aggregates about 1 μm thick appeared around the cell nucleus or in the center of cytoplast. The majority of the intermediate filaments are located near this ring and only few thin bundles are at the cell periphery. The second stage lasts approximately 6 h. In the presence of microtubules this is the last stage of collapse. Under depolymerization of the microtubules with nocodazole the collapse of intermediate filaments proceeds rapidly: the first stage takes 1 h, and second - almost 2 h. Lastly, under total depolymerization of microtubules in the cells (but not in the cytoplasts) almost total aggregation of all intermediate filaments can occur. They form compact mass that is located on one side of the nucleus. This is the third stage of the collapse, which lasts for 3 h. The analysis of different variants of intermediate filament collapses allows us to suggest that the bundles of filaments in vivo have intrinsic property to curl in loops. In intact cell curling of bundles is counteracted by the system, associated with microtubules system, which stretchs the filaments to the cell periphery. However, factors responsible for stretching of vimentin filaments have life time ∼16 h, in contrast to kinesin and dynein, whose activities remained not less than 24-28 h after inhibition of RNA synthesis.
|Number of pages||11|
|Publication status||Published - Jun 1 2004|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology