FREE AND CENTROSOME-ATTACHED MICROTUBULES - QUANTITATIVE ANALYSIS
AND THE MODELING OF TWO-COMPONENT SYSTEM
K. M. Smurova,1 I. B. Alieva,1, * I. A. Vorobjev 1, 2
1 A. N. Belozersky Institute, Moscow State University, and
2 Department of Cell Biology and Histology, Moscow State University;
* e-mail: irina_alieva@belozersky.msu.ru
In the internal cytoplasm of interphase cells the density of microtubules is the highest in the centrosome
area and decreases to the cell periphery. As a rule, the quantity of fluorescent microtubules cannot be counted up
in the internal cytoplasm, but it is possible to estimate microtubules quantity using measuring of their optical
density. In living 3T3 and CHO cells the microtubules optical density decreased according to different mathematical
dependences that apparently reflected the differences of their microtubule system organization. To determine
appropriateness that circumscribe the reduction of microtubules optical density from the centrosome region
to the direction of cell margin, we modeled cell contours with the certain ratio and interposition of centrosome-
attached and free microtubules in vector schedules CorelDraw program. The decrease of optical density
was analyzed in MetaMorph program as it was described earlier (Smurova et al., 2002). It was shown that fluorescent
microtubules optical density decreased exponentially (f = ae-bx) if the system joined only microtubules
growing from the centrosome up to the cell margin. The curve became smoother in the case of not all radial centrosome-
attached microtubules reached the margin, and adding of free microtubules into the system led to the
sharp fall in optical density in the centrosome area and to its gradual decrease at the cell periphery. The increase
in free microtubules quantity changed the character of the curve describing the reduction of optical density -
microtubule system which included free and centrosome-attached microtubules in proportions of 5 : 1 was described
by the equation of linear regression (f = k·x + b). Thus, the mathematical dependence describing the microtubules
distribution from the centrosome to the cell periphery, depends on the ratio of microtubules and their
relative positioning in the cell volume. The data obtained using model systems have coincided with the results of
experiments. The graphs which described the increase in microtubules optical density during microtubule repolymerization
after nocodazole treatment, corresponded to the graphs for model cells. Thus, the method we used
allows to analyze the microtubule system in the cases when the direct observation of individual microtubules is
difficult.
Key words: centrosome, free microtubules, centrosome-attached microtubules, video microscopy
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