ANAPHASE CHROMOSOME VELOCITY IS NOT PROPORTIONAL TO THE CONCENTRATION OF ORIENTED MATERIAL, INCLUDING MICROTUBULES, IN CHROMOSOMAL SPINDLE FIBRES OR TO THE RATE OF DECAY OF THE ORIENTED MATERIAL

To study the relationships between anaphase chromosome velocity, chromosomal spindle fibre birefringence and chromosomal spindle fibre microtubules, the effects of a range of temperatures on each of these were studied and compared in crane fly spermatocytes. Chromosome-to-pole velocity increased as temperature increased between 6(DEGREES) and 30(DEGREES)C.;As chromosome-to-pole movement occurs the birefringence does not decay, rather, the profile shortens from the kinetochore suggesting that the birefringent material disorganizes at the kinetochore.;These data do not support the "dynamic equilibrium" model for chromosome movement of Inoue and coworkers. The data also show that previous measurements of either whole or average spindle birefringences cannot be used to describe the birefringence of single chromsomal fibres alone and therefore cannot be used to describe temperature sensitive equilibria of single chromosomal spindle fibres, because chromosomal and continuous fibres have different temperature labilities. {In addition, the previous measurements are criticized also for other technical reasons.};Counts of kinetochore region microtubules in cells treated at different temperatures are consistent with the hypothesis that microtubules are responsible for 70 to 100% of the observed in vivo chromosomal spindle fibre birefringence.;Birefringence along the lengths of single chromosomal spindle fibres was obtained directly from video taped images of dividing cells using a video digitizer interfaced to a microcomputer. {This new analysis system is described. It can also be used for other types of measurements that require quantification of light intensities from TV or video tape.} Profiles of the distribution of birefringence along the lengths of chromosomal fibres demonstrate that while chromosomal fibre birefringence is not sensitive to temperatures between 10(DEGREES) and 25(DEGREES)C, the birefringence of continuous spindle fibres is temperature sensitive. These birefringence data are directly proportional to coefficients of birefringence and thus to concentration of oriented material responsible for birefringence. Although the birefringent oriented material of continuous fibres may be in a temperature sensitive "dynamic equilibrium", that of the chromosomal fibres is not (at least between 10(DEGREES) and 25(DEGREES)C).