Cell motility by labile association of molecules. The nature of mitotic spindle fibers and their role in chromosome movement.

摘要: This article summarizes our current views on the dynamic structure of mitotic spindle and its relation to chromosome movements. The following statements are based measurements birefringence fibers in living cells, normally developing or experimentally modified by various physical chemical agents, including high low temperatures, antimitotic drugs, heavy water, ultraviolet microbeam irradiation. Data were also obtained concomitantly with electron microscopy employing a new fixative through isolated protein. Spindle cells labile structures whose constituent filaments (microtubules) undergo cyclic breakdown reformation. state is maintained an equilibrium between pool protein molecules their linearly aggregated polymers, which constitute microtubules filaments. In under physiological conditions, association into polymers very weak (absolute value Δ F 25°C S ≃ 100 eu) addition water. proteins tend polymerize orienting centers as geometrical foci. centrioles, kinetochores, cell plate act successively during mitosis. Filaments more concentrated adjacent center yield higher birefringence. Astral rays, continuous fibers, chromosomal phragmoplast thus formed successive reorganization same molecules. During late prophase metaphase, polymerization takes place predominantly at kinetochores; metaphase anaphase, depolymerization prevalent near poles. When concentration high, fusiform bundles polymer precipitated out even absence obvious centers. shift from free increases length number Slow can be brought about concentrations colchicine gradual cooling, allows shorten perform work. controlled other factors provides plasusible mechanism chromosomes organelles, well surface, deformed moved temporarily organized arrays