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

This article summarizes our current views on the dynamic structure of the mitotic spindle and its relation to mitotic chromosome movements. The following statements are based on measurements of birefringence of spindle fibers in living cells, normally developing or experimentally modified by various physical and chemical agents, including high and low temperatures, antimitotic drugs, heavy water, and ultraviolet microbeam irradiation. Data were also obtained concomitantly with electron microscopy employing a new fixative and through measurements of isolated spindle protein. Spindle fibers in living cells are labile dynamic structures whose constituent filaments (microtubules) undergo cyclic breakdown and reformation. The dynamic state is maintained by an equilibrium between a pool of protein molecules and their linearly aggregated polymers, which constitute the microtubules or filaments. In living cells under physiological conditions, the association of the molecules into polymers is very weak (absolute value of DeltaF(25 degrees C) < 1 kcal), and the equilibrium is readily shifted to dissociation by low temperature or by high hydrostatic pressure. The equilibrium is shifted toward formation of polymer by increase in temperature (with a large increase in entropy: DeltaS(25 degrees C) approximately 100 eu) or by the addition of heavy water. The spindle proteins tend to polymerize with orienting centers as their geometrical foci. The centrioles, kinetochores, and cell plate act as orienting centers successively during mitosis. Filaments are more concentrated adjacent to an orienting center and yield higher birefringence. Astral rays, continuous fibers, chromosomal fibers, and phragmoplast fibers are thus formed by successive reorganization of the same protein molecules. During late prophase and metaphase, polymerization takes place predominantly at the kinetochores; in metaphase and anaphase, depolymerization is prevalent near the spindle poles. When the concentration of spindle protein is high, fusiform bundles of polymer are precipitated out even in the absence of obvious orienting centers. The shift of equilibrium from free protein molecules to polymer increases the length and number of the spindle microtubules or filaments. Slow depolymerization of the polymers, which can be brought about by low concentrations of colchicine or by gradual cooling, allows the filaments to shorten and perform work. The dynamic equilibrium controlled by orienting centers and other factors provides a plasusible mechanism by which chromosomes and other organelles, as well as the cell surface, are deformed or moved by temporarily organized arrays of microtubules or filaments.

Lysed BCG vaccines. 1. Observations on optimal conditions for BCG growth and lysis

As a first step towards the production of a lysed BCG vaccine that would have reduced toxicity and allergenicity and yet be immunogenic, the growth and lysis of BCG bacilli under strictly controlled conditions have been studied.BCG grown in both Dubos and Aldridge liquid media showed an arithmetic linear growth, preceded by a very short logarithmic phase. This suggested that some of the cell population became metabolically inactive at a very early stage, possibly owing to suboptimal conditions of growth.Glycine, lysozyme and lithium chloride initiated lysis of BCG growth in the aforementioned media 24-48 hours after inoculation. After 2 weeks' incubation approximately 50% of the original BCG culture was lysed and the viable count had fallen 1000-fold. The autolytic pattern of BCG in a nitrogen-deficient, chemically defined Aldridge medium is also described.

Lysed BCG vaccines. 2. The effect of lysis on the immunogenicity and allergenicity of BCG vaccines

The authors have attempted to prepare lysed BCG vaccines retaining the protective antigens of the BCG cell wall and yet eliciting in experimental animals limited sensitivity to the tuberculin substances, the advantage sought being to retain the usefulness of the tuberculin following vaccination as an indicator of superinfection.Experimental vaccines were prepared by growing and lysing BCG in both Dubos and Aldridge liquid media with glycine, lysosyme and lithium chloride; vaccines were also prepared by autolysis in Aldridge nitrogen-deficient, chemically defined medium.Glycine, lysozyme and lithium chloride significantly reduced both the protective and allergenic properties of the lysates. The best protection was afforded by BCG cells autolysed in Aldridge medium. Treatment of the BCG autolysates with lysozyme alone did not affect the protective capability of the vaccines and almost completely eliminated the allergenicity. It is suggested that these BCG lysates contain metabolically inactive cells, which do not multiply in vitro but may still provide sufficient antigen in vivo to ensure protection.