Cytoplasmic Microtubules and Radial‐Segmented Nuclei (Rieder Cells)

Abstract

This investigation is concerned with the basic mechanisms of the radial segmentation (RS) of nuclei in human lymphocytes and monocytes. Some experimental conditions fundamental to RS‐studies were also investigated. Osmotic variations were found to influence unspecifically the recording of the RS of nuclei in the experimental system used. The RS was inhibited by pH depression and by low concentrations of ethanol and hexylene glycol, i.e. agents that might be expected to stabilize cytoplasmic microtubules under the conditions prevailing. Through an effect analogous to that of other spindle poisons, the RS was inhibited by podophyllic acid ethylhydrazide and griseofulvin, i.e. agents that cause a rapid decomposition of microtubules. These findings are interpreted to indicate that the RS of nuclei is due to a contraction of intermitotic residues of the mitotic spindle, parallel to a slow dissociation of the molecular units of its constituent microtubules. The recording of the RS of nuclei may form a convenient screening test for metaphase‐blocking cytostatics.