Cytoplasmic Microtubules and Radial‐Segmented Nuclei (Rieder Cells)

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Abstract
In previous studies it was shown that cytoplasmic microtubules are instrumental structures in the formation of radial‐segmented (RS) nuclei in human lymphocytes and monocytes. The present study was concerned with the quantitative distribution of microtubule constituents in the cytoplasm of RS cells and with the course and position of individual microtubules. The quantitative distribution of microtubule constituents was evaluated from the presence of less stainable and highly refractile material in smears, thin sections, vital preparations and especially in RS cells treated with hexylene glycol, in order to extract non‐microtubular matter from the cytoplasm. On the ultrastructural level centrioles were demonstrated in the middle of the nuclear segments of RS nuclei. This finding supported the view developed from light microscopy studies that the cell centre is the point of convergence of the segments in RS nuclei. Cytoplasmic microtubules appeared to encircle the RS nuclei in the intersegmental clefts; the ends of the microtubules were probably inserted into the cell centre. The findings reported were thought to support the idea that RS is due to a contraction folding the nucleus in from the cytoplasmic side of the nuclear envelope.