Periodic Rotation of Chromosomes During the Mitotic Divisions in Secondary Spermatogonia of Newt, Cynops Pyrrhogaster

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Abstract
Mitosis was frequently observed in the secondary newt spermatogonia in in vitro cultures. From prometaphase to mid-anaphase, the whole set of the chromosomes rotated alternately clock-wise and counterclockwise generally in the same plane as the bottom of a plastic dish. The axis of rotation was almost always perpendicular to the bottom of a dish, passing through the central part of the cell. This chromosome rotation was so fast that it could be discerned directly by a phase contrast microscope. It was a rhythmic and regular motion with almost constant frequency and magnitude. The average period of each cycle during metaphase varied from cell to cell and between 70-20 s (0.9-3.0 rotations/min) and the average angle traversed during each motion also varied and between 10-90 degrees at 25.degree. C. By marking the cell surface with Fe particles, it was demonstrated that the inner part of the cell actively rotated and not the cell as a whole. Colcemid at the concentration of 1.0 .mu.g/ml reversibly arrested the chromosomal rotation and karyokinesis. Cytochalasin B (4.0 .mu.g/ml) also reversibly disturbed the rotation though the karyokinesis continued. Apparently the rotation of chromosomes as a set may be mediated by filamentous organelles such as microtubules in the mitotic spindle and cytoplasmic microfilaments.