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

Mitosis was frequently observed in the secondary spermatogonia of newt in in vitro cultures. From prometaphase to mid-anaphase, the whole set of the chromosomes rotated alternately clockwise 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 rotation of chromosomes was so fast that we could discern it directly by a phase contrast microscope. It was a rhythmic and regular motion with almost the constant frequency and magnitude. The average period of each cycle during metaphase varied from cell to cell and between 70 to 20 seconds (0.9–3.0 rotations/min) and the average angle traversed during each motion also varied and between 10 to 90 degrees at 25°C. By marking the cell surface with iron 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 μg/ml reversibly arrested the chromosomal rotation and karyokinesis. Cytochalasin B (4.0 μg/ml) also reversibly disturbed the rotation though the karyokinesis continued. These results suggest that the rotation of chromosomes as a set may be mediated by filamentous organelles such as microtubules in the mitotic spindle and cytoplasmic microfilaments.