Video motion analysis of mitotic events in living cells of the fungus <i>fusarium solani</i>

Abstract

Abstract An earlier, laser microbeam study produced evidence that, in Fusarium solani , extranuclear polar forces function at anaphase B of mitosis to pull apart the incipient daughter nuclei, whereas the central spindle functions primarily to limit the rate at which they separate. To elucidate further the various dynamics of mitotic anaphase, 8–14 mitoses in hyphae of F. solani were analyzed at 0.5–2.0‐sec intervals using high‐resolution, digitally processed, videotaped sequences. The spindle growth rate, although fluctuating frequently, averaged 0.6 μm/min during metaphase, increased to 3.6 μm/min during anaphase A and was maximal at 6.1 μm/min during anaphase B. Commonly, chromosomes migrated poleward during anaphase A at fluctuating rates, the average rate being an unprecedented 7.5 μm/min. During anaphase the mitotic apparatus migrated to and fro in the hyphae at rates of 3–15 μm/min, an apparent effect of opposing, fluctuating and typically unequal cytoplasmic forces applied to the two spindle poles. Thus, the molecular mechanisms underlying the various anaphase movements in F. solani do not operate entirely smoothly and uniformly. Accelerated growth of the central spindle is temporally associated with anaphase A and the development of asters. Thus, chromosome disjunction may allow the polar forces to increase the rate of spindle elongation. Microtubule dynamics and motor molecules appear to be adequate to account for the observed rates of mitotic movements.