Video motion analysis of mitotic events in living cells of the fungus fusarium solani

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 prdmin during metaphase, increased to 3.6 p d m i n during anaphase A and was maximal at 6.1 p d r n i n during anaphase B. Commonly, chromosomes migrated poleward during anaphase A at fluctuating rates, the average rate being an unprecedented 7.5 p d m i n . During anaphase the mitotic apparatus migrated to and fro in the hyphae at rates of 3-15 p d m i n , 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. soluni 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.

Mitosis in Filamentous Fungi: How We Got Where We Are

“…And so it remains to this day. One further, significant advance in describing anaphase A in filamentous fungi was the quantification of the rates of chromatid movement in N. haematococca (Aist and Bayles, 1988). This study showed that different chromatids migrate poleward at different rates and recorded the fastest rate of chromatid migration (7.5 µm/min) ever reported for any organism.…”

“…This result demonstrated the existence of both an astral pulling force (when the spindle was cut) and a spindle counterforce (when the spindle was left intact) which is an inward-directed force generated within the spindle that limits the rate at which the asters can separate the SPBs and elongate the spindle. Subsequent studies with the same fungus showed that the pulling force resides in the astral regions, that it requires the presence of astral MTs, and that it contributes to the rate of spindle elongation (Aist and Bayles, 1988;Aist et al, 1991). More recently, Bayles et al (1993) performed a comparable laser ablation experiment on anaphase B nuclei of the basidiomycete H. mompa and came to the same conclusion regarding the astral pulling force and the spindle counterforce.…”

“…First, the size of asters (in terms of either MT number or total MT length) varied greatly, even between the two asters of the same mitotic apparatus. This size difference could easily translate into transitory amplitude fluctuations in the astral pulling force, which would explain the oscillations of the mitotic apparatus during anaphase B (Aist and Bayles, 1988). Second, the spindle did not have a well-defined middle zone where anti-parallel, polar MTs overlapped.…”

Detection of spindle pushing forces in vivo during anaphase B in the fungus Nectria haematococca

“…[Aist and Bayles, 19881. Cultures were maintained and videotapes of mitosis were made as outlined by Aist and Bayles [1988].…”

Spindle positioning in fibroblasts supports an astral microtubule length dependent force generation at the basal membrane

“…Likewise, the intermittent character of spindle elongation remains to be explained with regard to external pulling forces and possible intrinsic elongating forces. Spindle elongation is intermittent also in Fusarium and fission yeast, and a pulling force is indicated to act on the polar bodies in anaphase in both species [Aist and Berns, 1981;Aist and Bayles, 1988;Hagan et al, 1990;Hagan and Hyams, 1996].…”