Prometaphase spindle maintenance by an antagonistic motor-dependent force balance made robust by a disassembling lamin-B envelope.
We tested the classical hypothesis that astral, prometaphase bipolar mitotic spindles are maintained by balanced outward and inward forces exerted on spindle poles by kinesin-5 and -14 using modeling of in vitro and in vivo data from Drosophila melanogaster embryos. Throughout prometaphase, puncta of both motors aligned on interpolar microtubules (MTs [ipMTs]), and motor perturbation changed spindle length, as predicted. Competitive motility of purified kinesin-5 and -14 was well described by a stochastic, opposing power stroke model incorporating motor kinetics and load-dependent detachment. Motor parameters from this model were applied to a new stochastic force-balance model for prometaphase spindles, providing a good fit to data from embryos. Maintenance of virtual spindles required dynamic ipMTs and a narrow range of kinesin-5 to kinesin-14 ratios matching that found in embryos. Functional perturbation and modeling suggest that this range can be extended significantly by a disassembling lamin-B envelope that surrounds the prometaphase spindle and augments the finely tuned, antagonistic kinesin force balance to maintain robust prometaphase spindles as MTs assemble and chromosomes are pushed to the equator.
Civelekoglu-Scholey
Gul
G
Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
Tao
Li
L
Brust-Mascher
Ingrid
I
Wollman
Roy
R
Scholey
Jonathan M
JM
D000818:Animals; D055592:Biophysical Phenomena; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology* / Q000196:embryology / Q000235:genetics / Q000502:physiology*; D016547:Kinesins / Q000235:genetics / Q000378:metabolism; D034921:Lamin Type B / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D049468:Prometaphase; D008941:Spindle Apparatus / Q000502:physiology*
D029721:Drosophila Proteins; C084034:Klp61F protein, Drosophila; D034921:Lamin Type B; D008869:Microtubule-Associated Proteins; C066696:ncd protein, Drosophila; D016547:Kinesins