Abstract
BackgroundAt the beginning of mitosis, the cell forms a spindle made of microtubules and associated proteins to segregate chromosomes. An important part of spindle architecture is a set of antiparallel microtubule bundles connecting the spindle poles. A key question is how microtubules extending at arbitrary angles form an antiparallel interpolar bundle.ResultsHere, we show in fission yeast that microtubules meet at an oblique angle and subsequently rotate into antiparallel alignment. Our live-cell imaging approach provides a direct observation of interpolar bundle formation. By combining experiments with theory, we show that microtubules from each pole search for those from the opposite pole by performing random angular movement. Upon contact, two microtubules slide sideways along each other in a directed manner towards the antiparallel configuration. We introduce the contour length of microtubules as a measure of activity of motors that drive microtubule sliding, which we used together with observation of Cut7/kinesin-5 motors and our theory to reveal the minus-end-directed motility of this motor in vivo.ConclusionRandom rotational motion helps microtubules from the opposite poles to find each other and subsequent accumulation of motors allows them to generate forces that drive interpolar bundle formation.
Highlights
At the beginning of mitosis, the cell forms a spindle made of microtubules and associated proteins to segregate chromosomes
Assay for spindle reassembly in fission yeast At the onset of mitosis in the fission yeast Schizosaccharomyces pombe, the two spindle pole bodies (SPBs) are embedded in the nuclear envelope, which remains intact during mitosis [36]
MTs extending from the opposite SPBs interact and form an antiparallel interpolar bundle and together with MTs that bind to kinetochores assemble the spindle
Summary
At the beginning of mitosis, the cell forms a spindle made of microtubules and associated proteins to segregate chromosomes. The genetic material is divided into two equal parts by the mitotic spindle This complex dynamic micro-machine is made of microtubules (MTs) emanating from the spindle poles, chromosomes, and a variety of accessory proteins [1, 2]. Some MTs extending from the spindle pole are bound to kinetochores on the chromosome, whereas others are bound to MTs extending from the opposite pole, in an antiparallel configuration known as interpolar or overlap bundles [3,4,5,6]. Stability of antiparallel bundles for combinations of motors and crosslinkers has been explored theoretically [25, 26]
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