Background At 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. Results Here, 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. Conclusion Random 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. Electronic supplementary material The online version of this article (10.1186/s12915-019-0656-2) contains supplementary material, which is available to authorized users.

At 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 two spindle poles. A key question is how microtubules extending at arbitrary angles form an antiparallel interpolar bundle. Here we show that microtubules meet at an oblique angle and subsequently rotate into antiparallel alignment. 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 of two microtubules, they slide sideways along each other towards the minus end, which we interpret as the action of minus end directed Cut7/kinesin-5 motors. In conclusion, random 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.

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Image analysis methods are recently in use for asphalt pavement surface texture characterization and analysis in terms of pavement friction performance assesment. These methods enable more detailed description of texture properties at both micro and macro texture levels which are important for friction realization as they result in a digital representation of pavement surface. In comparison to the traditional methods for texture characterization which result in one characteristic texture parameter, methods that are based on digital image analysis can yield more texture parameters describing both profile and spatial characteristics of inspected surface texture. Previous application of image analysis methods for pavement texture characterization showed that pavement texture and friction relationship could be described more thoroughly by including texture parameters other than standard mean texture depth and mean profile depth derived from traditional measuring procedures. The possibility of texture data acquisition by means of digital images that can be further processed and exploited for creation of a 3D digital pavement surface model is presented in this paper. A research was performed on selected pavements in use where orthographic photogrammetry method was applied for texture data acquisition. Images were used for creation of a 3D pavement surface model defined as a dense point cloud data with XYZ coordinates. From the created 3D digital texture model, selected texture parameters were calculated and compared to the frictional performance of the pavements determined for inspected surfaces by using standard pendulum device.