Fig. 8: CTM proteins form cork-like densities at MT plus ends and reduce protofilament flaring.
a,b, Left, slices (4.3 nm thick) of denoised tomograms showing MT plus ends grown in presence of EB3 alone (a) or CTM and EB3 (b). Right, an 8-nm-thick transverse cross-section of the corresponding MTs. The transverse cross-section (top right) is accompanied by its rotational average (bottom right) to indicate MT polarity. Scale bars: 25 nm. Independent experiments were run twice for controls and three time for CTM samples. c, Cork distribution in the CTM samples based on visual inspection for the presence of cork densities and based on chirality of the rotationally averaged cross-section for MT polarity. Total number of MT ends analyzed: plus ends, n = 60; minus ends, n = 38. d,e, The 3D rendered segmentation volumes of a free or dynamic MT plus end (d) and CTM-corked plus end (e). MT, gray; CTM density, green. Scale bars: 25 nm. f,g, A 3D model of manually traced protofilament shapes, accompanied by their transverse cross-sections. Scale bars: 25 nm. h, Distribution of protofilament length measured from the last segment within the MT wall until the tip of the protofilament. Total number of protofilaments analyzed: EB3, n = 329; CTM, n = 441. Lines represent the median (solid) and quartiles (dotted). ****P < 0.0001 (two-sided Mann–Whitney test). i, Protofilament length s.d. per MT. Total number of MTs analyzed: EB3, n = 26; CTM, n = 33. Bars represent the mean and error bars represent the s.e.m. ****P < 0.0001 (two-sided Mann–Whitney test). j, Schematic representation of parameters that were obtained from manual tracing of MT plus-end protofilaments. k, Average local protofilament curvature per MT. Total number of MTs analyzed: EB3, n = 25; CTM, n = 32. Bars represent the mean and error bars represent the s.e.m. **P = 0.0061 (two-sided Mann–Whitney test). l, MT raggedness plotted as s.d. of protofilament axial distance of last segment within the wall per MT. Total number of MTs analyzed: EB3, n = 26; CTM, n = 33. Bars represent the mean and error bars represent the s.e.m. **P = 0.002 (two-sided Mann–Whitney test). m, Schematic model of the CTM at an MT plus end.
