Polarised basal Myosin II pulses drive circumferential movement of MpT cells.

<p>(A–C) Stage 16 MpTs stained for Cut (green) and Baz (red) in control (A), <i>ctB>UAS-YFP-Zip^DN</i> (B), or <i>ctB>UAS-Sqh^E20E21</i> (C) embryos. Insets in (A–C) show cross-sections through tubules. (D) Basal view of ∼ten cells in the distal tubule region (dashed lines), showing Myosin II/Sqh::GFP (white) from <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s016" target="_blank">Movie S9</a>. Distal is to the right. (D′) Time-lapse images of the single cell arrowed in (D) (blue dashed lines) showing Myosin II (arrowhead) accumulating in dynamic pulses localised asymmetrically to the proximal cortex. Inter-pulse periods lack discernable Sqh::GFP accumulation (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s017" target="_blank">Movie S10</a>). (E, F) Still images from control (E, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s018" target="_blank">Movie S11</a>) or <i>EGFR^DN</i> (F) (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s019" target="_blank">Movie S12</a>) tubules (Myosin II/Sqh::mCherry, green; cell membranes, magenta). Proximal Myosin II pulses are absent in <i>EGFR^DN</i> tubules, only static puncta of Myosin II are seen (F, dashed arrow). (G) Basal area of a control (green), <i>EGFR^DN</i> (red) and YFP-<i>Zip^DN</i> (blue) MpT cell over time. Basal area and circumferential length fluctuate widely in control compared to <i>EGFR^DN</i> and YFP-<i>Zip^DN</i> cells. 1.0 represents normalised average area. (H) Histogram of the coordinates of MpT cell shape in relation to Myosin II pulses. Normalised length of D-P and circumferential cell axes (<i>n</i> = 15 pulses and 25 interpulses in 10 aMpT cells). While D-P length shows no significant difference between pulse (green) and interpulse (red) periods (<i>p</i> = 0.12>0.05), circumferential length decreases significantly during pulses (<i>p</i> = 0.02<0.05). 1.0 (dashed line) is the normalised average D-P or circumferential length; error bars ± standard deviation (SD). (I) Polar plot showing displacement of single cell centroids in control (green circles, <i>n</i> = 10 cells) and <i>EGFR^DN</i> (orange circles, <i>n</i> = 6 cells) MpTs. Tubule D-P axis 0°–180°, circumferential axis 90°–270°. Radial rings indicate speed of cell movement (µm min⁻¹) and central open circle marks the starting position for all cells. Control cell movement is biased along the circumferential axis (shaded green). <i>EGFR^DN</i> cells move very little and their final position remains aligned with the D-P axis. (J) Cartoon of cell-shape changes and movement caused by the proximal Myosin II pulse (green shading). Oscillating circumferential cell length (red and black arrows) correlates with myosin pulses, allowing cells to inch around the tubule circumference. Tubule outline and cell position over time is shown. Panels on the right show basal views of a cell labelled for membrane (GAP43::GFP, magenta) and Myosin II (Sqh::mCherry, green). Change in circumferential cell length (C, double headed arrow) during proximal Myosin II accumulation (white, J′–J′″) can be seen. Scale bar = 3 µm. See also <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s004" target="_blank">Figure S4B</a> and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s021" target="_blank">Movie S14</a>.