Convergent-extension movements drive MpT elongation.

<p>(A) Cartoon depicting embryonic MpT morphogenesis. At stage 13, MpTs are short, thick single-layered epithelial tubes with up to 12 cells surrounding the central lumen. Over 5–6 hours, the tubules elongate by cell rearrangement until just two cells surround the lumen. (B) Diagram showing the distal (red arrow) and proximal (blue arrow) aMpT regions, with the TC (pink) at the distal end. Arrowhead indicates the “kink” region. A-P, anterior-posterior; D-V, dorso-ventral embryonic axes. (C) Time-lapse sequence showing the morphogenesis of a <i>ctB>Stinger::dsRed</i> aMpT (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s008" target="_blank">Movie S1</a>). (D) Transverse sections of embryonic aMpTs stained with anti-FasII (stages 13–16). Sections taken from the distal region show that the number of cells surrounding the lumen decreases from 12 to 2. (E) MpTs increase in length from 82.1±0.8 µm at stage 13 to 330.6±24.2 µm 5 hours later (stage 16) (<i>n</i> = 4 aMpTs from four different embryos; ± standard error of the mean [SEM]). (F) Left panels, stills from live imaged <i>ctB>Stinger::dsRed</i> aMpT (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s009" target="_blank">Movie S2</a>) with 4-D reconstructions of distal region (right panels). Positions of tubule nuclei are represented as spheres. Circumferential rings of cells (black/white) rearrange into proximo-distally adjacent groups of cells by the end of tubule elongation. (G–G″) rotation of the tubule through 90° demonstrates the circumferential arrangement (two rings of cells, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002013#pbio.1002013.s010" target="_blank">Movie S3</a>). Star, TC. (H) 4-D reconstruction of a few distal cells in the top plane of an aMpT. Arrows indicate a cell (green) that intercalates between yellow and red neighbours. (I). Cartoon of MpT epithelium as a 2-D sheet. As the tubule elongates in the distal-proximal axis, circumferential neighbours intercalate.