Fig. 7. Loss of function of ntl disrupts convergence but not extension. See Movies 7-12 at http://dev.biologists.org/supplemental/. The wild-type data are from the same 4D recording used for Fig. 4. Time points shown across A-C are 8, 8.8 and 9.5 hpf. (A) Cellular movement pathways in the notochord/axial (green) and somite domains (red). The arrows show the directions of cell movements and their lengths show the speed (the movement history during 16 minutes). Disruption of convergence (i.e. failure of the field to narrow) is evident in the ntl^- axial domain: k_C for the axial domain in the mutant is -0.0017, when compared with -0.0073 for the wild-type notochord domain over the same time interval (8-9.5 hpf). Horizontally (ML) oriented tracks are largely missing in ntl mutant. However, extension, vertical lengthening of the field, is prominent in the mutant. (B) Intermixing does not occur between the notochord/axial domain (green) and the overlying midline epiblast (floorplate domain, magenta) in either the wild-type or ntl mutant (48 and 84 cells traced in wild-type and ntl epiblast, respectively). Side views made by 90° rotation of vertical strips of cells in the tracked data sets that are present at the dorsal midline at each time point. Accompanying these images, similar rotations from the original recorded BODIPY images reveal the boundary (Brachet's cleft) between the two layers of cells in the wild type (notochord and floorplate), but this boundary is less apparent in the mutant. (C) The thickness of the region of tracked dorsal mesodermal cells does not change greatly during convergence and extension in the wild type, and may decrease slightly during extension without convergence in the ntl mutant axial domain (green). Scale bar: 50 µm.

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