MZpitx2c mutants exhibit defects in convergence and extension of mesendodermal cells.
(a–c) In situ hybridization for hgg1 (prechordal plate) and noto/flh (notochord) expression at tailbud. Quantification of the distance between the hgg1 and noto domains is shown in (c); the distance measured is indicated by the lines shown in panels a and b. (d–f) Analysis of cell shapes in the notochord by mosaically labelling cells with membrane tdTomato and nuclear H2B-GFP. Quantification of the ratio between the mediolateral (ML) width and anterior-posterior (AP) length of cells in the notochord is shown in (f); n > 60 cells from at least four embryos. MZpitx2c mutants exhibit a reduced distance between the prechordal plate and notochord (b, c), and axial mesodermal cells of the notochord fail to intercalate and elongate mediolaterally (e, f), indicative of defects in mesodermal convergence and axis extension. (g–i) Analysis of lateral mesendodermal migration. Embryos were injected with photoconvertible kikGR mRNA at the 1 cell stage; a 100 μm2 region of mesendodermal cells located 90° from the dorsal organizer was photoconverted at shield stage and the photoconverted population was tracked until 90% epiboly (g, h). To quantify the extent of anterior migration, the length of the photoconverted population was measured (shown by the blue dashed lines) (i). Convergence towards the dorsal midline (shown by the yellow dashed lines) was assessed by measuring the circumferential angle of the location of the dorsal-most photoconverted cells from the dorsal midline (j). MZpitx2c mutants exhibit reduced dorsal convergence as well as reduced anterior extension of lateral mesendodermal cells during late gastrulation when compared to wild types (i, j). a-b, d-e: dorsal views, animal pole to the top; g-h: lateral views, dorsal to the right of the image. D, dorsal. **p<0.01, ****p<0.0001 by unpaired t-test. Scale bars, 100 μm (a, g) or 10 μm (d).