Fig. 4

The prospective adaxial cells in kny;tri double mutants fail to maintain their identity during early segmentation. (A–C) MyoD protein distribution detected by the human Myf5 antibody in the embryos also labeled with mGFP. Dashed lines highlight the somite-PSM boundary. (A′–C′) show only the MyoD protein expression. (D–F) At the 10-somite stage, MyoD protein was strongly expressed in one column of adaxial cells flanking the notochord. Weak MyoD expression was detected in the lateral somitic cells at this stage. (D′–F′) At the 10-somite stage, the notochord-adjacent adaxial cells were co-labeled by MyoD and F59 antibodies. Lines in (A′–C′, F′) indicate the somite-PSM boundary. (G) Quantification of the numbers of cells expressing MyoD protein at the 5-somite stage and cells co-labeled with MyoD and F59 antibodies at the 10-somite stage. Error bars represent standard deviation. (H–K) Cell tracing analyses of the prospective adaxial cell population. (H) Within the fluorescein-labeled cell population (red) in WT embryos (n = 6), only one column of cells immediately next to the notochord expressed MyoD protein at the 5-somite stage. (I) The notochord-adjacent cells continued to strongly express MyoD protein at the 10-somite stage. (J) In the double mutants (n = 6), at the 5-somite stage, majority of the fluorescein-labeled cells expressed MyoD. (K) At the 10-somite stage, only the column of cells flanking the notochord exhibit adaxial cell identity. (A–F, H–K) Dorsal views. NC, notochord. Scale bars: (A–F, A′–F′), 50 μm; (H–K) 20 μm.