(A) Axis extension was quantified at bud stage by measuring the axis extension angle α. Axis extension is reduced in mib1 morphants but restored upon coinjection of WT mib1 RNA. Lateral views of bud stage embryos, anterior up, dorsal to the right. (B) mib1 morphants present a widening of the notochord, somites, and neural plate. Dorsal views of 2 somite stage embryos, anterior up. dlx3 in situ hybridization outlines the neural plate, papc the somites and the adaxial cells lining the notochord. Widths indicated in microns. (C) Mib1 protein variants used in the study. (D) The mib1ta52b mutation has no effect on axis extension. (E) Constitutively activated Notch (NICD) fails to restore mib1 morphant axis extension. (F) mib1ta52b RNA injection restores mib1 morphant axis extension. (G,H) Axis extension is impaired in mib1tfi91 or mib1nce2a null mutants. On the left panel of (G) the mib1 morphant data from (A) are included for comparison. (I) In situ hybridization reveals reduced mib1 transcript levels in n = 27 mib1tfi91 mutant embryos. Dorsal views of bud stage embryos, anterior up. To warrant identical acquisition conditions, two embryos were photographed on a single picture. Scalebars: 200 µm. Boxes in (A,B, D–G) represent mean values ± SD. See Figure 1—source data 1 for complete statistical information
