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. 2018 Oct 5;7:e40045. doi: 10.7554/eLife.40045

Figure 2. The extracellular domains of DLL1 and DLL4 determine ligand behavior during somitogenesis.

Figure 2.

(A) Scheme of the targeting vector pMP8.CAG-Stop used to introduce inducible chimeric ligands into the Hprt locus, and of Cre-mediated activation of transgene (D1ECD_D4ICD or D4ECD_D1ICD) expression driven by the CAG promotor (CAG prom). 5’ hom and 3’ hom, Hprt 5’ and 3’ homology regions; ex1-3 (grey boxes), Hprt exons; neor, neomycin phosphotransferase; pA, polyadenylation signal; hHPRT prom, human Hprt promoter; DLL1/4iresdsRED, chimeric ORF–linked to dsRed tag by an internal ribosomal entry site (IRES). (B) Uncx expression in E9.5 wild type embryos (a, a’; n = 28), embryos lacking DLL1 in the mesoderm (b, b’; n = 12) and male embryos lacking DLL1 in the mesoderm that express either D1ECD_D4ICD (c, c’; n = 9) or D4ECD_D1ICD (d, d’; n = 8) showing that the extracellular domain of DLL1 but not of DLL4 can restore Uncx expression. (C) Whole mount immunofluorescent staining of wild type (a–c) and D4ECD_D1ICD/Y;T(s):Cre (d–f) PSMs using antibodies recognizing the extracellular domain of DLL4 showing co-localization of the exogenous chimeric ligand with pan-Cadherin (panCad) at the cell surface. Additional intracellular staining most likely reflects the presence of the ligand in the ER and trans Golgi as observed previously for DLL1 in cultured cells (Geffers et al., 2007; Müller et al., 2014) and for endogenous DLL1 and transgenic DLL4 in the PSM (Preuße et al., 2015). n = 3 for wild type, n = 4 for D4ECD_D1ICD/Y;T(s):Cre; Scale bar = 10 µm.