Notch signaling affects the balance between myotomal and mural cells derived from the lateral DM. (A) Histogram summarizing the relative phenotypic distribution of labeled cells derived from lateral DMs that were electroporated with either GFP, N1-ICD, N2-ICD, or Numb, 40 h after transfection. Notch overactivation biases cells to a mural fate at the expense of myotomal cells, whereas Numb biases cells to a myotomal fate at the expense of other fates. Results represent mean ± SEM. Significance of results of the different treatments was examined vis-a-vis GFP controls (*, P < 0.05; **, P < 0.01; ***, P < 0.001). (B–D) Electroporations of control GFP (B), N1-ICD/GFP (C), or Numb (D) to lateral E2.5 DMs. GFP or Numb immunoreactivity is green, QH1 is red, and HOECHST is blue. (B) In control GFP-treated epithelium, myotomal and dermal cells are produced along with mural and endothelial cells, which are seen in the wall of the CV. (C) Notch1 biases cells to a mural fate (see E–G). Note the presence of many GFP⁺/QH1⁻ cells in the walls of BVs. Similar results were obtained with N2-ICD. (D) Numb⁺ cells are predominantly localized in the myotome. (E–G) N2-ICD, N1-ICD, or GFP electroporations to lateral E2.5 DMs. SMA is red in E and desmin is red in F and G. HOECHST is blue. (E) N2-ICD electroporation enhances SMA expression on the treated side and also stimulates the number of GFP⁺/SMA⁺ cells in the wall of the CV and between the VLL and CV. This is also apparent in the enlarged image appearing in the inset. (F) N1-ICD had a similar effect as revealed by desmin immunostaining. (G) GFP electroporation does not increase desmin staining in the CV wall or between the CV and VLL. WD, Wolffian duct. Bars: (B) 26 μm; (C and D) 60 μm; (E and G) 81 μm; (F) 74 μm; (E and G, inset) 55 μm; (F, inset) 65 μm.