(
A) Coronal sections of E13.5
Tie2-Cre;R26-Tcf/Lef-LSL-H2B-GFP-6xMYC embryos near the cephalic flexure, immunostained for the indicated markers: ICAM2, MYC, LEF1, and DAPI. (
A’) Higher magnification of the boxed region in (
A). The boundary between CNS and peripheral tissues is marked on the DAPI image with red circles. The nuclear MYC signal reveals canonical Wnt signaling in CNS ECs (yellow arrows) but not in peripheral ECs (yellow arrowheads). LEF1 is present in CNS ECs (yellow arrows) but not in peripheral ECs (yellow arrowheads). LEF1 is also present in developing neurons in the ventral CNS. Scale bar in A: 200 um. Scale bar in A’: 50 um. (
B–E) Sections of P7
Tie2-Cre;R26-Tcf/Lef-LSL-H2B-GFP-6xMYC brain (
B), liver (
C), lung (
D), and kidney (
E). Immunostaining as in
Figure 6. The nuclear MYC signal reveals canonical Wnt signaling uniformly in CNS ECs and in a subset of renal vessels (yellow arrows). LEF1 levels are below the limit of detection in all or nearly all ECs in liver and lung and in the majority of ECs in the kidney. The sparse MYC-positive nuclei in liver and lung correspond to non-ECs, most likely tissue macrophages, based on the specificity of the
Tie2-Cre transgene (yellow arrowheads). Scale bar in (
B–E): 50 um.