Figure 6. DLL4 is required for LEC lacteal tip cell position and survival.

(A) DLL4 expression is important for tip cell competence. Control (Prox1-CreERT2 Rosa26-EYFP) and Dll4^ΔLEC (Dll4^fl/fl Prox1-CreERT2 Rosa26-EYFP) mice were injected with a reduced amount of tamoxifen to induce mosaic Cre activation. Representative images from WT and Dll4^ΔLEC mosaic lacteals (YFP, green; PROX1, red; LYVE1, blue.) (B) Decreased number of Dll4-deficient LECs. Percentage (mean ± SD) of YFP⁺ LECs in mosaic Cre recombination control and Dll4^ΔLEC Rosa26-YFP mice; n = 4. (C) Quantification of recombined YFP⁺ control or Dll4^ΔLEC cells in tip position. Percentage (mean ± SD) of YFP⁺ lacteal tip cells in mosaic Cre recombination control and Dll4^ΔLEC Rosa26-YFP mice; n = 4. (D) Quantification of recombined YFP⁺ control or Dll4^ΔLEC cells position on vertical axis of the lacteal. Position of YFP⁺ lacteal cells in mosaic Cre recombination control and Dll4^ΔLEC Rosa26-YFP mice as a percentage (mean ± SD) of lacteal length (lacteal base = 0, lacteal tip cell = 100); n = 4. (E) DLL4 depletion in vitro promotes apoptosis. Quantification of caspase-3⁺ LECs (caspase-3, red; β-catenin, green; DAPI, blue) 48 hours after transfection with two different siRNAs targeting DLL4. Mean percentage of caspase-3⁺ LECs. The graph represents pooled data of 2 independent experiments. Scale bars: 25 μm, A; 20 μm, E. *P < 0.05, 2-tailed unpaired Student’s t test.