(A) Generation of Tie1 whole-body inducible or lymphatic endothelium–specific Tie1-KO mice. Tie1 whole-body inducible KO (Tie1^WB–/–) was generated by crossing Tie1^fl mice with Rosa26^rtTA TetOCre mice and timed induction with Dox water. Tie1 lymphatic-specific Tie1 KO (Tie1^LEC–/–) was generated by crossing Tie1^fl mice with PdpnCre mice. (B) Gross phenotypes of Tie1^WB–/– embryos that were induced and examined at different time points (first number indicates the induction time point; second number indicates the harvest time point). White asterisk shows blood-filled lymphatics at E15.5 (5 of 7 of the Tie1^WB–/– embryos); arrow shows edema at E18.5 (7 of 9 of the Tie1^WB–/– embryos); and arrowhead shows chylous ascites at P2 (6 of 6 of the Tie1^WB–/– pups). (C) LEC-specific Tie1 KO resulted in a phenotype similar to that of whole-body KO. (D) Workflow of dermal LEC bulk RNA-Seq. E18.5 embryos induced at E13.5 were euthanized. The skin from each embryo was removed and placed in an Eppendorf tube for enzymatic digestion. The single-cell suspension was labeled with antibodies against CD45, CD31, and Lyve1. CD31⁺LYVE1⁺ cells were sorted into lysis buffer for RNA extraction. Bulk RNA-Seq was performed on the Illumina HiSeq 4000 system. (E) Number of differentially expressed genes using a P value of less than 0.01 as the cutoff. Down, downregulated; Up, upregulated. (F) Volcano plot shows some of the most differentially expressed genes including Ccl21a, valve genes and tip cell–enriched genes. (G) Heatmaps of manually selected vascular-relevant genes categorized as labeled. (H) Overlap between our data set (blue) and a data set from HUVECs with transcriptionally active FOXO1 (orange). Some commonly regulated genes are listed in the square, including tip cell genes (red), polarization genes (blue), ion channel genes (green), and valve genes (black).