(A) Schematics demonstrating the generation of PDPN-tk mouse strain or PDPN-Cre mouse strain with a 4-kb PDPN promoter sequence ligated to HSV viral tk sequence or Cre recombinase sequence, respectively, using the pCR2.1-TOPO vector. (B) YFP visualization of the eyes of PDPN-Cre; LSL-YFP and control mice. The expression of YFP and PDPN was examined in primary LECs isolated from IFA-induced benign lymphatic endothelial tumor (lymphangioma) in the PDPN-Cre; LSL-YFP mice. Scale bar, 20 μm. (C) Cell viability assay of GCV-treated primary LECs isolated from IFA-induced lymphangioma in PDPN-tk or WT control mice. (D) The comparison of IFA-induced lymphangioma formation in GCV-treated PDPN-tk mice, as compared with WT mice or PDPN-tk mice without GCV treatment (n = 6 mice per group). GCV treatment was conducted as daily intraperitoneal injections of 50 mg/kg body weight of GCV. (E) Histology of the lymphangioma tissue samples from PDPN-tk and WT mice. (F) Ki67 staining on the lymphangioma tissue samples from PDPN-tk and WT mice. (G) Immunofluorescence staining of PDPN (red) and Ki67 (green) on the lymphangioma tissues from PDPN-tk and WT mice. White arrows indicate the nuclei of PDPN and Ki67 double positive cells. Scale bars (E–G), 100 μm. Data are represented as mean ± SEM. Significance is determined using an unpaired two-tailed Student t test (*p < 0.05, **p < 0.01, ***p < 0.001). The underlying data can be found in S1 Data. Cre, Cre recombinase transgene; GCV, ganciclovir; H&E, hematoxylin and eosin; HSV, herpes simplex virus; IFA, incomplete Freund’s adjuvant; Ki67, cell proliferation antigen Ki-67; LEC, lymphatic endothelial cell; LSL, LoxP-Stop-LoxP; NS, not significant; pCR2.1-TOPO, topoisomerase I-activated pCR2.1-TOPO vector; PDPN, podoplanin; tk, thymidine kinase; WT, wild type; YFP, yellow fluorescent protein.