IL-7–Cre transgene activity during embryonic LN development. (A) IL-7–CrexR26-EYFP mouse embryos at different developmental stages were harvested, and dissected LN anlagen were analyzed for transgene-expressing (EYFP⁺) stromal cells. (B) E14.5 embryonic sections were stained with antibodies against EYFP, CD31, and Pdpn and analyzed by CLSM. EYFP⁺CD31⁺ cells (arrows) were found in the jugular lymph sac (jls) lining endothelium. (C) Neonatal inguinal LNs from IL-7–CrexR26-EYFP mice stained for EYFP (green), LyveI⁺ lymphatic endothelium (blue), and Pdpn⁺ parenchymal stroma (red). Scale bar represents 50 μm. (D) Higher magnification of boxed area in panel B. EYFP⁺LyveI⁺ LECs are indicated by arrows. Scale bar represents 20 μm.