Loss of CCBE1 or VEGFR3 signaling does not affect the development of lung cell types other than lymphatic vessels. (A–M) E18.5 Ccbe1^−/−, Vegfr3^kd/kd, and control littermate embryonic lungs were stained for markers of lung endothelial cells (PECAM), lung Clara cells (CC-10), alveolar Type II cells (pro-surfactant protein C [SPC]), Type I cells (PODOPLANIN [PDPN] and CAVEOLIN1 [CAV1]), lymphatic endothelial cells (PROX1 and LYVE1), mesenchyme (PDGFRα), vascular smooth muscle cells and pericytes (PDGFRβ, SM22 and NG2), blood vessels (vimentin and desmin), and mesothelium (Wilms Tumor 1 [WT1]). Bars, 50 µm. Representative images are shown from 3 control and 3 lymphatic-deficient embryos examined from 3 independent litters in each group. Arrows indicate PROX1⁺ nuclei surrounded by LYVE1⁺ cell membrane in lymphatic endothelial cells (F). (N) qPCR was used to measure relative mRNA expression levels of the indicated lung cell marker genes in littermate control and Ccbe1^−/− neonatal lungs after C-section at E18.5. Quantitative data are represented as mean and SEM from 5–7 control and 4–6 Ccbe1^−/− E18.5 embryos examined from 2 independent litters in each group. Asterisk indicates P < 0.05 compared with control.