Figure 2. Ccm2L is expressed in endothelial cells that participate in active cardiovascular growth.

A–E. In situ hybridization reveals endothelial-specific expression of Ccm2L. Shown are saggital sections of an E11.5 mouse embryo. Ccm2L signal is shown in pink (arrows) and DAPI staining of cell nuclei in blue. ao, aorta; cv, cardinal vein; a, atrium; v, ventricle. F. Quantitative RT-PCR measurement of mRNA transcripts encoding CCM1, CCM2, CCM2L, CCM3 and the endothelial-specific control gene TIE2 in cultured human microvascular endothelial cells from the skin (HMVEC) and heart (HMVEC-C), dermal lymphatic endothelial cells (LEC), and human primary keratinocytes (HPK) is shown. The black and red arrowheads indicate that no expression of TIE2 or CCM2L was detected in HPKs. N=4; error bars indicate SEM. G–K Ccm2L^GFP expression in the endocardium. Shown are low (above) and high (below) magnification images of cardiac trabeculae from E10.5 -E15.5 hearts following immunostaining for GFP (green) and the endothelial cell marker PECAM (red). K. Quantitation of Ccm2L^GFP-expressing endocardial cells during mouse cardiac development. N=5; error bars indicate SEM. L–N. Expression of Ccm2L^GFP in the dorsal aorta (da) and cardinal vein (cv) at E10.5. O–T Ccm2L^GFP is expressed in the endothelial cells of nascent vessels. Ccm2L^GFP was frequently detected in non-lumenized endothelial extensions of existing vessels (O), such as those that invade the neural tube (nt) at E10.5-E11.5 (P, Q), and microvasculature (R), and in newly formed microvasculature of the neonatal retina (S, T). Scale bars indicate 20 µm unless otherwise indicated. See also Supp. Fig. 1 and Supp. Table 1.