The Alk5 and Tgfbr2 are deleted in the lungs of L1cre(+);Alk5^loxP/loxP and L1cre(+);Tgfbr2^loxP/loxP mice, respectively, yet no noticeable pathologic signs were observed in the lungs of 2-month-old mutants. (A) PCR genotyping with primers β and γ (top) and Cre (bottom), showing L1cre(+);Alk5^loxP/loxP (lane 1) and L1cre(+);Alk5^+/+ (lane 2) mice. WT, wild-type allele (B) PCR amplification of the Alk5 null allele is specific for the lung. Genomic DNA isolated from the lung (top), liver (middle), and tail (bottom) were used as template to amplify the null allele by primers α and γ. Another primer set detecting a diploid genome (ie, Alk1 = control) was also included in the PCR reaction to demonstrate equal loading of the template. (C) PCR genotyping with primers x and y (top) and cre (bottom), showing L1cre(+);Tgfbr2^loxP/loxP (lane 3), L1cre(−);Tgfbr2^loxP/loxP (land 4), and L1cre(+);Tgfbr2^+/+ (lane 5) mice. (D) PCR amplification of the Tgfbr2 null allele is specific for the lung. Genomic DNA isolated from the lung (top), liver (middle), and tail (bottom) was used as template to amplify the null allele by primers x and z. Another primer set detecting a diploid genome (ie, Alk1) was also included in the PCR reaction to demonstrate equal loading of the template. (E-J) Histologic sections of the lungs of 2-month-old control (ie, L1cre(+);Alk5^+/+;R26R; E,H), L1cre(+);Alk5^loxP/loxP;R26R (F,I), and L1cre(+);Tgfbr2^loxP/loxP;R26R (G,J) mice. (E-G) Histologic sections of the X-gal stained lungs were counterstained with NFR, demonstrating that the Cre–mediated recombination has occurred in these lungs as expected. Insets are high magnification views showing that lacZ expression is restricted to pulmonary ECs, not in bronchial epithelial or smooth muscle cells. (H-J) Anti-αSMA antibody staining of the control and mutant lungs showing no specific pathologic signs. Insets show that similar thickness of the VSMC layers of distal arteries.