Fig. 7. Conditional deletion of Nmyc results in severely abnormal lung development. (A) Gross morphology of lungs at E18.5. The lung that is cre(+);Nmyc^flox/+ (middle panel) has a mosaic phenotype with some normal tissue (white box). By contrast, all cre(+);Nmyc^flox/flox lungs (right panel) had a much more uniform abnormal phenotype. (B) Sections of E18.5 lungs after staining with Hematoxylin and Eosin. In this case, two examples of cre(+);Nmyc^flox/+ lungs are shown (middle panels): the one on the left has a normal morphology and resembles a cre(-) lung (far left), whereas the one on the right is severely abnormal and resembles a cre(+);Nmyc^flox/flox lung (far right), except that regions of normal tissue are present (black box enlarged in inset). (C,D) Sections of wild-type and abnormal heterozygous cre(+);Nmyc^flox/flox or Nmyc^flox/+ lungs at E14.5 (C) and E15.5 (D). (E) Level of Nmyc RNA in conditional mutant lungs as measured by RT-PCR of total RNA. Note the significant decrease in RNA levels at E14.5-E16.5. Asterisk indicates abnormal cre(+);Nmyc^flox/+ lung at E15.5. (F) Nmyc antibody staining of wild-type and cre(+); Nmyc^flox/flox lungs at E18.5. Note there is only weak staining of cells in which Nmyc has been deleted. Scale bars: in B, 200 µm; in C,D, 100 µm; in F, 50 µm.