Fig 4.

Cre-mediated recombination in the embryonic and postnatal lung. Lung sections were obtained from mice killed at E14.5 (a and d), E15.5 (b and e), E16.5 (c and f), and PN 21 (g–i), and stained for AP with nuclear fast red counterstain. Recombination in the absence of doxycycline is rare (arrows) and can be seen only after E15.5 (a–c and g). Cell labeling was widespread after treatment of the dam with doxycycline from E6.5 to E14.5, E15.5, and E16.5 (d–f). Rare labeling was observed when exposed to doxycycline from E18.5 to PN9 (h) or PN2 to PN9 (i). [Bar = 30 μm (a–i).]