Rac1 is expressed in mouse and human developing lungs. A and B: qRT-PCR showing the expression of RAC1 in human fetal lungs between gestational weeks 10 and 21 (A) n = 3 at least, and in the developing mouse lung between embryonic day E11.5 and E18.5 (B), n = 3 for each time point. C–E: immunofluorescent staining showing active Rac1 (green) and DAPI (blue) in 12.5 (C), 15.2 (D), and 18 wk (E) gestational age human fetal lung. F–H: fluorescent staining using the fusion protein GST-PAK-PBD (red) and DAPI (blue) on 12.5 (F), 15.2 (G), and 18 wk (H) human fetal lung. I–J: immunofluorescent staining showing active Rac1 (green) and DAPI (blue) in E13 (I) and E14 mouse lung (J). K: negative control in absence of active-Rac1 antibody and only secondary antibody on E13 mouse lung. L and M: staining using the fusion protein GST-PAK-PBD (red) and DAPI (blue) on E13 (L) and E14 (M) mouse lung. N: negative control in presence of anti-GST and secondary antibody only on 12.5 wk human fetal lung. Staining was performed on slides from at least 3 independent samples. Scale bar is 50 μm.