L-WNK1 expression in the developing and adult heart. A and E: Whole-mount X-gal staining. B and G:In situHybridization with the L-WNK1 mRNA probe. C, D, and F: X-gal staining on frozen sections counterstained with eosin. A: At E13, the heart is undergoing remodeling and L-WNK1-nlacZ transgene was strongly expressed in the right atrium (RA), left atrium (LA), right ventricle (RV), and left ventricle (LV). B: L-WNK1 mRNA was detected in all the cardiac chambers. C: We detected at E12.5 strong β-galactosidase activity in precursors of the cardiac valves (asterisks) in the atrioventricular canal (avc). OFT, outflow tract; SV, sinus venosus. D: At E14.5, the transgene is strongly expressed in trabeculae (tr) of the ventricular wall (vw). E and F: Adult heart, showing ubiquitous expression of the transgene (lu, lung), confirmed by in situ hybridization analysis of myocardium (m) transverse sections (G). Original magnifications: ×10 (A, B); ×40 (C, D); ×2.5 (E); ×250 (F, G).