Murine pulmonary myocardium: Developmental analysis of cardiac gene expression

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Abstract
Long‐standing observations that cardiac muscle exists in the walls of the pulmonary and caval veins have recently been confirmed at the molecular level (Lyons et al. [1990] J. Cell Biol. 111:2427–2436; Springall et al. [1988] Thorax 43:44–52; Subramaniam et al. [1991] J. Biol. Chem. 266:24613–24620). Using ventricle‐ and atrial‐specific riboprobes, we determined that the pulmonary myocardium exhibits an atrial pattern of cardiac‐specific gene expression. Additionally, the developmental pattern of expression was studied using a riboprobe specific to the α‐cardiac myosin heavy chain (α‐MHC) gene transcript. We find that α‐MHC gene expression is first detectable in the lung between 13.9–14.3 days post‐coitum. Extension of the α‐MHC specific hybridization signal into the pulmonary venous bed progresses through the neonatal period. The data are consistent with the hypothesis that the extension of α‐MHC gene expression into the lung occurs via the migration of atrial myoblasts into the vein during atrial septation and remodeling of the sinus venosus and pulmonary venous trunk.