Abstract 16246: Versican Secretion from Endocardium is Required for Chamber Formation via The Recruitment of Cardiac Progenitors
Background: Linear heart tube from the primary heart field develops into a multi-chambered heart through the addition of new cardiomyocytes. Transcription factors involved in the secondary heart field development are known; however, microenvironment factors controlling cardiac progenitor recruitment remain unknown. We investigated the microenvironment around cardiac progenitors that affect integration into linear heart tube.
Methods and Results: Using forward-genetic N-ethyl-N-nitrosourea (ENU) mutagenesis screening, we identified a cardiovascular mutant Medaka fish called linear heart tube (lht). Mutant embryos showed hypomorphic ventricle, continued peristaltic pumping, and constricted outflow tract, failed looping, and terminated development at the linear heart tube stage. Positional cloning revealed a mutation in the 3'-untranslated region of versican, a proteoglycan gene. Versican mRNA was expressed in the dorsal side of outflow tract at the linear heart tube stage, and lht mutants showed normal development until the heart tube stage, with normal expression of early-differentiation markers amhc, vmhc, fli1, and cmlc2. However, ventricular chamber formation and cardiac jelly were disrupted, and there were fewer cardiomyocytes than in wild types. Phosphorylated-histone-H3 staining showed similar cardiomyocyte proliferation in linear heart tube between wild type and lht, but ventricle cardiomyocyte numbers increased only in wild type due to new cardiomyocytes. Photoconvertible Kaede labeled newly differentiated cardiomyocytes in the ventricular chamber from the outflow tract in wild type fish, but this recruitment was disrupted in lht mutant. To elucidate the in vivo role of versican in cardiac progenitor recruitment, we generated conditional versican knockout mice crossed with the VE-cadherin (deletion in endothelial & endocardial cells) Cre mouse line. VE-cadherin Cre, Versican null conditional mutants died around E9.5 to E10.5, while mutants showed abnormal looping, no glycosaminoglycan in cardiac jelly, hypoplastic right ventricle, constricted outflow tract, and no endocardial cushion formation.
Conclusion: Versican secretion from endocardium is required for the recruitment of cardiac progenitor cells.
- © 2012 by American Heart Association, Inc.