Outline of Lecture 17

Outline of Lecture 17 Heart Development I. Early heart development: cardiac crescent and heart tube - Only splanchnic mesoderm that migrates to the cardiac crescent become cardiogenic (committed to a cardiac fate) - Cardiogenesis requires BMP-2 (which induces Nkx2.5 expr) and an unidentified factor - Cardiac crescent gives rise to 2 lineages: endocardial and myocardial cells - Two endocardial tubes form by vasculogenesis then fuse to form a single heart tube - Heart tube is composed of inner endocardium and outer myocardium with cardiac jelly in between, and is enclosed by pericardial cavity - A/P positional cues cause heart tube to segment into distinct regions II. Looping of heart tube - Heart tube folds right to left, and L/R asymmetry is induced by Shh and nodal - Looping is regulated by eHAND, which is downstream of Nkx2.5 - Ventricular chamber growth follows looping, and is regulated by eHAND in right ventricle and dHAND in left ventricle; MEF2C may be involved with both - Trabeculae projects form inside ventricular area then fuse to give rise to thickened myocardium and remodeled cardiac myocytes - Also, epicardium forms from epicardial precursors III. Endocardial cushions - End