20 - Chamber-Specific Gene Expression and Regulation during Heart Development

Abstract

The regional differences in endogenous gene transcription between the prospective atria and ventricles begin to emerge after tubular heart formation. Several genes have been identified that are expressed in an atrial or ventricular chamber-specific fashion at some time during vertebrate embryo development. The timing to reach atrial chamber-specific expression of these genes during development is highly variable. AMHC1, encoding an atrial-specific myosin heavy chain (MyHC), is the earliest atrial-specific marker. AMHC1 is first expressed in the posterior region of the fusing chicken heart. In contrast to AMHC1 expression in the chicken, slow MyHC 3 in the quail is initially expressed throughout the tubular heart. As the heart chamberizes, expression of the slow MyHC 3 gene in the ventricles is downregulated, whereas expression in the atria is maintained. Similarly to slow MyHC 3, MLC-2a is initially expressed throughout the tubular heart at E 8 in the mouse embryo and is down regulated in the ventricular segment during chamber formation. Further, throughout embryonic and fetal development, atrial natriuretic factor (ANF) is expressed in both atrial and ventricular cardiomyocytes. Additionally, at specific times during development, expression of MLC-lv, MLC-2v, and βMyHC becomes ventricular chamber specific. Two models, an activation model and an inhibition model are used to depict regulation of chamber-specific expression of cardiac genes during embryonic development.