An atrioventricular canal domain defined by cardiac troponin I transgene expression in the embryonic myocardium

During early cardiac development the atrial myocardium is continuous with t he ventricular myocardium throughout the atrioventricular canal. The atriov entricular canal undergoes complex remodelling involving septation, formati on of atrioventricular valves and insulation between atria and ventricles e xcept at the level of the atrioventricular node. Understanding of these pro cesses has been hampered by the lack of markers specific for this heart reg ion. We have generated transgenic mice expressing beta-galactosidase under the control of the cardiac troponin I gene that show transgene expression m ainly confined to the atrioventricular canal myocardium during early embryo nic development. With further development beta-galactosidase positive cells are observed in the atrioventricular node and in the lower rim of both rig ht and left atria, supporting the view that atrioventricular canal myocardi um contributes to the atrioventricular node and is in part incorporated int o the lower rim of the atria. These results identify the atrioventricular c anal myocardium as a distinct transcriptional domain.