RT Journal Article SR Electronic T1 Regulation of Chamber-Specific Gene Expression in the Developing Heart by Irx4 JF Science JO Science FD American Association for the Advancement of Science SP 1161 OP 1164 DO 10.1126/science.283.5405.1161 VO 283 IS 5405 A1 Bao, Zheng-Zheng A1 Bruneau, Benoit G. A1 Seidman, J. G. A1 Seidman, Christine E. A1 Cepko, Constance L. YR 1999 UL http://science.sciencemag.org/content/283/5405/1161.abstract AB The vertebrate heart consists of two types of chambers, the atria and the ventricles, which differ in their contractile and electrophysiological properties. Little is known of the molecular mechanisms by which these chambers are specified during embryogenesis. Here a chicken iroquois-related homeobox gene,Irx4, was identified that has a ventricle-restricted expression pattern at all stages of heart development. Irx4 protein was shown to regulate the chamber-specific expression of myosin isoforms by activating the expression of the ventricle myosin heavy chain–1 (VMHC1) and suppressing the expression of the atrial myosin heavy chain–1 (AMHC1) in the ventricles. Thus, Irx4 may play a critical role in establishing chamber-specific gene expression in the developing heart.