REGULATION OF CARDIAC MESODERMAL AND NEURAL CREST DEVELOPMENT BY THE BHLH TRANSCRIPTION FACTOR, DHAND

dHAND and eHAND are related basic helix-loop-helix (bHLH) transcriptio n factors that are expressed in mesodermal and neural crest-derived st ructures of the developing heart. In contrast to their homogeneous exp ression during avian cardiogenesis, during mouse heart development we show that dHAND and eHAND are expressed in a complementary fashion and are restricted to segments of the heart tube fated to form the right and left ventricles, respectively. dHAND and eHAND represent the earli est cardiac chamber-specific transcription factors yet identified. Tar geted gene deletion of dHAND in mouse embryos resulted in embryonic le thality at embryonic day 10.5 from heart failure. Our description of t he cardiac phenotype of dHAND mutant embryos is the first demonstratio n of a single gene controlling the formation of the mesodermally deriv ed right ventricle and the neural crest-derived aortic arches and reve als a novel cardiogenic subprogramme for right ventricular development .