MCAT elements are essential for cardiac gene expression during development. 
Avian transcriptional enhancer factor-1 (TEF-1) proteins are muscle-enriched and 
contribute to MCAT binding activities. However, direct activation of MCAT-driven 
promoters by TEF-1-related proteins has not been uniformly achieved. Divergent 
TEF (DTEF)-1 is a unique member of the TEF-1 multigene family with abundant 
transcripts in the heart but not in skeletal muscle. Herein we show that DTEF-1 
proteins are highly expressed in the heart. Protein expression is activated at 
very early stages of chick embryogenesis (Hamburger-Hamilton stage 4, 16-18 h), 
after which DTEF-1 becomes abundant in the sinus venosus and is expressed in the 
trabeculated ventricular myocardium and ventricular outflow tracts. By chromatin 
immunoprecipitation, DTEF-1 interacts with the cardiac troponin T (cTnT) 
promoter in vivo. DTEF-1 also interacts with MEF- 2 by coimmunoprecipitation and 
independently or cooperatively (with MEF-2) trans-activates the cTnT promoter. 
DTEF-1 isoforms do not activate the cTnT promoter in fibroblasts or skeletal 
muscle. DTEF-1 expression occurs very early in chick embryogenesis (16-18 h), 
preceding sarcomeric protein expression, and it activates cardiac promoters. As 
such, DTEF-1 may be an early marker of the myocardial phenotype. DTEF-1 
trans-activates the cTnT promoter in a tissue-specific fashion independent of 
AT-rich, MEF-2, or GATA sites. The observed spatial pattern suggests decreasing 
levels of expression from the cardiac inlet to the ventricular outflow tracts, 
which may mark a cardiogenic or differentiation pathway that parallels the 
direction of flow through the developing chick heart.