The transcription factors Gli2 (glioma-associated factor 2), which is a 
transactivator of Sonic Hedgehog (Shh) signalling, and myocyte enhancer factor 
2C (MEF2C) play important roles in the development of embryonic heart muscle and 
enhance cardiomyogenesis in stem cells. Although the physiological importance of 
Shh signalling and MEF2 factors in heart development is well known, the 
mechanistic understanding of their roles is unclear. Here, we demonstrate that 
Gli2 and MEF2C activated each other's expression while enhancing 
cardiomyogenesis in differentiating P19 EC cells. Furthermore, dominant-negative 
mutant proteins of either Gli2 or MEF2C repressed each other's expression, while 
impairing cardiomyogenesis in P19 EC cells. In addition, chromatin 
immunoprecipitation (ChIP) revealed association of Gli2 to the Mef2c gene, and 
of MEF2C to the Gli2 gene in differentiating P19 cells. Finally, 
co-immunoprecipitation studies showed that Gli2 and MEF2C proteins formed a 
complex, capable of synergizing on cardiomyogenesis-related promoters containing 
both Gli- and MEF2-binding elements. We propose a model whereby Gli2 and MEF2C 
bind each other's regulatory elements, activate each other's expression and form 
a protein complex that synergistically activates transcription, enhancing 
cardiac muscle development. This model links Shh signalling to MEF2C function 
during cardiomyogenesis and offers mechanistic insight into their in vivo 
functions.