Regulation of scleraxis function by interaction with the bHLH protein E47

Scleraxis is a basic helix-loop-helix (bHLH) protein whose function has been postulated to be preconfigurative of sclerotomal mesenchymal patterning during early embryonic development by regulating expression of differentiation-specific genes, particularly those involved in chondrogenesis. To gain understanding of the molecular action of scleraxis we test the hypothesis that it heterodimerizes with another bHLH protein to activate gene expression. Transient coexpression of scleraxis and E47, a candidate bHLH protein, showed that scleraxis dimerizes with E47 in vivo and that this complex binds to a classic E-box DNA sequence better than either factor alone. Further, when expressed together, scleraxis and E47 synergistically enhanced transcription from a promoter containing multiple E-box binding sites.