There have now been shown to be four genes, myoD, myogenin, myf5 and mrf4, the expression of each of which has ability to convert fibroblasts into muscle The encoded proteins are all members ofof the HLh TF family The hlh group of proteins produce a diverse range of hetro- and homodimeric TFs that each have different activities and rolesThere have now been shown to be four genes, myoD, myogenin, myf5 and mrf4, the expression of each of which has ability to convert fibroblasts into muscle. The encoded proteins are all members of of the HLH TF family. The HLH group of proteins produce a diverse range of hetro- and homodimeric TFs that each have different activities and roles