Control of skeletal muscle-specific transcription: involvement of paired homeodomain and MADS domain transcription factors.

In the last few years, many aspects of skeletal muscle-specific gene regulation have been explained by the activity of the helix-loop helix (HLH) myogenic regulatory factors of the MyoD family, which are sequentially expressed during skeletal muscle formation. However, evidence is accumulating that muscle specific transcription requires functional interactions of these muscle-specific HLH factors with other regulatory proteins whose expression is not only restricted to skeletal muscle. These regulators include the SRF and MEF2 MADS domain and the MHox paired homeodomain transcription factors. Together with the aforementioned HLH factors, they build an increasingly complex network of regulatory factors. Two members of the Pax multigenic family of developmental control transcription factors, Pax-3 and 7, have been shown to be expressed not only in nervous tissue but also in skeletal muscle precursor cells. Their possible involvement in the control of muscle-specific transcription is discussed in light of known molecular properties of Pax gene products described in other biological systems.