Muscle-specific genes

G-quadruplex structures could potentially be generated in vivo by the association of two adjacent hairpin structures of two neighboring G-rich sequences within single-stranded DNA. This model was supported to some degree by the demonstration that two representative G-rich oligonucleotides from the mouse ot7 integrin promoter, which were located 85 base pairs apart, adopted a heterodimeric G-quadruplex structure. 

By virtue of its helix-loop-helix motif, MyoD is able to form homodimers, as well as heterodimers, with other ubiquitously expressed helix-loop-helix proteins, such as E12 and E47. MyoD-E-protein heterodimers bind to E-box DNA more tightly than MyoD homodimers and act as stronger activators of transcription. MyoD-E47 heterodimers were found to bind to bimolecular G-quadruplex structures more weakly than MyoD homodimers. Specifically, MyoD heterodimers bound more tightly to E-box DNA than to bimolecular G-quadruplex structures of promoter sequences of the sMtCK and ot7 integrin, as reflected by 

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Browning, C.L., Culberson, D.E., Aragon, I.V., Fillmore, R.A., Croissant, J.D., Schwartz, R.J. et al. (1998) The developmental regulated expression of serum response factor plays a key role in the control of smooth muscle-specific genes. Dev. Biol., 194, 18-37. 

Wasserman WW, Fickett JW. Identification of regulatory regions, which confer muscle-specific gene expression. J Mol Biol 1998 278 167-181. 

Baker, R. and Schubiger, G. (1995). Ectoderm induces muscle-specific gene expression in Drosophila embryos. Development 727 1387-1398. 

Knockout mice and Drosophila mutants have been used to explore the roles of MRF and MEF proteins in conferring myogenic specificity in intact animals, extending the work in cell culture. These experiments demonstrated the importance of three of the MRF proteins and of MEF proteins for distinct steps in muscle development (see Figure 22-14). The function of the fourth myogenic protein, Mrf4, is not entirely clear It may be expressed later and help maintain differentiated muscle cells and by combinatorial control to ensure that only muscle-specific genes are activated. 

Recent work shows that histone acetylases and deacety-lases are also crucial for regulating muscle-specific genes. As... 

ARAKAWA, E., HASEGAWA, K., YANAI, N., OBINATA, M. MATSUDA, Y. 2000. A mouse bone marrow stromal cell line, TBR-B, shows inducible expression of smooth muscle-specific genes. FEBS Lett, 481, 193-6. 

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