Organization and Myogenic Restricted Expression of the Murine Serum Response Factor Gene
A ROLE FOR AUTOREGULATION*
Abstract
Serum response factor (SRF), a member of an ancient family of DNA-binding proteins, is generally assumed to be a ubiquitous transcription factor involved in regulating growth factor-responsive genes. However, avian SRF was recently shown (Croissant, J. D., Kim, J.-H., Eichele, G., Goering, L., Lough, J., Prywes, R., and Schwartz, R. J. (1996) Dev. Biol. 177, 250–264) to be preferentially expressed in myogenic lineages and is required for regulating post-replicative muscle gene expression. Given the central importance of SRF for the muscle tissue-restricted expression of the striated α-actin gene family, we wanted to determine how SRF might contribute to this muscle-restricted expression. Here we have characterized the murine SRF genomic locus, which has seven exons interrupted by six introns, with the entire locus spanning 11 kilobases. Murine SRF transcripts were processed to two 3′-untranslated region polyadenylation signals, yielding 4.5- and 2.5-kilobase mRNA species. Murine SRF mRNA levels were the highest in adult skeletal and cardiac muscle, but barely detected in liver, lung, and spleen tissues. During early mouse development,in situ hybridization analysis revealed enrichment of SRF transcripts in the myotomal portion of somites, the myocardium of the heart, and the smooth muscle media of vessels of mouse embryos. Likewise, murine SRF promoter activity was tissue-restricted, being 80-fold greater in primary skeletal myoblasts than in liver-derived HepG2 cells. In addition, SRF promoter activity increased 6-fold when myoblasts withdrew from the cell cycle and fused into differentiated myotubes. A 310-base pair promoter fragment depended upon multiple intact serum response elements in combination with Sp1 sites for maximal myogenic restricted activity. Furthermore, cotransfected SRF expression vector stimulated SRF promoter transcription, whereas dominant-negative SRF mutants blocked SRF promoter activity, demonstrating a positive role for an SRF-dependent autoregulatory loop.
Footnotes
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↵* This work was supported by National Institutes of Health Grants R01 HL50422 and P01 HL49953.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) .
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↵‡ To whom correspondence should be addressed: Dept. of Cell Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Tel.: 713-798-6649; Fax: 713-798-7799.
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↵1 The abbreviations used are: SRF, serum response factor; mSRF, murine serum response factor; SRE, serum response element; bp, base pair(s); kbp, kilobase pair(s); GST, glutathione S-transferase; PCR, polymerase chain reaction.
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↵2 J. D. Croissant, J.-H. Kim, G. Eichele, L. Goering, J. Lough, R. Prywes, and R. J. Schwartz, submitted for publication.
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- Received May 6, 1997.
