1: Mol Cell Biol. 2004 May;24(9):3757-68. HRC is a direct transcriptional target of MEF2 during cardiac, skeletal, and arterial smooth muscle development in vivo. Anderson JP, Dodou E, Heidt AB, De Val SJ, Jaehnig EJ, Greene SB, Olson EN, Black BL. Cardiovascular Research Institute, University of California, San Francisco, California 94143-0130, USA. The HRC gene encodes the histidine-rich calcium-binding protein, which is found in the lumen of the junctional sarcoplasmic reticulum (SR) of cardiac and skeletal muscle and within calciosomes of arterial smooth muscle. The expression of HRC in cardiac, skeletal, and smooth muscle raises the possibility of a common transcriptional mechanism governing its expression in all three muscle cell types. In this study, we identified a transcriptional enhancer from the HRC gene that is sufficient to direct the expression of lacZ in the expression pattern of endogenous HRC in transgenic mice. The HRC enhancer contains a small, highly conserved sequence that is required for expression in all three muscle lineages. Within this conserved region is a consensus site for myocyte enhancer factor 2 (MEF2) proteins that we show is bound efficiently by MEF2 and is required for transgene expression in all three muscle lineages in vivo. Furthermore, the entire HRC enhancer sequence lacks any discernible CArG motifs, the binding site for serum response factor (SRF), and we show that the enhancer is not activated by SRF. Thus, these studies identify the HRC enhancer as the first MEF2-dependent, CArG-independent transcriptional target in smooth muscle and represent the first analysis of the transcriptional regulation of an SR gene in vivo. PMID: 15082771 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 2: Cold Spring Harb Symp Quant Biol. 2002;67:97-105. Regulation of cardiac growth and development by SRF and its cofactors. Wang D, Passier R, Liu ZP, Shin CH, Wang Z, Li S, Sutherland LB, Small E, Krieg PA, Olson EN. Department of Molecular Biology, University of Texas, Southwestern Medical Center at Dallas, Dallas, Texas 75390-9148, USA. PMID: 12858529 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: J Biol Chem. 2003 May 9;278(19):17263-8. Epub 2003 Feb 28. Upstream stimulatory factor represses the induction of carnitine palmitoyltransferase-Ibeta expression by PGC-1. Moore ML, Park EA, McMillin JB. Department of Pathology and Laboratory Medicine, The University of Texas Medical School at Houston, UT-Houston Health Science Center, The Texas Medical Center, Houston, Texas 77030, USA. Transcriptional regulation of carnitine palmitoyltransferase-1beta (CPT-1beta) is coordinated with contractile gene expression through cardiac-enriched transcription factors, GATA4 and SRF. Metabolic modulation of CPT-1beta promoter activity has been described with the stimulation of gene expression by oleate that is mediated through the peroxisome proliferator-activated receptor (PPAR) pathway. The coactivator, peroxisomal proliferator-activated receptor gamma coactivator (PGC-1), enhances gene expression through interactions with nuclear hormone receptors and the myocyte enhancer factor 2 (MEF2) family. PGC-1 and MEF2A synergistically activate CPT-1beta promoter activity. This stimulation is enhanced by mutation of the E-box sequences that flank the MEF2A binding site. These elements bind the upstream stimulatory factors (USF1 and USF2), which activate transcription in CV-1 fibroblasts. However, overexpression of the USF proteins in myocytes depresses CPT-1beta activity and significantly reduces MEF2A and PGC-1 synergy. Co-immunoprecipitation studies demonstrate that PGC-1 and USF2 proteins can physically interact. Our studies demonstrate that PGC-1 stimulates CPT-1beta gene expression through MEF2A. USF proteins have a novel role in repressing the expression of the CPT-1beta gene and modulating the induction by the coactivator, PGC-1. PMID: 12611894 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Biochem Biophys Res Commun. 2002 Jun 21;294(4):791-7. TEF-1 and MEF2 transcription factors interact to regulate muscle-specific promoters. Maeda T, Gupta MP, Stewart AF. Cardiovascular Institute, School of Medicine, University of Pittsburgh, BST 1704.3, PA 15213, USA. Many muscle-specific genes are regulated by transcriptional enhancer factor-1 (TEF-1), serum response factor (SRF), and myocyte enhancer factor-2 (MEF2) transcription factors. TEF-1 interacts with the MADS domain of SRF and together SRF and TEF-1 co-activate the skeletal alpha-actin promoter. MEF2 factors also contain a MADS domain with 50% amino acid identity to the SRF MADS domain. Because of this sequence divergence, some SRF co-factors do not interact with MEF2. To demonstrate that TEF-1 factors could also interact with MEF2 through its MADS domain, we used co-immunoprecipitation and GST pull-down assays in vitro and a mammalian two-hybrid assay in vivo. The MADS domain was not sufficient for MEF2 interaction with TEF-1, because additional sequences in the activation domains of both proteins were required for in vivo association. The physiological significance of this interaction was also demonstrated by transient transfection assays using muscle-specific promoters. Our results suggest that by their interaction with MEF2 factors, TEF-1 factors can control MEF2-dependent muscle-specific gene expression. PMID: 12061776 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 5: J Biol Chem. 2001 Sep 14;276(37):34637-50. Epub 2001 Jul 16. Differential binding of an SRF/NK-2/MEF2 transcription factor complex in normal versus neoplastic smooth muscle tissues. Phiel CJ, Gabbeta V, Parsons LM, Rothblat D, Harvey RP, McHugh KM. Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA. The malignant potential of smooth muscle tumors correlates strongly with the disappearance of gamma-smooth muscle isoactin, a lineage-specific marker of smooth muscle development. In this paper, we identify a 36-base pair regulatory motif containing an AT-rich domain, CArG box, and a non-canonical NK-2 homeodomain-binding site that has the capacity to regulate smooth muscle-specific gene expression in cultured intestinal smooth muscle cells. Serum-response factor associates with an NK-2 transcription factor via protein-protein interactions and binds to the core CArG box element. Our studies suggest that the NK-2 transcription factor that associates with serum-response factor during smooth muscle differentiation is Nkx2-3. Myocyte-specific enhancer factor 2 binding to this regulatory complex was also observed but limited to uterine smooth muscle tissues. Smooth muscle neoplasms displayed altered transcription factor binding when compared with normal myometrium. Differential nuclear accessibility of serum-response factor protein during smooth muscle differentiation and neoplastic transformation was also observed. Thus, we have identified a unique regulatory complex whose differential binding properties and nuclear accessibility are associated with modulating gamma-smooth muscle isoactin-specific gene expression in both normal and neoplastic tissues. PMID: 11457859 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 6: J Biol Chem. 2001 Mar 9;276(10):7575-85. Epub 2000 Nov 28. Control of cardiac-specific transcription by p300 through myocyte enhancer factor-2D. Slepak TI, Webster KA, Zang J, Prentice H, O'Dowd A, Hicks MN, Bishopric NH. Department of Molecular and Cellular Pharmacology, University of Miami, Florida 33101, USA. The transcriptional integrator p300 regulates gene expression by interaction with sequence-specific DNA-binding proteins and local remodeling of chromatin. p300 is required for cardiac-specific gene transcription, but the molecular basis of this requirement is unknown. Here we report that the MADS (MCM-1, agamous, deficiens, serum response factor) box transcription factor myocyte enhancer factor-2D (MEF-2D) acts as the principal conduit for cardiac transcriptional activation by p300. p300 activation of the native 2130-base pair human skeletal alpha-actin promoter required a single hybrid MEF-2/GATA-4 DNA motif centered at -1256 base pairs. Maximal expression of the promoter in cultured myocytes and in vivo correlated with binding of both MEF-2 and p300, but not GATA-4, to this AT-rich motif. p300 and MEF-2 were coprecipitated from cardiac nuclear extracts by an oligomer containing this element. p300 was found exclusively in a complex with MEF-2D at this and related sites in other cardiac-restricted promoters. MEF-2D, but not other MEFs, significantly potentiated cardiac-specific transcription by p300. No physical or functional interaction was observed between p300 and other factors implicated in skeletal actin transcription, including GATA-4, TEF-1, or SRF. These results show that, in the intact cell, p300 interactions with its protein targets are highly selective and that MEF-2D is the preferred channel for p300-mediated transcriptional control in the heart. PMID: 11096067 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 7: EMBO J. 2000 Jun 1;19(11):2615-28. Solution structure of the MEF2A-DNA complex: structural basis for the modulation of DNA bending and specificity by MADS-box transcription factors. Huang K, Louis JM, Donaldson L, Lim FL, Sharrocks AD, Clore GM. Laboratory of Chemical Physics, Building 5, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0510, USA. The solution structure of the 33 kDa complex between the dimeric DNA-binding core domain of the transcription factor MEF2A (residues 1-85) and a 20mer DNA oligonucleotide comprising the consensus sequence CTA(A/T)(4)TAG has been solved by NMR. The protein comprises two domains: a MADS-box (residues 1-58) and a MEF2S domain (residues 59-73). Recognition and specificity are achieved by interactions between the MADS-box and both the major and minor grooves of the DNA. A number of critical differences in protein-DNA contacts observed in the MEF2A-DNA complex and the DNA complexes of the related MADS-box transcription factors SRF and MCM1 provide a molecular explanation for modulation of sequence specificity and extent of DNA bending ( approximately 15 versus approximately 70 degrees ). The structure of the MEF2S domain is entirely different from that of the equivalent SAM domain in SRF and MCM1, accounting for the absence of cross-reactivity with other proteins that interact with these transcription factors. PMID: 10835359 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 8: J Mol Biol. 2000 Mar 24;297(2):437-49. Crystal structure of MEF2A core bound to DNA at 1.5 A resolution. Santelli E, Richmond TJ. Institut fur Molekularbiologie und Biophysik, ETH Zurich, Zurich, CH, Switzerland. Members of the myocyte enhancer factor-2 (MEF2) family of transcription factors bind to and activate transcription through A+T-rich DNA sequences found primarily, but not exclusively, in the promoters of muscle-specific genes. Their importance has been established for myogenic development and in activation of the immediate-early gene, c-jun, and recently further functional roles in the immune system have emerged. The MEF2 factors belong to the MADS-box superfamily, sharing homology in a 58 amino acid domain that mediates DNA binding and dimerization. The structures of two MADS-box proteins, SRF and MCM1, bound to their cognate DNA have been previously reported and shown to share extensive similarity in their mode of DNA binding. We have solved the structure of MEF2A 2-78 bound to its DNA consensus sequence at 1.5 A resolution. It reveals how the absence of amino acids N-terminal to the MADS-box contributes to the DNA binding properties of MEF2 proteins and shows that the MEF domain C-terminal to the MADS-box adopts a conformation considerably different from the same region in SRF and MCM1. Copyright 2000 Academic Press. PMID: 10715212 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 9: J Biol Chem. 1999 Oct 22;274(43):30832-42. Nuclear protein binding at the beta-myosin heavy chain A/T-rich element is enriched following increased skeletal muscle activity. Vyas DR, McCarthy JJ, Tsika RW. Department of Biomedical Sciences, School of Veterinary Medicine, University of Missouri-Columbia, Columbia, Missouri 65211, USA. In adult mouse skeletal muscle, beta-myosin heavy chain (betaMyHC) gene expression is primarily restricted to slow-type I fibers but can be induced in fast-type II fibers by mechanical overload (MOV). Our previous transgenic analyses have delimited an 89-base pair (bp) MOV-responsive region (-293 to -205), and shown that mutation of the MCAT and C-rich elements within this region did not abolish betaMyHC transgene induction by MOV. In this study we describe an A/T-rich element (betaA/T-rich; -269 5'-GGAGATATTTTT-3' -258) located within this 89-bp region that, only under MOV conditions, revealed enriched binding as characterized by electrophoretic mobility shift assays and dimethyl sulfate and diethyl pyrocarbonate interference footprinting. Direct, competition, and supershift electrophoretic mobility shift assays revealed highly enriched specific binding activity at the betaA/T-rich element that was antigenically distinct from GATA-4, MEF2A-D, SRF, and Oct-1, nuclear proteins that were previously shown to bind A/T-rich elements. In vitro translated GATA-4, MEF2C, SRF, and Oct-1 bound to consensus GATA, MEF2, SRE, and Oct-1 elements, respectively, but not to the betaA/T-rich element. Two-dimensional UV cross-linking of the bromodeoxyuridine-substituted betaA/T-rich element with mechanically overloaded plantaris (MOV-P) nuclear extract detected two proteins (44 and 48 kDa). Our results indicate that the betaA/T-rich element may function in vivo as a betaMyHC MOV-inducible element during hypertrophy of adult skeletal muscle by binding two distinct proteins identified only in MOV-P nuclear extract. PMID: 10521475 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 10: J Biochem (Tokyo). 1997 Nov;122(5):939-46. Mouse Mef2b gene: unique member of MEF2 gene family. Morisaki T, Sermsuvitayawong K, Byun SH, Matsuda Y, Hidaka K, Morisaki H, Mukai T. Department of Bioscience, National Cardiovascular Center Research Institute, Suita, Osaka. morisaki@ri.ncvc.go.jp The myocyte enhancer factor 2 (MEF2) gene family, which belongs to the MADS [MCM1, agamous, deficiens, serum response factor (SRF)] superfamily, is thought to play an important role in differentiation of myocytes, including cardiomyocytes. To better understand the mouse Mef2 gene family, the mouse Mef2b gene, which was found to be expressed in undifferentiated embryonal cells, was characterized. The Mef2b gene was found to be more than 30 kb in length, consisting of 11 exons. Eight exons correspond to coding regions and the remaining 3 exons for the 5' part are alternatively used. Two internal exons are subject to alternative splicing, resulting in production of four subtypes of mouse MEF2B peptides. Fluorescence in situ hybridization (FISH) and inter-specific backcross analysis identified the Mef2b gene locus. Mef2b gene was expressed in heart or skeletal muscle of early mouse embryo, but not in those of adult mouse. Functionally, mouse MEF2B did not exhibit DNA binding with the MEF2 consensus element in vitro, but did cause transcriptional activation of the MEF2 element, although it was less effective than human MEF2B. Based on these results, mouse MEF2B seems to have a unique character, distinct from other MEF2 family members. PMID: 9443808 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 11: Mol Biol Cell. 1997 Jul;8(7):1243-59. Determination of floral organ identity by Arabidopsis MADS domain homeotic proteins AP1, AP3, PI, and AG is independent of their DNA-binding specificity. Riechmann JL, Meyerowitz EM. Division of Biology, California Institute of Technology, Pasadena 91125, USA. The MADS domain homeotic proteins APETALA1 (AP1), APETALA3 (AP3), PISTILLATA (PI), and AGAMOUS (AG) combinatorially specify the identity of Arabidopsis floral organs. AP1/AP1, AG/AG, and AP3/PI dimers bind to similar CArG box sequences; thus, differences in DNA-binding specificity among these proteins do not seem to be the origin of their distinct organ identity properties. To assess the overall contribution that specific DNA binding could make to their biological specificity, we have generated chimeric genes in which the amino-terminal half of the MADS domain of AP1, AP3, PI, and AG was substituted by the corresponding sequences of human SRF and MEF2A proteins. In vitro DNA-binding assays reveal that the chimeric proteins acquired the respective, and distinct, DNA-binding specificity of SRF or MEF2A. However, ectopic expression of the chimeric genes reproduces the dominant gain-of-function phenotypes exhibited by plants ectopically expressing the corresponding Arabidopsis wild-type genes. In addition, both the SRF and MEF2 chimeric genes can complement the pertinent ap1-1, ap3-3, pi-1, or ag-3 mutations to a degree similar to that of AP1, AP3, PI, and AG when expressed under the control of the same promoter. These results indicate that determination of floral organ identity by the MADS domain homeotic proteins AP1, AP3, PI, and AG is independent of their DNA-binding specificity. In addition, the DNA-binding experiments show that either one of the two MADS domains of a dimer can be sufficient to confer a particular DNA-binding specificity to the complex and that sequences outside the amino-terminal basic region of the MADS domain can, in some cases, contribute to the DNA-binding specificity of the proteins. PMID: 9243505 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 12: Mol Cell Biol. 1997 May;17(5):2876-87. DNA binding by MADS-box transcription factors: a molecular mechanism for differential DNA bending. West AG, Shore P, Sharrocks AD. Department of Biochemistry and Genetics, Medical School, University of Newcastle upon Tyne, United Kingdom. The serum response factor (SRF) and myocyte enhancer factor 2A (MEF2A) represent two human members of the MADS-box transcription factor family. Each protein has a distinct biological function which is reflected by the distinct specificities of the proteins for coregulatory protein partners and DNA-binding sites. In this study, we have investigated the mechanism of DNA binding utilized by these two related transcription factors. Although SRF and MEF2A belong to the same family and contain related DNA-binding domains, their DNA-binding mechanisms differ in several key aspects. In contrast to the dramatic DNA bending induced by SRF, MEF2A induces minimal DNA distortion. A combination of loss- and gain-of-function mutagenesis identified a single amino acid residue located at the N terminus of the recognition helices as the critical mediator of this differential DNA bending. This residue is also involved in determining DNA-binding specificity, thus indicating a link between DNA bending and DNA-binding specificity determination. Furthermore, different basic residues within the putative recognition alpha-helices are critical for DNA binding, and the role of the C-terminal extensions to the MADS box in dimerization between SRF and MEF2A also differs. These important differences in the molecular interactions of SRF and MEF2A are likely to contribute to their differing roles in the regulation of specific gene transcription. PMID: 9111360 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 13: Am J Physiol. 1997 Apr;272(4 Pt 1):C1394-404. Telokin expression in A10 smooth muscle cells requires serum response factor. Herring BP, Smith AF. Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202, USA. Telokin transcription is initiated from a smooth muscle-specific promoter located in an intron of the smooth muscle myosin light chain kinase gene. We have previously identified a 310-base pair fragment of the promoter that mediates A10 smooth muscle cell-specific expression of telokin. In the current study, telokin-luciferase reporter gene assays in A10 cells and REF52 nonmuscle cells revealed that the promoter region between -81 and +80 contains the regulatory elements required to mediate the in vitro cell specificity of the promoter. Several positive-acting elements, including an E box, myocyte enhancer factor 2 (MEF2)-TATA box, and CArG-serum response element, were identified within this region. Telokin transcription in A10 smooth muscle cells requires all three transcription initiation sites and an AT-rich sequence between -71 and -62 that includes a TATA box. MEF2 interacts with the AT-rich region with low affinity; however, MEF2 binding is not required for transcriptional activity in A10 cells. Binding of serum response factor (SRF) to a CArG element proximal to the TATA sequence is also critical for high levels of transcription in A10 cells. Together these data suggest that an AT-rich motif, acting in concert with SRF and an unusual transcription initiation mechanism, is required for the cell-specific expression of the telokin promoter in A10 smooth muscle cells. PMID: 9142867 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 14: Mol Cell Biol. 1995 Aug;15(8):4076-85. DNA binding specificity determinants in MADS-box transcription factors. Nurrish SJ, Treisman R. Transcription Laboratory, Imperial Cancer Research Fund Laboratories, London, United Kingdom. The MADS box is a conserved sequence motif found in the DNA binding domain of a family of transcription factors which possess related but distinct DNA binding specificities. We investigated the basis of differential sequence recognition by the MADS-box proteins serum response factor (SRF), MCM1, and MEF2A, using chimeric proteins and site-directed mutants in conjunction with gel mobility shift and binding site selection assays. Deletion of sequences immediately N terminal to the SRF MADS box alters its preferred binding site to that of MEF2A, although the resulting protein still weakly binds SRF-specific sites: exclusive binding to MEF2 sites requires further mutations, at MADS-box residues 11 to 15. In contrast to SRF, the sequence specificity of MCM1 (and of MEF2A) is determined entirely by sequences within its MADS box, and mutation of only SRF MADS-box residue 1 is sufficient to alter its binding specificity to that of MCM1. However, changes at both MADS-box positions 1 and 11 to 15 are necessary and sufficient to alter the specificity of the MCM1 MADS box to that of MEF2, and vice versa. The role of SRF MADS-box residues which differ from those present in the other proteins was investigated by selection of functional SRF variants in yeast cells. SRF MADS-box position 1 was always a glycine in the variants, but many different sequences at the other nonconserved MADS-box residues were compatible with efficient DNA binding. We discuss potential mechanisms of DNA recognition by MADS-box proteins. PMID: 7623803 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 15: Dev Biol. 1994 Dec;166(2):683-95. Activation of Xenopus MyoD transcription by members of the MEF2 protein family. Wong MW, Pisegna M, Lu MF, Leibham D, Perry M. Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston 77030. Members of the MEF2 family of DNA binding proteins interact with a set of AT-rich sequences commonly found in the promoters and enhancers of muscle-specific genes. We have shown that a MEF2 binding site precisely overlaps the TFIID binding site (TATA box) in the Xenopus MyoDa (XMyoDa) promoter and appears to play an important role in muscle-specific activity of this promoter. To further investigate the potential role of MEF2 in the regulation of XMyoDa transcription, we have analyzed the appearance of factors that interact with the XMyoDa TATA/MEF2 site during early amphibian development. Proteins that bind specifically to this site were present at low levels during early development and increased in abundance during gastrulation and neurulation. Two related cDNAs were isolated that encode proteins that recognize the XMyoDa TATA motif. Both proteins are highly homologous to each other, belong to the MADS (MCM1 agamous deficiens SRF) protein family, and are most highly related to the mammalian MEF2A gene products. Xenopus MEF2A (XMEF2A) transcripts accumulated preferentially in forming somites after the appearance of XMyoD transcripts. Ectopic expression of XMEF2A and other members of the MEF2 gene family activated transcription of a reporter gene controlled by the XMyoDa promoter. Transcriptional activation of the XMyoDa promoter required only the conserved DNA binding domain of XMEF2A and was independent of a domain necessary for activity when this factor was bound to multiple upstream sites. These results suggest that the XMyoDa promoter can be activated by binding of MEF2 to the XMyoDa TATA motif and indicate that MEF2-dependent transcriptional activation occurs by different mechanisms depending on the location of the MEF2 binding site. We suggest that XMEF2 expression in myogenic cells contributes to the activation and stabilization of XMyoDa transcription during muscle cell differentiation. PMID: 7813786 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 16: Int J Dev Biol. 1994 Dec;38(4):591-604. Control of skeletal muscle-specific transcription: involvement of paired homeodomain and MADS domain transcription factors. Duprey P, Lesens C. Laboratoire de Biologie Moleculaire de la Differenciation, UFR de Biochimie, Universite Paris VII Denis Diderot, France. 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. Publication Types: Review Review, Tutorial PMID: 7779681 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 17: Development. 1993 Aug;118(4):1095-106. A fourth human MEF2 transcription factor, hMEF2D, is an early marker of the myogenic lineage. Breitbart RE, Liang CS, Smoot LB, Laheru DA, Mahdavi V, Nadal-Ginard B. Howard Hughes Medical Institute, Boston, Massachusetts. The transition from multipotent mesodermal precursor to committed myoblast and its differentiation into a mature myocyte involve molecular events that enable the cell to activate muscle-specific genes. Among the participants in this process is the myocyte-specific enhancer factor 2 (MEF2) family of tissue-restricted transcription factors. These factors, which share a highly conserved DNA-binding domain including a MADS box, are essential for the expression of multiple muscle genes with cognate target MEF2 sites in cis. We report here a new human MEF2 factor, hMEF2D, which is unique among the members of this family in that it is present not only in myotubes but also in undifferentiated myoblasts, even before the appearance of myogenin. hMEF2D comprises several alternatively spliced products of a single gene, one of which is the human homolog of the Xenopus SRF-related factor SL-1. Like its relatives, cloned hMEF2D is capable of activating transcription via sequence-specific binding to the MEF2 site, recapitulating endogenous tissue-specific MEF2 activity. Indeed, while MEF2D mRNAs are ubiquitous, the protein is highly restricted to those cell types that contain this activity, implicating posttranscriptional mechanisms in the regulation of MEF2D expression. Alternative splicing may be important in this process: two alternative MEF2D domains, at least one of which is specifically included during myogenic differentiation, also correlate precisely with endogenous MEF2 activity. These findings provide compelling evidence that MEF2D is an integral link in the regulatory network for muscle gene expression. Its presence in undifferentiated myoblasts further suggests that it may be a mediator of commitment in the myogenic lineage. PMID: 8269842 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------