Myocyte Enhancer Factor 2A Is Transcriptionally Autoregulated

Abstract

MEF2 (myocyte enhancer factor 2) proteins are a small family of transcription factors that play pivotal roles in striated muscle differentiation, development, and metabolism, in neuron survival and synaptic formation, and in lymphocyte selection and activation. Products of the four mammalian MEF2 genes, MEF2A, MEF2B, MEF2C, and MEF2D, are expressed with overlapping but distinct temporospatial patterns. Toward analysis of MEF2A functions and the determinants of its regulated expression, we have mapped and begun studies of the transcriptional control regions of this gene. Heterogeneous 5 -untranslated regions of MEF2A mRNAs result from use of alternative promoters and splicing patterns. The two closely approximated TATA-less promoters are ϳ65 kb upstream of the exon containing the sole initiation codon. Ribonuclease protection and primer extension assays show that each promoter is active in various adult tissues. A canonical MEF2 site overlies the major promoter 1 transcription start site. This element specifically binds MEF2 factors, including endogenous nuclear MEF2A according to chromatin immunoprecipitation studies, and is critical to MEF2A transcription in myocytes. The site exerts reciprocal control of the alternative promoters, silencing promoter 1 and activating promoter 2 under some conditions. Erk5 and p38 MAPK signaling stimulate MEF2A expression by activating both promoters from the MEF2 element. MEF2A transcription is therefore subject to positive or negative regulation by its protein products, depending on signaling activities that influence MEF2 factor trans-activity. The sole MEF2 gene of the cephalochordate amphioxus has a similar regulatory region structure, suggesting that this mode of autoregulatory control is conserved among higher metazoan MEF2 genes.

Complex functions of Mef2 splice variants in the differentiation of endoderm and of a neuronal cell type in a sea anemone

“…Alternative splicing leads to the presence or absence of the so-called -, -and -domains, which affect protein function as a transcriptional activator or can even change it into a repressor (Martin et al, 1994;Zhu and Gulick, 2004;Zhu et al, 2005). An extra level of transcriptional, and possibly translational, regulation of Mef2A is conveyed by the use of two alternative promoters autoregulated by Mef2A protein and by the generation of several variants of the 5ЈUTR by alternative splicing of the non-coding exons (Ramachandran et al, 2008). The situation in Drosophila is probably different in that it is not the particular splice isoforms but the amount of the protein that defines the identity of the differentiating cells (Gunthorpe et al, 1999).…”

Nuclear Respiratory Factor 1 Controls Myocyte Enhancer Factor 2A Transcription to Provide a Mechanism for Coordinate Expression of Respiratory Chain Subunits

“…Ribonuclease protection assays (RPA) and radiolabeled cRNA probe syntheses were carried out as described (17,18). Human MEF2A and murine mef2a, mef2c, and mef2d cRNA probes have been described (17)(18)(19). Templates for other cRNA probes were PCR amplicon fragments subcloned into pBluescript, oriented to permit cRNA production from the vector T7 promoter.…”

MEF2 Transcription Factors Regulate Distinct Gene Programs in Mammalian Skeletal Muscle Differentiation

“…Knockdown of MEF2 Proteins in C2C12 Myoblasts-The four mammalian MEF2 factors display different temporal expression patterns in C2C12 differentiation (11,21). Therefore, we focused our analysis of the individual MEF2 isoform knockdowns on differentiation day 3, because this reflects the time at which the four MEF2 proteins are co-expressed in myotubes.…”