Identification of MRF4: a new member of the muscle regulatory factor gene family.

Abstract

We have identified a rat cDNA encoding MRF4, a new member of the muscle regulatory factor gene family that includes MyoD1, myogenin, and Myf-5. MRF4 encodes a predicted 27-kD protein that contains a conserved helix-loop-helix motif, which is a common feature of this gene family. Northern analyses indicate that MRF4 is expressed solely in skeletal muscle tissue but is not detected in most embryonic muscle cell lines. Transfection of MRF4 into C3H10T1/2 fibroblasts produces stable myogenic lineages at frequencies that are equal to or greater than those obtained when MyoD1 or myogenin are introduced into these cells. Expression of the MRF4 cDNA leads to expression of the endogenous MyoD1 and myogenin genes, although C3H10T1/2 cells expressing MyoD1 or myogenin cDNAs do not express MRF4. Interestingly, the endogenous MyoD1 and myogenin genes are negatively regulated by serum and by purified growth factors since MRF4-transfected C3H10T1/2 cells activate MyoD1 and myogenin expression only in mitogen-depleted, differentiation-induced muscle cultures. The myofiber-specific expression pattern of MyoD1 and myogenin in these cells suggests that the primary role for this muscle regulatory factor gene family may be in regulating specific terminal differentiation events that are crucial for normal skeletal muscle development.[Key Words: MRF4; muscle regulatory factor; MyoD 1; myogenin; Myf-5: C3H 10T 1/2 cells]

Modulation of contractile protein gene expression in fetal murine crural muscles: Emergence of muscle diversity

“…The "down-regulation" of the genes encoding MyoD and myogenin prior to birth suggests that they are unlikely to play a direct role in the activation of genes such as MHCPB that are not expressed until the postnatal period, when myf-6 (MRF4) is the major myogenic regulatory gene expressed (Rhodes and Konieczny, 1989). This also indicates that high levels of MyoD and myogenin probably are not essential for the maintenance of contractile protein gene expression during the postnatal period.…”

Differentiation-dependent mechanisms of transcriptional regulation of the catalytic subunit of phosphorylase kinase

“…In the set of experiments indicated, PhK-γ Luc reporter constructs were co-transfected into 3T3 cells with pEMSVscribeα2 expression plasmids that encoded one of the four members of the MyoD family of transcription factors. MyoD, myogenin, myf5 and MRF4 were provided [11,[18][19][20]. In these experiments 1.5 µg of Luc reporter plasmid and 0.5 µg of MyoD plasmid were used in the transfection mixture together with 1 µg of the pRSV-lacZ galactosidase plasmid.…”

Identification of a muscle factor related to MyoD in a fish species

“…The MyoD gene identified by substract cloning for myoblast specific RNA is the prototype of a family of master regulators of skeletal myogenesis which includes in vertebrates three other members namely myogenin, Myf5 and MRF4 identified subsequently [1][2][3][4][5]. All these genes encode proteins that share a highly conserved central region termed the basic/helix-loop-helix(B-HLH) domain related to the c-myc superfamily and contain sequences essential for both dimerisation and DNA binding [6].…”

“…Nucleotide sequence analysis and amino acid comparison showed that this cDNA called TMyoD encodes a polypeptide of 276 amino acids with 70% identity to the entire Xenopus MyoD protein and 92% identity within the basic and myc-like region. Results from Northern blotting showed that the corresponding transcript is expressed both in adult and embryonic skeletal musculature and in an in vitro myogenesis system, but is undetectable in cardiac and smooth muscles and in non muscle tissues.Key words: MyoD; Myogenesis; Teleost; (Satellite cell)The MyoD gene identified by substract cloning for myoblast specific RNA is the prototype of a family of master regulators of skeletal myogenesis which includes in vertebrates three other members namely myogenin, Myf5 and MRF4 identified subsequently [1][2][3][4][5]. All these genes encode proteins that share a highly conserved central region termed the basic/helix-loop-helix(B-HLH) domain related to the c-myc superfamily and contain sequences essential for both dimerisation and DNA binding [6].…”

“…All these genes encode proteins that share a highly conserved central region termed the basic/helix-loop-helix(B-HLH) domain related to the c-myc superfamily and contain sequences essential for both dimerisation and DNA binding [6]. In multipotential 10T1/2 cells, transfection experiments have shown that forced expression of these exogenous myogenic factors is sufficient to drive them down the muscle differentiation pathway suggesting their functions in myogenic lineage determination [1][2][3][4][5]. In contrast to vertebrates whose genome encodes multiple members of the MyoD family, invertebrates, including Sea urchin [7], C. elegans [8] and Drosophila [9], appear to contain only a single myogenic factor encoding gene.…”