Expression Of Myogenic Transcription Factors Research Articles

Decreased expression of myogenic transcription factors and myosin heavy chains inCaenorhabditis elegansmuscles developed during spaceflight

The molecular mechanisms underlying muscle atrophy during spaceflight are not well understood. We have analyzed the effects of a 10-day spaceflight on Caenorhabditis elegans muscle development. DNA microarray, real-time quantitative PCR, and quantitative western blot analyses revealed that the amount of MHC in both body-wall and pharyngeal muscle decrease in response to spaceflight. Decreased transcription of the body-wall myogenic transcription factor HLH-1 (CeMyoD) and of the three pharyngeal myogenic transcription factors, PEB-1, CEH-22 and PHA-4 were also observed. Upon return to Earth animals displayed reduced rates of movement, indicating a functional defect. These results demonstrate that C. elegans muscle development is altered in response to spaceflight. This altered development occurs at the level of gene transcription and was observed in the presence of innervation, not simply in isolated cells. This important finding coupled with past observations of decreased levels of the same myogenic transcription factions in vertebrates after spaceflight raises the possibility that altered muscle development is a contributing factor to spaceflight-induced muscle atrophy in vertebrates.

Early changes in rat diaphragm biology with mechanical ventilation.

To better characterize the effects of 24-hour mechanical ventilation on diaphragm, the expression of myogenic transcription factors, myosin heavy chains, and sarcoplasmic/endoplasmic reticulum calcium-ATPase pumps was examined in rats. In the diaphragm of mechanically ventilated animals, the mRNA of MyoD, myosin heavy chain-2a and -2b, and sarcoplasmic/endoplasmic reticulum calcium-ATPase-1a decreased, whereas myogenin mRNA increased. In the diaphragm of anesthetized and spontaneously breathing rats, only the mRNA of MyoD and myosin heavy chain-2a decreased. MyoD and myogenin protein expression followed the changes at the mRNA, whereas the myosin heavy chain isoforms did not change. Parallel experiments involving the gastrocnemius were performed to assess the relative contribution of muscle shortening versus immobilization-induced deconditioning on muscle regulatory factor expression. Passive shortening produced no additional effects compared with immobilization-induced deconditioning. The overall changes followed a remarkably similar pattern except for MyoD protein expression, which increased in the gastrocnemius and decreased in the diaphragm while its mRNA diminished in both muscles. The early alterations in the expression of muscle protein and regulatory factors may serve as underlying molecular basis for the impaired diaphragm function seen after 24 hours of mechanical ventilation. Whether immobilization-induced deconditioning and/or passive shortening play a role in these alterations could not be fully unraveled.

Inversely related expression of epidermal- and heart-type fatty acid binding proteins during myogenic differentiation of C2C12 myoblasts

Following our report that heart-type (H-) fatty acid binding protein (FABP) was strongly up-regulated in differentiating myotubes, we examined the role of FABP and their effect on oleic acid uptake in the differentiation of mouse C2C12 myoblasts to myotubes in vitro. A second epidermal-type (E-) FABP is already expressed in the myoblast stage and is down-regulated at the onset of myogenic differentiation. This down-regulation is paralleled by that of β-actin, whereas mRNA expression of myogenic transcription factors and of H-FABP increases. These findings were verified at the protein level, which indicated that a basal level of FABPs, independent of the type, is always present during differentiation. Both FABPs were identified by their intracellular binding of oleic acid. This may explain that the change in oleic acid uptake into C2C12 cells at different stages of differentiation was negligible. Yet, the transition from E-FABP expressing myoblasts to H-FABP expressing myotubes was accompanied by a shift in preferential incorporation of oleic acid from triacylglycerols to phospholipids, perhaps necessary for terminal differentiation. The comparison of the expression of H-FABP with that of master myogenic transcription factors demonstrates that this fatty acid binding protein is not involved in the initiation of differentiation. The combination of a particular FABP and the cell in which it is expressed determines the fatty acid uptake. Cette etude examine le role des proteines de liaison des acides gras (FABP) de type cardiaque et leur effet sur la captation de l'acide oleique dans la differenciation de myoblastes C2C12 de souris en myotubes in vitro. Une FABP de type epidermique est exprimee au stade myoblaste et diminue au debut de la differenciation myogenique. Cette regulation est parallele a celle de la β-actine alors que l'expression de l'ARNm des facteurs de transcription myogenique et les FABP du type cardiaque augmentent. Les resultats montrent que ces proteines de liaison des acides gras ne sont pas impliquees dans la differenciation terminale.

Purkinje Fibers of the Avian Heart Express a Myogenic Transcription Factor Program Distinct from Cardiac and Skeletal Muscle

A rhythmic heart beat is coordinated by conduction of pacemaking impulses through the cardiac conduction system. Cells of the conduction system, including Purkinje fibers, terminally differentiate from a subset of cardiac muscle cells that respond to signals from endocardial and coronary arterial cells. A vessel-associated paracrine factor, endothelin, can induce embryonic heart muscle cells to differentiate into Purkinje fibers both in vivo and in vitro. During this phenotypic conversion, the conduction cells down-regulate genes characteristic of cardiac muscle and up-regulate subsets of genes typical of both skeletal muscle and neuronal cells. In the present study, we examined the expression of myogenic transcription factors associated with the switch of the gene expression program during terminal differentiation of heart muscle cells into Purkinje fibers. In situ hybridization analyses and immunohistochemistry of embryonic and adult hearts revealed that Purkinje fibers up-regulate skeletal and atrial muscle myosin heavy chains, connexin-42, and neurofilament protein. Concurrently, a cardiac muscle-specific myofibrillar protein, myosin-binding protein-C (cMyBP-C), is down-regulated. During this change in transcription, however, Purkinje fibers continue to express cardiac muscle transcription factors, such as Nkx2.5, GATA4, and MEF2C. Importantly, significantly higher levels of Nkx2.5 and GATA4 mRNAs were detected in Purkinje fibers as compared to ordinary heart muscle cells. No detectable difference was observed in MEF2C expression. In culture, endothelin-induced Purkinje fibers from embryonic cardiac muscle cells dramatically down-regulated cMyBP-C transcription, whereas expression of Nkx2.5 and GATA4 persisted. In addition, myoD, a skeletal muscle transcription factor, was up-regulated in endothelin-induced Purkinje cells, while Myf5 and MRF4 transcripts were undetectable in these cells. These results show that during and after conversion from heart muscle cells, Purkinje fibers express a unique myogenic transcription factor program. The mechanism underlying down-regulation of cardiac muscle genes and up-regulation of skeletal muscle genes during conduction cell differentiation may be independent from the transcriptional control seen in ordinary cardiac and skeletal muscle cells.