Neuregulin induces the expression of transcription factors and myosin heavy chains typical of muscle spindles in cultured human muscle.
Neuregulin (NRG) (also known as ARIA, GGF, and other names) is a heparin sulfate proteoglycan secreted into the neuromuscular junction by innervating motor and sensory neurons. An integral part of synapse formation, we have analyzed NRG-induced changes in gene expression over 48 h in primary human myotubes. We show that in addition to increasing the expression of acetylcholine receptors on the myotube surface, NRG treatment results in a transient increase of several members of the early growth response (Egr) family of transcription factors. Three Egrs, Egr1, -2, and -3, are induced within the first hour of NRG treatment, with Egr1 and -3 RNA levels showing the most significant increases of approximately 9- and 16-fold, respectively. Also noted was a corresponding increase in protein levels for both of these transcription factors. Previous literature indicates that Egr3 expression is required for the formation of muscle spindle fibers, sensory organs that are distinct from skeletal muscle contractile fibers. At the molecular level, muscle spindle fibers express a unique subset of myosin heavy chains. Two isoforms of the myosin heavy chain, the slow development and neonatal, were found to be increased in our myotube cultures after 48 h of treatment with NRG. Taken together, these results indicate that not only can NRG induce the expression of a transcription factor key to spindle fiber development (Egr3), but that a portion of this developmental process can be replicated in vitro.
Microarray Unit, Genetics and Genomics Section, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Christian
C
Jacobson
David
D
Duggan
Gerald
G
Fischbach
D018171:Agrin / Q000494:pharmacology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics; D051766:Early Growth Response Protein 1; D051767:Early Growth Response Protein 2; D051776:Early Growth Response Protein 3; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics; D009470:Muscle Spindles / Q000187:drug effects / Q000378:metabolism; D032448:Myoblasts, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D020890:Neuregulin-1; D020033:Protein Isoforms / Q000235:genetics; D012313:RNA / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics*
D018171:Agrin; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; C497326:EGR2 protein, human; C079945:EGR3 protein, human; D051766:Early Growth Response Protein 1; D051767:Early Growth Response Protein 2; D017874:Immediate-Early Proteins; C094131:NRG1 protein, human; D009419:Nerve Tissue Proteins; D020890:Neuregulin-1; D020033:Protein Isoforms; D011994:Recombinant Proteins; D014157:Transcription Factors; D051776:Early Growth Response Protein 3; D012313:RNA; D018995:Myosin Heavy Chains