Unknown,Transcriptomics,Genomics,Proteomics

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Gene expression profiling on innervated and denervated muscles of Smad4 KO and control mice.

ABSTRACT: To identify novel atrophy-related genes, which are controlled by BMP signaling, we performed gene expression profiling on innervated and 14 days denervated muscles of Smad4 knockout and control mice, focusing on genes that were differentially upregulated in denervated Smad4-/- muscles compared to controls. Among the different genes our attention was attracted by a gene that encodes for a novel f-box protein (Fbxo30) belonging to the SCF complex family of the ubiquitin ligases. Cell size is determined by the balance between protein synthesis and degradation. This equilibrium is affected by hormones, nutrients, energy levels, mechanical stress and cytokines. Mutations that inactivate Myostatin lead to important muscle growth in animals and humans. However, the signals and pathways responsible for this hypertrophy remain largely unknown. Here we find that BMP signaling, acting through Smad1/5/8, is the fundamental hypertrophic signal. Inhibition of BMP signaling causes muscle atrophy, abolishes the hypertrophic phenotype of Myostatin knockout and strongly exacerbates the effects of denervation and fasting. BMP-Smad1/5/8 negatively regulates a novel gene (Fbxo30) that encodes an ubiquitin ligase, that is required for muscle loss. Collectively, these data identify a critical role for the BMP pathway in adult muscle maintenance, growth and atrophy. Gene expression profiling on innervated and 14 days denervated muscles of Smad4 knockout and control mice. Three independent experiments were performed for each experimental condition using different animals for each experiment.

ORGANISM(S): Mus musculus

SUBMITTER: Marco Sandri

PROVIDER: E-GEOD-49826 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:In skeletal muscle, the pattern of electrical activity regulates the expression of proteins involved in synaptic transmission, contraction and metabolism. Disruptions in electrical activity, resulting from prolonged bed-rest, cast-immobilization or trauma, inevitably lead to muscle atrophy. The mechanisms that regulate muscle atrophy are poorly understood, but it seems likely that changes in gene expression play a key role in initiating and maintaining a muscle atrophy program. Previously, we found that Runx1, a transcription factor previously termed AML1, was substantially induced in muscle following denervation. More recently, we sought to determine whether this increase in Runx1 expression may be causally related to the morphological changes in skeletal muscle that accompany muscle disuse, notably muscle atrophy. We found that Runx1 is indeed required to sustain muscle and to minimize atrophy following denervation. Experiments described here are designed to identify the genes that are regulated by Runx1 in skeletal muscle with the particular goal of identifying genes that regulate muscle atrophy. We propose to use microarray analysis to identify genes, expressed in skeletal muscle, that are mis-regulated in mice lacking Runx1. We inactivated runx1 selectively in skeletal muscle and found that denervated myofibers in mutant mice atrophy far more (90% atrophy) than in wild-type mice (30% atrophy). We therefore reason that Runx1 activates and/or represses genes that are required to sustain muscle and to minimize atrophy. We generated MCK::cre; runx1f/- and runx1f/- control mice. In normal mice, an increase in runx1 expression is detected by two days after denervation and is maximal by five days after denervation. Muscle atrophy is first evident between one and two weeks after denervation. As we wish to avoid detecting global changes in gene expression that are associated with late stages of muscle atrophy, we plan to denervate muscle for three or five days and to compare gene expression in dissected innervated and denervated muscles from mutant and control mice. We will generate thirty samples for comparison-5 replicates per condition: Samples 1-3 from runx1f/- control mice. (1) innervated tibialis anterior muscles (TA); (2) 3-day-denervated TA; (3) 5-day-denervated TA. Samples 4-6 from MCK::cre; runx1f/- mice. (4) innervated TA; (5) 3-day-denervated TA; (6) 5-day-denervated TA. We obtain sufficient total RNA (10 micrograms) from each dissected muscle to avoid pooling samples. We will analyze adult mice of the same age (~six weeks after birth; most will be littermates) and sex-male. It is difficult to anticipate how many genes will be identified in this screen, as few target genes for Runx1 have been identified in any cell type and none in skeletal muscle. Moreover, although we would prefer to focus our attention on genes that are strongly dependent upon Runx1 expression (e.g. more than 5-fold difference in expression in wild-type and mutant mice), we do not know the extent to which target gene expression will depend upon Runx1. For these reasons, in these experiments, we will analyze expression from five âidenticalâ samples, so that we can be confident that even small (e.g. three-fold) differences in expression can be reliably determined. Importantly, in order to confirm results obtained from the microarray data, we will use other assays (RNase protection) to measure RNA expression of candidate genes in innervated and denervated muscles of wild-type and mutant mice.

Project description:In skeletal muscle, the pattern of electrical activity regulates the expression of proteins involved in synaptic transmission, contraction and metabolism. Disruptions in electrical activity, resulting from prolonged bed-rest, cast-immobilization or trauma, inevitably lead to muscle atrophy. The mechanisms that regulate muscle atrophy are poorly understood, but it seems likely that changes in gene expression play a key role in initiating and maintaining a muscle atrophy program. Previously, we found that Runx1, a transcription factor previously termed AML1, was substantially induced in muscle following denervation. More recently, we sought to determine whether this increase in Runx1 expression may be causally related to the morphological changes in skeletal muscle that accompany muscle disuse, notably muscle atrophy. We found that Runx1 is indeed required to sustain muscle and to minimize atrophy following denervation. Experiments described here are designed to identify the genes that are regulated by Runx1 in skeletal muscle with the particular goal of identifying genes that regulate muscle atrophy. We propose to use microarray analysis to identify genes, expressed in skeletal muscle, that are mis-regulated in mice lacking Runx1. We inactivated runx1 selectively in skeletal muscle and found that denervated myofibers in mutant mice atrophy far more (90% atrophy) than in wild-type mice (30% atrophy). We therefore reason that Runx1 activates and/or represses genes that are required to sustain muscle and to minimize atrophy. We generated MCK::cre; runx1f/- and runx1f/- control mice. In normal mice, an increase in runx1 expression is detected by two days after denervation and is maximal by five days after denervation. Muscle atrophy is first evident between one and two weeks after denervation. As we wish to avoid detecting global changes in gene expression that are associated with late stages of muscle atrophy, we plan to denervate muscle for three or five days and to compare gene expression in dissected innervated and denervated muscles from mutant and control mice. We will generate thirty samples for comparison-5 replicates per condition: Samples 1-3 from runx1f/- control mice. (1) innervated tibialis anterior muscles (TA); (2) 3-day-denervated TA; (3) 5-day-denervated TA. Samples 4-6 from MCK::cre; runx1f/- mice. (4) innervated TA; (5) 3-day-denervated TA; (6) 5-day-denervated TA. We obtain sufficient total RNA (10 micrograms) from each dissected muscle to avoid pooling samples. We will analyze adult mice of the same age (~six weeks after birth; most will be littermates) and sex-male. It is difficult to anticipate how many genes will be identified in this screen, as few target genes for Runx1 have been identified in any cell type and none in skeletal muscle. Moreover, although we would prefer to focus our attention on genes that are strongly dependent upon Runx1 expression (e.g. more than 5-fold difference in expression in wild-type and mutant mice), we do not know the extent to which target gene expression will depend upon Runx1. For these reasons, in these experiments, we will analyze expression from five “identical” samples, so that we can be confident that even small (e.g. three-fold) differences in expression can be reliably determined. Importantly, in order to confirm results obtained from the microarray data, we will use other assays (RNase protection) to measure RNA expression of candidate genes in innervated and denervated muscles of wild-type and mutant mice. Keywords: other

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Gene expression profiling on innervated and denervated muscles of Smad4 KO and control mice.

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