Project description:STAC3 was identified as a nutritionally regulated gene from an Atlantic salmon subtractive hybridization library with highest expression in skeletal muscle. Salmon STAC3 mRNA was highly correlated with myogenin and myoD1a expression during differentiation of a salmon primary myogenic culture and was regulated by amino acid availability. In zebrafish embryos, STAC3 was initially expressed in myotomal adaxial cells and in fast muscle fibres post-segmentation. Morpholino knockdown resulted in defects in myofibrillar protein assembly, particularly in slow muscle fibres, and decreased levels of the hedgehog receptor patched. The function of STAC3 was further characterized in vitro using the mammalian C2C12 myogenic cell line. STAC3 mRNA expression increased during the differentiation of the C2C12 myogenic cell line. Knockdown of STAC3 by RNAi inhibited myotube formation, and microarray analysis revealed that transcripts involved in cell cycle, focal adhesion, cytoskeleton and the pro-myogenic factors IGFBP-5 and IGF2 were down regulated. RNAi-treated cells had suppressed AKT signalling and exogenous IGF2 was unable to rescue the phenotype, however, IGF/AKT signalling was not blocked. Overexpression of STAC3, which results in increased levels of IGFBP-5 mRNA, did not lead to increased differentiation. In synchronized cells, STAC3 mRNA was most abundant during the G1 phase of the cell cycle. RNAi-treated cells were smaller, had higher proliferation rates and decreased proportion of cells in G1 phase when compared to controls, suggesting a role in the G1 phase checkpoint. These results identify STAC3 as a new gene required for myogenic differentiation and myofibrillar protein assembly in vertebrates. We identified STAC3 as being essential for myogenic differentiation. The goal of the microarray analysis was to identify genes that were up- or down-regulated in C2C12 cells when STAC3 expression was inhibited by interfering RNA (RNAi). The microarray compares the C2C12 mouse myogenic cell line between control samples to samples treated with an interfering RNA directed at STAC3. The mouse C2C12 cell line was used at two time points: day 0, which was 24 hours after adding the RNAi, with cells growing in growth media (non-differentiating), and day 1, which was 48 hours after the interfering RNAi was added, and 24 hours after switching to differentiation media. RNAi-treated cells were transfected with an RNAi directed against STAC3, and control cells were transfected with a high-GC content control RNAi. Total RNA was extracted from control and RNAi-treated samples at two time points, at day 0 (24 h after treating with RNAi, while samples were still in growth media), and at day 1 (cells grown in differentiation media for 24h, 48 h after RNAi treatment). At each time point, STAC3 RNAi-treated cells were compared to controls. For the array comparison, at day 0, triplicate biological samples + one technical replicate were used for the controls, and four biological samples were used for the RNAi-treated cells. At day 1, four biological samples and one technical replicate were used for controls and RNAi-treated cells. Technical replicate identifiers are appended by _r.

Project description:STAC3 was identified as a nutritionally regulated gene from an Atlantic salmon subtractive hybridization library with highest expression in skeletal muscle. Salmon STAC3 mRNA was highly correlated with myogenin and myoD1a expression during differentiation of a salmon primary myogenic culture and was regulated by amino acid availability. In zebrafish embryos, STAC3 was initially expressed in myotomal adaxial cells and in fast muscle fibres post-segmentation. Morpholino knockdown resulted in defects in myofibrillar protein assembly, particularly in slow muscle fibres, and decreased levels of the hedgehog receptor patched. The function of STAC3 was further characterized in vitro using the mammalian C2C12 myogenic cell line. STAC3 mRNA expression increased during the differentiation of the C2C12 myogenic cell line. Knockdown of STAC3 by RNAi inhibited myotube formation, and microarray analysis revealed that transcripts involved in cell cycle, focal adhesion, cytoskeleton and the pro-myogenic factors IGFBP-5 and IGF2 were down regulated. RNAi-treated cells had suppressed AKT signalling and exogenous IGF2 was unable to rescue the phenotype, however, IGF/AKT signalling was not blocked. Overexpression of STAC3, which results in increased levels of IGFBP-5 mRNA, did not lead to increased differentiation. In synchronized cells, STAC3 mRNA was most abundant during the G1 phase of the cell cycle. RNAi-treated cells were smaller, had higher proliferation rates and decreased proportion of cells in G1 phase when compared to controls, suggesting a role in the G1 phase checkpoint. These results identify STAC3 as a new gene required for myogenic differentiation and myofibrillar protein assembly in vertebrates. We identified STAC3 as being essential for myogenic differentiation. The goal of the microarray analysis was to identify genes that were up- or down-regulated in C2C12 cells when STAC3 expression was inhibited by interfering RNA (RNAi). The microarray compares the C2C12 mouse myogenic cell line between control samples to samples treated with an interfering RNA directed at STAC3. The mouse C2C12 cell line was used at two time points: day 0, which was 24 hours after adding the RNAi, with cells growing in growth media (non-differentiating), and day 1, which was 48 hours after the interfering RNAi was added, and 24 hours after switching to differentiation media.

Project description:Wnt/M-NM-2-catenin signaling is involved in various aspects of skeletal muscle development and regeneration. In addition, Wnt3a and M-NM-2-catenin are required for muscle-specific gene transcription in embryonic carcinoma cells and satellite-cell proliferation during adult skeletal muscle regeneration. Downstream targets of canonical Wnt signaling are cyclin D1 and c-myc. However, both target genes are suppressed during differentiation of mouse myoblast cells, C2C12. Underlying molecular mechanisms of M-NM-2-catenin signaling during myogenic differentiation remain unknown. Using C2C12 cells, we examined intracellular signaling and gene transcription during myoblast proliferation and differentiation. We confirmed that several Wnt signaling components, including Wnt9a, Sfrp2 and porcupine, were consistently upregulated in differentiating C2C12 cells. Troponin T-positive myotubes were decreased by Wnt3a overexpression, but not Wnt4. TOP/FOP reporter assays revealed that co-expression with Wnt4 reduced Wnt3a-induced luciferase activity, suggesting that Wnt4 signaling counteracted Wnt3a signaling in myoblasts. FH535, a small-molecule inhibitor of M-NM-2-catenin/Tcf complex formation, reduced basal M-NM-2-catenin in cytoplasm and decreased myoblast proliferation. K252a, a protein kinase inhibitor, increased membrane-bound M-NM-2-catenin and enhanced myoblast fusion. Treatments with K252a or Wnt4 resulted in increased cytoplasmic vesicles containing phosphorylated M-NM-2-catenin (Tyr654) during myogenic differentiation. These results suggest that various Wnt ligands control subcellular M-NM-2-catenin localization, which regulate myoblast proliferation and myotube formation. Wnt signaling via M-NM-2-catenin likely acts as a molecular switch that regulates the transition from cell proliferation to myogenic differentiation. Control cells (day 0) prior to differentiation induction with n=4; differentiated for two days with n=3; differentiated for four days with n=3.

Dataset Information

Analysis of gene expression in hTERT/cdk4 immortalized human myoblasts compared to their primary populations in both undifferentiatied (myoblast) and differentiated (myotube) states

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