Bower, N.I., Castillo, D.G., Cole, N.J., Hollway, G.E., Lee, H.T., Assinder, S., and Johnston, I.A. (2012) STAC3 is required for myotube formation and myogenic differentiation in vertebrate skeletal muscle. The Journal of biological chemistry. 287(52):43936-43949.
STAC3 was identified as a nutritionally regulated gene from an Atlantic salmon subtractive hybridisation 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 characterised 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 synchronised 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.