Calcineurin-mediated signaling in skeletal muscle

Calcineurin (Cn; protein phosphatase 2B) is a calcium-activated phosphatase that is highly conserved among eukaryotes. Calcineurin dephosphorylates a wide variety of substrates making it a versatile second messenger for intra cellular calcium signals in many tissues. In muscle, Cn transduces signals that determine fiber type, hypertrophy, and commitment to the myogenic line age. Calcineurin-mediated fiber transitions of fast to slow involve the nuc leocytoplasmic shuttling of the transcription factor, NEAT. Less is known a bout the Cn-mediated signaling pathways that promote muscle hypertrophy and expression of the fast phenotype, although they are undoubtedly intertwine d with a variety of other signaling pathways. This paper reviews Cn-depende nt signaling in muscle with special emphasis on the role of Cn in mediating fiber type transitions and muscle hypertrophy. To open the door on the rol e and extent of Cn-mediated signaling in livestock, evidence is presented t hat in callipyge lambs Cn actively mediates muscle hypertrophy in a fiber t ype-specific manner. Increased understanding of Cn-dependent signaling in l ivestock will enhance our ability to control and select for extent of muscl ing and meat quality attributes.