Molecular characterization of myostatin from the skeletal muscle of the African lungfish， Protopterus annectens， and changes in its mRNA and protein expression levels during three phases of aestivation.

African lungfishes can aestivate and remain torpid without food and water for years， but disuse muscle atrophy is not prominent during aestivation. This study aimed to clone myostatin (mstn/Mstn)， a factor associated with disuse muscle atrophy in mammals， from the skeletal muscle of the African lungfish Protopterus annectens， and to determine its mRNA expression level and protein abundance therein during the induction， maintenance， and arousal phases of aestivation. The complete coding cDNA sequence of mstn comprised 1128?bp， encoding for 376 amino acids with an estimated molecular mass of 42.9?kDa. It was grouped together with Mstn/MSTN of coelacanth and tetrapods in a clade separated from teleost Mstn. After 6 days (the induction phase) of aestivation， the mstn transcript level in the muscle increased significantly， while the protein abundance of Mstn remained comparable to the control. Following that， a significant increase in the expression levels of mstn/Mstn occurred on day 12 (the early maintenance phase) of aestivation. After 6 months of aestivation (the prolonged maintenance phase)， the expression levels of mstn/Mstn returned to control levels， indicating the possible impediment of a drastic increase in muscle degradation to prevent muscle atrophy. During 1-3 days of arousal from aestivation， the expression levels of mstn/Mstn in the muscle remained comparable to the control. Hence， tissue reconstruction/regeneration of certain organs might not involve the mobilization of amino acids from the muscle during the early arousal. These results provide insights into how aestivating P. annectens regulates the expression of mstn/Mstn possibly to ameliorate disuse muscle atrophy.