During premolt, increasing ecdysteroid levels cause claw muscle atrophy in Gecarcinus lateralis, allowing withdrawal of the claw at ecdysis. Myostatin (Gl-Mstn) is negatively correlated to ecdysteroids, while protein synthesis is up-regulated to allow myofibril remodeling during premolt. In mammals, glucocorticoids inhibit mechanistic Target of Rapamycin (mTOR)-dependent protein synthesis. Our hypothesis is that ecdysteroids inhibit Gl-Mstn expression through the ecdysteroid receptor. Gl-Mstn, in turn, inhibits protein synthesis via mTOR signaling. Using DNA walking, an ecdysteroid receptor response element (EcRE) was located near the 5’ end of the Gl-Mstn promoter, suggesting that Gl-Mstn expression is directly regulated by ecdysteroids. Limb bud autotomy, which suspends premolt by lowering hemolymph ecdysteroids levels, decreased Gl-EF2, Gl-Rheb, Gl-mTOR and Gl-S6K mRNA in LBs, increased Gl-Mstn expression in claw muscle, and had no effect on these genes in thoracic muscle. After one week of daily 20-hydroxyecdysone injections of intermolt animals, Gl-Rheb mRNA levels were significantly increased in claw muscle, but Gl-Mstn mRNA level was unchanged. These results indicated a difference in response to ecdysteroids between intermolt and premolt tissues. The Gl-Mstn promoter was fused to luciferase and transfected into HeLa cells, along with Uca pugilator EcR (Up-EcR) and Up-RXR, to determine whether the EcRE is functional. Ecdysteroids had no effect on expression of the reporter gene in HeLa cells. The data suggest that Gl-Mstn expression is regulated by ecdysteroids. However, there was no consistent linkage between expression of Gl-Mstn and expression of mTOR signaling components in claw and LB muscles.