Meeting Abstract

P2.141  Saturday, Jan. 5  Effects of ecdysteroids on myostatin and mTOR signaling expression in crustacean skeletal muscle COSENZA, K. S.*; CHANG, E. S.; MYKLES, D. L.; Colorado State Univ; UC Davis Bodega Marine Lab; Colorado State Univ kcosenza@rams.colostate.edu

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 thoracic muscle, which does not atrophy during premolt, ecdysteroid levels and Gl-Mstn mRNA are not correlated. 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 Smad transcription factors. In Homo sapiens, Smad response elements occur in the promoters of three genes (Rheb, PRAS40, and TSC) in the mTOR signaling pathway. Using DNA walking, an ecdysone receptor (EcR) response element was located near the 5’ end of the Gl-Mstn promoter region (932 bp), suggesting that Gl-Mstn expression is regulated by ecdysteroids. Gl-Mstn, Gl-EF2, Gl-mTOR, Gl-Rheb, Gl-Akt, and Gl-S6K mRNAs were quantified by qPCR. After two weeks of daily 20-hydroxyecdysone (20E) injections, Gl-Mstn mRNA levels were significantly decreased in claw muscle. By contrast, a single 20E injection had no effect on gene expression over 24 h. Limb bud autotomy, which suspends premolt by lowering hemolymph ecdysteroid, increased Gl-mRNA levels in claw muscle. Unexpectedly, expression of Gl-mTOR, Gl-Rheb, Gl-Akt, and Gl-S6K was increased by LBA. 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. Supported by NSF (IBN-0618203).