**PhD Seminar** Effect of molting hormones (ecdysteroids) on myostatin and mTOR expression in skeletal muscle and limb regenerates in the blackback land crab, Gecarcinus lateralis


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.

Speaker: Kathy Cosenza

Speaker Institution: Department of Biology, Colorado State University

Event Date: 01-21-2015

Event Start Time: 4:00 PM

Event Location: Yates 206

Mixer Time: 3:30 PM

Mixer Location: Yates 206

Host: Don Mykles