Meeting Abstract

P2.94  Wednesday, Jan. 5   Rheb, an activator of the mTOR complex, in the blackback land crab, Gecarcinus lateralis: cloning and effects of molting on expression in skeletal muscle PITTS, N.L.*; ABUHAGR, A.M.; MACLEA, K.S.; COVI, J.A.; BADER, B.D.; CHANG, E.S.; MYKLES, D.L.; Colorado State University; UC Davis Bodega Marine Lab pittsn@lamar.colostate.edu

Muscle in the propodus of the chelipeds must atrophy to successfully withdraw the claw from the old exoskeleton at molt. In G. lateralis, global protein synthesis increases in atrophic claw muscles coincident with hemolymph ecdysteroid levels. From this data we conclude that ecdysteroids, either directly or indirectly, stimulate metazoan Target Of Rapamycin (mTOR), a protein kinase complex that promotes translation. The purpose of this study was to examine the cellular mechanisms involved for this muscle atrophy. The insulin/mTOR pathway, previously shown to be important for growth and development in insects, is a likely target of ecdysteroid regulation. Complete cDNAs for Rheb (Ras homolog enriched in brain), a key activator of mTOR, were cloned from three crustacean species. Along with previously cloned partial cDNAs for upstream and downstream members of the mTOR pathway, Gl-Akt, Gl-mTOR, Gl-s6k, real-time PCR analysis was completed to monitor transcript levels of the mTOR components following molting induced by either eyestalk ablation (ESA) or multiple limb autotomy (MLA). Levels of Rheb increased dramatically during ESA or MLA and were correlated with hemolymph ecdysteroid titers in the claw muscle, but not thoracic muscle, in both molting paradigms. Increases in the levels of the other three transcripts were also observed with ESA and MLA. These data indicate that Gl-Rheb is an important activator of crustacean mTOR signaling in the molt cycle in response to ecdysteroids. The other mTOR components may also contribute to a lesser degree to the regulation of this process. Supported by NSF (IBN-0618203).