title: Roles of mechanistic target of rapamycin and transforming growth factor-β signaling in the molting gland (Y-organ) of the blackback land crab, Gecarcinus lateralis.
abstract: Molting in decapod crustaceans is controlled by molt-inhibiting hormone (MIH), an eyestalk neuropeptide that suppresses production of ecdysteroids by a pair of molting glands (Y-organs or YOs). Eyestalk ablation (ESA) activates the YOs, which hypertrophy and increase ecdysteroid secretion. At mid premolt, which occurs 7-14days post-ESA, the YO transitions to the committed state; hemolymph ecdysteroid titers increase further and the animal reaches ecdysis ~3weeks post-ESA. Two conserved signaling pathways, mechanistic target of rapamycin (mTOR) and transforming growth factor-β (TGF-β), are expressed in the Gecarcinus lateralis YO. Rapamycin, an mTOR antagonist, inhibits YO ecdysteroidogenesis in vitro. In this study, rapamycin lowered hemolymph ecdysteroid titer in ESA G. lateralis in vivo; levels were significantly lower than in control animals at all intervals (1-14days post-ESA). Injection of SB431542, an activin TGF-β receptor antagonist, lowered hemolymph ecdysteroid titers 7 and 14days post-ESA, but had no effect on ecdysteroid titers at 1 and 3days post-ESA. mRNA levels of mTOR signaling genes Gl-mTOR, Gl-Akt, and Gl-S6k were increased by 3days post-ESA; the increases in Gl-mTOR and Gl-Akt mRNA levels were blocked by SB431542. Gl-elongation factor 2 and Gl-Rheb mRNA levels were not affected by ESA, but SB431542 lowered mRNA levels at Days 3 and 7 post-ESA. The mRNA level of an activin TGF-β peptide, Gl-myostatin-like factor (Mstn), increased 5.5-fold from 0 to 3days post-ESA, followed by a 50-fold decrease from 3 to 7days post-ESA. These data suggest that (1) YO activation involves an up regulation of the mTOR signaling pathway; (2) mTOR is required for YO commitment; and (3) a Mstn-like factor mediates the transition of the YO from the activated to the committed state.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Ali M
authors.initials: AM
authors.lastname: Abuhagr
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Kyle S
authors.initials: KS
authors.lastname: MacLea
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Megan R
authors.initials: MR
authors.lastname: Mudron
authors.affiliation: Bodega Marine Laboratory, University of California, Davis, Bodega Bay, CA 94923, USA.
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Chang
authors.affiliation: Bodega Marine Laboratory, University of California, Davis, Bodega Bay, CA 94923, USA.
authors.forename: Ernest S
authors.initials: ES
authors.lastname: Chang
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA. Electronic address: Donald.Mykles@ColoState.edu.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Mykles
mesh_terms: D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D003386:Brachyura / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D004149:Dioxoles / Q000494:pharmacology; D026461:Ecdysteroids / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006458:Hemolymph / Q000187:drug effects / Q000378:metabolism; D018978:Molting / Q000502:physiology; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D004149:Dioxoles; D026461:Ecdysteroids; D016212:Transforming Growth Factor beta; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus
keywords: Activin; Akt; Crustacean; Ecdysteroid; Molting; Myostatin, Rheb; Target of rapamycin; Transforming growth factor-β; Y-organ; p70 S6 kinase