Molecular regulation of growth and molting in decapod crustaceans
Date
2014
Authors
Mudron, Megan Reese, author
Mykles, Donald L., advisor
Garrity, Deborah M., committee member
Curthoys, Norman P., committee member
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Abstract
The green shore crab, Carcinus maenas, is a highly invasive species that inhabits coastal temperate zones worldwide. The reaction of C. maenas to acute temperature change was determined in six tissues (heart, gill, thoracic ganglion, eyestalk ganglion, Y-organ, and claw muscle) using genetic markers for temperature-induced metabolic stress, including HSP70, AMPKγ, mTOR, and Rheb. Animals were exposed to temperatures between 5° and 30°C for 1 or 2 h. mRNA levels in six tissues were quantified by quantitative RT-PCR (qPCR). The results indicate that C. maenas tolerated a wide temperature range, requiring 2-h exposures at 5 °C and 30 °C to affect tissue-specific changes in gene expression. Cm-HSP70 expression was robustly increased at 30 °C in all tissues. Ecdysteroids produced from the molting gland (Y-organ or YO) induce molting in decapod crustaceans. Reduction in molt-inhibiting hormone (MIH) activates the YO and animals enter premolt. At mid-premolt, YOs transition to the committed state, during which ecdysteroid production increases further. In blackback land crab (Gecarcinus lateralis), a tropical decapod species, SB1431542, an inhibitor of Activin receptors, decreases hemolymph ecdysteroid titers in premolt animals, suggesting that an Activin-like transforming-growth factor (TGF-β) is produced by the activated YO and drives the transition of the YO to the committed state. Myostatin (Gl-Mstn) is an Activin-like factor that is highly expressed in skeletal muscle. Rapamycin lowers hemolymph ecdysteroid titers by inhibiting mTOR, which controls global translation of mRNA into protein. Endpoint RT-PCR established that Gl-Mstn was expressed in the YO, not just muscle tissue. YOs were harvested from intact (intermolt) animals and from animals at 1, 3, 5, 7, and 14 days post-ESA. Quantitative PCR was used to quantify the effects of molt induction by eyestalk ablation (ESA) on gene expression. Expression of mTOR components peaked at 3 days post-ESA, which is consistent with the increased activity required for activation of the YO. Gl-Mstn expression also peaked at 3 days post-ESA, which is before the transition to the committed state at 7 days post-ESA. These results indicate that mTOR components are involved in activation of the YO, and Mstn is involved in transitioning the YO to the committed state.
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Subject
AMPK
crustacean
HSP70
molting
mTOR
myostatin