Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item The functional importance and significance of ecdysteroids in molt-cycle regulation of the blue crab, Callinectes sapidus(2014) Techa, Sirinart; Chung, Sook J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study aims to expand our understanding of how ecdysteroids and neuropeptide hormones (MIH/CHH) regulate molting in crustaceans using the blue crab Callinectes sapidus as a model animal. The hypothesis of this study is that ecdysteroids have a stimulatory effect on MIH/CHH production in eyestalks while generating both positive and negative feedback on ecdysteroidogenesis in Y-organs. Since ecdysteroids exert their signals through an ecdysteroid receptor complex, composed of an ecdysone receptor (EcR) and its partner, the retinoid-X receptor (RXR), the functional activity of ecdysteroids on tissues of interest is examined through EcR expression. Endogenous levels of ecdysteroids as well as expression in EcR, RXR and MIH/CHH are assayed in both embryonic and juvenile molt cycles. Similar patterns of changes in these two cycles suggest that molting control is driven by the same mechanisms in each. During embryonic molt, the correlation of ecdysteroid levels and MIH/CHH expression suggests that ecdysteroids are involved in MIH/CHH production. Using an in vitro system, stimulation of MIH expression occurs in eyestalks incubated with ponasterone A (PoA) and 20-hydroxyecdysone (20-HE) in the ratio found endogenously (3:1) and in ecdysteroid concentrations of 75 and 150 ng/ml. The in vivo response of MIH expression to depletion of ecdysteroid signals was examined by RNAi knockdown of an ecdysone receptor that was found to reduce the levels of MIH to those found by MIH knockdown, providing support for the hypothesis that ecdysteroids stimulate MIH expression through an ecdysone receptor. This study also found evidence suggesting that crustaceans have long-loop feedback for ecdysteroids in the neuroendocrine axis, which is similar to that found in insects.Item ECDYSONE AND RETINOID-X RECEPTORS OF THE BLUE CRAB, Callinectes sapidus: CLONING AND TEMPORAL EXPRESSION PATTERNS IN EYESTALK GANGLIA AND Y-ORGANS DURING THE MOLT CYCLE(2012) Techa, Sirinart; Chung, Jum Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The molt cycle in decapod crustaceans, including the blue crab, Callinectes sapidus, is supressed by the crustacean hyperglycemic hormone (CHH) neuropeptide family and stimulated by ecdysteroids (Ecds). The Ecds are thought to act on both eyestalk ganglia (ES) and Y-organs (YO) where the CHH neuropeptides and Ecds are synthesized, respectively. Since the resultant responses of Ecds are mediated through their nuclear receptors: ecdysone receptor (EcR) and retinoid-X receptor (RXR), the temporal expression of EcR-RXR in ES and YO during the molt cycle may reveal the regulatory role of Ecd on the activity of these two organs. In this study, the full-legnth cDNA sequences of C. sapidus EcR1a and RXR1, and the coding region of three other isoforms of EcR and RXR, were isolated. Moreover, temporal distributions of C. sapidus specific isoforms: CasEcR and CasRXR, were examined in ES and YO at different molt stages