20 (OH) ecdysone-induced transition from intermolt to premolt protein biosynthesis patterns in the hypodermis of the crayfish, Astacus leptodactylus, in vitro

What is molt-inhibiting hormone? The role of an ecdysteroidogenesis inhibitor in the crustacean molting cycle

The in vivo molt-inhibitory effects of the ecdysone biosynthesis inhibitors 3-hydroxy-L-kynurenine and xanthurenic acid were investigated. These ecdysone biosynthesis inhibitors, isolated from the eyestalks of blue crabs (Callinectes sapidus), were injected into eyestalk-ablated crayfish (Procambarus clarkii). The active factor was found to be species-nonspecific within crabs and crayfish. The seasonal profiles of the xanthurenic acid and ecdysone titers exhibited a staggered relationship. Moreover, the activity of a 3-hydroxy-L-kynurenine aminotransferase varied during the molting cycle. The data suggested that 3-hydroxy-L-kynurenine, which is secreted from the X-organ-sinus gland complex of crustaceans, is released into the hemolymph, and after accumulating at the surface of the Y-organ, is converted into the active form, xanthurenic acid. Xanthurenic acid was found to profoundly repress ecdysteroidogenesis in vitro.

Hepatopancreatic multi-transcript expression patterns in the crayfish Cherax quadricarinatus during the moult cycle

Alterations of hepatopancreatic multi-transcript expression patterns, related to induced moult cycle, were identified in male Cherax quadricarinatus through cDNA microarray hybridizations of hepatopancreatic transcript populations. Moult was induced by X-organ sinus gland extirpation or by repeated injections of 20-hydroxyecdysone. Manipulated males were sacrificed at premoult or early postmoult, and a reference population was sacrificed at intermoult. Differentially expressed genes among the four combinations of two induction methods and two moult stages were identified. Biologically interesting clusters revealing concurrently changing transcript expressions across treatments were selected, characterized by a general shift of expression throughout premoult and early postmoult vs. intermoult, or by different premoult vs. postmoult expressions. A number of genes were differentially expressed in 20-hydroxyecdysone-injected crayfish vs. X-organ sinus gland extirpated males.

Search for hepatopancreatic ecdysteroid-responsive genes during the crayfish molt cycle: from a single gene to multigenicity

The expression of the vitellogenin gene of the red-claw crayfish Cherax quadricarinatus (CqVg) was previously demonstrated in male crayfish during an endocrinologically induced molt cycle. The hypothesis that this expression is under the direct control of ecdysteroids was tested in this study both in vivo and in vitro. Unlike vitellogenin of insects, CqVg was not found to be ecdysteroid-responsive. Thus, a multigenic approach was employed for the identification of other hepatopancreatic ecdysteroid-responsive genes by a cDNA microarray. For the purposes of this study, a multi-parametric molt-staging technique, based on X-ray detection of gastrolith growth, was developed. To identify ecdysteroid-responsive genes during premolt, the molt cycle was induced by two manipulations, 20-hydroxyecdysone administration and X-organ–sinus gland complex removal; both resulted in significant elevation of ecdysteroids. Two clusters of affected genes (129 and 122 genes, respectively) were revealed by the microarray. It is suggested that only genes belonging to similarly responsive (up- or downregulated) gene clusters in both manipulations (102 genes) could be considered putative ecdysteroid-responsive genes. Some of these ecdysteroid-responsive genes showed homology to genes controlling chitin metabolism, proteases and other cellular activities, while 56.8% were unknown. The majority of the genes were downregulated, presumably by an energetic shift of the hepatopancreas prior to ecdysis. The effect of 20-hydroxyecdysone on representative genes from this group was confirmed in vitro using a hepatopancreas tissue culture. This approach for ecdysteroid-responsive gene identification could also be implemented in other tissues for the elucidation of ecdysteroid-specific signaling pathways during the crustacean molt cycle.

Tissue-specific patterns and steady-state concentrations of ecdysteroid receptor and retinoid-X-receptor mRNA during the molt cycle of the fiddler crab, Uca pugilator

In the fiddler crab, Uca pugilator, we have investigated the temporal expression of receptors in various tissues using probes that encode Uca ecdysteroid receptor (UpEcR) and retinoid-X-receptor (UpRXR) gene homologs. During molt stages C4 through D1-4, UpEcR and UpRXR transcripts are expressed in regenerating limb buds, gills, eyestalks, hypodermis, hepatopancreas, muscle from nonregenerating walking legs, and the large cheliped. Some of these tissues have not previously been recognized as ecdysteroid-target tissues. Levels of ecdysteroids in the hemolymph fluctuate significantly during the molt cycle of U. pugilator. The variation in steady-state concentrations of UpEcR transcripts in tissues from C4 to D1-4 implies molt cycle-related differences in the potential of these tissues to respond to changing titers of ecdysteroids in the hemolymph. In singly autotomized crabs, highest concentrations of UpEcR transcript in some tissues did not coincide with the highest levels of circulating ecdysteroids, suggesting that UpEcR expression in these tissues is not dependent on high ecdysteroid titers and may be induced by low or rising concentrations of ecdysteroids. UpEcR and UpRXR genes were expressed simultaneously in tissues, supporting the possibility of heterodimerization for EcR and RXR in vivo. In some tissues, however, levels of transcripts differed, suggesting other possible receptor interactions. Moreover, UpEcR expression in tissues from multiply autotomized crabs differed from the expression patterns in tissues from singly autotomized crabs.

An ecdysteroid-responsive gene in a lobster - a potential crustacean member of the steroid hormone receptor superfamily

The role of ecdysteroids in modulating exoskeletal growth during the moult cycle of Crustacea has been well described. However, little is known about the action of ecdysteroids at the level of gene transcription and regulation in Crustacea. This paper reports the cloning of an ecdysteroid responsive gene, HHR3, a potential Manduca sexta MHR3 homologue in the American lobster, Homarus americanus. Levels of HHR3 expression are up-regulated in response to in vivo injections of premoult concentrations (10(-6) M) of 20-hydroxyecdysone in the epidermal and muscle tissue of the lobster after 6 h. Maximal mRNA levels are observed after 21 h before returning to basal levels. In muscle tissue, elevated levels of HHR3 mRNA follow a time course similar to elevated actin mRNA expression in response to hormonal injection. In contrast, in eyestalk tissue, the HHR3 levels decline up to 21 h post-injection before rising to basal levels after 48 h. Eyestalk, epidermal and leg muscle tissue was extracted over the moult cycle to determine the levels of expression. In muscle, HHR3 is high during the premoult period that corresponds to the period of the moult cycle when the ecdysteroid titre is high. In the epidermis, HHR3 levels are also high during the premoult with elevated levels maintained into the postmoult period. In the eyestalk, mRNA levels of HHR3 show an opposite pattern of expression with low levels during premoult and postmoult and high levels found during the intermoult period. Our results provide novel evidence for an ecdysteroid responsive gene in a crustacean that has many similarities to MHR3 in Manduca and DHR3 in Drosophila melanogaster. This raises the question of whether a similar cascade of ecdysteroid responsive genes exist in other members of Arthropoda such as the Crustacea, as has been demonstrated in Drosophila. In addition, we provide further evidence for negative feedback regulation of ecdysteroids at the site of moult-inhibiting hormone (MIH) production in the lobster eyestalk.

Protein production and the molting cycle in the crayfish Astacus leptodactylus (Nordmann, 1842). II. Hemocyanin and protein synthesis in the midgut gland

The midgut gland from the crayfish Astacus leptodactylus synthesizes and secretes hemocyanin and proteins linearly for at least 24 hr in vitro. There are no sex-specific differences in the rate of protein and hemocyanin synthesis. During a standard incubation of 5 hr, up to 64% of the newly synthesized protein represents hemocyanin, which is also the predominant secretory protein. There are pronounced changes in the rate of hemocyanin synthesis during the molting cycle which coincide with corresponding changes in total protein synthesis. The titer of protein and hemocyanin synthesis during an intermolt phase exhibits a biphasic profile with the highest values in intermolt stage C4 and in premolt stage D1.

Ecdysteroids in relation to the molt cycle of the American lobster, Homarus americanus. II. excretion of metabolites

Ecdysteroid (Ecd) excretion patterns were followed during the molt cycle of adult male and female lobsters. Homarus americanus. Urine was the major route of Ecd elimination, amounting to greater than or equal to 96% of the excreted radioimmunoassay activity for all molt stages. The other identified route of Ecd elimination from the hemolymph was the feces, which accounted for the remaining 4% of the total Ecd excretion. High polarity metabolites (HP), including 20,26-dihydroxyecdysone (2026E) and 20-hydroxyecdysonoic acid (20EA), were the major types of Ecds found in the urine. Other urinary Ecd components included 20-hydroxyecdysone (20E), ecdysone (E), and ponasterone A (P). The major portion of urinary HP was composed of conjugates of 2026E, 20E, E, P, and other unidentified metabolites. The fecal Ecds were predominately HP and apolar metabolites. Apolar fecal Ecds were hydrolyzable to release 20EA, 2026E, 20E, E, P, and other metabolites. By means of intubation, [3H]E was placed directly into the cardiac stomach of lobsters. The gut pathway formed an apolar conjugate of [3H]E which was found exclusively in the feces. Lobsters are therefore capable of excreting ingested Ecds without absorption.

Ecdysteroids in relation to the molt cycle of the American lobster, Homarus americanus. I. Hemolymph titers and metabolites

Hemolymph ecdysteroid (Ecd) titers were measured using radioimmunoassay (RIA) during the molt cycle of the American lobster, Homarus americanus. Individual animals showed small, transitory rises of Ecds which increased in magnitude with the onset of premolt and culminated in a large premolt peak at morphological stages D2(2)-D3(1). Male lobsters had significant postmolt peaks and late premolt titers that remained high until ecdysis. In females, postmolt peaks were absent and late premolt titers reached basal levels before ecdysis. At least seven different Ecd metabolites were identified by high-performance liquid chromatography-RIA analyses. High polarity products (HP) were the most abundant metabolites in virtually every molt stage. Titers of HP were significantly higher in males during late postmolt-early intermolt and in late premolt. Levels of 20-hydroxyecdysone (20E) were equivalent in both sexes and correlated with the morphological changes associated with premolt. Evidence was also obtained for the presence of ecdysone, ponasterone A, and other as yet unidentified metabolites. The pattern of Ecd metabolites in the hemolymph supports other data indicative of 20E as the major molting hormone. Metabolism of 20E is primarily toward more polar compounds, including conjugates.