The successful induction of molting in the adult male lobster (Homarus americanus) with a slow-release form of ecdysterone

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.

Humoral factors reduce gap junction sensitivity to cytoplasmic pH. II. In vitro manipulations

Our previous studies demonstrated a diurnal rhythm in the response of gap junctions between crayfish giant axons to acidification and that the response was reduced after eyestalk ablation, sinus gland removal, or visual stress. In this paper we describe experiments to test whether compounds in the circulating hemolymph were responsible for modulation of the responsiveness gap junction channels to intracellular pH. In axons from destalked animals in which the hemolymph had been replaced with normal saline, the maximal junctional resistance after acidification (Rjmax) reached control values. In contrast, Rjmax reached only 30% of control after acidification in axons from animals that had been destalked but not perfused. Hemolymph drawn after eyestalk ablation was tested on axons from control animals. Treatment with hemolymph drawn 1 day after destalking resulted in control Rjmax values, while treatment with hemolymph drawn 7 days after destalking resulted in Rjmax values of only 5-40%. Similarly, pretreatment for 1 h with 100 microM ecdysterone resulted in low Rjmax values. These experimental results suggest that a circulating compound, most likely ecdysterone or a related molecule, regulates the physiological properties of gap junctions from crayfish lateral axons.

Ecdysteroid titers and Y-organ activity during late anecdysis and proecdysis in the fiddler crab, Uca pugilator

The titer of ecdysone in hemolymph and the ratio of ecdysone to other radioimmunoassay(RIA)-active hemolymph ecdysteroids were compared to in vitro secretion of ecdysone in Y-organs removed from eyestalkless fiddler crabs at various times following eyestalk ablation. Using high-pressure liquid chromatography (HPLC) and RIA it was established that ecdysone, 20-hydroxyecdysone, and RIA-active metabolites are present in the hemolymph at the end of anecdysis and throughout proecdysis. There was little correlation between in vitro secretory activity and total ecdysone in circulation. Ratios of ecdysone and 20-hydroxyecdysone changed during proecdysis as did the percentage of total RIA activity attributable to both. Positive correlations were observed between in vitro Y-organ secretion rates and amounts of ecdysteroids extracted from hemolymph and added to incubation media.

Effects of exogenous ecdysterone upon moulting, proecdysial development, and limb regeneration in the prawn Palaemon elegans

Injection of small doses of ecdysterone accelerated moulting and proecdysis in the prawn Palaemon elegans. Injection of large doses of ecdysterone (1-10 micrograms) markedly accelerated proecdysis, but death always occurred prior to or during moulting and was accompanied by abnormal setal development and retarded cuticle formation. Dose-response curves were obtained for a range of hormone doses from 10 to 0.01 micrograms by administering ecdysterone during postmoult (stages A-B) and early premoult (stages DE0-DL0). Accelerated proecdysis and viable moulting were more marked in the group injected during early premoult (stages DE0-DL0). The sensitivity threshold for prawns injected during this time was less than 40 ng g-1 but could not be determined more precisely in view of the range of ecdysterone concentrations used. In contrast, the sensitivity threshold for ecdysterone administered during postmoult (stages A-B) was much higher, between 0.4 and 2 micrograms g-1. The possible mechanisms controlling sensitivity thresholds for ecdysterone are discussed. The effect of ecdysterone on limb regeneration was also studied. Within the concentration range used, ecdysterone was found to have no effect on the rate of limb regeneration.

Molt induction in lobsters (Homarus americanus) by intramuscular injection of ecdysterone triacetate

The principal component of the successful, molt-inducing ecdysterone acetate mixture was established as ecdysterone triacetate and shown to have the same activity as the acetate mixture. The triacetate induced ecdysis in male lobsters collected in winter and summer and in female lobsters collected in winter. Intramuscular injections of triacetate in ethanol were as effective as those with oil emulsions.