Metabolism of alpha-ecdysone in intermolt land crabs (Gecarcinus lateralis)

Role of ecdysone and eyestalk factors in regulating regeneration in larval crustaceans

Megalopae of the mud crab Rhithropanopeus harrisii can regenerate autotomized limbs. Regeneration during the megalopal stage required a significant delay in ecdysis to the first crab. Megalopae that failed to initiate regeneration complete ecdysis significantly faster than do controls. Exposure of intermolt- and premolt-stage megalopae to exogenous ecdysone significantly reduced (greater than or equal to 30%) the number of animals completing regeneration. The regeneration-induced delay in ecdysis was not significantly different in animals exposed to ecdysone. The molt cycle of nonregenerating megalopae exposed to ecdysone was further accelerated. Eyestalk ablation did not significantly reduce the molt cycle duration of regenerating animals. Eyestalkless nonregenerating animals did not display accelerated ecdysis. It is hypothesized that two additional hormonal factors are involved in "fine tuning" the molt cycle of regenerating animals. One located outside the eyestalks extends the molt cycle to accommodate regeneration. The second factor accelerates ecdysis in nonregenerating animals and appears to be produced in the eyestalks.

Ecdysteroids in the shrimp Palaemon serratus: relations with molt cycle

Ecdysteroids were studied during the molt cycle of the shrimp Palaemon serratus using radioimmunoassay and HPLC. Continuous presence of ecdysteroids was observed in whole extracts, with two hormonal peaks: a minor peak during stage B and a major one during stage D2. The ecdysteroid titers were generally higher in females than in males. The ecdysteroid peak at stage B was more pronounced in the integument (cuticle and epidermis) than in other tissues and, at this time, 20-hydroxyecdysone was the predominant form. The observed 20-hydroxyecdysone peaks in stages B and D2 are correlatable to the previously reported rise in integumental carbonic anhydrase activity.

Ecdysteroid metabolism in a crab: Carcinus maenas L

Ponasterone A (25-deoxy-20-hydroxyecdysone) and 20-hydroxyecdysone were the major ecdysteroids detected in crab hemolymph, although some ecdysone was also present. The metabolism of ponasterone A was examined in intermolt and premolt crabs either by injecting the radiolabeled hormone or by incubating tissues in its presence. Metabolites were extracted from the surrounding seawater and from tissues and separated by high-performance liquid chromatography. Ponasterone A metabolism proceeds through (1) C-25 and C-26 hydroxylation, followed by formation of inactivation products via oxidation of the terminal alcoholic group to a carboxylic residue, (2) conjugation, (3) "binding" to very polar compounds and (4) side-chain scission. The conversion of ponasterone A into 20-hydroxyecdysone, inokosterone (25-deoxy-20, 26-dihydroxyecdysone), 20, 26-dihydroxyecdysone and ecdysonoic acids, as well as the formation of conjugates and of very polar compounds, occurs in various tissues. These metabolites were excreted by both intermolt and premolt crabs.

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.

Ponasterone A: a new ecdysteroid from the embryos and serum of brachyuran crustaceans

The apolar ecdysteroid present in the developing embryo of the blue crab, Callinectes sapidus Rathbun, is tentatively identified as ponasterone A (2 beta, 14 alpha, 20,22-pentahydroxy-5, beta-cholest-7-en-6-one) on the basis of chromatographic, immunological, and mass spectral evidence. The apolar ecdysteroid present in the serum of land crabs, Gecarcinus lateralis, in the late premolt stages of the intermolt cycle is also tentatively identified as ponasterone A on the basis of chromatographic and immunological evidence.