Ecdysone metabolism in premolt land crabs (Gecarcinus lateralis)

Crustacean ecdysteriods in reproduction and embryogenesis

Ecdysteroids are the molting hormones in Crustacea, as in other arthropods. They also subserve functions in the control of reproduction and embryogenesis. The available evidence indicate that the ecdysteroids are sequestered into the ovary by binding to yolk precursor proteins. Steroidogenic ability of the ovary is yet to be demonstrated in Crustacea. Despite several investigations, the role of ecdysteroids in oocyte maturation is not fully known. However, the embryonic ecdysteroids undergo significant fluctuation, correlated to specific developmental stages, including the secretion of embryonic envelopes and cuticle. Ecdysteroid metabolism in the eggs seems to be active throughout embryogenesis inasmuch as the free ecdysteroids are rapidly converted into conjugates, and vice versa; in addition to their inactivation into excretory ecdysteroidic acids. Eyestalk neuropeptides such as molt inhibiting hormones have a dominant role on the ecdysteroid synthesis by Y-organ, although recent evidence suggests a stimulatory role for yet another endocrine gland, the mandibular organ on Y-organ synthesis.

Role of the midgut gland in metabolism and excretion of ecdysteroids by lobsters, Homarus americanus

The chromatographic profile of ecdysteroids (Ecds) from the midgut gland (MG) of juvenile female lobsters, Homarus americanus, was examined using high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) over four stages of the molt cycle. Upon initial examination, highly polar Ecd conjugates appeared to be the principal metabolites found in all molt stages. HPLC fractions containing apolar Ecds initially exhibited low RIA activity. Upon hydrolysis with a Helix pomatia enzyme preparation and reanalysis, significant amounts of other Ecds were released. Amounts of apolar Ecd conjugates were estimated, at their highest levels, to be at least 50% of the total Ecds in MGs of molt stage D3 lobsters. Only the MG formed significant amounts of apolar Ecds upon in vitro culture with [3H]ecdysone ([3H]E). Epidermis and antennal gland significantly increased their rates of [3H]E metabolism in vitro between molt stages C4 and D1. This result further supports the idea that regulation of ecdysteroid metabolism, at least in selected tissues, may be important in the molt cycle regulation of hormone titers. Using gel filtration column chromatography and sucrose density gradient centrifugation analyses, evidence was found for association of apolar Ecds with a protein(s) from MG cytosol. The protein was estimated to have a molecular weight of 180,000-200,000 and specifically bound apolar Ecds.

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 the embryos and sera of the crabs, Cancer magister and C. anthonyi

Ecdysteroids in the embryos and sera of ovigerous brachyuran crabs, Cancer magister and C. anthonyi, were measured and characterized by radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC). C. magister embryos displayed a biphasic pattern of ecdysteroid fluctuation during development; titers decreased until mid embryogenesis and then increased and peaked prior to hatching. HPLC-RIA analysis indicated increasing ecdysone concentrations from mid embryogenesis to hatching. Endogenous biosynthesis of ecdysone by the embryos is suggested. In contrast, ecdysteroid titers in the embryos of C. anthonyi showed a steady decrease from very high initial concentrations. The decrease in titers of ecdysone and 20-hydroxyecdysone is suggestive of utilization of maternally derived ecdysteroids rather than endogenous biosynthesis during the shorter embryogenic period for C. anthonyi. Ecdysteroid concentrations did not differ with respect to location of the embryo within the egg mass. Serum ecdysteroids in C. magister females generally showed a monotonic pattern during brooding. However, for C. anthonyi females, increasing and decreasing titers were observed during the brood and interbrood periods, respectively. These fluctuations suggest mobilization of the ecdysteroids to the ovaries for subsequent storage and utilization during embryogenesis. The evolutionary significance of these differing patterns of ecdysteroid metabolism in these congeners is discussed.

Ecdysteroid titers during the molt cycle of Orchestia cavimana (Crustacea, Amphipoda)

Ecdysteroids were analyzed during a molt cycle in adult males of the crustacean Orchestia cavimana; levels were determined in the hemolymph and in whole bodies, using radioimmunoassay. Results show a single and sharp peak at the end of D1 stage, reaching 810 pg eq/microliter in the hemolymph (a 230-fold increase compared to the middle of intermolt). From B stage to the beginning of D1, levels are very low but increase regularly and significantly. The amplitude and the temporal position of the peak are discussed in detail, in relation to the precision of the staging (17 different stages can be easily made in Orchestia) and to the cuticle cycle (the hormonal peak occurs ca. 10 hr before the beginning of cuticle synthesis at D2). Preliminary experiments, using monoclonal antibodies during the period of low ecdysteroid titers or high-performance liquid chromatography followed by polyclonal RIA during the peak period, suggest that the immunoreactive hormone in O. cavimana behaves like 20-hydroxyecdysone. However, other minor compounds have been detected (some unknown, others migrating like ecdysone and ponasterone A in HPLC).

Studies on the biosynthesis of ecdysone by the Y-organs of Carcinus maenas

High specific activity tritiated ecdysone precursor, 2,22,25-trideoxyecdysone, was incubated with Y-organs from intermoult and premoult shore crabs. Several metabolites were identified among which ecdysone and 25-deoxyecdysone. The concomitant production of these 2 molecules by Y-organs and their subsequent hydroxylation at C-20 by peripheral tissues, provide an explanation for the presence of both 20-hydroxyecdysone and ponasterone A (25-deoxy-20-hydroxyecdysone) in the circulating haemolymph of crabs.

Biosynthesis of ecdysteroids from cholesterol by crab Y-organs, and eyestalk suppression of cholesterol uptake and secretory activity, in vitro

Precursor incorporation studies were conducted in vitro with activated Y-organs from 48-hr de-eyestalked Cancer antennarius donors. When the glands were prelabeled in vivo by systemic injection of [3H]cholesterol 12 hr prior to removal, and subsequently incubated 24 hr in label-free medium, the glands secreted 3H-labeled ecdysone. The glands also secreted an unidentified ecdysteroid with comigrating 3H-label with characteristic retention time on normal-phase HPLC of 4 min (4-min unknown). The compound is less polar, and is secreted in a quantity and apparent specific activity approximately fivefold greater, than ecdysone. Compared with chromatographic retention times and competitive binding curves of authentic standards, the 4-min unknown was determined not to be ponasterone A, inokosterone, makisterone, or several other possible products or intermediates. In contrast with Y-organs from intact donors, those from de-eyestalked crabs exhibit greatly increased cholesterol uptake and secretion of both ecdysone and 4-min unknown in vitro. All three responses were suppressed in dose-dependent manner by eyestalk extract in the dose range, 1-4 eyestalk equivalents/Y-organ. Secretion of 4-min unknown was the response most sensitive to eyestalk extract (requiring the least dose for 50% inhibition).

Effect of Y-organ removal on limb regeneration and molting in the terrestrial crab, Sesarma haematocheir

The effect of Y-organ removal on limb regeneration and molting was investigated in the crab, Sesarma haematocheir. Basal growth of regenerating limb bud was achieved independently of the Y-organs. However, bilateral removal of the Y-organ inhibited premolt growth and molting. It was also found that removal of the Y-organs from crabs at stage D2 inhibited further premolt growth of regenerating limb bud and molting. Ecdysterone injections in Y-organless crabs induced premolt growth of regenerating limb bud and gastrolith formation, but were insufficient to induce molting.

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.