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

The effects of farnesoic acid and 20-hydroxyecdysone on vitellogenin gene expression in the lobster, Homarus americanus, and possible roles in the reproductive process

Reproduction in female lobster (Homarus americanus) is characterized by the maturation of the ovary, with a gradual increase in its size as a result of uptake of yolk protein precursor, vitellogenin (Vg) to the final product vitellin (Vn). Vn is formed by aggregation of several Vg subunits. In most decapods, the hepatopancreas is the major site of vitellogenin biosynthesis. The production of vitellogenin is controlled by endocrine factors. In this study, the effect of farnesoic acid (FA) and 20-hydroxyecdysone (20E) on production of vitellogenin by hepatopancreas (HaVg1) was investigated by in vitro organ explant HaVg1 gene expression was stimulated by FA or 20E in a dose-dependent manner. A 2-fold and 2.2-fold increase in HaVg1 gene expression was observed with 4.2 microM FA and 0.7 microM 20E, respectively. The stimulatory effect by either FA or 20E was observed principally during the first 90 min. Stimulation of HaVg1 gene expression by FA and 20E together is greater (3.3-fold increase) than that of either hormone alone. This stimulation was also observed within the first 90 min. To study the synergistic effect of these two hormones, FA and 20E were tested separately and together at low concentration (42.3 nM and 6.7 nM, respectively). Combined use of FA and 20E increased HaVg1 gene expression synergistically, but not additively. These findings should contribute to our understanding of lobster reproduction and provide insights into manipulation of lobster reproduction in aquaculture or under captive conditions.

Expression and release patterns of neuropeptides during embryonic development and hatching of the green shore crab, Carcinus maenas

Crustacean ecdysis is controlled by at least three neuropeptides:moult-inhibiting hormone (MIH), which represses ecdysteroid synthesis;crustacean hyperglycaemic hormone (CHH), which not only influences ecdysteroid synthesis but also water uptake during moulting; and crustacean cardioactive peptide (CCAP), which is involved in stereotyped ecdysis behaviour. During embryonic development, moulting takes place in the egg, but there is little information regarding developmental expression of these neuropeptides during this period or during hatching – an event that is analogous to eclosion in insects. To address this problem, we determined expression profiles of MIH and CHH mRNA by quantitative RT-PCR, together with developmental peptide expression studies [confocal immunocytochemistry (ICC) and radioimmunoassay(RIA)]. Likely homologous events relating to neuropeptide surges of both CHH and CCAP were seen during larval hatching, when compared to the adult moult,and cell-specific copy concentration of both MIH and CHH mRNAs was identical to that of the adult during late embryonic development. We measured parallel mRNA and peptide expression of two neuropeptides (red pigment-concentrating hormone RPCH) and pigment-dispersing hormone (PDH) during development, as these have roles as neuromodulators and as classical neurohormonal roles. For MIH and CHH, gene expression was in accordance with peptide expression, but novel sites of CHH expression were found (abdominal peripheral neurones), the expression and release patterns of which may be related to larval eclosion and water uptake necessary for eggshell rupture and hatching. For RPCH and PDH,gene transcription and peptide expression were not in accordance. A significant contribution of maternally derived (non-translated) PDH mRNA to the embryo was seen, and for RPCH, high-level mRNA and peptide expression during late embryogenesis is related to a long ignored, but potentially important release site – the enigmatic post-commissural organs –which are the most prominent structures expressing RPCH during late embryogenesis.

Shell protein characteristics and vitellogenin-like proteins in brine shrimp Artemia franciscana exposed to municipal effluent and 20-hydroxyecdysone

We developed biomarkers to monitor the endocrine-disrupting potential of contaminants and municipal effluents in aquatic arthropods. Artemia fransciscana shrimp were cultured and exposed to increasing concentrations of 20-hydroxyecdysone (20HE) and solid phase (C-8) municipal effluent extract (MEE) for 48 h at 20 degrees C. The levels of vitellogenin (Vtg)-like proteins, alkali-labile phosphates in total proteins and acetylcholinesterase (AChE) activity were determined in soft tissues. The levels of acid-soluble, alkali-soluble (sclerotin), neutral-soluble (arthropodin) proteins and chitin were determined to characterize the maturation state of shells. Both 20HE and the municipal effluent extract readily increased the total activity of acetylcholinesterase, alkali-labile phosphates in proteins and vitellogenin-like proteins in brine shrimp. In shells, 20HE and the effluent extract increased the proportion of chitin in shells and acid-soluble proteins but were not statistically significant for the latter. The proportion of sclerotin was increased by 20HE but was not changed by the effluent extract. The proportion of arthropodin was decreased by both 20HE and the effluent extract. Correlation analysis revealed that, as expected, the proportion of acid-soluble protein for biomineralisation and chitin levels were positively correlated and the proportion of arthropodin and sclerotin were negatively correlated in shells exposed to 20HE. Principal component analysis revealed that the proportion of chitin, arthropodin, sclerotin and acid-soluble proteins explained 63% of the responses. Shell protein and carbohydrate contents, controlled by the molting hormone 20HE, could be used as efficient markers for ecdysial properties of various contaminants. The municipal effluent appears to contain ecdysial-like chemicals that are capable of producing changes in shell protein composition that are similar to 20HE.

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.

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.