Hormones in the Lives of Crustaceans: An Overview1

Changes in ecdysteroid levels and expression patterns of ecdysteroid-responsive factors and neuropeptide hormones during the embryogenesis of the blue crab, Callinectes sapidus

Embryogenesis requires the involvement and coordination of multiple networks of various genes, according to a timeline governing development. Crustacean embryogenesis usually includes the first molt, a process that is known to be positively controlled by ecdysteroids. We determined the amounts of ecdysteroids, as well as other related factors: the ecdysone receptor (CasEcR), the retinoid X receptor (CasRXR), the molt-inhibiting hormone (CasMIH), and crustacean hyperglycemic hormone (CasCHH) during the ovarian and embryonic developments of Callinectes sapidus. In summary, the ovaries at stages 1-4 have expression levels of maternal CasEcR and CasRXR 10-50 times higher than levels seen in embryos at the yolk stage. This large difference in the amount of the these factors in C. sapidus ovaries suggests that these maternal ecdysteroid-responsive factors may be utilized at the initiation of embryogenesis. During embryogenesis, the changes in total ecdysteroids and levels of CasEcR and CasRXR expression are similar to those observed in juvenile molts. The full-length cDNA sequence of the C. sapidus BTB domain protein (CasBTBDP) initially isolated from Y-organ cDNA, contains only Broad-Complex, Tramtrack, and Bric a brac (BTB) domains. The levels of CasBTBDP are kept constant throughout embryogenesis. The expression profiles of CasMIH and CasCHH are similar to the titers of ecdysteroids. However, the timing of their appearance is followed by increases in CasEcRs and CasRXRs, implying that the expressions of these neuropeptides may be influenced by ecdysteroids. Moreover, the ecdysteroid profile during embryogenesis may track directly with the timing of organogenesis of Y-organs and their activity. Our work reports, for first time, the observed expression and changes of ecdysteroid-responsive factors, along with CasCHH and CasMIH, during embryogenesis in the crustacean C. sapidus.

Crustacean hyperglycemic hormones of two cold water crab species, Chionoecetes opilio and C. japonicus: isolation of cDNA sequences and localization of CHH neuropeptide in eyestalk ganglia

Crustacean hyperglycemic hormone (CHH) is primarily known for its prototypical function in hyperglycemia which is induced by the release of CHH. The CHH release takes place as an adaptive response to the energy demands of the animals experiencing stressful environmental, physiological or behavioral conditions. Although >63 decapod CHH nucleotide sequences are known (GenBank), the majority of them is garnered from the species inhabiting shallow and warm water. In order to understand the adaptive role of CHH in Chionoecetes opilio and Chionoecetes japonicus inhabiting deep water environments, we first aimed for the isolation of the full-length cDNA sequence of CHH from the eyestalk ganglia of C. opilio (ChoCHH) and C. japonicus (ChjCHH) using degenerate PCR and 5' and 3' RACE. Cho- and ChjCHH cDNA sequences are identical in 5' UTR and ORF with 100% sequence identity of the putative 138aa of preproCHHs. The length of 3' UTR ChjCHH cDNA sequence is 39 nucleotides shorter than that of ChoCHH. This is the first report in decapod crustaceans that two different species have the identical sequence of CHH. ChoCHH expression increases during embryogenesis of C. opilio and is significantly higher in adult males and females. C. japonicus males have slightly higher ChjCHH expression than C. opilio males, but no statistical difference. In both species, the immunostaining intensity of CHH is stronger in the sinus gland than that of X-organ cells. Future studies will enable us to gain better understanding of the comparative metabolic physiology and endocrinology of cold, deep water species of Chionoecetes spp.

Characterization, expression, and function analysis of gonad-inhibiting hormone in Oriental River prawn, Macrobrachium nipponense and its induced expression by temperature

Gonad-inhibiting hormone (GIH) is a member of crustacean hyperglycemic hormone family and plays a major role in regulating reproduction in crustaceans. In this study, a full-length cDNA of GIH of Oriental River prawn, Macrobrachium nipponense (Mn-GIH) was cloned from the eyestalk. A 1350 bp full-length Mn-GIH cDNA harbored 336 bp of an open reading frame encoding signal peptide of 112 amino acid residues. Sequence analysis revealed that the overall cDNA sequence and specific functional sites of Mn-GIH were highly conserved with those in other crustacean species. Expression analysis by quantitative real-time PCR demonstrated its tissue-specific, larval developmental stage-specific, and ovary developmental stage-specific expression pattern, respectively. The RNAi by GIH-ds-RNA in vivo injection was effective in this study and resulted a 50% (day 1), 83% (day 5) and 63% (day 9) down-regulation compared to control. The obvious changes of gonad somatic index (GSI) rate also provided strong evidence to the inhibition effects of GIH on ovary maturation and spawning. Four temperature gradients (12 °C ± 1 °C, 17 °C ± 1 °C, 22 °C ± 1 °C, 27 °C ± 1 °C) were set to imitate the temperature in breeding and non-breeding seasons. The observed expression profiles suggest that Mn-GIH did not display a high level expression as supposed to maintain an immature ovary state under low temperature (12 °C). The results indicated that GIH was probably activated to concentrating and working by a proper temperature before reaching to breeding season.

An insulin-like growth factor found in hepatopancreas implicates carbohydrate metabolism of the blue crab Callinectes sapidus

Hyperglycemia that is caused by the release of crustacean hyperglycemic hormone (CHH) from the sinus gland to hemolymph is one of the hallmark physiological phenomena, occurring in decapod crustaceans experiencing stressful conditions. However, the mechanism(s) by which such elevated glucose levels return to resting levels is still unknown. Interestingly, noted is a difference in the clearance rate of hemolymph glucose between adult females and adult males of the blue crab, Callinectes sapidus: the former with more rapid clearance than the latter. The presence of an endogenous-insulin-like molecule is suggested in C. sapidus because an injection of bovine insulin, significantly reduces the levels of hemolymph glucose that were previously elevated by emersion stress or the glucose injection. Using 5' and 3' RACE, the full-length cDNA of an insulin-like molecule is isolated from the hepatopancreas of an adult female C. sapidus and shows the same putative sequence of an insulin-like androgenic gland factor (IAG) but differs in 5' and 3' UTR sequences. A knock-down study using five injections of double-stranded RNA of CasIAG-hep (dsRNA-CasIAG-hep, 10μg/injection) over a 10-day period reduces CasIAG-hep expression by ∼50%. The levels of hemolymph glucose are also kept higher in dsRNA-CasIAG-hep injected group than those treated with dsRNA-green fluorescent protein (dsRNA-IAG-hep) or saline. Most importantly, the hepatopancreas of dsRNA-CasIAG-hep injected animals contains amounts of carbohydrate (glucose, trehalose, and glycogen) significantly lower than those of control groups, indicating that the function of CasIAG-hep in carbohydrate metabolism in crustaceans is similar to carbohydrate metabolism in vertebrates.

Cloning of prophenoloxidase from hemocytes of the blue crab, Callinectes sapidus and its expression and enzyme activity during the molt cycle

The arthropods cuticle undergoes dramatic morphological and biochemical changes from being soft to hardness through each molting process. Prophenoloxidase (PPO) known as a key enzyme in the arthropod innate immune system involved in the melanization reaction, has been related with the initial shell-hardening process, specifically in the sclerotization of the protein matrix in the new cuticle. Since hemocytes have been reported as the main PPO source in arthropods, the transport of hemocyte PPO into the newly laid, soft cuticle has been proposed for shell-hardening occurring during and immediately after ecdysis. In order to define the role of hemocyte PPO in the shell-hardening of crustaceans, the full-length cDNA sequence (2806 nt) of hemocytes PPO of the blue crab Callinectes sapidus (CasPPO-hemo) is isolated using degenerate PCR and 5'-3' RACE. CasPPO-hemo encodes a putative PPO (672 aa) showing three hemocyanin domains: N, M, and C in order and two copper binding sites (CuA & CuB). The sequence analysis identifies the putative CasPPO-hemo as zymogen which requires the cleavage at the N-terminus for its activation. Hemocyte extract (CasHLS) contains the PO, the activity of which depends on the in vitro activation of trypsin. The expression levels of CasPPO-hemo are kept constant during the molt cycle. The increase in the number of hemocytes at early premolt correlates with the elevated PO activity, while at late premolt, the increment in hemocyte numbers does not reflect on the PO activity. The functional importance of the changes in the levels of CasHLS-PO activity during molt cycle is discussed in relation to cuticle hardening process.

Analysis of gene expression in Homarus americanus larvae exposed to sublethal concentrations of endosulfan during metamorphosis

Agricultural pesticide runoff has been suspected as the cause of numerous fish kills in rivers throughout Prince Edward Island but the impact on the surrounding marine environment is unknown. Endosulfan, an organochlorine pesticide, is a potent neurotoxin and molt inhibitor used to combat the Colorado potato beetle however it has the potential to affect non-target organisms including the American lobster (Homarus americanus). Metamorphosis is a critical stage of development and the effects of contaminant exposure during this time are largely unknown in lobster. A 14day endosulfan exposure was performed to identify the effects on survival, development and gene expression in lobster larvae during metamorphosis; all of which were predicted to be negatively impacted. The higher endosulfan concentrations resulted in greater mortality and a significant increase in the number of days required to reach metamorphosis in surviving animals. A custom made H. americanus microarray was used for monitoring the changes in expression of 14,592 genes at the termination of the exposure. Genes with >1.5 fold change and identified as being significant at p<0.05 using one-way ANOVA were selected for further analysis. A total of 707 genes were identified as being significantly differentiated, however with only ~40% annotation of the array, the majority of these genes were unknown. Annotated genes of interest were involved in many processes: development, metabolism, immunity and oxidative stress response and gene regulation. Nine genes of interest (histone H1, farnesoic acid O-methyltransferase, cuticle protein, glutathione S-transferase, thioredoxin, NADH dehydrogenase, ecdysone nuclear receptor Fushi tarazu F1 (FTZ-F1), ferritin and ecdysone inducible protein E75 (EIP-E75)) were selected for RT-qPCR validation of the microarray results. The RT-qPCR method was more sensitive than the microarray yet detected similar expression patterns. The two highest endosulfan concentrations resulted in increased mortalities, developmental delays in reaching metamorphosis and significant changes in gene expression. This research provides a foundation for using microarray gene expression profiles as screening tools for exploring the impact of environmental contaminants on lobster.

Cloning of an insulin-like androgenic gland factor (IAG) from the blue crab, Callinectes sapidus: implications for eyestalk regulation of IAG expression

In malacostracan crustaceans, sex differentiation is uniquely regulated by a hormone secreted by the male-specific androgenic gland (AG). An isopod AG hormone was the first to be structurally elucidated and was found to belong to the insulin superfamily of proteins. Recently, it has been found that the AGs of several decapod crustaceans express insulin-like androgenic gland factors (IAGs), whose function is believed to be similar to that of the isopod AG hormone. Here we report the isolation from the blue crab Callinectes sapidus of the full-length cDNA encoding a candidate insulin-like AG hormone, termed Cas-IAG. The predicted protein Cas-IAG was encoded as a precursor consisting of a signal peptide, the B chain, the C peptide, and the A chain in that order. While the AG was the main source of Cas-IAG expression, as found in other decapod species, the hepatopancreas of male Callinectes sapidus crabs displayed minor Cas-IAG expression. Eyestalk ablation confirmed the presence of a possible endocrine axis between the eyestalk ganglia and the AG, implying that Cas-IAG expression is negatively regulated by (a) substance(s) present in the eyestalk ganglia.

Expression of ecdysteroids and cytochrome P450 enzymes during lipid turnover and reproduction in Calanus finmarchicus (Crustacea: Copepoda)

The marine copepod Calanus finmarchicus is the most abundant zooplankton species in the northern regions of the Atlantic Ocean and the Barents Sea. Very little is known about molecular regulation of hormone metabolism, moulting and reproduction in copepods. To investigate these processes, we sampled adult male and female copepods (females at three distinct reproductive stages) and copepodites stage five (CV) from the culture at SINTEF/NTNU Sealab. Copepods were individually photographed, analyzed biometrically (body size, length and lipid storage size) and for ecdysteroid concentrations. In addition, we analyzed copepods for gene expression of three putative cytochrome P450 enzymes possibly involved in ecdysteroid regulation: CYP301A1, CYP305A1 and CYP330A1. The CV group exhibited the highest ecdysteroid concentrations and the largest lipid storage size, and a significant positive correlation was found between these parameters. Also, two of the P450 enzymes (CYP305A1 and CYP330A1) were more highly expressed at CV than at the adult stage, suggesting that these P450 enzymes are involved in ecdysteroid synthesis and lipid storage regulation. The expression of CYP330A1 was higher in newly moulted females than in females that had produced eggs. In addition, we observed that ecdysteroid concentrations were higher in females with large egg sacs, suggesting that ecdysteroids may be involved in egg maturation and reproduction. The CYP301A1 was more highly expressed in males and post-spawning females, and may be involved in ecdysteroid degradation since these groups also exhibited the lowest ecdysteroid concentrations.

Preparation of two recombinant crustacean hyperglycemic hormones from the giant freshwater prawn, Macrobrachium rosenbergii, and their hyperglycemic activities

Crustacean hyperglycemic hormone (CHH) is released from the X-organ/sinus gland complex located in the eyestalks, and regulates glucose levels in the hemolymph. In the giant freshwater prawn (Macrobrachium rosenbergii), two cDNAs encoding different CHH molecules were previously cloned by other workers. One of these (Mar-CHH-2) was expressed only in the eyestalks, whereas the other (Mar-CHH-L) was expressed in the heart, gills, antennal gland, and thoracic ganglion, but not in the eyestalks. However, their biological activities had not yet been characterized. Therefore, in this study, recombinant Mar-CHH-2 (rMar-CHH-2) and Mar-CHH-L (rMar-CHH-L) were produced using an E. coli expression system, by expression in bacterial cells and recovery in the insoluble fraction. Thereafter, rMar-CHH-2 and rMar-CHH-L were subjected to refolding and were subsequently purified by reversed-phase HPLC. The rMar-CHH-2 and rMar-CHH-L thus obtained exhibited the same disulfide bond arrangements as those of other CHHs reported previously, indicative of natural conformation. In in vivo bioassay, rMar-CHH-2 showed significant hyperglycemic activity, whereas rMar-CHH-L had no effect. These results indicate that Mar-CHH-L does not function as a CHH, but may have some other, unknown function.

Spatial and temporal distribution of the ecdysteroid receptor (EcR) in haemocytes and epidermal cells during wound healing in the crayfish, Procambarus clarkii

Wound healing in crustaceans preserves the integrity of the integument and prevents entry of pathogens. We studied the interaction between the moulting hormones (ecdysteroids) and the cellular events under the wound during wound healing with or without bacteria infection. Wounding of the carapace by abrasion induced a rapid increase in circulating ecdysteroid levels to a low sustained plateau level for about 12 days, followed by a sharp premoult peak and moulting. Within 48h of wounding, the nuclear receptor for ecdysteroids (EcR) appeared in the nuclei of haemocytes (hyaline, semigranular and granulocytes), visualized by confocal laser scanning microscopy and anti-EcR. Hyaline haematocytes aggregated in layers below the wound site and granulocytes engaged in phagocytosis. Therefore, the immune system responds directly and rapidly to ecdysteroids. Epidermal cells developed EcR only several days after the haemocytes and only under intact carapace, not under the wound where they appeared apoptotic. At the wound margin, EcR-positive epidermal cells and fibroblasts proceeded to migrate across the wound between the layers of haemocytes. Epidermis was fully regenerated by day 15; at this time the ecdysteroid titre began rising towards a premoult peak and EcR disappeared from the nuclei of epidermal cells suggesting that high amounts of ecdysteroids exert negative control on EcR. When bacteria were injected at the time of wounding, both the plateau level of ecdysteroid titre and the cellular events of wound healing were prolonged by 5-7 days, showing that healing of the wound is slower and that the duration of the plateau phase of the titre depends on the degree of assault on the animal. We conclude that the low levels of ecdysteroids induced by wounding activate the immune system to begin healing below the wound and also stimulate adjacent epidermal cells to commence the process of wound repair.

The role of allatostatins in juvenile hormone synthesis in insects and crustaceans

Allatostatins are pleiotropic neuropeptides for which one function in insects is the inhibition of juvenile hormone synthesis. Juvenile hormone, an important regulator of development and reproduction in insects, is produced by the corpora allata. Mandibular organs, the crustacean homologs of insect corpora allata, produce precursors of juvenile hormone with putatively similar functions. Three types of allatostatins in insects have been isolated: FGLamides, W(X)(6)Wamides, and PISCFs. All act rapidly and reversibly; however, although these types occur in all groups of insects studied, they act as inhibitors of juvenile hormone production in only some groups. Only the FGLamide-type peptides have been isolated in crustaceans, in which they may function to stimulate production of hormone by the mandibular glands, as occurs in early cockroach embryos. Much remains to be learned in order to understand the role of allatostatins in the modulation of hormone production.

Inhibition of ovarian development by methyl farnesoate in the tadpole shrimp, Triops longicaudatus

Methyl farnesoate (MF), a putative crustacean hormone, is the immediate precursor of insect juvenile hormone III (JHIII) in the biosynthetic pathway. We examined whether MF, shown to inhibit adult metamorphosis in several crustacean species, is a juvenilizing factor in the tadpole shrimp, Triops longicaudatus. Oocyte production was chosen as a parameter for measuring reproductive development. MF was administered to juveniles by ingestion via biological vector (Artemia nauplii), MF-coated food pellets, and MF liposome food pellets. Artemia were incubated in 30 microl of 5 microg/ml MF. The MF-coated and MF liposome pellets were prepared with MF concentrations ranging between 0.1 microg/g and 10 microg/g MF by weight. Groups of tadpole shrimp were treated with these vectors from the time of hatching for 5 or 10 days in laboratory and field studies. The treatment groups of all the MF vectors showed reductions in oocyte production. Lower concentrations of MF (0.75 microg/g-3.8 microg/g MF) appeared to have a physiological effect on fecundity, but higher concentrations (10 microg/g MF) reduced somatic growth. MF-coated pellets (1 microg/g MF) administered to adults (after 5 days) caused no difference in oocyte production. The observed reductions of fecundity and the disparity of results between MF treatment on juveniles and adults suggest that MF may regulate ovarian development.

The screening of chemicals for juvenoid-related endocrine activity using the water flea Daphnia magna

U.S. Environmental Protection Agency is charged with developing a screening and testing paradigm for detecting endocrine toxicity of chemicals that are subject to regulation under the Food Quality Protection and the Safe Drinking Water Acts. In this study, we developed and evaluated a screening assay that could be employed to detect juvenoid-related endocrine-modulating activity in an invertebrate species. Juvenoid activity, anti-juvenoid activity, and juvenoid potentiator activity of chemicals was assessed using the water flea Daphnia magna. Male sex determination is under the regulatory control of juvenoid hormone, presumably methyl farnesoate, and this endpoint was used to detect juvenoid modulating activity of chemicals. Eighteen chemicals were evaluated for juvenoid agonist activity. Positive responses were detected with the juvenoid hormones methyl farnesoate and juvenile hormone III along with the insect growth regulating insecticides pyriproxyfen, fenoxycarb, and methoprene. Weak juvenoid activity also was detected with the cyclodiene insecticide dieldrin. Assays performed repetitively with compounds that gave either strong positive, weak positive, or negative response were 100% consistent indicating that the assay is not prone to false positive or negative responses. Five candidate chemicals were evaluated for anti-juvenoid activity and none registered positive. Four chemicals (all trans-retinoic acid, methoprene, kinoprene, bisphenol A) also were evaluated for their ability to potentiate the activity of methyl farnesoate. All registered positive. Results demonstrate that an in vivo assay with a crustacean species customarily employed in toxicity testing can be used to effectively screen chemicals for juvenoid-modulating activity.