Molecular characterization and gene expression pattern of two putative molt-inhibiting hormones from Litopenaeus vannamei

Structure-Based Functional Analysis of a Hormone Belonging to an Ecdysozoan Peptide Superfamily: Revelation of a Common Molecular Architecture and Residues Possibly for Receptor Interaction

A neuropeptide (Sco-CHH-L), belonging to the crustacean hyperglycemic hormone (CHH) superfamily and preferentially expressed in the pericardial organs (POs) of the mud crab Scylla olivacea, was functionally and structurally studied. Its expression levels were significantly higher than the alternative splice form (Sco-CHH) in the POs, and increased significantly after the animals were subjected to a hypo-osmotic stress. Sco-CHH-L, but not Sco-CHH, significantly stimulated in vitro the Na⁺, K⁺-ATPase activity in the posterior (6th) gills. Furthermore, the solution structure of Sco-CHH-L was resolved using nuclear magnetic resonance spectroscopy, revealing that it has an N-terminal tail, three α-helices (α2, Gly⁹-Asn²⁸; α3, His³⁴-Gly³⁸; and α5, Glu⁶²-Arg⁷²), and a π-helix (π4, Cys⁴³-Tyr⁵⁴), and is structurally constrained by a pattern of disulfide bonds (Cys⁷-Cys⁴³, Cys²³-Cys³⁹, and Cys²⁶-Cys⁵²), which is characteristic of the CHH superfamily-peptides. Sco-CHH-L is topologically most similar to the molt-inhibiting hormone from the Kuruma prawn Marsupenaeus japonicus with a backbone root-mean-square-deviation of 3.12 Å. Ten residues of Sco-CHH-L were chosen for alanine-substitution, and the resulting mutants were functionally tested using the gill Na⁺, K⁺-ATPase activity assay, showing that the functionally important residues (I2, F3, E45, D69, I71, and G73) are located at either end of the sequence, which are sterically close to each other and presumably constitute the receptor binding sites. Sco-CHH-L was compared with other members of the superfamily, revealing a folding pattern, which is suggested to be common for the crustacean members of the superfamily, with the properties of the residues constituting the presumed receptor binding sites being the major factors dictating the ligand-receptor binding specificity.

The Crustacean Hyperglycemic Hormone Superfamily: Progress Made in the Past Decade

Early studies recognizing the importance of the decapod eyestalk in the endocrine regulation of crustacean physiology-molting, metabolism, reproduction, osmotic balance, etc.-helped found the field of crustacean endocrinology. Characterization of putative factors in the eyestalk using distinct functional bioassays ultimately led to the discovery of a group of structurally related and functionally diverse neuropeptides, crustacean hyperglycemic hormone (CHH), molt-inhibiting hormone (MIH), gonad-inhibiting hormone (GIH) or vitellogenesis-inhibiting hormone (VIH), and mandibular organ-inhibiting hormone (MOIH). These peptides, along with the first insect member (ion transport peptide, ITP), constitute the original arthropod members of the crustacean hyperglycemic hormone (CHH) superfamily. The presence of genes encoding the CHH-superfamily peptides across representative ecdysozoan taxa has been established. The objective of this review is to, aside from providing a general framework, highlight the progress made during the past decade or so. The progress includes the widespread identification of the CHH-superfamily peptides, in particular in non-crustaceans, which has reshaped the phylogenetic profile of the superfamily. Novel functions have been attributed to some of the newly identified members, providing exceptional opportunities for understanding the structure-function relationships of these peptides. Functional studies are challenging, especially for the peptides of crustacean and insect species, where they are widely expressed in various tissues and usually pleiotropic. Progress has been made in deciphering the roles of CHH, ITP, and their alternatively spliced counterparts (CHH-L, ITP-L) in the regulation of metabolism and ionic/osmotic hemostasis under (eco)physiological, developmental, or pathological contexts, and of MIH in the stimulation of ovarian maturation, which implicates it as a regulator for coordinating growth (molt) and reproduction. In addition, experimental elucidation of the steric structure and structure-function relationships have given better understanding of the structural basis of the functional diversification and overlapping among these peptides. Finally, an important finding was the first-ever identification of the receptors for this superfamily of peptides, specifically the receptors for ITPs of the silkworm, which will surely give great impetus to the functional study of these peptides for years to come. Studies regarding recent progress are presented and synthesized, and prospective developments remarked upon.

Molecular characterization, RNA interference and recombinant protein approach to study the function of the putative Molt Inhibiting Hormone (FmMIH1) gene from the shrimp Fenneropenaeus merguiensis

The Molt Inhibiting Hormone gene and cDNA of the banana shrimp Fenneropenaeus merguiensis (FmMIH1) has been cloned and characterized. FmMIH1 possesses most of the characteristics of the eyestalk CHH/MIH/GIH family subtype-II neuropeptides. FmMIH1 open reading frame consists of 315 bp encoding for 105 amino acid residues. The mature peptide of FmMIH1 consists of 76 amino acid residues, a glycine residue at position 11 of the mature peptide and 6 cysteine residues located in the conserved position. In addition to eyestalk, high levels of FmMIH1 transcript could also be detected in the intestine. FmMIH1 transcript level is low throughout the post-molt, early to mid-intermolt and premolt. However, a sharp increase could be observed in late intermolt (C3 stage). Both alignment and phylogenetic analysis reveal that FmMIH1 is most similar to the MIH1 of other shrimps. For functional assay, RNA interference results show that a significant 2.3 days (P < 0.05) reduction in molt cycle duration could be observed in shrimp receiving dsFmMIH1 injection. Surprisingly, injection of recombinant FmMIH1 could also cause a significant reduction of the molt cycle (average 1.9 days, P < 0.05). We hypothesize that the recombinant protein is biological inactive but it competes with the endogenous MIH for carrier protein binding and consequently reduces the amount of biological MIH that could reach the targets. In conclusion, the result of this study will provide us new insight in molting/growth control in crustacean.

Comparative transcriptomic characterization of the eyestalk in Pacific white shrimp (Litopenaeus vannamei) during ovarian maturation

In crustaceans, some of fundamental regulatory processes related to a range of physiological functions, including ovarian maturation, molting, glucose homeostasis, osmoregulation, etc., occur in the organs of the eyestalk. Additionally, reproduction is regulated by neuropeptide hormones and other proteins released from secretory sites (X-organ/sinus gland, XO/SG) within the eyestalk. As unilateral eyestalk ablation was the most common method used to artificially induce ovarian maturation for farmed Litopenaeus vannamei, to better understand the reproductive regulation mechanism in L. vannamei, we have investigated the transcriptomes of the eyestalk during five ovary developmental stages with or without eyestalk ablation by high-throughput Illumina sequencing technology. The raw reads were assembled and clustered into 127,031 unigenes. Meanwhile, the differentially expressed genes (DEGs) between ovarian development stages were identified. We examined, through DEG enrichment analysis, eyestalk gene expression patterns for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, comparing natural to artificially induced ovarian maturation. We also identified a variety of transcripts that appear to be differentially expressed throughout ovarian maturation. These include transcripts that encode G-protein coupled receptors (GPCRs) and neuropeptides, such as the crustacean hyperglycemic hormone (CHH), molt-inhibiting hormone (MIH), and crustacean female sex hormone (CFSH). Furthermore, numerous exoskeleton formation-related genes were found to be down-regulated during ovarian maturation, including cuticle-like proteins, eclosion hormone (EH), and gastrolith-like proteins, of which the latter are the first reported in L. vannamei. Our work is the first reproduction-related investigation of L. vannamei focusing on the eyestalk at the whole transcriptome level. These findings provide novel insight into the function of the eyestalk in reproduction regulation.

Penaeid shrimp genome provides insights into benthic adaptation and frequent molting

Crustacea, the subphylum of Arthropoda which dominates the aquatic environment, is of major importance in ecology and fisheries. Here we report the genome sequence of the Pacific white shrimp Litopenaeus vannamei, covering ~1.66 Gb (scaffold N50 605.56 Kb) with 25,596 protein-coding genes and a high proportion of simple sequence repeats (>23.93%). The expansion of genes related to vision and locomotion is probably central to its benthic adaptation. Frequent molting of the shrimp may be explained by an intensified ecdysone signal pathway through gene expansion and positive selection. As an important aquaculture organism, L. vannamei has been subjected to high selection pressure during the past 30 years of breeding, and this has had a considerable impact on its genome. Decoding the L. vannamei genome not only provides an insight into the genetic underpinnings of specific biological processes, but also provides valuable information for enhancing crustacean aquaculture.

The Pacific white shrimp Litopenaeus vannamei is an important aquaculture species and a promising model for crustacean biology. Here, the authors provide a reference genome assembly, and show that gene expansion is involved in the regulation of frequent molting as well as benthic adaptation of the shrimp.

Characterization, expression patterns of molt-inhibiting hormone gene of Macrobrachium nipponense and its roles in molting and growth

The oriental river prawn, Macrobrachium nipponense, is an important commercial aquaculture resource in China. In order to overwinter, M. nipponense displays decreased physiological activity and less consumption of energy. Sudden warming would trigger molting and cause an extensive death, resulting in huge economic losses. Therefore, it is of great practical significance to study the molting mechanism of oriental river prawns. Molt-inhibiting hormone gene (MIH) plays a major role in regulating molting in crustaceans. In this study, a full length MIH cDNA of M. nipponense (Mn-MIH) was cloned from the eyestalk. The total length of the Mn-MIH was 925 bp, encoding a protein of 119 amino acids. Tissue distribution analysis showed that Mn-MIH was highly expressed in the eyestalk, and that it had relatively low expression in gill, ovary, and abdominal ganglion. Mn-MIH was detected in all developmental stages, and changed regularly in line with the molting cycle of the embryo and larva. Mn-MIH varied in response to the molting cycle, suggesting that Mn-MIH negatively regulates ecdysteroidogenesis. Mn-MIH inhibition by RNAi resulted in a significant acceleration of molting cycles in both males and females, confirming the inhibitory role of MIH in molting. After long-term RNAi males, but not females had significant weight gain, confirming that Mn-MIH plays an important role in growth of M. nipponense. Our work contributes to a better understanding of the role of Mn-MIH in crustacean molting and growth.

Transcriptomic information from Pacific white shrimp (Litopenaeus vannamei) ovary and eyestalk, and expression patterns for genes putatively involved in the reproductive process

The increased use of massive sequencing technologies has enabled the identification of several genes known to be involved in different mechanisms associated with reproduction that so far have only been studied in vertebrates and other model invertebrate species. In order to further investigate the genes involved in Litopenaeus vannamei reproduction, cDNA and SSH libraries derived from female eyestalk and gonad were produced, allowing the identification of expressed sequences tags (ESTs) that potentially have a role in the regulation of gonadal maturation. In the present study, different transcripts involved in reproduction were identified and a number of them were characterized as full-length. These transcripts were evaluated in males and females in order to establish their tissue expression profiles during developmental stages (juvenile, subadult and adult), and in the case of females, their possible association with gonad maturation was assessed through expression analysis of vitellogenin. The results indicated that the expression of vitellogenin receptor (vtgr) and minichromosome maintenance (mcm) family members in the female gonad suggest an important role during previtellogenesis. Additionally, the expression profiles of genes such as famet, igfbp and gpcr in brain tissues suggest an interaction between the insulin/insulin-like growth factor signaling pathway (IIS) and methyl farnesoate (MF) biosynthesis for control of reproduction. Furthermore, the specific expression pattern of farnesoic acid O-methyltransferase suggests that final synthesis of MF is carried out in different target tissues, where it is regulated by esterase enzymes under a tissue-specific hormonal control. Finally, the presence of a vertebrate type steroid receptor in hepatopancreas and intestine besides being highly expressed in female gonads, suggest a role of that receptor during sexual maturation.

Differential effects of silencing crustacean hyperglycemic hormone gene expression on the metabolic profiles of the muscle and hepatopancreas in the crayfish Procambarus clarkii

In order to functionally characterize the metabolic roles of crustacean hyperglycemic hormone (CHH), gene expression of CHH in the crayfish (Procambarus clarkii) was knocked down by in vivo injection of CHH double-stranded RNA (dsRNA), followed by metabolomic analysis of 2 CHH target tissues (the muscle and hepatopancreas) using nuclear magnetic resonance spectroscopy. Compared to the levels in untreated and saline-injected (SAI) animals, levels of CHH transcript, but not those of molt-inhibiting hormone (a CHH-family peptide), in the eyestalk ganglia of CHH dsRNA-injected (DSI) animals were significantly decreased at 24, 48, and 72 hour post injection (hpi), with concomitant changes in levels of CHH peptide in the sinus gland (a neurohemal organ) and hemolymph. Green fluorescence protein (GFP) dsRNA failed to affect levels of CHH transcript in the eyestalk ganglia of GFP DSI animals. Number of metabolites whose levels were significantly changed by CHH dsRNA was 149 and 181 in the muscle and 24 and 12 in the hepatopancreas, at 24 and 48 hpi, respectively. Principal component analysis of these metabolites show that metabolic effects of silencing CHH gene expression were more pronounced in the muscle (with the cluster of CHH DSI group clearly being separated from that of SAI group at 24 hpi) than in the hepatopancreas. Moreover, pathway analysis of the metabolites closely related to carbohydrate and energy metabolism indicate that, for CHH DSI animals at 24 hpi, metabolic profile of the muscle was characterized by reduced synthesis of NAD⁺ and adenine ribonucleotides, diminished levels of ATP, lower rate of utilization of carbohydrates through glycolysis, and a partially rescued TCA cycle, whereas that of the hepatopancreas by unaffected levels of ATP, lower rate of utilization of carbohydrates, and increased levels of ketone bodies. The combined results of metabolic changes in response to silenced CHH gene expression reveal that metabolic functions of CHH on the muscle and hepatopancreas are more diverse than previously thought and are differential between the two tissues.

Moult-inhibiting fusion protein augments while polyclonal antisera attenuate moult stages and duration in Penaeus monodon

Moulting in crustaceans is regulated by moult-inhibiting hormone (MIH) of the CHH family neuropeptides. The inhibitory functions of MIH have pivotal roles in growth and reproduction of Penaeus monodon. In this study, we report the expression of a thioredoxin-fused mature MIH I protein (mf-PmMIH I) of P. monodon in a bacterial system and its use as antigen to raise polyclonal antiserum (anti-mf-PmMIH I). The mature MIH I gene of 231bp, that codes for 77 amino acids, was cloned into the Escherichia coli thioredoxin gene fusion expression system. The translation expression vector construct (mf-PmMIH I+pET32a+) upon induction produced 29.85kDa mature MIH I fusion protein (mf-PmMIH I). The purified fusion protein was used as exogenous MIH I and as antigen to raise polyclonal antisera. When fusion protein (mf-PmMIH I) was injected into D2 and D3 stages of juvenile shrimp, the moult cycle duration was extended significantly to 16.67±1.03 and 14.67±1.03days respectively compared to that of 11.67±1.03days in controls. Moult duration was further reduced to 8.33±0.82days when polyclonal antiserum (anti-mf-PmMIH I - 1:500 dilutions) was injected. Anti-mf-PmMIH I immunolocalized MIH I producing neurosecretory cells in the eyestalk of P. monodon. In short, the present manuscript reports an innovative means of moult regulation in P. monodon with thioredoxin fused MIH I and antisera developed.

Metabolic effects of parasitization by the barnacle Polyascus plana (Cirripedia: Rhizocephala: Sacculinidae) on a grapsid host, Metopograpsus thukuhar

Pathophysiological studies of rhizocephalan infections are rare. We describe differences in the levels of tissue and hemolymph metabolites between Polyascus plana-parasitized and unparasitized individuals of Metopograpsus thukuhar. Crabs were assigned to either a parasitized (carrying at least 1 externa, i.e. a protruding reproductive body) or an unparasitized (not carrying externae and determined to be rootlet-free by a barnacle 18S rRNA-based polymerase chain reaction) group. Quantification of metabolites showed that muscle glycogen levels were significantly lower and hepatopancreas levels were significantly higher in parasitized crabs compared to unparasitized crabs; hepatopancreas triacylglycerol levels were significantly higher and hemolymph levels significantly lower in parasitized hosts, and there was no significant difference in muscle triacylglycerol levels between unparasitized and parasitized animals. Glucose levels in the hepatopancreas, muscle, and hemolymph were all significantly higher in parasitized hosts. Significant levels of glucose, triacylglycerol, and glycogen were present in the barnacle externae. In addition, levels of crustacean hyperglycemic hormone in the sinus glands were not significantly different between unparasitized and parasitized animals. Glucose mobilized from the muscle is likely converted to glycogen and triacylglycerol in the rootlet-infiltrated hepatopancreas of parasitized hosts, and the eyestalk neuroendocrine system appears not to be significantly impaired, in terms of hormone production and storage, by parasitization.

A novel CHH gene from the Pacific white shrimp Litopenaeus vannamei was characterized and found highly expressed in gut and less in eyestalk and other extra-eyestalk tissues

The crustacean hyperglycemic hormone (CHH) family is an important group of neuropeptides involved in controlling growth, reproduction, and stress response in decapod species. In this study, a new gene containing 4 exons-3 introns flanked by canonical 5'-GT-AG-3' intron splice-site junctions was isolated from Litopenaeus vannamei. Two full length transcripts of this CHH were isolated from eyestalk and pericardial tissue of males and females using rapid amplification of cDNA ends (RACE). Transcripts sequences were 1578bp in length in males pericardial tissues and in males and females eyestalk with 100% identity, but the transcript isolated from females pericardial tissues was shorter (974bp). The differences in transcripts length is a result of two polyadenylation sites present in the 3'UTR resulting in two transcription termination signals. Transcript sequences encoded one unique protein that can be classified as type I CHH subfamily because of the 4 exons and 3 introns structure, although the CPRP region is not-well conserved and there is no amidation in the C-terminal of the deduced amino acid sequence. Furthermore, there is a glycine inserted in the mature peptide not at position 12 as in type II CHHs but after amino acid 31 and the phylogenetic analysis did not group the peptide within type I, but closer to type II CHHs. We demonstrated by endpoint-PCR, qPCR, and in situ hybridization (ISH), that this gene is expressed in neuroendocrine organs known to express CHHs in penaeid shrimp, including X-organ and optic nerve in eyestalk, supraesophageal ganglion (SoG), but it is also expressed in other organs as gill, gut, pericardial cavity, as well as in terminal ampoule or spermatophore and vas deferens of males.

Differential regulation of hepatopancreatic vitellogenin (VTG) gene expression by two putative molt-inhibiting hormones (MIH1/2) in Pacific white shrimp (Litopenaeus vannamei)

Molt-inhibiting hormone (MIH), a peptide member of the crustacean hyperglycemic hormone (CHH) family, is commonly considered as a negative regulator during the molt cycle in crustaceans. Phylogenetic analysis of CHH family peptides in penaeidae shrimps suggested that there is no significant differentiation between MIH and vitellogenesis-inhibiting hormone (VIH, another peptide member of CHH family), by far the most potent negative regulator of crustacean vitellogenesis known. Thus, MIH may also play a role in regulating vitellogenesis. In this study, two previously reported putative MIHs (LivMIH1 and LivMIH2) in the Pacific white shrimp (Litopenaeus vannamei) were expressed in Escherichia coli, purified by immobilized metal ion affinity chromatography (IMAC) and further confirmed by western blot. Regulation of vitellogenin (VTG) mRNA expression by recombinant LivMIH1 and LivMIH2 challenge was performed by both in vitro hepatopancreatic primary cells culture and in vivo injection approaches. In in vitro primary culture of shrimp hepatopancreatic cells, only LivMIH2 but not LivMIH1 administration could improve the mRNA expression of VTG. In in vivo injection experiments, similarly, only LivMIH2 but not LivMIH1 could stimulate hepatopancreatic VTG gene expression and induce ovary maturation. Our study may provide evidence for one isoform of MIH (MIH2 in L. vannamei) may serve as one of the mediators of the physiological progress of molting and vitellogenesis. Our study may also give new insight in CHH family peptides regulating reproduction in crustaceans, in particular penaeidae shrimps.

Expansion of the Litopenaeus vannamei and Penaeus monodon peptidomes using transcriptome shotgun assembly sequence data

The shrimp Litopenaeus vannamei and Penaeus monodon are arguably the most important commercially farmed crustaceans. While expansion of their aquaculture has classically relied on improvements to rearing facilities, these options have largely been exhausted, and today a shift in focus is occurring, with increased investment in manipulating the shrimp themselves. Hormonal control is one strategy for increasing aquaculture output. However, to use it, one must first understand an animal's native hormonal systems. Here, transcriptome shotgun assembly (TSA) data were used to expand the peptidomes for L. vannamei and P. monodon. Via an established bioinformatics workflow, 41 L. vannamei and 25 P. monodon pre/preprohormone-encoding transcripts were identified, allowing for the prediction of 158 and 106 distinct peptide structures for these species, respectively. The identified peptides included isoforms of allatostatin A, B and C, as well as members the bursicon, CAPA, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31, eclosion hormone, FLRFamide, GSEFLamide, intocin, leucokinin, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, orcomyotropin, pigment dispersing hormone, proctolin, red pigment concentrating hormone, RYamide, SIFamide, short neuropeptide F and tachykinin-related peptide families. While some of the predicted peptides are known L. vannamei and/or P. monodon isoforms (which vet the structures of many peptides identified previously via mass spectrometry and other means), most are described here for the first time. These data more than double the extant catalogs of L. vannamei and P. monodon peptides and provide platforms from which to launch future physiological studies of peptidergic signaling in these two commercially important species.

Transcriptome and peptidome characterisation of the main neuropeptides and peptidic hormones of a euphausiid: the Ice Krill, Euphausia crystallorophias

Background

The Ice krill, Euphausia crystallorophias is one of the species at the base of the Southern Ocean food chain. Given their significant contribution to the biomass of the Southern Ocean, it is vitally important to gain a better understanding of their physiology and, in particular, anticipate their responses to climate change effects in the warming seas around Antarctica.

Methodology/Principal Findings

Illumina sequencing was used to produce a transcriptome of the ice krill. Analysis of the assembled contigs via two different methods, produced 36 new pre-pro-peptides, coding for 61 neuropeptides or peptide hormones belonging to the following families: Allatostatins (A, B et C), Bursicon (α and β), Crustacean Hyperglycemic Hormones (CHH and MIH/VIHs), Crustacean Cardioactive Peptide (CCAP), Corazonin, Diuretic Hormones (DH), the Eclosion Hormone (EH), Neuroparsin, Neuropeptide F (NPF), small Neuropeptide F (sNPF), Pigment Dispersing Hormone (PDH), Red Pigment Concentrating Hormone (RPCH) and finally Tachykinin. LC/MS/MS proteomics was also carried out on eyestalk extracts, which are the major site of neuropeptide synthesis in decapod crustaceans. Results confirmed the presence of six neuropeptides and six precursor-related peptides previously identified in the transcriptome analyses.

Conclusions

This study represents the first comprehensive analysis of neuropeptide hormones in a Eucarida non-decapod Malacostraca, several of which are described for the first time in a non-decapod crustacean. Additionally, there is a potential expansion of PDH and Neuropeptide F family members, which may reflect certain life history traits such as circadian rhythms associated with diurnal migrations and also the confirmation via mass spectrometry of several novel pre-pro-peptides, of unknown function. Knowledge of these essential hormones provides a vital framework for understanding the physiological response of this key Southern Ocean species to climate change and provides a valuable resource for studies into the molecular phylogeny of these organisms and the evolution of neuropeptide hormones.

Crustacean hyperglycemic hormone precursor transcripts in the hemocytes of the crayfish Procambarus clarkii: novel sequence characteristics relating to gene splicing pattern and transcript stability

It was demonstrated in a previous study (Wu et al., 2012b) that crustacean hyperglycemic hormone (CHH) gene is expressed in the hemocyte of Procambarus clarkii. In the present study, 2 additional cDNAs (CHH2-L and tCHH2) from the hemocyte and a CHH gene (CHH2) from the abdominal muscle of the same species were cloned. Analyses of the cDNA and genomic sequences suggested that, similar to other previously reported CHH genes, 2 precursor transcripts (CHH2 and CHH2-L) would be derived from CHH2 gene through a process of RNA alternative splicing, and CHH2 and CHH2-L each encode a precursor containing a signal peptide, a CHH precursor-related peptide, and a mature peptide. Further, tCHH2 sequence consists of exon I, exon II, and a truncated segment of intron II of CHH2 gene, followed by a previously unknown 3'sequence. It is suggested that, because the truncation disrupts the highly conserved RNA splice acceptor site, the truncated segment is retained within tCHH2, resulting in encoding a precursor containing the typical precursor components except the mature peptide is truncated with only 40 residues. In addition, unlike 2 other previously identified transcripts (referred to as CHH1 and CHH1-L), CHH2-L, CHH2, tCHH2 contain in the 3'-UTRs 3-5 AU-rich elements (AREs). The data showed that multiple CHH genes are expressed in crayfish hemocytes. Novel sequence characteristics of the transcripts result in an RNA splicing pattern that yields a transcript (tCHH2) encoding a precursor with an atypical truncated mature peptide and possibly leads to a different expression dynamics of the precursors encoded by the ARE-containing transcripts.

Neuroendocrine responses of a crustacean host to viral infection: effects of infection of white spot syndrome virus on the expression and release of crustacean hyperglycemic hormone in the crayfish Procambarus clarkii

The objectives of the present study were to characterize the changes in crustacean hyperglycemic hormone (CHH) transcript and peptide levels in response to infection of white spot syndrome virus (WSSV) in a crustacean, Procambarus clarkii. After viral challenge, significant increase in virus load began at 24 h post injection (hpi) and the increase was much more substantial at 48 and 72 hpi. The hemolymph CHH levels rapidly increased after viral challenge; the increase started as early as 3 hpi and lasted for at least 2 d after the challenge. In contrast, the hemolymph glucose levels did not significantly changed over a 2 d period in the WSSV-infected animals. The CHH transcript and peptide levels in tissues were also determined. The CHH transcript levels in the eyestalk ganglia (the major site of CHH synthesis) of the virus-infected animals did not significantly change over a 2 d period and those in 2 extra-eyestalk tissues (the thoracic ganglia and cerebral ganglia) significantly increased at 24 and 48 hpi. The CHH peptide levels in the eyestalk ganglia of the virus-infected animals significantly decreased at 24 and 48 hpi and those in the thoracic ganglia and cerebral ganglia remained unchanged over a 2 d period. These data demonstrated a WSSV-induced increase in the release of CHH into hemolymph that is rapid in onset and lasting in duration. Changes in the CHH transcript and peptide levels implied that the WSSV-induced increase in hemolymph CHH levels primarily resulted from an enhanced release from the eyestalk ganglia, but the contribution of the 2 extra-eyestalk tissues to hemolymph pool of CHH increased as viral infection progressed. The combined patterns of change in the hemolymph glucose and CHH levels further suggest that the virus-enhanced CHH release would lead to higher glycolytic activity and elevated glucose mobilization presumably favorable for viral replication.

Stimulation of molt by RNA interference of the molt-inhibiting hormone in the crayfish Cherax quadricarinatus

In crustaceans, molting is known to be under the control of neuropeptide hormones synthesized and secreted from the eyestalk ganglia. While the role of molt-inhibiting hormone (MIH) in regulating molting has been described in several species using classical methods, an in vivo specific MIH targeted manipulation has not been described yet. In the present study, an MIH cDNA was isolated and sequenced from the eyestalk ganglia of the Australian freshwater red claw crayfish Cherax quadricarinatus (Cq) by 5' and 3' RACE. We analyzed the putative Cq-MIH based on sequence homology, a three dimensional structure model and transcript's tissue specificity. We further examined the involvement of Cq-MIH in the control of molt in the crayfish through RNAi by in vivo injections of Cq-MIH double-stranded RNA, which resulted in, similarly to eyestalk ablation, acceleration of molt cycles. This acceleration was reflected by a significant reduction (up to 32%) in molt interval and an increased rate in molt mineralization index (MMI), which correlated with the induction of ecdysteroid hormones compared to control. Altogether, this study provides a proof of function for the involvement of the Cq-MIH gene in molt regulation in the crayfish.

Two type I crustacean hyperglycemic hormone (CHH) genes in Morotoge shrimp (Pandalopsis japonica): cloning and expression of eyestalk and pericardial organ isoforms produced by alternative splicing and a novel type I CHH with predicted structure shared with type II CHH peptides

Crustacean hyperglycemic hormone (CHH) peptide family members play critical roles in growth and reproduction in decapods. Three cDNAs encoding CHH family members (Pj-CHH1ES, Pj-CHH1PO, and Pj-CHH2) were isolated by a combination of bioinformatic analysis and conventional cloning strategies. Pj-CHH1ES and Pj-CHH1PO were products of the same gene that were generated by alternative mRNA splicing, whereas Pj-CHH2 was the product of a second gene. The Pj-CHH1 and Pj-CHH2 genes had four exons and three introns, suggesting the two genes arose from gene duplication. The three cDNAs were classified in the type I CHH subfamily, as the deduced amino acid sequences had a CHH precursor-related peptide sequence positioned between the N-terminal signal sequence and C-terminal mature peptide sequence. The Pj-CHH1ES isoform was expressed at a higher level in the eyestalk X-organ/sinus gland (XO/SG) complex and at a lower level in the gill. The Pj-CHH1PO isoform was expressed at higher levels in the XO/SG complex, brain, abdominal ganglion, and thoracic ganglion and at a lower level in the epidermis. Pj-CHH2 was expressed at a higher level in the thoracic ganglion and at a lower level in the gill. Real-time polymerase chain reaction was used to quantify the effects of eyestalk ablation on the mRNA levels of the three Pj-CHHs in the brain, thoracic ganglion, and gill. Eyestalk ablation reduced expression of Pj-CHH1ES in the brain and Pj-CHH1PO and Pj-CHH2 in the thoracic ganglion. Sequence alignment of the Pj-CHHs with CHHs from other species indicated that Pj-CHH2 had an additional alanine at position #9 of the mature peptide. Molecular modeling showed that the Pj-CHH2 mature peptide had a short alpha helix (α1) in the N-terminal region, which is characteristic of type II CHHs. This suggests that Pj-CHH2 differs in function from other type I CHHs.

The eyes have it: A brief history of crustacean neuroendocrinology

To help celebrate the 50th anniversary of General and Comparative Endocrinology, the history of only a small portion of crustacean endocrinology is presented here. The field of crustacean endocrinology dates back to the decades prior to the establishment of General and Comparative Endocrinology and the first article about crustacean endocrinology published in this journal was concerned with the anatomy of neurosecretory and neurohemal structures in brachyuran crabs. This review looks at the history of neuroendocrinology in crustaceans during that time and tries to put perspective on the future of this field.

The CHH-superfamily of multifunctional peptide hormones controlling crustacean metabolism, osmoregulation, moulting, and reproduction

Apart from providing an up-to-date review of the literature, considerable emphasis was placed in this article on the historical development of the field of "crustacean eyestalk hormones". A role of the neurosecretory eyestalk structures of crustaceans in endocrine regulation was recognized about 80 years ago, but it took another half a century until the first peptide hormones were identified. Following the identification of crustacean hyperglycaemic hormone (CHH) and moult-inhibiting hormone (MIH), a large number of homologous peptides have been identified to this date. They comprise a family of multifunctional peptides which can be divided, according to sequences and precursor structure, into two subfamilies, type-I and -II. Recent results on peptide sequences, structure of genes and precursors are described here. The best studied biological activities include metabolic control, moulting, gonad maturation, ionic and osmotic regulation and methyl farnesoate synthesis in mandibular glands. Accordingly, the names CHH, MIH, and GIH/VIH (gonad/vitellogenesis-inhibiting hormone), MOIH (mandibular organ-inhibiting hormone) were coined. The identification of ITP (ion transport peptide) in insects showed, for the first time, that CHH-family peptides are not restricted to crustaceans, and data mining has recently inferred their occurrence in other ecdysozoan clades as well. The long-held tenet of exclusive association with the eyestalk X-organ-sinus gland tract has been challenged by the finding of several extra nervous system sites of expression of CHH-family peptides. Concerning mode of action and the question of target tissues, second messenger mechanisms are discussed, as well as binding sites and receptors. Future challenges are highlighted.

Molt-inhibiting hormone from Chinese mitten crab (Eriocheir sinensis): Cloning, tissue expression and effects of recombinant peptide on ecdysteroid secretion of YOs

Molt-inhibiting hormone (MIH), a member of the crustacean hyperglycemic hormone (CHH) family, inhibits the synthesis of ecdysteroid in Y-organ (YO) and plays a significant role in the regulation of molting and growth of crustaceans. A complete cDNA sequence encoding MIH (Ers-MIH, GenBank Accession No.: DQ341280) was cloned from eyestalk of Chinese mitten crab (Eriocheir sinensis) by 5' and 3' RACEs and PCR cloning. The full-length cDNA consists of 1457 bp with a 330 bp open reading frame, encoding 110 amino acids, containing a 75 amino acid mature peptide. The deduced amino acid sequence contains a typical CHH domain. Transcripts of Ers-MIH mRNA were detected in eyestalk by Northern blotting. The production of purified recombinant Ers-MIH (rErs-MIH) expressed in Escherichia coli was 0.3g/L. The LC-ESI-MS analysis showed that two peptide fragments of the recombinant protein were identical to the deduced amino acid sequence of Ers-MIH. By in vitro assay on E. sinensis YOs, a cGMP mediated suppression of rErs-MIH on ecdysteroidogenesis could be observed. Accumulation of cGMP in YOs showed a concentration-dependent manner within 0.01-1 nmol/mL of rErs-MIH; ecdysteroid secretion was inhibited significantly at the range of 0.01-100 nmol/mL rErs-MIH; furthermore, a significant inhibition effect on ecdysteroid releasing was shown when cGMP analog (8-Br-cGMP) concentration rose up to 100 nmol/mL. This study would facilitate to investigate the roles of MIH in molt cycle regulation.

Computational analysis and structure predictions of CHH-related peptides from Litopenaeus vannamei

The crustaceans produce several related peptides that belong to the crustacean hyperglycemic hormone (CHH) family. While these peptides have similar amino acid sequences, they have diverse biological functions that must arise, in part, from differences in the 3D shape of these peptides. However, it is generally accepted that peptides with a high degree of sequence similarity also have a similar 3-D structure. We used the solution structure of one peptide in the crustacean hyperglycemic hormone family, the molt-inhibiting hormone of the kuruma prawn (Marsupenaeus japonicus), to predict the shape of the five known peptides related to CHH in the Pacific white shrimp, Litopenaeus vannamei. The high similarity of the 3-D structures of these peptides suggests a common fold for the entire family. Nevertheless, minor differences in the shape of these peptides were observed, which may be the basis for their different biological properties.

Cloning and expression profiles of two isoforms of a CHH-like gene specifically expressed in male Chinese shrimp, Fenneropenaeus chinensis

Two full-length cDNA sequences (Fc-CHH1, Fc-CHH2) encoding a crustacean hyperglycemic hormone (CHH) precursor homolog and their DNA sequences were cloned from Chinese shrimp Fenneropenaeus chinensis. The deduced amino acid sequences of them are predicted to contain a signal peptide and a mature peptide. The mature peptides of Fc-CHH1 and Fc-CHH2 shared 78% identity, but they showed low identities (less than 40%) to CHH peptides from other species. Both Fc-CHH1 and Fc-CHH2 proteins contain six highly conserved cysteine residues which are characteristic of the CHH family peptides. The transcripts of Fc-CHH1 and Fc-CHH2 were shown to be specifically present in the spermatophore sac of mature male Chinese shrimp through reverse transcription-polymerase chain reaction (RT-PCR) detection. The transcripts of Fc-CHH1 and Fc-CHH2 begin to appear at the immature stage (115 days after the first post-larvae stage) when the spermatophore sac was first observed to be appeared. In situ hybridization analyses showed that Fc-CHH1 and Fc-CHH2 transcripts located at the epithelial cells in the internal wall of the spermatophore sac. In the cloned DNA sequences of Fc-CHH1 and Fc-CHH2, the predicted transcription factor binding sites in the 5' flanking sequences are different from those previously reported for CHH family genes of crustacean. To our knowledge, these are novel CHH-like genes expressed specifically in male shrimp. Their function needs to be further investigated.

Molecular cloning and differential expression pattern of two structural variants of the crustacean hyperglycemic hormone family from the mud crab Scylla olivacea

Two full-length cDNA sequences encoding a crustacean hyperglycemic hormone (CHH) precursor were cloned from tissues of the mud crab Scylla olivacea. Sco-CHH (S. olivacea CHH) was cloned from eyestalk ganglia, whereas Sco-CHH-L (S. olivacea CHH-like peptide) was cloned from extra-eyestalk tissues (pericardial organ and thoracic ganglia). Each conceptually translated precursor is expected to be processed into a signal peptide, a CHH precursor-related peptide (CPRP), and a mature CHH or CHH-like peptide. The two precursors are identical in amino acid sequence through the 40th residue of the mature peptide, but different from each other substantially in the C-terminus. Both CHH variants contain the six highly conserved cysteine residues characteristic of the CHH family peptides, and share higher sequence identities with other brachyuran CHH sequences than with those of other taxonomic groups. As determined by reverse transcription-polymerase chain reaction (RT-PCR), the transcripts of Sco-CHH and Sco-CHH-L were present in eyestalk ganglia and several extra-eyestalk tissues (the thoracic ganglia, pericardial organ, brain, circumesophageal connectives, and gut). Sco-CHH was the predominant form in eyestalk ganglia, while Sco-CHH-L was the predominant form in several extra-eyestalk tissues. Neither transcript was expressed in the muscle, hepatopancreas, ovary, testis, heart, or gill. Antisera were raised against synthetic peptides corresponding to a stretch of sequence-specific to the C-terminus of Sco-CHH or Sco-CHH-L. Western blot analyses of tissues expressing Sco-CHH and Sco-CHH-L detected a Sco-CHH immunoreactive protein in the sinus gland, and a Sco-CHH-L immunoreactive protein in the pericardial organ. Immunohistochemical analyses of the eyestalk ganglia localized both Sco-CHH and Sco-CHH-L immunoreactivity to the sinus gland, and only Sco-CHH immunoreactivity to the X-organ somata; analyses of the pericardial organs also localized both Sco-CHH and Sco-CHH-L immunoreactivity to the anterior and posterior bars, as well as to longitudinal trunks joining the two bars. The combined data provided supporting evidence that Sco-CHH and Sco-CHH-L are co-localized in the same tissue.

Effects of elevated ecdysteroid on tissue expression of three guanylyl cyclases in the tropical land crab Gecarcinus lateralis: possible roles of neuropeptide signaling in the molting gland

Two eyestalk (ES) neuropeptides, molt-inhibiting hormone (MIH) and crustacean hyperglycemic hormone (CHH), increase intracellular cGMP levels in target tissues. Both MIH and CHH inhibit ecdysteroid secretion by the molting gland or Y-organ (YO), but apparently through different guanylyl cyclase(GC)-dependent pathways. MIH signaling may be mediated by nitric oxide synthase (NOS) and NO-sensitive GC. CHH binds to a membrane receptor GC. As molting affects neuropeptide signaling, the effects of ecdysteroid on the expression of the land crab Gecarcinus lateralis β subunit of a NO-sensitive GC (Gl-GC-Iβ), a membrane receptor GC (Gl-GC-II) and a NO-insensitive soluble GC (Gl-GC-III) were determined. Gl-GC-Iβ isoforms differing in the absence or presence of an N-terminal 32-amino acid sequence and Gl-GC-III were expressed at higher mRNA levels in ES ganglia, gill,hepatopancreas, ovary and testis, and at lower levels in YO, heart and skeletal muscle. Three Gl-GC-II isoforms, which vary in the length of insertions (+18, +9 and +0 amino acids) within the N-terminal ligand-binding domain, differed in tissue distribution. Gl-GC-II(+18) was expressed highly in striated muscle (skeletal and cardiac muscles); Gl-GC-II(+9) was expressed in all tissues examined (ES ganglia, YO, gill, hepatopancreas, striated muscles and gonads); and Gl-GC-II(+0) was expressed in most tissues and was the dominant isoform in ES and thoracic ganglia. ES ablation, which increased hemolymph ecdysteroid, increased Gl-GC-II(+18) mRNA level in claw muscle. Using real-time RT-PCR, ES ablation increased Gl-GC-Iβ, Gl-GC-III and ecdysone receptor mRNA levels in the YOs ∼ten-, ∼four- and∼twofold, respectively, whereas Gl-GC-II mRNA level was unchanged. A single injection of 20-hydroxyecdysone into intact animals transiently lowered Gl-GC-Iβ in hepatopancreas, testis and skeletal muscle, and certain Gl-GC-II isoforms in some of the tissues. These data suggest that YO and other tissues can modulate responses to neuropeptides by altering GC expression.