Characterization of cDNA encoding molt-inhibiting hormone of the crab, Cancer pagurus; expression of MIH in non-X-organ tissues

Molecular cloning of crustacean hyperglycemic hormone (CHH) family members (CHH, molt-inhibiting hormone and mandibular organ-inhibiting hormone) and their expression levels in the Jonah crab, Cancer borealis

The crustacean hyperglycemic hormone (CHH) neuropeptide family has multiple functions in the regulation of hemolymph glucose levels, molting, ion, and water balance and reproduction. In crab species, three neuroendocrine tissues: the eyestalk ganglia (medulla terminalis X-organ and -sinus gland = ES), the pericardial organ (PO), and guts synthesize a tissue-specific isoforms of CHH neuropeptides. Recently the presence of the mandibular organ-inhibiting hormone (MOIH) was reported in the stomatogastric nervous system (STNS) that regulates the rhythmic muscle movements in esophagus, cardiac sac, gastric and pyloric ports of the foregut. In this study, we aimed to determine the presence of a tissue-specific CHH isoform in the Jonah crab, Cancer borealis using PCR with degenerate primers and 5', 3' rapid amplification of cDNA ends (RACE) in the ES. PO, and STNS. The analysis of CHH sequences shows that C. borealis has one type of CHH isoform, unlike other crab species. We also isolated the cDNA sequence of molt-inhibiting hormone (MIH) in the ES and MOIH in the ES and STNS. The presence of CHH, MOIH and MIH in the sinus gland of adult females and males is confirmed by using a dot-blot assay with the putative peaks collected from RP-HPLC and anti-Cancer sera for CHH, MIH, and MOIH. The present of crustacean female sex hormone (CFSH) in the sinus gland of adult females was examined with a dot-blot assay with anti-Callinectes CFSH serum. Levels of CHH, MOIH, and MIH in the sinus gland and their expressions in the eyestalk ganglia are estimated in the adult males, where CHH is the predominant form among these neuropeptides.

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.

Crustacean hyperglycemic hormone of Portunus trituberculatus: evidence of alternative splicing and potential roles in osmoregulation

The crustacean hyperglycemic hormone (CHH) gene of Portunus trituberculatus (Pt-CHH) consists of four exons and three introns spanning 3849 bp in size and generating two mature mRNA, Pt-CHH1, and Pt-CHH2. The primary gene transcript produces a cDNA encoding for the putative Pt-CHH2 from exons 1, 2, 3, and 4 and an alternative transcript encodes for a putative Pt-CHH1 peptide from exons 1, 2, and 4. A promoter fragment of about 3 kb was obtained by genomic walking. The tissue-specific expression pattern is examined by reverse transcriptase chain reaction, and the results show that Pt-CHH1 is detected in the eyestalk, brain, muscle, and blood. However, Pt-CHH2 is detected in the ganglia thoracalis and gill. The results indicate that the expression of Pt-CHH2 in the gill might suggest a potential role in osmoregulation. The Pt-CHH transcript level in the gill increases when the crab is exposed to low salinity. The injection of dsRNA for Pt-CHH causes a significant reduction in Pt-CHH2 transcript level and the activity of Na+/K+-ATPase, and carbonic anhydrase (CA) show a serious decrease. In conclusion, this study provides molecular evidence to support the osmoregulatory function of Pt-CHH2.

Identification of molt-inhibiting hormone and ecdysteroid receptor cDNA sequences in Gammarus pulex, and variations after endocrine disruptor exposures

In amphipods, growth, development and reproduction are mediated by the molt, which is a hormonally controlled process and which, therefore, could be impacted by endocrine disruption compounds (EDC). The molt process is controlled by both X-organ (XO) and Y-organ (YO) through a variety of hormones and receptors including the molt-inhibiting hormone (MIH) and the ecdysteroid receptor (EcR). However, although many studies were devoted to characterize MIH and EcR in crustaceans, only few works evaluated their variations under EDCs exposures. Consequently, the present work aimed to characterize MIH and EcR genes of the amphipod Gammarus pulex, as well as to study their relative expression variations after exposure to four EDCs, proved in vertebrates: ethinylestradiol (estrogen), 4-hydroxytamoxifen (anti-estrogen), 17α-methyltestosterone (androgen) and cyproterone acetate (anti-androgen). PCR amplification allowed to obtain 204 bp length and 255 bp length fragments, encoding for partial sequences of 68 amino acids and 85 amino acids, which correspond to EcR and MIH, respectively, and which are highly conserved in crustacean species. Results highlighted MIH and EcR expressions mainly in G. pulex head, which is the localization of XO and YO. Moreover, irrespective of the EDC exposure, increases of MIH and EcR relative expressions were observed, as it was observed after the exposure to 20-hydroxyecdysone (20HE), the natural molt hormone, used as positive control. Therefore, it appeared that tested EDCs behaved like 20HE, suggesting that their effects could occur through the ecdysteroids pathways, and so impact the molt process of G. pulex on the long term. Finally, the present study is a first step in the possibility of using MIH and EcR relative expressions as biomarkers of exposure for EDCs risk assessment. However additional studies must first be carried out to better characterize and understand their variations, and also better predicted consequences for the exposed amphipods.

Elevated expression of neuropeptide signaling genes in the eyestalk ganglia and Y-organ of Gecarcinus lateralis individuals that are refractory to molt induction

Molting is induced in decapod crustaceans via multiple leg autotomy (MLA) or eyestalk ablation (ESA). MLA removes five or more walking legs, which are regenerated and become functional appendages at ecdysis. ESA eliminates the primary source of molt-inhibiting hormone (MIH) and crustacean hyperglycemic hormone (CHH), which suppress the production of molting hormones (ecdysteroids) from the molting gland or Y-organ (YO). Both MLA and ESA are effective methods for molt induction in Gecarcinus lateralis. However, some G. lateralis individuals are refractory to MLA, as they fail to complete ecdysis by 12weeks post-MLA; these animals are in the "blocked" condition. Quantitative polymerase chain reaction was used to quantify mRNA levels of neuropeptide and mechanistic target of rapamycin (mTOR) signaling genes in YO, eyestalk ganglia (ESG), thoracic ganglion (TG), and brain of intact and blocked animals. Six of the seven neuropeptide signaling genes, three of four mTOR signaling genes, and Gl-elongation factor 2 (EF2) mRNA levels were significantly higher in the ESG of blocked animals. Gl-MIH and Gl-CHH mRNA levels were higher in the TG and brain of blocked animals and levels increased in both control and blocked animals in response to ESA. By contrast, mRNA levels of Gl-EF2 and five of the 10 MIH signaling pathway genes in the YO were two to four orders of magnitude higher in blocked animals compared to controls. These data suggest that increased MIH and CHH synthesis in the ESG contributes to the prevention of molt induction by MLA in blocked animals. The up-regulation of MIH signaling genes in the YO of blocked animals suggests that the YO is more sensitive to MIH produced in the ESG, as well as MIH produced in brain and TG of ESA animals. Both the up-regulation of MIH signaling genes in the YO and of Gl-MIH and Gl-CHH in the ESG, TG, and brain appear to contribute to some G. lateralis individuals being refractory to MLA and ESA.

Localization and expression of molt-inhibiting hormone and nitric oxide synthase in the central nervous system of the green shore crab, Carcinus maenas, and the blackback land crab, Gecarcinus lateralis

In decapod crustaceans, molting is controlled by the pulsatile release of molt-inhibiting hormone (MIH) from neurosecretory cells in the X-organ/sinus gland (XO/SG) complex in the eyestalk ganglia (ESG). A drop in MIH release triggers molting by activating the molting gland or Y-organ (YO). Post-transcriptional mechanisms ultimately control MIH levels in the hemolymph. Neurotransmitter-mediated electrical activity controls Ca²⁺-dependent vesicular release of MIH from the SG axon terminals, which may be modulated by nitric oxide (NO). In green shore crab, Carcinus maenas, nitric oxide synthase (NOS) protein and NO are present in the SG. Moreover, C. maenas are refractory to eyestalk ablation (ESA), suggesting other regions of the nervous system secrete sufficient amounts of MIH to prevent molting. By contrast, ESA induces molting in the blackback land crab, Gecarcinus lateralis. Double-label immunofluorescence microscopy and quantitative polymerase chain reaction were used to localize and quantify MIH and NOS proteins and transcripts, respectively, in the ESG, brain, and thoracic ganglion (TG) of C. maenas and G. lateralis. In ESG, MIH- and NOS-immunopositive cells were closely associated in the SG of both species; confocal microscopy showed that NOS was localized in cells adjacent to MIH-positive axon terminals. In brain, MIH-positive cells were located in a small number of cells in the olfactory lobe; no NOS immunofluorescence was detected. In TG, MIH and NOS were localized in cell clusters between the segmental nerves. In G. lateralis, Gl-MIH and Gl-crustacean hyperglycemic hormone (CHH) mRNA levels were ~10⁵-fold higher in ESG than in brain or TG of intermolt animals, indicating that the ESG is the primary source of these neuropeptides. Gl-NOS and Gl-elongation factor (EF2) mRNA levels were also higher in the ESG. Molt stage had little or no effect on CHH, NOS, NOS-interacting protein (NOS-IP), membrane Guanylyl Cyclase-II (GC-II), and NO-independent GC-III expression in the ESG of both species. By contrast, MIH and NO receptor GC-I beta subunit (GC-Iβ) transcripts were increased during premolt and postmolt stages in G. lateralis, but not in C. maenas. MIH immunopositive cells in the brain and TG may be a secondary source of MIH; the release of MIH from these sources may contribute to the difference between the two species in response to ESA. The MIH-immunopositive cells in the TG may be the source of an MIH-like factor that mediates molt inhibition by limb bud autotomy. The association of MIH- and NOS-labeled cells in the ESG and TG suggests that NO may modulate MIH release. A model is proposed in which NO-dependent activation of GC-I inhibits Ca²⁺-dependent fusion of MIH vesicles with the nerve terminal membrane; the resulting decrease in MIH activates the YO and the animal enters premolt.

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.

Molt regulation in green and red color morphs of the crab, Carcinus maenas: gene expression of molt-inhibiting hormone signaling components

In decapod crustaceans, regulation of molting is controlled by the X-organ/sinus gland complex in the eyestalks. The complex secretes molt-inhibiting hormone (MIH), which suppresses production of ecdysteroids by the Y-organ (YO). MIH signaling involves NO and cGMP in the YO, which expresses NO synthase (NOS) and NO-sensitive guanylyl cyclase (GC-I). Molting can generally be induced by eyestalk ablation (ESA), which removes the primary source of MIH, or by multiple leg autotomy (MLA). In our work on Carcinus maenas, however, ESA has limited effects on hemolymph ecdysteroid titers and animals remain in intermolt by 7 days post-ESA, suggesting that adults are refractory to molt induction techniques. Consequently, the effects of ESA and MLA on molting and YO gene expression in C. maenas green and red color morphotypes were determined at intermediate (16 and 24 days) and long-term (~90 days) intervals. In intermediate-interval experiments, ESA of intermolt animals caused transient 2- to 4-fold increases in hemolymph ecdysteroid titers during the first 2 weeks. In intermolt animals, long-term ESA increased hemolymph ecdysteroid titers 4 to 5-fold by 28 days post treatment, but there was no late premolt peak (&gt;400 pg/μl) characteristic of late premolt animals and animals did not molt by 90 days post-ESA. There was no effect of ESA and MLA on the expression of Cm-elongation factor 2 (EF2), Cm-NOS, the beta subunit of GC-I (Cm-GC-Iβ), a membrane receptor GC (Cm-GC-II), and a soluble NO-insensitive GC (Cm-GC-III) in green morphs. Red morphs were affected by prolonged ESA and MLA treatments, as indicated by large decreases in Cm-EF2, Cm-GC-II, and Cm-GC-III mRNA levels. ESA accelerated the transition of green morphs to the red phenotype in intermolt animals, indicating that molting and integument color changes are not necessarily coupled. ESA delayed molting in premolt green morphs, whereas intact and MLA animals molted by 30 days post treatment. There were significant effects on YO gene expression in intact animals; Cm-GC-Iβ mRNA increased during premolt and Cm-GC-III mRNA decreased during premolt and increased during postmolt. Cm-MIH transcripts were detected in eyestalk ganglia, brain, and thoracic ganglion from green intermolt animals and ESA had no significant effect on Cm-MIH mRNA levels in brain and thoracic ganglion. The data suggest that MIH in the brain and thoracic ganglion prevents molt induction in green ESA animals.

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.

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.

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.

Identification of putative crustacean neuropeptides using in silico analyses of publicly accessible expressed sequence tags

The development of expressed sequence tags (ESTs) for crustacean cDNA libraries and their deposition in publicly accessible databases has generated a rich resource for peptide discovery in this commercially and ecologically important arthropod subphylum. Here, we have conducted in silico searches of these databases for unannotated ESTs encoding putative neuropeptide precursors using the BLAST program tblastn, and have predicted the mature forms of the peptides encoded by them. The primary strategy used was to query the database with known decapod prepro-hormone sequences or, in some instances, insect precursor protein sequences. For neuropeptides for which no prepro-hormones are known, the peptides themselves were used as queries. For those peptides expected to originate from a common precursor, the individual sequences were combined, with each peptide flanked by a dibasic processing site and, if amidated, a glycine residue. Using these approaches, 13 unannotated ESTs encoding putative neuropeptide precursors were found. For example, using the first strategy, putative Marsupenaeus japonicus prepro-hormones encoding B-type allatostatins, neuropeptide F (NPF), and orcokinins were identified. Similarly, several Homarus americanus ESTs encoding putative orcokinin precursors were found. In addition to the decapod prepro-hormones, ESTs putatively encoding a NPF isoform and a red pigment concentrating hormone-like peptide were identified from the cladoceran Daphnia magna, as was one EST putatively encoding multiple tachykinin-related peptides from the isopod Eurydice pulchra. Using the second strategy, we identified a Carcinus maenas EST encoding HIGSLYRamide, a peptide recently discovered via mass spectrometry from Cancer productus. Using mass spectral methods we confirmed that this peptide is also present in Carcinus maenas. Collectively over 50 novel crustacean peptides were predicted from the identified ESTs, providing a strong foundation for future investigations of the evolution, regulation and function of these and related molecules in this arthropod taxon.

Crustacean hyperglycemic hormone from the tropical land crab, Gecarcinus lateralis: cloning, isoforms, and tissue expression

Crustacean hyperglycemic hormone (CHH) regulates carbohydrate metabolism, molting, and ion and water transport. cDNAs encoding four CHH isoforms (designated EG-CHH-A, -B, -C, and -D) were cloned from eyestalk ganglia (EG) from land crab, Gecarcinus lateralis. The isoforms differed in the 3' region of the open reading frame and/or the length of the 3' untranslated region. All encoded essentially identical preprohormones containing a 28-amino acid (aa) signal peptide, a 42-aa precursor related peptide and a 72-aa mature CHH. All deduced aa sequences had the six cysteines, two arginines, one aspartate, one phenylalanine, and one arginine originally identified as characteristic of this neuropeptide family. There was a single aa difference between the EG-CHH-D mature hormone and the other three isoforms. The EG-CHH isoforms were expressed in EG, hindgut, and thoracic ganglion. A fifth CHH isoform, designated pericardial organ (PO)-CHH, was similar to the PO-CHH isoform described in green crab, Carcinus maenas. It was expressed in hindgut and testis, but not in eyestalk ganglia; its expression in PO was not determined. The deduced aa sequence of the PO-CHH was identical to that of the EG-CHH isoforms through aa #40 of the mature peptide. The divergent aa sequence between positions #41 and #73 was encoded by an insertion of a 111-bp sequence absent in EG-CHH cDNAs. The data suggest that EG-CHH and PO-CHH isoforms are generated by alternative splicing of at least two CHH genes.

Molt-inhibiting hormone from the tropical land crab, Gecarcinus lateralis: cloning, tissue expression, and expression of biologically active recombinant peptide in yeast

Molt-inhibiting hormone (MIH), a member of the crustacean hyperglycemic neuropeptide hormone family, inhibits ecdysteroidogenesis in the molting gland or Y-organ (YO). A cDNA encoding MIH of the land crab (Gel-MIH) was cloned from eyestalk ganglia (EG) by a combination of reverse transcriptase polymerase chain reaction (RT-PCR) and 3'- and 5'-rapid amplification of cDNA ends (RACE). The cDNA (1.4 kb) encoded MIH prohormone containing a 35 amino acid signal peptide and a 78 amino acid mature peptide. The mature peptide had the six cysteines, one glycine, two arginines, one aspartate, one phenylalanine, and one asparagine in identical positions in the highly conserved sequence characteristic of other crustacean MIHs. Gel-MIH was expressed only in the EG, as determined by RT-PCR; it was not detected in Y-organ, heart, integument, gill, testis, ovary, hepatopancreas, thoracic ganglion, or skeletal muscle. A cDNA encoding the mature peptide was used to express recombinant MIH (rMIH) using a yeast (Pichia pastoris) expression system. Two constructs were designed to yield either a mature MIH fusion protein with a c-myc epitope and histidine (His) tag at the carboxyl terminus or an untagged mature protein without the c-myc and His sequences. Immunoreactive peptides were detected in Western blots of the cell culture media with both MIH constructs, indicating secretion of the processed rMIH into the medium. Culture media containing the untagged mature peptide significantly inhibited ecdysteroid secretion by YOs from land crab and green crab (Carcinus maenas) cultured in vitro, indicating that the Gel-rMIH was biologically active.

Members of the crustacean hyperglycemic hormone (CHH) peptide family are differentially distributed both between and within the neuroendocrine organs of Cancer crabs: implications for differential release and pleiotropic function

The crustacean hyperglycemic hormone (CHH) family of peptides includes CHH, moult-inhibiting hormone (MIH) and mandibular organ-inhibiting hormone (MOIH). In the crab Cancer pagurus, isoforms of these peptides, as well as CHH precursor-related peptide (CPRP), have been identified in the X-organ-sinus gland (XO-SG) system. Using peptides isolated from the C. pagurus SG, antibodies to each family member and CPRP were generated. These sera were then used to map the distributions and co-localization patterns of these peptides in the neuroendocrine organs of seven Cancer species: Cancer antennarius, Cancer anthonyi, Cancer borealis, Cancer gracilis, Cancer irroratus, Cancer magister and Cancer productus. In addition to the XO-SG, the pericardial organ (PO) and two other neuroendocrine sites contained within the stomatogastric nervous system, the anterior cardiac plexus (ACP) and the anterior commissural organ (ACO), were studied. In all species, the peptides were found to be differentially distributed between the neuroendocrine sites in conserved patterns: i.e. CHH, CPRP, MIH and MOIH in the XO-SG, CHH, CPRP and MOIH in the PO, and MOIH in the ACP (no immunolabeling was found in the ACO). Moreover, in C. productus (and probably in all species), the peptides present in the XO-SG and PO were differentially distributed between the neurons within each of these neuroendocrine organs (e.g. CHH and CPRP in one set of XO somata with MIH and MOIH co-localized in a different set of cell bodies). Taken collectively, the differential distributions of CHH family members and CPRP both between and within the neuroendocrine organs of crabs of the genus Cancer suggests that each of these peptides may be released into the circulatory system in response to varied, tissue-specific cues and that the PO- and/or ACP-derived isoforms may possess functions distinct from those classically ascribed to their release from the SG.

Characterization of a molt-inhibiting hormone (MIH) of the crayfish, Orconectes limosus, by cDNA cloning and mass spectrometric analysis

The structure of the precursor of a molt-inhibiting hormone (MIH) of the American crayfish, Orconectes limosus was determined by cloning of a cDNA based on RNA from the neurosecretory perikarya of the X-organ in the eyestalk ganglia. The open reading frame includes the complete precursor sequence, consisting of a signal peptide of 29, and the MIH sequence of 77 amino acids. In addition, the mature peptide was isolated by HPLC from the neurohemal sinus gland and analyzed by ESI-MS and MALDI-TOF-MS peptide mapping. This showed that the mature peptide (Mass 8664.29 Da) consists of only 75 amino acids, having Ala75-NH2 as C-terminus. Thus, C-terminal Arg77 of the precursor is removed during processing, and Gly76 serves as an amide donor. Sequence comparison confirms this peptide as a novel member of the large family, which includes crustacean hyperglycaemic hormone (CHH), MIH and gonad (vitellogenesis)-inhibiting hormone (GIH/VIH). The lack of a CPRP (CHH-precursor related peptide) in the hormone precursor, the size and specific sequence characteristics show that Orl MIH belongs to the MIH/GIH(VIH) subgroup of this larger family. Comparison with the MIH of Procambarus clarkii, the only other MIH that has thus far been identified in freshwater crayfish, shows extremely high sequence conservation. Both MIHs differ in only one amino acid residue ( approximately 99% identity), whereas the sequence identity to several other known MIHs is between 40 and 46%.

Crustacean neuropeptide genes of the CHH/MIH/GIH family: implications from molecular studies

The crustacean eyestalk CHH/MIH/GIH gene family represents a unique group of neuropeptide originally identified in crustaceans. These neuropeptides shared a high degree of amino acid identity, and the conservation of cysteine residues at the same relative positions. Based on their biological, biochemical, and molecular properties, they can be divided into the CHH and MIH subtypes with two major members in each subtype. In the shrimp, the CHH-subtypes can be divided into two forms (CHH-A and CHH-B). The CHH-A gene also comprises several isoforms which shared a high overall sequence identity. Although the MIH subtypes are postulated to have evolved from the CHH subtypes, the number of major MIH subtypes in each species has yet to be confirmed. While most of the genes consist of the basic plan of three exons and two introns, other alternative spliced variants have recently been described. Moreover, these alternative forms are usually expressed in non-eyestalk tissues. These findings suggest that these neuropeptides may have a broader spectrum of functions in crustaceans. The results from phylogenetic analysis suggest that the evolution of this group of neuropeptides occurs in a manner similar is to the gene duplication and mutation events hypothesized for the origin of the prolactin and growth hormone gene family of the vertebrate pituitary system.