Demonstration of substances immunologically related to the identified arthropod neuropeptides AKH/RPCH in the CNS of several invertebrate species

The evolution and nomenclature of GnRH-type and corazonin-type neuropeptide signaling systems

Gonadotropin-releasing hormone (GnRH) was first discovered in mammals on account of its effect in triggering pituitary release of gonadotropins and the importance of this discovery was recognized forty years ago in the award of the 1977 Nobel Prize for Physiology or Medicine. Investigation of the evolution of GnRH revealed that GnRH-type signaling systems occur throughout the chordates, including agnathans (e.g. lampreys) and urochordates (e.g. sea squirts). Furthermore, the discovery that adipokinetic hormone (AKH) is the ligand for a GnRH-type receptor in the arthropod Drosophila melanogaster provided evidence of the antiquity of GnRH-type signaling. However, the occurrence of other AKH-like peptides in arthropods, which include corazonin and AKH/corazonin-related peptide (ACP), has complicated efforts to reconstruct the evolutionary history of this family of related neuropeptides. Genome/transcriptome sequencing has revealed that both GnRH-type receptors and corazonin-type receptors occur in lophotrochozoan protostomes (annelids, mollusks) and in deuterostomian invertebrates (cephalochordates, hemichordates, echinoderms). Furthermore, peptides that act as ligands for GnRH-type and corazonin-type receptors have been identified in mollusks. However, what has been lacking is experimental evidence that distinct GnRH-type and corazonin-type peptide-receptor signaling pathways occur in deuterostomes. Importantly, we recently reported the identification of two neuropeptides that act as ligands for either a GnRH-type receptor or a corazonin-type receptor in an echinoderm species - the common European starfish Asterias rubens. Discovery of distinct GnRH-type and corazonin-type signaling pathways in this deuterostomian invertebrate has demonstrated for the first time that the evolutionarily origin of these paralogous systems can be traced to the common ancestor of protostomes and deuterostomes. Furthermore, lineage-specific losses of corazonin signaling (in vertebrates, urochordates and nematodes) and duplication of the GnRH signaling system in arthropods (giving rise to the AKH and ACP signaling systems) and quadruplication of the GnRH signaling system in vertebrates (followed by lineage-specific losses or duplications) accounts for the phylogenetic distribution of GnRH/corazonin-type peptide-receptor pathways in extant animals. Informed by these new insights, here we review the history of research on the evolution of GnRH/corazonin-type neuropeptide signaling. Furthermore, we propose a standardized nomenclature for GnRH/corazonin-type neuropeptides wherein peptides are either named "GnRH" or "corazonin", with the exception of the paralogous GnRH-type peptides that have arisen by gene duplication in the arthropod lineage and which are referred to as "AKH" (or red pigment concentrating hormone, "RCPH", in crustaceans) and "ACP".

Locust corpora cardiaca contain an inactive adipokinetic hormone

A neuropeptide from the migratory locust, Locusta migratoria, has been identified as a novel member of the family of adipokinetic hormones (AKHs). The peptide is probably synthesised in the brain because it is the first AKH found in the storage lobe, whilst the three 'classic' Locusta AKHs are present in the glandular lobe of the corpora cardiaca. In locusts, the peptide has no biological activity usually associated with AKHs. There is only 36-56% sequence identity with the three Lom-AKHs, but 78% identity with the Drosophila melanogaster AKH, Drm-HrTH. The new peptide is active in the American cockroach, Periplaneta americana, and was provisionally named 'L. migratoria hypertrehalosaemic hormone', Lom-HrTH; its biological role in locusts remains to be established. The high degree of identity with Drm-HrTH suggests that Lom-HrTH is an ancient molecule.

Regulation of crustacean neurosecretory cell activity

1. The X organ-sinus gland system is a conglomerate of 150-200 neurosecretory cells in the eyestalk of crustaceans. It is the source of a host of peptide neurohormones which partake in the control of a wide range of physiological functions. Distinct families of X organ peptides have been chemically characterized: (a) two chromatophorotropic hormones of small sizes, one of 8 residues and the other of 15-20 residues; and (b) three metabotropic hormones of high molecular weight (70-80 residues), related to the control of blood sugar levels, molting, and gonad activity. Some of these hormones have been identified only in crustaceans; others are common to various arthropod groups. A number of peptides orginally described in other zoological groups are also present in the X organ-sinus gland system; such is the case for members of the FMRF-amide family, enkephalins, and other peptides. 2. Cells specifically containing each hormone have been located in the X organ and some information is available on the cellular and molecular substrate of the biosynthesis, transport, storage, and release of various hormones. The electrical activity of X organ neurons has been recorded at the cell soma, arborizations, axons, and neurosecretory terminals. Conspicuous regional differences have been defined for the various patterns of activity, as well as the distribution of their underlying ion currents. 3. The release of hormones and the electrical activity of X organ neurons are regulated by environmental and endogenous influences, such as light and darkness, stress, and circadian rhythms. These influences appear to be mediated by a host of neurotransmitters/modulators, most noticeably, gamma-aminobutyric acid, 5-hydroxytryptamine and other amines, and enkephalins. Each of these mediators acts upon a definite ionic substrate(s) and exerts specific regulatory effects on X organ cell activity. A given neuron may be under the control of more than one neurotransmitter, and a transmitter may mediate different and even opposite influences on different neurons.

Localization of a crustacean hyperglycemic hormone-like immunoreactivity in the neuroendocrine system of Euscorpius carpathicus (L.) (Scorpionida, Chactidae)

The neuroendocrine system of Euscorpius carpathicus was immunohistochemically localized using a polyclonal antiserum raised against a purified Homarus americanus crustacean hyperglycemic hormone (Hoa-cHHA). There were cross-reactions in E. carpathicus procerebral and subesophageal neurosecretory cells, neurohemal organs, and intra- and extraganglionic neurosecretory tracts. Among the neurohemal structures, the Kwartirnikov's organ, the Tropfenkomplex, and the coxal disc reacted strongly. In Euscorpius, the differing results between adults and juveniles suggest neurosecretory variations related to developmental stage. These immunohistochemical observations suggest the presence of substances related to the cHH in scorpions; however, in this heterologous system, it is not at present possible to assess physiological significance.

Cockroach allatostatin-like immunoreactivity in the central nervous system of the freshwater snails Bulinus globosus (Planorbidae) and Stagnicola elodes (Lymnaeidae)

Allatostatin-like immunoreactivity was demonstrated in the central nervous system (CNS) neurons of the freshwater pulmonate snails Bulinus globosus (Planorbidae) and Stagnicola elodes (Lymnaeidae). Immunopositive neurons were localized using a monoclonal antibody highly specific to allatostatin I (APSGAQRLYGFGL-amide) from the cockroach Diploptera punctata. All CNS ganglia in both snail species contained immunopositive neurons. The pedal ganglia showed large numbers (80-100) of neurons in Bulinus and Stagnicola. Large numbers of immunopositive cells were also found in the cerebral (60) and buccal ganglia (20) of Bulinus. Other ganglia contained fewer immunopositive cells, but these cells were most concentrated in the cerebral (Stagnicola) and left parietal (Bulinus) ganglia and the visceral ganglia of both species. The high concentration of immunopositive cells in the pedal ganglia and axons demonstrable in the pedal nerves suggests that one possible function for a molluscan allatostatin-like peptide would be to modulate muscular function. Extract of Stagnicola CNS effected 50% inhibition of juvenile hormone synthesis by corpora allata of D. punctata at between 15 and 30 CNS equivalents, providing further evidence that the molluscan immunoreactive material is a peptide, or peptides, with sequence similarity to the active part of the D. punctata allatostatins.

Neuronal pathways of classical crustacean neurohormones in the central nervous system of the woodlouse, Oniscus asellus (L.)

Neuropeptide-immunoreactive neurons have been mapped by immunocytochemistry in whole-mount preparations and sections of the central nervous system of Oniscus asellus . We tested rabbit antisera against decapod crustacean hyperglycemic hormone (CHH), moult inhibiting hormone (MIH ), pigment dispersing hormone (PDH) and red pigment concentrating hormone (RPCH). four CHH- and three PDH-immunoreactive neurons localized in the superior median protocerebrum of the brain constitute neurosecretory pathways to the neurohaemal sinus gland. No immunoreactive structures have been detected with an antiserum against MIH of Carcinus maenus . Another, newly identified neurosecretory pathway is formed by a group of RPCH-immunoreactive neurons in the mandibular ganglion. These neurons project to the neurohaemal lateral cephalic nerve plexus, further PDH- and RPCH-immunoreactive neurons and fibres occur in the brain and the ventral nerve cord (VNC). Two groups of PDH-immunoreactive neurons supply brain and optic lobe neuropils, the bases of the ommatidia, and probably give rise to descending fibres innervating all VNC-neuropils. Two groups and five individuals of RPCH-immunoreactive neurons that innervate several brain neuropils or occur as ascending neurons in the VNC have been reconstructed. The CHH-immunoreactive neurons, and distinct types of PDH- and RPCH-immunoreactive neurons obviously belong to classical hormone-producing neurosecretory pathways. At least the CHH-immunoreactive cells seem to be part of an isopod homologue of the decapod X-organ. The existence of other PDH- and RPCH-immunoreactive interneurons suggests additional functions of these peptides as neurotransmitters or neuromodulators, which is in agreement with similar observations in the decapod central nervous system.

Quantitation of peptide hormone in single cultured secretory neurons of the crab, Cardisoma carnifex

The content of crustacean hyperglycemic hormone (CHH) in single cultured neurons of the crab Cardisoma carnifex was determined by a sensitive enzyme-linked immunosorbent assay (ELISA), using purified CHH (1-50 pg) of the crab Carcinus maenas as standard. The somata were dissociated from the group of approximately 150 peptidergic neurons that form the X-organ--sinus gland neuroendocrine system. As previously reported, the neurons show immediate regenerative outgrowth in defined culture conditions, and develop, generally, into one of two morphological types: cells that produce broad, lamelliform growth cones (veils), and others that are characterized by branching of neurites. In this study, all but one of 64 veiling cells taken after various times in culture up to 12 days contained CHH. They could be readily categorized as having "high" (> 33 pg; mean 86 +/- 5, S.E., n = 47) or "low" (< or = 33 pg; mean 22 +/- 2.5; n = 17) Carcinus CHH equivalents. Thus, CHH is associated with neurons showing veiling outgrowth, but veiling neurons with low CHH form a distinct, but not morphologically distinguishable group. They may contain an isoform of CHH with limited cross-reactivity. In 24 branching neurons assayed, Carcinus CHH equivalents averaged 7.2 +/- 2 pg. This figure includes 14 neurons in which CHH was undetectable, and one that had 40 pg of Carcinus CHH equivalents. There was no significant change of the hormone content in cells of either type during 6 days of culturing.

Isolation and primary structure of a novel adipokinetic peptide from the pyrgomorphid grasshopper, Phymateus leprosus

Using a heterologous bioassay, monitoring lipid increase in the haemolymph of migratory locusts, two peptides have been purified from methanolic extracts of corpora cardiaca of the pyrgomorphid grasshopper, Phymateus leprosus. The structures of both peptides were elucidated by a combination of Edman degradation, after deblocking the N-terminal pyroglutamic acid residue, and mass spectrometric techniques. One peptide is an octapeptide (pGlu-Leu-Asn-Phe-Ser-Thr-Gly-Trp-NH2) which also occurs in desert locusts; the second peptide is a novel decapeptide member of the AKH-family (pGlu-Leu-Thr-Phe-Thr-Pro-Asn-Trp-Gly-Ser-NH2).

The detection of AKH/HrTH-like peptides in Ascaridia galli and Ascaris suum using an insect hyperglycaemic bioassay

Evidence for the presence of adipokinetic hormone/hypertrehalosaemic hormone (AKH/HrTH)-like peptides in the parasitic nematodes Ascaridia galli and Ascaris suum has been obtained using insect bioassays which measure hyperglycaemic responses to peptides belonging to the AKH/HrTH family of insect hormones. A peptide fraction extracted from heads and tails of Ascaridia galli evoked a dose-dependent hyperglycaemic response when injected into the cockroach, Periplaneta americana. Maximal bioactivity was obtained with material that was equivalent to 38 mg (wet weight) of nematode. Bioactivity appeared to be highest in extracts from heads and tails of both male and female worms and could be fractionated into at least three peaks of hyperglycaemic activity by reversed-phase high-performance liquid chromatography. An extract from heads and tails of A. suum also evoked a hyperglycaemic response when injected into the cockroach, Blaberus discoidalis. The bioactivity was inactivated on incubation with pure endopeptidase 24.11, confirming the peptidic nature of the bioactive material. These results provide evidence for the existence of peptides related to the insect AKH/HrTH family of peptides in parasitic nematodes.

Localization of messenger RNAs encoding crustacean hyperglycemic hormone and gonad inhibiting hormone in the X-organ sinus gland complex of the lobster Homarus americanus

The localization of messenger RNAs encoding the crustacean hyperglycemic hormone, involved in regulation of carbohydrate metabolism and the gonad inhibiting hormone, which inhibits vitellogenesis, was studied in the eyestalk of the lobster Homarus americanus using complementary RNA probes for in situ hybridization. For the detection of gonad inhibiting hormone messenger RNA, we cloned and sequenced a partial complementary DNA encoding lobster gonad inhibiting hormone and for crustacean hyperglycemic hormone messenger RNA detection an available complementary DNA was used. This approach reveals that there is a frequent but inconsistent cellular co-localization of the two neurohormones. Furthermore, our data show that male lobsters contain an equal number of neuroendocrine gonad inhibiting hormone cells as female lobsters. An additional study, involving the use of in situ hybridization in combination with immunocytochemistry, shows that the synthetic activity of the crustacean hyperglycemic hormone- and gonad inhibiting hormone-producing cells can be followed at the messenger RNA as well as the protein level. This reveals that when strong immunostaining is present, the messenger RNA staining is usually weak or absent and vice versa. In conclusion, the presence of cells, containing only gonad inhibiting hormone messenger RNA or only crustacean hyperglycemic hormone messenger RNA, indicates that lobster crustacean hyperglycemic hormone and gonad inhibiting hormone originate from two different precursors. Co-localization of the two neurohormone messenger RNAs confirms the co-localization at the peptidergic level found by immunocytochemistry and thus these findings were not due to cross-reactions between the two antisera.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptidergic neurons of the crab, Cardisoma carnifex, in defined culture maintain characteristic morphologies under a variety of conditions

Peptidergic neurons dissociated from the neurosecretory cell group, the X-organ, of adult crabs (Cardisoma carnifex) show immediate outgrowth on unconditioned plastic dishes in defined medium. Most of the neurons can be categorized as small cells, branchers or veilers. A fourth type, "superlarge," found occasionally, has a soma diameter greater than 40 microns and multipolar outgrowth. We report here the effects on morphology that follow alterations of the standard defined culturing conditions. The three common types of neurons are present when cells are grown in crab saline or saline with L-glutamine and glucose (saline medium). Changes of pH between 7.0 to 7.9 have no effect. Osmolarity changes cause transient varicosities in small cells. In some veilers, pits rapidly appear in the veil and then disappear within 35 min. In cultures at 26 degrees C instead of 22 degrees C, veilers extend processes from the initial veil in a pattern similar to branchers, and the processes of adjacent veilers sometimes form appositions. Culturing in higher [K+]o medium ([K+]o = 15-110 mM; standard = 11 mM) has no long-term effect, but growth is arrested by [K+]o greater than 30 mM. Cultures were also grown in media in which [Ca2+]o ranged from 0.1 microM to 26 mM (standard = 13 mM). Outgrowth occurred from all neuronal types in all [Ca2+]o tested. Thus, the expression of different outgrowth morphologies occurs under a wide variety of culturing conditions.

Binding proteins for a peptide hormone in the shrimp, Sicyonia ingentis: evidence from photoaffinity labeling with red pigment concentrating hormone analogs

Two photoaffinity analogs of the crustacean erythrophore (red pigment) concentrating hormone (RPCH) have been synthesized and shown to cause pigment concentration in the shrimp Sicyonia ingentis. These two modified oligopeptides have azidosalicylamide groups which allow introduction of an 125I label and enable photochemically induced covalent attachment to a specific binding site. Incubation of [125I]-ASA-Glu1-CC-2 with the 100,000g membrane pellet and cytosol fraction from epidermis, eyestalks, muscle, and central nervous system (CNS), followed by irradiation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and autoradiography results in covalent modification of certain protein bands in the membranes of selected tissues. Two such proteins were observed in neural tissues and showed competitive displacement by excess RPCH, indicative of specific high-affinity binding. This is the first report of peptide hormone-binding proteins in an invertebrate and provides further evidence of a role for RPCH as a neurotransmitter in the CNS.

The presence of peptides related to the adipokinetic hormone/red pigment-concentrating hormone family in the nematode, Panagrellus redivivus

Immunocytochemistry using polyclonal antisera raised to fragments or derivatives of locust adipokinetic hormone (AKH) I and IIs (Schooneveld et al., 1983, 1985, 1986) selectively stained cells in the nervous system of the free-living nematode, Panagrellus redivivus. Antiserum 528 (raised to the C-terminus of AKH IIs) stained the dorsal cephalic papillary cell bodies and the anterior nerve ring. Fibres in the lateral cords were stained with antiserum 241 that recognises the C-terminus of AKH I. Substances reacting to antisera 433 (raised to the N-terminal sequence of AKH I and IIs) 528 and 241 were present in the preanal ganglion and associated ventral nerve fibres. In males, all three antisera stained fibres leading to the base of the spicules. A peptide fraction from whole P. redivivus evoked an adipokinetic response in the locust, Schistocera gregaria which was dose dependent and was abolished by treatment with endopeptidase 24:11 but not by boiling or by incubation with leucine aminopeptidase. The adipokinetic activity was reduced by over 70% on incubation of the peptide fraction with pyroglutamyl aminopeptidase. The same fraction induced hyperglycaemia when injected into the cockroach, Periplaneta americana. These results are consistent with the existence in P. redivivus of peptides that are structurally related to the arthropod adipokinetic hormone/red pigment-concentrating hormone (AKH/RPCH) family.

L-(3H) glutamate binding to a membrane preparation from the optic lobe of the giant freshwater prawn Macrobrachium rosenbergii de Man

Membrane preparation from the optic lobe of the giant freshwater prawn, Macrobrachium rosenbergii de Man, was examined for the presence of specific L-(3H) glutamate binding. The optic lobes were isolated from live animals. The tissue was homogenized and the membrane fraction isolated by differential centrifugation. The membrane suspension was incubated with 10-1,000 nM of L-(3H) glutamate at 37 degrees C for 60 min. Nonspecific binding was determined by incubating the mixture with 100 microM L-glutamate. L-(3H) glutamate specifically bound to the membrane fraction with a dissociation equilibrium constant (Kd) of 205 nM and maximum number of binding sites (Bmax) of 2.04 n mol/mg protein. By using LIGAND computerized program, the saturation isotherm binding pattern indicates a single type of binding. To determine the type of glutamate receptors, competitive inhibition and IC50 of several glutamate agonists and antagonists were determined. The study reveals a metabotropic type of binding site.

The fruitfly Drosophila melanogaster contains a novel charged adipokinetic-hormone-family peptide

A member of the RPCH/AKH (red-pigment-concentrating hormone/adipokinetic hormone) family of arthropod neuropeptides was identified in the fruitfly Drosophila melanogaster, and its structure was determined by automated Edman degradation and m.s. using fast-atom-bombardment ionization and a tandem hybrid instrument capable of high sensitivity. The sequence of this peptide, which we call 'DAKH', is pGlu-Leu-Thr-Phe-Ser-Pro-Asp-Trp-NH2 (where pGlu is pyroglutamic acid and Trp-NH2 is tryptophan carboxyamide). H.p.l.c. analyses of extracts of the three body segments revealed that more than 80% of the peptide is contained in the thorax. Although DAKH is typical of family members in its general structure and distribution in the animal, it is unique in containing a residue which is charged under physiological conditions. The evolutionary significance of this change is considered.

Continuous darkness stimulates body growth of the juvenile giant freshwater prawn, Macrobrachium rosenbergii de Man

The effect of photoperiod on growth of juvenile giant freshwater prawns, Macrobrachium rosenbergii de Man, was tested. The prawns were divided into four groups and each group was reared under one of the following light-dark conditions: continuous darkness (L0:D24), 12 hr light: 12 hr dark (L12:D12), 16 hr light: 8 hr dark (L16:D8), and 20 hr light: 4 hr dark (L20:D4). Body size was determined at the age of 45, 75, and 110 days by measuring total length, orbital length, and carapace length; body weight was determined at the age of 110 days. At 110 days of age, the prawns reared under L0:D24 photoperiod were significantly longer and heavier than those reared under other light-dark conditions. The survival rate of the prawns reared under L0:D24 photoperiod was also higher than that of other groups. This study indicates a positive effect of continuous darkness on growth and survival rate of juvenile giant freshwater prawns, M. rosenbergii.

Identification and characterization of adipokinetic hormone (Locusta migratoria)-like immunoreactivity in the human cerebrospinal fluid

Using an antiserum raised against locust adipokinetic hormone I, considerable quantity of adipokinetic hormone-like immunoreactivity was demonstrated in the human cerebrospinal fluid. The immunoreactivity was characterized by gel permeation and high performance liquid chromatography. The main immunoreactive component in the cerebrospinal fluid coeluted with adipokinetic hormone I. These results suggest that adipokinetic hormone may contribute to the neuronal function in the human central nervous system.

Crustacean peptidergic neurons in culture show immediate outgrowth in simple medium

The survival and outgrowth of neurons in culture has usually required conditioning factors. We now report that crustacean neurons, taken from the peptidergic neurosecretory system of the eyestalk of crabs (Cardisoma carnifex) and lobsters (Panulirus marginatus), show immediate outgrowth, sustained for a week or more, in defined medium as simple as physiological saline with glucose and glutamine. The neurons show peptide hormone immunoreactivity that is prominent at growth cones, exhibit differences in form correlated with their immunoreactivity, release peptides to the medium, and have voltage-dependent currents, including a well-sustained Ca current. Cd blocks secretion, growth, and the Ca current. Peptidergic secretory neurons may be able to utilize existing membrane from their store of granules and already active synthetic, transport, and secretory mechanisms for immediate outgrowth.