Mass spectrometric characterization and physiological actions of GAHKNYLRFamide, a novel FMRFamide-like peptide from crabs of the genus Cancer

New insights from small rhythmic circuits

Small rhythmic circuits, such as those found in invertebrates, have provided fundamental insights into how circuit dynamics depend on individual neuronal and synaptic properties. Degenerate circuits are those with different network parameters and similar behavior. New work on degenerate circuits and their modulation illustrates some of the rules that help maintain stable and robust circuit function despite environmental perturbations. Advances in neuropeptide isolation and identification provide enhanced understanding of the neuromodulation of circuits for behavior. The advent of molecular studies of mRNA expression provides new insight into animal-to-animal variability and the homeostatic regulation of excitability in neurons and networks.

A genetically encoded tool for reconstituting synthetic modulatory neurotransmission and reconnect neural circuits in vivo

Chemogenetic and optogenetic tools have transformed the field of neuroscience by facilitating the examination and manipulation of existing circuits. Yet, the field lacks tools that enable rational rewiring of circuits via the creation or modification of synaptic relationships. Here we report the development of HySyn, a system designed to reconnect neural circuits in vivo by reconstituting synthetic modulatory neurotransmission. We demonstrate that genetically targeted expression of the two HySyn components, a Hydra-derived neuropeptide and its receptor, creates de novo neuromodulatory transmission in a mammalian neuronal tissue culture model and functionally rewires a behavioral circuit in vivo in the nematode Caenorhabditis elegans. HySyn can interface with existing optogenetic, chemogenetic and pharmacological approaches to functionally probe synaptic transmission, dissect neuropeptide signaling, or achieve targeted modulation of specific neural circuits and behaviors.

Engineering de novo synapse-like connections between neurons could enhance our understanding of neuronal circuits and how they generate behaviour. The authors present a two-component system that creates synthetic neuromodulatory connections to manipulate intracellular Ca2+ levels in in vivo neural circuits.

To what extent may peptide receptor gene diversity/complement contribute to functional flexibility in a simple pattern-generating neural network?

Peptides are known to contribute to central pattern generator (CPG) flexibility throughout the animal kingdom. However, the role played by receptor diversity/complement in determining this functional flexibility is not clear. The stomatogastric ganglion (STG) of the crab, Cancer borealis, contains CPGs that are models for investigating peptidergic control of rhythmic behavior. Although many Cancer peptides have been identified, their peptide receptors are largely unknown. Thus, the extent to which receptor diversity/complement contributes to modulatory flexibility in this system remains unresolved. Here, a Cancer mixed nervous system transcriptome was used to determine the peptide receptor complement for the crab nervous system as a whole. Receptors for 27 peptide families, including multiple receptors for some groups, were identified. To increase confidence in the predicted sequences, receptors for allatostatin-A, allatostatin-B, and allatostatin-C were cloned, sequenced, and expressed in an insect cell line; as expected, all three receptors trafficked to the cell membrane. RT-PCR was used to determine whether each receptor was expressed in the Cancer STG. Transcripts for 36 of the 46 identified receptors were amplified; these included at least one for each peptide family except RYamide. Finally, two peptides untested on the crab STG were assessed for their influence on its motor outputs. Myosuppressin, for which STG receptors were identified, exhibited clear modulatory effects on the motor patterns of the ganglion, while a native RYamide, for which no STG receptors were found, elicited no consistent modulatory effects. These data support receptor diversity/complement as a major contributor to the functional flexibility of CPGs.

Neuropeptide discovery in Proasellus cavaticus: Prediction of the first large-scale peptidome for a member of the Isopoda using a publicly accessible transcriptome

In silico transcriptome mining is one of the most effective methods for neuropeptide discovery in crustaceans, particularly for species that are small, rare or from geographically inaccessible habitats that make obtaining the large pools of tissue needed for other peptide discovery platforms impractical. Via this approach, large peptidomes have recently been described for members of many of the higher crustacean taxa, one notable exception being the Isopoda; no peptidome has been predicted for any member of this malacostracan order. Using a publicly accessible transcriptome for the isopod Proasellus cavaticus, a subcentimeter subterranean ground water dweller, the first in silico-predicted peptidome for a member of the Isopoda is presented here. BLAST searches employing known arthropod neuropeptide pre/preprohormone queries identified 49 transcripts as encoding putative homologs within the P. cavaticus transcriptome. The proteins deduced from these transcripts allowed for the prediction of 171 distinct mature neuropeptides. The P. cavaticus peptidome includes members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, diuretic hormone 31, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone α2, leucokinin, myosuppressin, neuroparsin, neuropeptide F, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, sulfakinin, tachykinin-related peptide and trissin families, as well as many linker/precursor-related sequences that may or may not represent additional bioactive molecules. Interestingly, many of the predicted P. cavaticus neuropeptides possess structures identical (or nearly so) to those previously described from members of several other malacostracan orders, i.e., the Decapoda, Amphipoda and Euphausiacea, a finding that suggests broad phylogenetic conservation of bioactive peptide structures, and possibly functions, may exist within the Malacostraca.

Peptidergic signaling in the crab Cancer borealis: Tapping the power of transcriptomics for neuropeptidome expansion

The crab Cancer borealis has long been used as a model for understanding neural control of rhythmic behavior. One significant discovery made through its use is that even numerically simple neural circuits are capable of producing an essentially infinite array of distinct motor outputs via the actions of locally released and circulating neuromodulators, the largest class being peptides. While much work has focused on elucidating the peptidome of C. borealis, no investigation has used in silico transcriptome mining for peptide discovery in this species, a strategy proven highly effective for identifying neuropeptides in other crustaceans. Here, we mined a C. borealis neural transcriptome for putative peptide-encoding transcripts, and predicted 200 distinct mature neuropeptides from the proteins deduced from these sequences. The identified peptides include isoforms of allatostatin A, allatostatin B, allatostatin C, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31 (DH31), diuretic hormone 44 (DH44), FMRFamide-like peptide, GSEFLamide, HIGSLYRamide, insulin-like peptide (ILP), intocin, leucokinin, neuroparsin, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, short neuropeptide F and SIFamide. While some of the predicted peptides were known previously from C. borealis, most (159) are new discoveries for the species, e.g., the isoforms of CCHamide, DH31, DH44, GSEFLamide, ILP, intocin and neuroparsin, which are the first members of these peptide families identified from C. borealis. Collectively, the peptides predicted here approximately double the peptidome known for C. borealis, and in so doing provide an expanded platform from which to launch new investigations of peptidergic neuromodulation in this species.

The complexity of small circuits: the stomatogastric nervous system

The crustacean stomatogastric nervous system is a long-standing test bed for studies of circuit dynamics and neuromodulation. We give a brief update on the most recent work on this system, with an emphasis on the broader implications for understanding neural circuits. In particular, we focus on new findings underlining that different levels of dynamics taking place at different time scales all interact in multiple ways. Dynamics due to synaptic and intrinsic neuronal properties, neuromodulation, and long-term gene expression-dependent regulation are not independent, but influence each other. Extensive research on the stomatogastric system shows that these dynamic interactions convey robustness to circuit operation, while facilitating the flexibility of producing multiple circuit outputs.

Inter-animal variability in the effects of C-type allatostatin on the cardiac neuromuscular system in the lobster Homarus americanus

Although the global effects of many modulators on pattern generators are relatively consistent among preparations, modulators can induce different alterations in different preparations. We examined the mechanisms that underlie such variability in the modulatory effects of the peptide C-type allatostatin (C-AST; pQIRYHQCYFNPISCF) on the cardiac neuromuscular system of the lobster Homarus americanus. Perfusion of C-AST through the semi-intact heart consistently decreased the frequency of ongoing contractions. However, the effect of C-AST on contraction amplitude varied between preparations, decreasing in some preparations and increasing in others. To investigate this variable effect, we examined the effects of C-AST both peripherally and centrally. When contractions of the myocardium were elicited by controlled stimuli, C-AST did not alter heart contraction at the periphery (myocardium or neuromuscular junction) in any hearts. However, when applied either to the semi-intact heart or to the cardiac ganglion (CG) isolated from hearts that responded to C-AST with increased contraction force, C-AST increased both motor neuron burst duration and the number of spikes per burst by about 25%. In contrast, CG output was increased only marginally in hearts that responded to C-AST with a decrease in contraction amplitude, suggesting that the decrease in amplitude in those preparations resulted from decreased peripheral facilitation. Our data suggest that the differential effects of a single peptide on the cardiac neuromuscular system are due solely to differential effects of the peptide on the pattern generator; the extent to which the peptide induces increased burst duration is crucial in determining its overall effect on the system.

Distribution and physiological effects of B-type allatostatins (myoinhibitory peptides, MIPs) in the stomatogastric nervous system of the crab Cancer borealis

The crustacean stomatogastric ganglion (STG) is modulated by a large number of amines and neuropeptides that are found in descending pathways from anterior ganglia or reach the STG via the hemolymph. Among these are the allatostatin (AST) B types, also known as myoinhibitory peptides (MIPs). We used mass spectrometry to determine the sequences of nine members of the AST-B family of peptides that were found in the stomatogastric nervous system of the crab Cancer borealis. We raised an antibody against Cancer borealis allatostatin-B1 (CbAST-B1; VPNDWAHFRGSWa) and used it to map the distribution of CbAST-B1-like immunoreactivity (-LI) in the stomatogastric nervous system. CbAST-B1-LI was found in neurons and neuropil in the commissural ganglia (CoGs), in somata in the esophageal ganglion (OG), in fibers in the stomatogastric nerve (stn), and in neuropilar processes in the STG. CbAST-B1-LI was blocked by preincubation with 10(-6) M CbAST-B1 and was partially blocked by lower concentrations. Electrophysiological recordings of the effects of CbAST-B1, CbAST-B2, and CbAST-B3 on the pyloric rhythm of the STG showed that all three peptides inhibited the pyloric rhythm in a state-dependent manner. Specifically, all three peptides at 10(-8) M significantly decreased the frequency of the pyloric rhythm when the initial frequency of the pyloric rhythm was below 0.6 Hz. These data suggest important neuromodulatory roles for the CbAST-B family in the stomatogastric nervous system.

Crustacean neuroendocrine systems and their signaling agents

Decapod crustaceans have long served as important models for the study of neuroendocrine signaling. For example, the process of neurosecretion was first formally demonstrated by using a member of this order. In this review, the major decapod neuroendocrine organs are described, as are their phylogenetic conservation and neurochemistry. In addition, recent advances in crustacean neurohormone discovery and tissue mapping are discussed, as are several recent advances in our understanding of hormonal control in this group of animals.

Crustacean neuropeptides

Crustaceans have long been used for peptide research. For example, the process of neurosecretion was first formally demonstrated in the crustacean X-organ-sinus gland system, and the first fully characterized invertebrate neuropeptide was from a shrimp. Moreover, the crustacean stomatogastric and cardiac nervous systems have long served as models for understanding the general principles governing neural circuit functioning, including modulation by peptides. Here, we review the basic biology of crustacean neuropeptides, discuss methodologies currently driving their discovery, provide an overview of the known families, and summarize recent data on their control of physiology and behavior.

A review of FMRFamide- and RFamide-like peptides in metazoa

Neuropeptides are a diverse class of signalling molecules that are widely employed as neurotransmitters and neuromodulators in animals, both invertebrate and vertebrate. However, despite their fundamental importance to animal physiology and behaviour, they are much less well understood than the small molecule neurotransmitters. The neuropeptides are classified into families according to similarities in their peptide sequence; and on this basis, the FMRFamide and RFamide-like peptides, first discovered in molluscs, are an example of a family that is conserved throughout the animal phyla. In this review, the literature on these neuropeptides has been consolidated with a particular emphasis on allowing a comparison between data sets in phyla as diverse as coelenterates and mammals. The intention is that this focus on the structure and functional aspects of FMRFamide and RFamide-like neuropeptides will inform understanding of conserved principles and distinct properties of signalling across the animal phyla.

Identification of a calcitonin-like diuretic hormone that functions as an intrinsic modulator of the American lobster, Homarus americanus, cardiac neuromuscular system

In insects, a family of peptides with sequence homology to the vertebrate calcitonins has been implicated in the control of diuresis, a process that includes mixing of the hemolymph. Here, we show that a member of the insect calcitonin-like diuretic hormone (CLDH) family is present in the American lobster, Homarus americanus, serving, at least in part, as a powerful modulator of cardiac output. Specifically, during an ongoing EST project, a transcript encoding a putative H. americanus CLDH precursor was identified; a full-length cDNA was subsequently cloned. In silico analyses of the deduced prepro-hormone predicted the mature structure of the encoded CLDH to be GLDLGLGRGFSGSQAAKHLMGLAAANFAGGPamide (Homam-CLDH), which is identical to a known Tribolium castaneum peptide. RT-PCR tissue profiling suggests that Homam-CLDH is broadly distributed within the lobster nervous system, including the cardiac ganglion (CG), which controls the movement of the neurogenic heart. RT-PCR analysis conducted on pacemaker neuron- and motor neuron-specific cDNAs suggests that the motor neurons are the source of the CLDH message in the CG. Perfusion of Homam-CLDH through the isolated lobster heart produced dose-dependent increases in both contraction frequency and amplitude and a dose-dependent decrease in contraction duration, with threshold concentrations for all parameters in the range 10(-11) to 10(-10) mol l(-1) or less, among the lowest for any peptide on this system. This report is the first documentation of a decapod CLDH, the first demonstration of CLDH bioactivity outside the Insecta, and the first detection of an intrinsic neuropeptide transcript in the crustacean CG.

The peptide hormone pQDLDHVFLRFamide (crustacean myosuppressin) modulates the Homarus americanus cardiac neuromuscular system at multiple sites

pQDLDHVFLRFamide is a highly conserved crustacean neuropeptide with a structure that places it within the myosuppressin subfamily of the FMRFamide-like peptides. Despite its apparent ubiquitous conservation in decapod crustaceans, the paracrine and/or endocrine roles played by pQDLDHVFLRFamide remain largely unknown. We have examined the actions of this peptide on the cardiac neuromuscular system of the American lobster Homarus americanus using four preparations: the intact animal, the heart in vitro, the isolated cardiac ganglion (CG), and a stimulated heart muscle preparation. In the intact animal, injection of myosuppressin caused a decrease in heartbeat frequency. Perfusion of the in vitro heart with pQDLDHVFLRFamide elicited a decrease in the frequency and an increase in the amplitude of heart contractions. In the isolated CG, myosuppressin induced a hyperpolarization of the resting membrane potential of cardiac motor neurons and a decrease in the cycle frequency of their bursting. In the stimulated heart muscle preparation, pQDLDHVFLRFamide increased the amplitude of the induced contractions, suggesting that myosuppressin modulates not only the CG, but also peripheral sites. For at least the in vitro heart and the isolated CG, the effects of myosuppressin were dose-dependent (10(-9) to 10(-6) mol l(-1) tested), with threshold concentrations (10(-8)-10(-7) mol l(-1)) consistent with the peptide serving as a circulating hormone. Although cycle frequency, a parameter directly determined by the CG, consistently decreased when pQDLDHVFLRFamide was applied to all preparation types, the magnitudes of this decrease differed, suggesting the possibility that, because myosuppressin modulates the CG and the periphery, it also alters peripheral feedback to the CG.

Combining in silico transcriptome mining and biological mass spectrometry for neuropeptide discovery in the Pacific white shrimp Litopenaeus vannamei

The shrimp Litopenaeus vannamei is arguably the most important aquacultured crustacean, being the subject of a multi-billion dollar industry worldwide. To extend our knowledge of peptidergic control in this species, we conducted an investigation combining transcriptomics and mass spectrometry to identify its neuropeptides. Specifically, in silico searches of the L. vannamei EST database were conducted to identify putative prepro-hormone-encoding transcripts, with the mature peptides contained within the deduced precursors predicted via online software programs and homology to known isoforms. MALDI-FT mass spectrometry was used to screen tissue fragments and extracts via accurate mass measurements for the predicted peptides, as well as for known ones from other species. ESI-Q-TOF tandem mass spectrometry was used to de novo sequence peptides from tissue extracts. In total 120 peptides were characterized using this combined approach, including 5 identified both by transcriptomics and by mass spectrometry (e.g. pQTFQYSRGWTNamide, Arg(7)-corazonin, and pQDLDHVFLRFamide, a myosuppressin), 49 predicted via transcriptomics only (e.g. pQIRYHQCYFNPISCF and pQIRYHQCYFIPVSCF, two C-type allatostatins, and RYLPT, authentic proctolin), and 66 identified solely by mass spectrometry (e.g. the orcokinin NFDEIDRAGMGFA). While some of the characterized peptides were known L. vannamei isoforms (e.g. the pyrokinins DFAFSPRLamide and ADFAFNPRLamide), most were novel, either for this species (e.g. pEGFYSQRYamide, an RYamide) or in general (e.g. the tachykinin-related peptides APAGFLGMRamide, APSGFNGMRamide and APSGFLDMRamide). Collectively, our data not only expand greatly the number of known L. vannamei neuropeptides, but also provide a foundation for future investigations of the physiological roles played by them in this commercially important species.

Monitoring neuropeptides in vivo via microdialysis and mass spectrometry

Neuropeptides are important signaling molecules that regulate many essential physiological processes. Microdialysis offers a way to sample neuropeptides in vivo. When combined with liquid chromatography-mass spectrometry detection, many known and unknown neuropeptides can be identified from a live organism. This chapter describes sample preparation techniques and general strategies for the mass spectral analysis of neuropeptides collected via microdialysis sampling. Methods for the in vitro microdialysis of a neuropeptide standard as well as the in vivo microdialysis sampling of neuropeptides from a live crab are described.

Correlations in ion channel mRNA in rhythmically active neurons

Background

To what extent do identified neurons from different animals vary in their expression of ion channel genes? In neurons of the same type, is ion channel expression highly variable and/or is there any relationship between ion channel expression that is conserved?

Methodology/Principal Findings

To address these questions we measured ion channel mRNA in large cells (LCs) of the crab cardiac ganglion. We cloned a calcium channel, caco, and a potassium channel, shaker. Using single-cell quantitative PCR, we measured levels of mRNA for these and 6 other different ion channels in cardiac ganglion LCs. Across the population of LCs we measured 3–9 fold ranges of mRNA levels, and we found correlations in the expression of many pairs of conductances

Conclusions/Significance

In previous measurements from the crab stomatogastric ganglion (STG), ion channel expression was variable, but many pairs of channels had correlated expression. However, each STG cell type had a unique combination of ion channel correlations. Our findings from the crab cardiac ganglion are similar, but the correlations in the LCs are different from those in STG neurons, supporting the idea that such correlations could be markers of cell identity or activity.

Expanding the Crustacean neuropeptidome using a multifaceted mass spectrometric approach

Jonah crab Cancer borealis is an excellent, long-served model organism for many areas of physiology, including the study of endocrinology and neurobiology. Characterizing the neuropeptides present in its nervous system provides the first critical step toward understanding the physiological roles of these complex molecules. Multiple mass spectral techniques were used to comprehensively characterize the neuropeptidome in C. borealis, including matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), MALDI time-of-flight (TOF)/TOF MS and nanoflow liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nanoLC-ESI-Q-TOF MS/MS). To enhance the detection signals and expand the dynamic range, direct tissue analysis, tissue extraction, capillary electrophoresis (CE) and off-line HPLC separation have also been employed. In total, 142 peptides were identified, including 85 previously known C. borealis peptides, 22 peptides characterized previously from other decapods, but new to this species, and 35 new peptides de novo sequenced for the first time in this study. Seventeen neuropeptide families were revealed including FMRFamide-related peptide (FaRP), allatostatin (A and B type), RYamide, orcokinin, orcomyotropin, proctolin, crustacean cardioactive peptide (CCAP), crustacean hyperglycemic hormone precursor-related peptide (CPRP), crustacean hyperglycemic hormone (CHH), corazonin, pigment-dispersing hormone (PDH), tachykinin, pyrokinin, SIFamide, red pigment concentrating hormone (RPCH) and HISGLYRamide. Collectively, our results greatly increase the number and expand the coverage of known C. borealis neuropeptides, and thus provide a stronger framework for future studies on the physiological roles played by these molecules in this important model organism.

Presence and distribution of FMRFamide-like immunoreactivity in the cyprid of the barnacle Balanus amphitrite (Cirripedia, Crustacea)

The presence and distribution of FMRFamide-like peptides (FLPs) in the cyprid larvae of the barnacle Balanus amphitrite were investigated using immunohistochemical methods. Barnacles are considered to be one of the most important constituents of animal fouling communities, and the cyprid stage is specialized for settlement and metamorphosis in to the sessile adult condition. FLPs immunoreactive (IR) neuronal cell bodies were detected in both the central and the peripheral nervous system. One bilateral group of neurons somata was immunodetected in the brain, and IR nerve fibers were observed in the neuropil area and optic lobes. Intense immunostaining was also observed in the frontal filament complex: frontal filament tracts leaving the optic lobes and projecting towards the compound eyes, swollen nerve endings in the frontal filament vesicles, and thin nerve endings in the external frontal filament. Thin IR nerve fibers were also present in the cement glands. Two pairs of neuronal cell bodies were immunodetected in the posterior ganglion; some of their axons appear to project to the cirri. FLPs IR neuronal cell bodies were also localized in the wall of the dilated midgut and in the narrow hindgut; their processes surround the gut wall and allow gut neurons to synapse with one another. Our data demonstrated the presence of FLPs IR substances in the barnacle cyprid. We hypothesize that these peptides act as integrators in the central nervous system, perform neuromuscular functions for thoracic limbs, trigger intestinal movements and, at the level of the frontal filament, play a neurosecretory role.

Combining microdialysis, NanoLC-MS, and MALDI-TOF/TOF to detect neuropeptides secreted in the crab, Cancer borealis

Microdialysis is a useful technique for sampling neuropeptides in vivo, and decapod crustaceans are important model organisms for studying how these peptides regulate physiological processes. However, to date, no microdialysis procedure has been reported for sampling neuropeptides from crustaceans. Here we report the first application of microdialysis to sample neuropeptides from the hemolymph of the crab, Cancer borealis. Microdialysis probes were implanted into the pericardial region of live crabs, and the resulting dialysates were desalted, concentrated, and analyzed by LC-ESI-QTOF and MALDI-TOF/TOF mass spectrometry. Analysis of in vitro microdialysates of hemolymph revealed more neuropeptides and fewer protein fragments than hemolymph prepared by typical analysis methods. Mass spectra of in vivo dialysates displayed neuropeptides from 10 peptide families, including the RFamide, allatostatin, and orcokinin families. In addition, GAHKNYLRFa, SDRNFLRFa, and TNRNFLRFa were sequenced from hemolymph dialysates. The detection of these neuropeptides in the hemolymph suggests that they are functioning as hormones as well as neuromodulators. In vivo microdialysis offers the capability to further study these and other neuropeptides in crustacean hemolymph, complementing current tissue-based studies and extending our knowledge of hormonal regulation of physiological states.

Mass spectral characterization of peptide transmitters/hormones in the nervous system and neuroendocrine organs of the American lobster Homarus americanus

The American lobster Homarus americanus is a decapod crustacean with both high economic and scientific importance. To facilitate physiological investigations of peptide transmitter/hormone function in this species, we have used matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and nanoscale liquid chromatography coupled to electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nanoLC-ESI-Q-TOF MS/MS) to elucidate the peptidome present in its nervous system and neuroendocrine organs. In total, 84 peptides were identified, including 27 previously known H. americanus peptides (e.g., VYRKPPFNGSIFamide [Val(1)-SIFamide]), 23 peptides characterized previously from other decapods, but new to the American lobster (e.g., pQTFQYSRGWTNamide [Arg(7)-corazonin]), and 34 new peptides de novo sequenced/detected for the first time in this study. Of particular note are a novel B-type allatostatin (TNWNKFQGSWamide) and several novel FMRFamide-related peptides, including an unsulfated analog of sulfakinin (GGGEYDDYGHLRFamide), two myosuppressins (QDLDHVFLRFamide and pQDLDHVFLRFamide), and a collection of short neuropeptide F isoforms (e.g., DTSTPALRLRFamide and FEPSLRLRFamide). Our data also include the first detection of multiple tachykinin-related peptides in a non-brachyuran decapod, as well as the identification of potential individual-specific variants of orcokinin and orcomyotropin-related peptide. Taken collectively, our results not only expand greatly the number of known H. americanus neuropeptides, but also provide a framework for future studies on the physiological roles played by these molecules in this commercially and scientifically important species.

SIFamide peptides in clawed lobsters and freshwater crayfish (Crustacea, Decapoda, Astacidea): a combined molecular, mass spectrometric and electrophysiological investigation

Recently, we identified the peptide VYRKPPFNGSIFamide (Val(1)-SIFamide) in the stomatogastric nervous system (STNS) of the American lobster Homarus americanus using matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry (MALDI-FTMS). Given that H. americanus is the only species thus far shown to possess this peptide, and that a second SIFamide isoform, Gly(1)-SIFamide, is broadly conserved in other decapods, including another astacidean, the crayfish Procambarus clarkii, we became interested both in confirming our identification of Val(1)-SIFamide via molecular methods and in determining the extent to which this isoform is conserved within other members of the infraorder Astacidea. Here, we present the identification and characterization of an H. americanus prepro-SIFamide cDNA that encodes the Val(1) isoform. Moreover, we demonstrate via MALDI-FTMS the presence of Val(1)-SIFamide in a second Homarus species, Homarus gammarus. In contrast, only the Gly(1) isoform was detected in the other astacideans investigated, including the lobster Nephrops norvegicus, a member of the same family as Homarus, and the crayfish Cherax quadricarinatus, P. clarkii and Pacifastacus leniusculus, which represent members of each of the extant families of freshwater astacideans. These results suggest that Val(1)-SIFamide may be a genus (Homarus)-specific isoform. Interestingly, both Val(1)- and Gly(1)-SIFamide possess an internal dibasic site, Arg(3)-Lys(4), raising the possibility of the ubiquitously conserved isoform PPFNGSIFamide. However, this octapeptide was not detected via MALDI-FTMS in any of the investigated species, and when applied to the isolated STNS of H. americanus possessed little bioactivity relative to the full-length Val(1) isoform. Thus, it appears that the dodeca-variants Val(1)- and Gly(1)-SIFamide are the sole bioactive isoforms of this peptide family in clawed lobsters and freshwater crayfish.

Combining MALDI-FTMS and bioinformatics for rapid peptidomic comparisons

Increasing research efforts in large-scale mass spectral analyses of peptides and proteins have led to many advances in technology and method development for collecting data and improving the quality of data. However, the resultant large data sets often pose significant challenges in extracting useful information in a high-throughput manner. Here, we describe one such method where we analyzed a large mass spectral data set collected using decapod crustacean nervous tissue extracts separated via high-performance liquid chromatography (HPLC) coupled to high-resolution matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS). Following their acquisition, the data collected from discrete LC fractions was compiled and analyzed using an in-house developed software package that deisotoped, compressed, calibrated, and matched peaks to a list of known crustacean neuropeptides. By processing these data via bioinformatics tools such as hierarchical clustering, more than 110 neuropeptides that belong to 14 peptide families were mapped in five crustacean species. Overall, we demonstrate the utility of MALDI-FTMS in combination with a bioinformatics software package for the elucidation and comparison of peptidomes of varying crustacean species. This study established an effective methodology and will provide the basis for future investigations into more comprehensive comparative peptidomics with larger collection of species and phyla in order to gain a deeper understanding of the evolution and diversification of peptide families.

Peptides in the brain: mass spectrometry-based measurement approaches and challenges

The function and activity of almost every circuit in the human brain are modified by the signaling peptides (SPs) surrounding the neurons. As the complement of peptides can vary even in adjacent neurons and their physiological actions can occur over a broad range of concentrations, the required figures of merit for techniques to characterize SPs are surprisingly stringent. In this review, we describe the formation and catabolism of SPs and highlight a range of mass spectrometric techniques used to characterize SPs. Approaches that supply high chemical information content, direct tissue profiling, spatially resolved data, and temporal information on peptide release are also described. Because of advances in measurement technologies, our knowledge of SPs has greatly increased over the last decade, and SP discoveries will continue as the capabilities of modern measurement approaches improve.

Multiple modulators act on the cardiac ganglion of the crab, Cancer borealis

Neuromodulators can change the output of neural circuits. The crustacean cardiac ganglion (CG) drives the contractions of the heart. The CG is a direct target for neurohormones that are released from the pericardial organs and other neuroendocrine sites. In this study, we have characterized for the first time the physiological actions of the peptides red pigment concentrating hormone (RPCH), Cancer borealis tachykinin-related peptide Ia (CabTRP Ia) and allatostatin III type A (AST-3) on the isolated CG of the crab, Cancer borealis. RPCH and CabTRP Ia excited the CG while AST-3 strongly inhibited its motor output. We also studied the actions of other peptides and small molecule transmitters known to be present in C. borealis. Dopamine, serotonin, proctolin, crustacean cardioactive peptide (CCAP), a number of extended FLRFamide peptides, and cholinergic agonists increased the activity of the CG, GABA inhibited the CG, while other substances had little or no significant effect on the CG motor pattern. These results demonstrate, in one species, that the CG is multiply modulated. We suggest that multiple modulators may be important to regulate and coordinate the activity of the heart and other organs in response to external stimuli or the endogenous physiological state.

Regulation of the crab heartbeat by FMRFamide-like peptides: multiple interacting effects on center and periphery

We are studying the functional "logic" of neuromodulatory actions in a simple central pattern generator (CPG)-effector system, the heart of the blue crab Callinectes sapidus. The rhythmic contractions of this heart are neurogenic, driven by rhythmic motor patterns generated by the cardiac ganglion (CG). Here we used anatomical and physiological methods to examine the sources and actions on the system of the FMRFamide-like peptides (FLPs) TNRNFLRFamide (F(1)), SDRNFLRFamide (F(2)), and GYNRSFLRFamide, an authentic Callinectes FLP. Immunohistochemical localization revealed a plexus of FLP-immunoreactive fibers in the pericardial organs (POs), from which modulators are released to reach the heart as circulating neurohormones. Combined backfill and immunohistochemical experiments indicated that the FLPs in the POs originated in the CNS, from large neurosecretory cells in the B cluster of the first thoracic neuromere. In physiological experiments, we examined the actions of the FLPs on the intact working heart, on the semi-intact heart in which we could record the motor patterns as well as the muscle contractions, on the isolated CG, and in a preparation developed to assess direct actions on the muscle with controlled patterns of motor neuron spikes. The FLPs had strong positive chronotropic and inotropic effects. Dissection of these effects suggested that they were produced through at least two primary actions of the FLPs exerted both on the heart muscle and on the CG. These primary actions elicited numerous secondary consequences mediated by the feedforward and feedback interactions that integrate the activity of the complete, coupled CPG-effector system.

Mass spectrometric characterization and physiological actions of VPNDWAHFRGSWamide, a novel B type allatostatin in the crab, Cancer borealis

The neural networks in the crustacean stomatogastric ganglion are modulated by neuroactive substances released locally into the neuropil of the stomatogastric ganglion and by circulating hormones released by neuroendocrine structures including the pericardial organs. Using nanoscale liquid chromatography coupled to electrospray ionization quadrupole-time-of-flight mass spectrometry, we have identified and sequenced a novel B type allatostatin (CbAST-B1), VPNDWAHFRGSWamide, present in the pericardial organs of the crabs, Cancer borealis, and Cancer productus. We describe the physiological actions of CbAST-B1 on the pyloric rhythm of the stomatogastric ganglion of the crab, Cancer borealis. CbAST-B1 reduces the pyloric network frequency in a dose-dependent manner. The effect of bath-applied CbAST-B1 depends on the preceding physiological state of the preparation. Surprisingly, despite marked amino-acid sequence dissimilarity between the novel CbAST-B1 and the A type allatostatin family of peptides (AST-A), the physiological effects of CbAST-B1 are similar to those of AST-A.

Neutral loss of water from the b ions with histidine at the C-terminus and formation of the c ions involving lysine side chains

Neutral loss of water from the amide bond induced by the His side chain has been reported. The proposed fragmentation pathway is a retro-Ritter reaction catalyzed by the imidazole nitrogen. In our MS/MS study of the neuropeptide GAHKNYLRFamide, we observed that the neutral loss of water from the b(3) ion is abundant. The b(3) ion has a His residue at the C-terminus. As reported previously, in the b ions with His at the C-terminus, the imidazole residue is connected to the carbonyl carbon to form a five-membered ring. Therefore, it is unlikely that the neutral loss of water from the b(3) ion is catalyzed by the imidazole nitrogen. Through MS2 and MS3 studies of a synthetic peptide standard AGHKLL and its chemically labeled and isotope-encoded forms, we discovered that the water loss from the b(3) ion involves the carbonyl group of His, the hydrogen connected to the alpha-carbon of Gly, and the amide hydrogen of His. We also discovered the formation of an unusual c(x) ion in peptides with a Lys or Arg residue at the (x + 1) position of the peptide.

Neuromodulation of central pattern generators in invertebrates and vertebrates

Central pattern generators are subject to extensive modulation that generates flexibility in the rhythmic outputs of these neural networks. The effects of neuromodulators interact with one another, and modulatory neurons are themselves often subject to modulation, enabling both higher order control and indirect interactions among central pattern generators. In addition, modulators often directly mediate the interactions between functionally related central pattern generators. In systems such as the vertebrate respiratory central pattern generator, multiple pacemaker types interact to produce rhythmic output. Modulators can then alter the relative contributions of the different pacemakers, leading to substantial changes in motor output and hence to different behaviors. Surprisingly, substantial changes in some aspects of the circuitry of a central pattern generator, such as a several-fold increase in synaptic strength, can sometimes have little effect on the output of the CPG, whereas other changes have profound effects.

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.