A new biological activity for the neuropeptide FMRFamide: experimental evidence for a secretagogue effect on amylase secretion in the scallop Pecten maximus

Neuropeptidome of the Cephalopod Sepia officinalis: Identification, Tissue Mapping, and Expression Pattern of Neuropeptides and Neurohormones during Egg Laying

Cephalopods exhibit a wide variety of behaviors such as prey capture, communication, camouflage, and reproduction thanks to a complex central nervous system (CNS) divided into several functional lobes that express a wide range of neuropeptides involved in the modulation of behaviors and physiological mechanisms associated with the main stages of their life cycle. This work focuses on the neuropeptidome expressed during egg-laying through de novo construction of the CNS transcriptome using an RNAseq approach (Illumina sequencing). Then, we completed the in silico analysis of the transcriptome by characterizing and tissue-mapping neuropeptides by mass spectrometry. To identify neuropeptides involved in the egg-laying process, we determined (1) the neuropeptide contents of the neurohemal area, hemolymph (blood), and nerve endings in mature females and (2) the expression levels of these peptides. Among the 38 neuropeptide families identified from 55 transcripts, 30 were described for the first time in Sepia officinalis, 5 were described for the first time in the animal kingdom, and 14 were strongly overexpressed in egg-laying females as compared with mature males. Mass spectrometry screening of hemolymph and nerve ending contents allowed us to clarify the status of many neuropeptides, that is, to determine whether they were neuromodulators or neurohormones.

Diversity of the RFamide Peptide Family in Mollusks

Since the initial characterization of the cardioexcitatory peptide FMRFamide in the bivalve mollusk Macrocallista nimbosa, a great number of FMRFamide-like peptides (FLPs) have been identified in mollusks. FLPs were initially isolated and molecularly characterized in model mollusks using biochemical methods. The development of recombinant technologies and, more recently, of genomics has boosted knowledge on their diversity in various mollusk classes. Today, mollusk FLPs represent approximately 75 distinct RFamide peptides that appear to result from the expression of only five genes: the FMRFamide-related peptide gene, the LFRFamide gene, the luqin gene, the neuropeptide F gene, and the cholecystokinin/sulfakinin gene. FLPs display a complex spatiotemporal pattern of expression in the central and peripheral nervous system. Working as neurotransmitters, neuromodulators, or neurohormones, FLPs are involved in the control of a great variety of biological and physiological processes including cardiovascular regulation, osmoregulation, reproduction, digestion, and feeding behavior. From an evolutionary viewpoint, the major challenge will then logically concern the elucidation of the FLP repertoire of orphan mollusk classes and the way they are functionally related. In this respect, deciphering FLP signaling pathways by characterizing the specific receptors these peptides bind remains another exciting objective.

Localization of αvβ3-like integrin in cultivated larval cells of the mussel Mytilus trossulus during neuronal and muscle differentiation

Using immunofluorescence phenotyping, the expression of αvβ3-like integrin was examined during neuronal and muscle differentiation in cell cultures derived from trochophore larvae of the mussel Mytilus trossulus. We have demonstrated that some mussel cells grown on fibronectin in vitro express the extracellular matrix (ECM) αvβ3 integrin-like receptor. At the same time, the distribution of αvβ3-like integrin is not ubiquitous, i.e. it depends on the cell type and the time of cultivation. Using immunohistochemical staining, we have found that only in some cells this integrin is co-localized with molluscan neuronal markers, neurotransmitters serotonin (5-HT) or Phe-Met-Arg-Phe-NH(2) neuropeptide (FMRFamide), and also with filament actin but not with paramyosin. Although we have previously shown that an integrin-dependent mechanism is involved in cell adhesion and differentiation of muscle cells of Mytilus, in this study, αvβ3-like integrin has not been found to participate in fibronectin adhesion of muscle cells but may be a linking agent between the ECM and the neuron-like cells.

Characterization of a novel LFRFamide neuropeptide in the cephalopod Sepia officinalis

From a single LC-MS/MS analysis, a new C-terminally extended RFamide neuropeptide was characterized in Sepia officinalis. The experimental strategy was based on the specific neutral loss associated with RFamide breakdown. Mass losses of 17 Da (C-terminally amide) and 320 Da (RFamide) have been observed for three known peaks of m/z 581.7 (FLRFamide), 599.8 (FMRFamide), 1096.3 (ALSGDAFLRFamide) and one unknown of m/z 752.8. The primary sequence of the peptide of m/z 752.8 was GNLFRFamide. MS/MS analyses revealed that this novel neuropeptide, called sepFRF1, is largely distributed in the central nervous system of cuttlefish of both sexes. Probably transported in the visceral nerve from the subesophageal mass (the peptide was not detected in the hemolymph), this neuropeptide targeted the rectum in agreement with its peripheral distribution. From concentrations as low as 10(-9)M, sepFRF1 increased the frequency, tonus and amplitude of rectal contractions. SepFRF1 is the first RFamide peptide identified in Sepia officinalis that is not derived from the FaRPs precursor. SepFRF1 could belong to a RFamide subfamily identified in gastropods and may be involved in feeding behavior.

The influence of diet and feeding state on FMRFamide-related peptides in the gut of Locusta migratoria L

Gut tissues of 2-week post-ecdysis female Locusta migratoria L. were assayed for FMRFamide-like immunoreactivity (FLI) during various feeding states using both radioimmunoassay and immunohistochemistry. The feeding states investigated were: (a) 48- and 24-h starved; (b) 5-, 30-, or 60-min post-feeding initiation; and (c) a diet of wheat grass, carrots, or apples. We determined: (1) the feeding state of a locust influences FLI in all gut tissues; (2) variations in diet appear to influence FLI in all gut tissues; (3) more than one FMRFamide-related peptide (FaRP) responds to differences in diet and state of starvation in the gut tissues; and (4) the protein poor diets (carrot and apple), in conjunction with the assertion that protein to carbohydrate ratio in the diet is the key component for nutrient balancing, suggests that FaRPs may play a role in maintaining balanced nutrient content in the locust.

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first-fifth instar larvae, 1-3- and 14-17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.

In vitro release of digestive enzymes by FMRF amide related neuropeptides and analogues in the lepidopteran insect Opisina arenosella (Walk.)

The insect neuropeptides FMRF amide, leucomyosupressin (LMS) and neuropeptide analogues leucosulfakinins (FLSK and LSK II Ser (SO(3)H)), perisulfakinin (PSK), proleucosulfakinin (PLSK), 14A[phi1]WP-I, 542phi1, and 378A[5b]WP-I were assayed for their effects on the release of amylase and protease from the midgut tissue of larvae of Opisina arenosella. In the bioassay, empty midgut tubes ligated at both ends using hair were incubated with insect saline containing neuropeptides/analogues in a bioassay apparatus at 37 degrees C for 30 min. After incubation the contents of the midgut preparations were analyzed for amylase and protease activity. In control experiments, the midgut preparations were incubated in insect saline without neuropeptides. The results of the study reveal that for stimulating amylase release from midgut tissue, the peptides require an FXRF amide (X may be methionine or leucine) sequence at the C-terminal. The presence of HMRF amide at C-terminal of peptides may inhibit the release of amylase. Meanwhile, peptides with both FMRF and HMRF amide sequence at the C-terminal are found to be effective in stimulating protease release. The tetrapeptide segment at the C-terminal probably represent the active core of the neuropeptide.

Characterization of a novel Sepia officinalis neuropeptide using MALDI-TOF MS and post-source decay analysis

A novel neuropeptide acting as a myosuppressor on esophagus, funnel and mantle muscular fibers has been isolated from the stellar ganglia of the mollusk cephalopod Sepia officinalis by means of HPLC analysis. Fractions were monitored using a myotropic bioassay. After three separation steps, MALDI-TOF spectrum revealed one main peak at m/z 756.6. The partial N-terminal and C-terminal digestions by exopeptidases followed by MALDI-TOF analysis allowed the determination of the nature of the two C-terminal and N-terminal amino acids. Post Source Decay fragmentation of the molecular ion accurately determined the following primary sequence: Val-Tyr-Ser-Ala-Pro-Tyr-Gly-OH. The mapping of this heptapeptide performed in ESI-MS revealed that its distribution is restricted to the stellar ganglia, the giant fibers III, and the nervous bundle containing the giant fibers II and the palleal nerve. The neuropeptide was not detected in the hemolymph suggesting a release by nerve endings next to the targets.

Acinar primary cell culture from the digestive gland of Pecten maximus (L.): an original model for ecotoxicological purposes

The purpose of this study was to establish an original primary acinar cell culture model for the mollusc bivalve Pecten maximus (L.), and to define its values and limits for subsequent ecotoxicological applications. To prevent microbial contaminations occurring frequently in invertebrate cell cultures, a perfusion of the stomach-digestive gland complex was performed in situ using a sterile salt solution containing broad-range antibiotics. Digestive acini were isolated using a pronase enzyme that was removed by several washings of the acinar suspension, after which their viability and functionality were determined by three different assays: fluorescein diacetate (FDA) de-esterification, 3-4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium (MTT) reduction and neutral red (NR) incorporation describing de-esterification, mitochondrial dehydrogenase and lysosome activity, respectively. The kinetic conditions for these assays were defined beforehand. The results showed that digestive acini could be maintained in vitro both cytologically and functionally for at least 96 h, which is sufficient for many ecotoxicological applications. Preliminary contamination assays, according to the function studied (cell esterases, mitochondrial respiration, lysosomal incorporation), indicated that polycyclic aromatic hydrocarbons had a negative effect on the survival of acini in vitro.

Stimulation of alpha-amylase release in the scallop Pecten maximus by the myosuppressins. Structure-activity relationships

The insect myosuppressin LMS (pGlu-Asp-Val-Asp-His-Val-Phe-Leu-Arg-Phe-NH2) elicits potent stimulation of the release of the digestive enzyme alpha-amylase from cell suspensions of the stomach-digestive gland complex of the scallop Pecten maximus. The myosuppressins are members of the FMRFamide-like peptide superfamily, which immunocytochemical data confirm is present in the scallop. Structure-activity studies indicated that the two most critical residues for bioactivity are Arg and Phe. Bioactivity of the peptide can be maintained if the basic, aromatic residue His is replaced by another basic residue (Lys) and another aromatic residue (Trp), but not the aromatic Tyr, indicating a sensitivity to the introduction of a phenolic OH group. A restricted-conformation analogue containing a cyclopropyl-Ala residue in position 8 (Cpa-MS) demonstrates an ability to antagonize the amylase secretion activity of LMS at microM concentrations. This result provides evidence that the myosuppressins adopt a tight turn in the C-terminal tetrapeptide active core region while binding to the scallop digestive gland receptor. Cpa-MS may provide a useful tool to neuroendocrinologists studying in vitro and in vivo digestive processes in mollusks and other invertebrates.

Peptidergic control of egg-laying in the cephalopod Sepia officinalis: involvement of FMRFamide and FMRFamide-related peptides

The peptidergic control of egg-laying was investigated in Sepia officinalis by using a myotropic bioassay. Three myotropic high-performance liquid chromatography fractions were obtained from optic lobe extracts. In the first fraction, FMRFamide (FMRFa) and FLRFa were isolated and sequenced. FMRFa-related peptides then were sought by dotting immunobinding of optic lobes extracts. The four immunoreactive fractions detected revealed the occurrence of FMRFa, FLRFa, FIRFa, and ALSGDAFLRFa predicted by the precursor already cloned from the optic lobes of S. officinalis (J Exp Biol 200:1483-9;1997). These peptides clearly appeared to be involved in the regulation of oocyte transport through the oviduct: the tetrapeptides FMRFa and FLRFa stimulated the contractions, whereas FIRFa and ALSGDAFLRFa lowered the tonus, the frequency, and the amplitude of the contractions. The occurrence of FaRPs in the nervous endings of the accessory sex glands suggested that this peptide family is involved in the regulation of secretory processes of the egg capsule. Indeed, FMRFa modulates the contractions of the main nidamental glands in vitro and, thus, should induce mechanical release of the secretion in vivo during ovulation. These results show that the FaRPs could play an important role in the synchronization of ovulation and egg capsule coating.