FMRFamide-related peptides from the kidney of the snail, Helisoma trivolvis

Effect of Air Exposure-Induced Hypoxia on Neurotransmitters and Neurotransmission Enzymes in Ganglia of the Scallop Azumapecten farreri

The nervous system expresses neuromolecules that play a crucial role in regulating physiological processes. Neuromolecule synthesis can be regulated by oxygen-dependent enzymes. Bivalves are a convenient model for studying air exposure-induced hypoxia. Here, we studied the effects of hypoxia on the expression and dynamics of neurotransmitters, and on neurotransmitter enzyme distribution, in the central nervous system (CNS) of the scallop Azumapecten farreri. We analyzed the expression of the neurotransmitters FMRFamide and serotonin (5-HT) and the choline acetyltransferase (CHAT) and universal NO-synthase (uNOS) enzymes during air exposure-induced hypoxia. We found that, in early-stage hypoxia, total serotonin content decreased in some CNS regions but increased in others. CHAT-lir cell numbers increased in all ganglia after hypoxia; CHAT probably appears de novo in accessory ganglia. Short-term hypoxia caused increased uNOS-lir cell numbers, while long-term exposure led to a reduction in their number. Thus, hypoxia weakly influences the number of FMRFamide-lir neurons in the visceral ganglion and does not affect peptide expression in the pedal ganglion. Ultimately, we found that the localization and level of synthesis of neuromolecules, and the numbers of cells expressing these molecules, vary in the scallop CNS during hypoxia exposure. This indicates their possible involvement in hypoxia resistance mechanisms.

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.

Expression of the SOFaRP2 gene in the central nervous system of the adult cuttlefish Sepia officinalis

FMRFamide-related Peptides (FaRPs) are involved in a variety of physiological processes, including reproduction, feeding, development, body patterning and osmoregulation in vertebrates and invertebrates. Here we investigate the expression pattern of cuttlefish Sepia officinalis FaRP2 gene in the brain by in situ hybridization. The SOFaRP2 gene was found to be expressed most intensively in the posterior chromatophore lobe, vasomotor lobe and subvertical lobe. In addition, positive staining was also found in the fin lobe, brachial lobe, anterior chromatophore lobe, anterior, dorsal and lateral basal lobes, inferior and superior frontal lobes, and optic lobe. The expression pattern of SOFaRP2 suggests its involvement in chromatophore regulation, feeding behavior, and learning and memory.

Marked changes in neuropeptide expression accompany broadcast spawnings in the gastropod Haliotis asinina

Introduction

A huge diversity of marine species reproduce by synchronously spawning their gametes into the water column. Although this species-specific event typically occurs in a particular season, the precise time and day of spawning often can not be predicted. There is little understanding of how the environment (e.g. water temperature, day length, tidal and lunar cycle) regulates a population’s reproductive physiology to synchronise a spawning event. The Indo-Pacific tropical abalone, Haliotis asinina, has a highly predictable spawning cycle, where individuals release gametes on the evenings of spring high tides on new and full moons during the warmer half of the year. These calculable spawning events uniquely allow for the analysis of the molecular and cellular processes underlying reproduction. Here we characterise neuropeptides produced in H. asinina ganglia that are known in egg-laying molluscs to control vital aspects of reproduction.

Results

We demonstrate that genes encoding APGWamide, myomodulin, the putative proctolin homologue whitnin, FMRFamide, a schistosomin-like peptide (SLP), a molluscan insulin-related peptide (MIP) and a haliotid growth-associated peptide (HGAP) all are differentially expressed in the anterior ganglia during the two week spawning cycle in both male and female abalone. Each gene has a unique and sex-specific expression profile. Despite these differences, expression levels in most of the genes peak at or within 12 h of the spawning event. In contrast, lowest levels of transcript abundance typically occurs 36 h before and 24 h after spawning, with differences in peak and low expression levels being most pronounced in genes orthologous to known molluscan reproduction neuromodulators.

Conclusions

Exploiting the predictable semi-lunar spawning cycle of the gastropod H. asinina, we have identified a suite of evolutionarily-conserved, mollusc-specific and rapidly-evolving neuropeptides that appear to contribute to the regulation of spawning. Dramatic increases and decreases in ganglionic neuropeptide expression levels from 36 h before to 24 h after the broadcast spawning event are consistent with these peptides having a regulatory role in translating environmental signals experienced by a population into a synchronous physiological output, in this case, the release of gametes.

Conorfamide-Sr2, a gamma-carboxyglutamate-containing FMRFamide-related peptide from the venom of Conus spurius with activity in mice and mollusks

A novel peptide, conorfamide-Sr2 (CNF-Sr2), was purified from the venom extract of Conus spurius, collected in the Caribbean Sea off the Yucatan Peninsula. Its primary structure was determined by automated Edman degradation and amino acid analysis, and confirmed by electrospray ionization mass spectrometry. Conorfamide-Sr2 contains 12 amino acids and no Cys residues, and it is only the second FMRFamide-related peptide isolated from a venom. Its primary structure GPM gammaDPLgammaIIRI-nh2, (gamma, gamma-carboxyglutamate; -nh2, amidated C-terminus; calculated monoisotopic mass, 1468.72Da; experimental monoisotopic mass, 1468.70Da) shows two features that are unusual among FMRFamide-related peptides (FaRPs, also known as RFamide peptides), namely the novel presence of gamma-carboxyglutamate, and a rather uncommon C-terminal residue, Ile. CNF-Sr2 exhibits paralytic activity in the limpet Patella opea and causes hyperactivity in the freshwater snail Pomacea paludosa and in the mouse. The sequence similarities of CNF-Sr2 with FaRPs from marine and freshwater mollusks and mice might explain its biological effects in these organisms. It also resembles FaRPs from polychaetes (the prey of C. spurius), which suggests a natural biological role. Based on these similarities, CNF-Sr2 might interact with receptors of these three distinct types of FaRPs, G-protein-coupled receptors, Na+ channels activated by FMRFamide (FaNaCs), and acid-sensing ion channels (ASICs). The biological activities of CNF-Sr2 in mollusks and mice make it a potential tool to study molecular targets in these and other organisms.

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.

Peripheral connections of FMRFamide-like immunoreactive neurons in the snail, helix pomatia: an immunogold electron microscopic study

Using a postembedding immunogold electron microscopic method, the ultrastructure and synaptic connections of FMRFamide-like immunoreactive varicosities were investigated in different peripheral organs of the snail Helix pomatia, including the heart (auricle), intestine, hepatopancreas, upper tentacle and salivary gland. The FMRFamide-like immunoreactive varicosities contained granules and vesicles as described in a previous study of the CNS of this species, and additionally, based on their granule content, two novel types of varicosities were found in the auricle. A selective accumulation of gold particles over the granules could be demonstrated. The FMRFamide-like immunoreactive varicosities formed unspecialized contacts with postsynaptic target cells in all peripheral organs investigated, with the exception of the tentacle retractor muscle. Both the neuro-muscular and the neuro-glandular contacts were characterized by either unspecialized close apposition of the 'pre- and postsynaptic' membranes or the immunoreactive elements faced the target cell(s) across a relatively wide extracellular space. In the tentacle retractor muscle some of the neuromuscular contacts showed appositions of electron dense material along the presynaptic membrane, clustering of agranular synaptic vesicles and intersynaptic cleft material. The present observations support previous electrophysiological findings and suggest a versatile modulatory role of FMRFamide and related substances in the Helix PNS.