Drosophila neuropeptides in regulation of physiology and behavior

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.

/pdf/a-review-of-fmrfamide-and-rfamide-like-peptides-in-metazoa-22a1qcu165.pdf

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

The effects of the extended FLRFamide-like peptides, TNRNFLRFamide and SDRNFLRFamide, were studied on the stomach musculature of the crab Cancer borealis. Peptide-induced modulation of nerve-evoked contractions was used to screen muscles. All but 2 of the 17 muscles tested were modulated by the peptides. In several muscles of the pyloric region, peptides induced long-lasting myogenic activity. In other muscles, the peptides increased the amplitude of nerve-evoked contractions, excitatory junctional potentials, and excitatory junctional currents, but produced no apparent change in the input resistance of the muscle fibers. The threshold concentration was 10−10 M for TNRNFLRFamide and between 10−9 M to 10−8 M for SDRNFLRFamide. The absence of direct peptidecontaining innervation to these muscles and the wide-spread sensitivity of these muscles to the peptides suggest that TNRNFLRFamide and SDRNFLRFamide may be released from neurosecretory structures to modulate stomatogastric musculature hormonally. We speculate that hormonally released peptide will be crucial for maintaining appreciable muscle contraction in response to low-frequency and low-intensity motor discharge.

TNRNFLRFamide and SDRNFLRFamide modulate muscles of the stomatogastric system of the crab Cancer borealis

Since the initial characterization of the cardioexcitatory peptide FMRFamide in the bivalve mollusk Macrocallista nimbosa, a great number of FMRFamide-like peptides (FLPs) has ibeen 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 (FaRP) gene, the LFRFamide gene, the luqin gene, the neuropeptide F (NPF) gene and the cholecystokinin/sulfakinin (CCK/SK) gene. FLPs display a complex spatiotemporal pattern of expression in the central and peripheral nervous system. Working either 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.

/pdf/diversity-of-the-rfamide-peptide-family-in-mollusks-1sy7zwmz64.pdf

Diversity of the RFamide Peptide Family in Mollusks.

Neuronal signalling involves multiple neuropeptides that are diverse in structure and function. Complex patterns of tissue-specific expression arise from alternate RNA splicing of neuropeptide-encoding gene transcripts. The pattern of expression and its role in cell signalling is diffecult to study at the level of single neurons in the complex vertebrate brain. However, in the model molluscan system, Lymnaea, it is possible to show that alternate mRNA expression of the FMRFamide gene is specific to single identified neurons. Two different transcripts are expressed in a mutually exclusive manner in different neurons. Post-translational processing of the two precursor proteins leads to completely distinct sets of neuropeptide transmitters. The function of these transmitter cocktails, resulting from alternate mRNA splicing, was studied physiologically in identified neurons forming part of a behaviourally important network regulating heartbeat.

Alternative mRNA splicing of the FMRFamide gene and its role in neuropeptidergic signalling in a defined neural network.

Based on the sequencing of genomic and cDNA clones, we were able to determine that the FMRFamide gene consists of five exons covering at least 20 kb and predict the presence of further novel peptides. The exons are alternatively spliced: exon I (hydrophobic leader sequence) to exon II (tetrapeptides) and exon I to exons III (heptapeptides), IV, and V. A cDNA clone encoding the heptapeptides is described and has also been shown to encode further novel peptides SKPYMRFamide, HDYMRFamide, and SSFPRYamide. Analysis of the right internal parietal nerve using mass spectrometry showed that the novel peptide SKPYMRFamide was cleaved from the precursor. This peptide excites neurons, suggesting a physiological function in the CNS.

https://www.jneurosci.org/content/jneuro/14/11/6564.full.pdf

Genomic organization of the FMRFamide gene in Lymnaea: multiple exons encoding novel neuropeptides

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Genomic organization of the FMRFamide gene in Lymnaea: multiple exons encoding novel neuropeptides