Journal of Neurology & Neurophysiology

Neuropeptides Found and their Functions Characterized in Crinoid Echinoderms

Vivek Gupta^{* *}Correspondence: Vivek Gupta, Editorial Office, Journal of Neurology and Neurophysiology, Belgium, Email:

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Introduction

In order to create the first thorough identification of neuropeptide precursors in crinoids, we have investigated transcriptome/genome sequencing data from three species of feather stars: Anneissia japonica, Antedon mediterranea, and Florometra serratissima. There are numerous putative crinoid neuropeptide precursors among them, as well as members of bilaterian neuropeptide precursor families. We have examined the expression of a few neuropeptides in larvae (doliolaria), post-metamorphic pentacrinoids, and adults using A. mediterranea as an experimental model, revealing novel details on the cellular structure of crinoid nervous systems. As a result, F-type SALMF amide precursor transcripts were discovered utilizing mRNA in situ hybridization in a hitherto unidentified population of peptidergic cells situated dorso-laterally in doliolaria.

Also, using immunohistochemistry, it was discovered that adults' ectoneural and entoneural compartments of the nervous system had calcitonin-type neuropeptides as did pentacrinoids' circumoral nerve ring, oral tube foot, and aboral nerve centre. Additionally, functional analysis of a neuropeptide of the vasopressin/oxytocin type (crinotocin), which is expressed in the brachial nerve of the arms of A. mediterranean, revealed that this peptide alters the mechanical behavior of arm preparations in vitro in a dose-dependent manner. This is the first known biological effect of a neuropeptide in a crinoid. Finally, our findings lay the groundwork for further investigation of neuropeptide production and function in crinoids, a sister group to eleutherozoan echinoderms. They offer fresh insights on neuropeptide signaling in echinoderms.

The diversity of neuropeptides that have been found in bilaterian and non-bilaterian phyla reflects the fact that neuronal secretion of peptides that serve as intercellular signaling molecules (neuropeptides) is an evolutionary old trait of nervous systems. Moreover, it has been suggested that neuropeptide signaling has a pre-metazoan origin. The bigger precursor proteins that become neuropeptides feature an Nterminal signal peptide that directs the molecules to the endoplasmic reticulum lumen for release. One or more neuropeptides that are surrounded by monobasic or dibasic cleavage sites can be found in the precursor proteins. Furthermore, post-translational changes of neuropeptides can take place during the processing of neuropeptide precursors. The most frequent of these modifications is the transformation of a glycine residue at the C-terminus into an amide group, which protects against carboxypeptidases.

Additional post-translational changes of neuropeptides include tyrosine sulfation, intramolecular and/or intermolecular production of disulphide bridges between cysteine residues, and conversion of an N-terminal glutamine to pyroglutamate, which is protective against aminopeptidases. Typically, neuropeptides operate on other cells by attaching to certain G-Protein Coupled Receptors (GPCRs), modulating synaptic transmission locally and/or functioning systemically as hormones. Neuropeptides' cellular effects become apparent at the organ/organismal level, where they influence physiological processes and/or behavior. Consequently, neuropeptides have a crucial role in controlling activities including eating and digesting, osmoregulation, growth, locomotion, and reproduction.

Transcriptome/genome sequencing has made it much easier to study the development of neuropeptide signaling networks. Initially, this was limited to commonly studied "model" species like humans, mice, the nematode Caenorhabditis elegans, and the insect Drosophila melanogaster. Comparison and functional characterization of neuropeptide signaling systems in these species provided important insights into the relationships between neuropeptides and the evolutionary origins of various neuropeptide types. Yet, as transcriptome/genome sequencing has expanded to include a larger range of animal species, significant new insights into the evolution of neuropeptides have been discovered.

The phylum Echinodermata is one of the animal groups that have proved crucial for reconstructing the evolutionary history of neuropeptide signaling systems (e.g., starfish, brittle stars, sea urchins, sea cucumbers, feather stars). Echinoderms and hemichordates are classified as ambulacrarian deuterostomes in the phylum Chordata, which includes vertebrates, urochordates, and cephalochordates. As such, they serve as an important evolutionary link between studies on neuropeptide systems in protostome invertebrates (such as arthropods, nematodes, mollusks, and annelids) and vertebrates. The application of antibodies to neuropeptides found in other phyla allowed for the first time the visualization of neuropeptide expression in echinoderm nervous systems (e.g., the molluscan cardio active peptide FMRF amide).