Evidence for the Presence of Molecules Related to the Neuropeptide CGRP in Two Cephalopods, <i>Sepia officinalis </i>and <i>Nautilus macromphalus</i>: Comparison with Its Target Organ Distribution

Abstract

Calcitonin gene-related peptide (CGRP) is a neuropeptide mainly involved in brain and cardiovascular functions in mammals. We investigated its presence and potential roles in two cephalopods, Sepia officinalis and Nautilus macromphalus. CGRP-like, but not calcitonin (CT)-like, molecules were detected by specific radioimmuno- and radioreceptor assays in the brain, optic lobes, branchial heart or afferent branchial vein and kidney. Gel exclusion chromatography of cephalopod brain extracts, followed by SDS-PAGE, indicated that CGRP-like molecules had a molecular weight of around 3 kDa, close to that of human CGRP. The distribution of CGRP target organs was characterized by binding studies in cuttlefish. Specific CGRP binding sites were detected in the brain, optic lobes, and kidney, indicating potential autocrine/paracrine roles of CGRP. Specific CGRP binding sites were also detected in the gills and shell sac that do not contain the peptide itself, indicating potential endocrine roles of CGRP. Accordingly, high circulating levels of CGRP-like molecules were detected in hemolymph of both cuttlefish and nautilus, unlike the situation in mammals. CGRP binding sites were further characterized in the cuttlefish gills by the Scatchard method. Our study indicates that the brain neurotransmitter role of CGRP could represent an ancient role in metazoa, already present in cephalopods and conserved among vertebrates. In contrast, the endocrine role of CGRP, which was suggested in cephalopods and also present in teleosts, may have been lost during the evolution of the tetrapod lineage. Our data support the hypothesis that CGRP represents the ancestral molecule of the CT/CGRP family appeared in metazoa before the vertebrate emergence.

Involvement of calcitonin and its receptor in the control of calcium-regulating genes and calcium homeostasis in zebrafish (Danio rerio)

“…Furthermore, in a mollusk phylum presenting real cerebralization, both cephalopod CGRP and its specific binding sites were colocalized in the CNS. (40,47) Therefore, the situation that we observed in zebrafish is concordant with the current theory suggesting that this local action of CGRP represents an ancient role in metazoa. The role of CT in calcium homeostasis remains to be clarified in teleosts, because contradictory conclusions have been reported so far.…”

“…However, in the European eel, specific CT binding sites have been detected in the brain, gill, heart, and kidneys, similar to the present study. (40) In pufferfish, a CTR sequence has been cloned from heart RNA, (26) but the situation in other organs was not investigated. In vertebrates, CT appears to perform a common endocrine function, with production in UBB or thyroid, and acts on CNS, heart, and osmoregulatory organs.…”

Directive 2010/63/EU on animal welfare: a review on the existing scientific knowledge and implications in cephalopod aquaculture research

“…For instance, cephalopods share some similar molecules to marine vertebrates and mammals that might be related to various brain functions (e.g. olfactory systems, in learning and memory processes, or in autonomic functions), however, its exact role remains to be determined (Lafont et al. 2006).…”