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Abstract

Animal nervous systems utilize a wide array of neuropeptides and the study of these can provide insight into the architecture, function and evolution of nervous systems. Contrary to other neurotransmitters such as acetylcholine or serotonin, which mainly transfer action potentials between neurons, neuropeptides are released slower and are often in- volved in triggering physiological, developmental and behavioral events such as feeding, reproduction, settlement and metamorphosis. Up until now, nothing is known about the neuropeptides in brachiopods, an understudied group of the Trochozoa. Using comparative genomics and transcriptomics, we identified 14 neuropeptides that are expressed in the nervous system of the brachiopod, Terebratalia transversa. Some of these neuropeptides are present in a wide range of metazoans, (e.g., 7B2, insulin-related peptides, vasotocin-neurophysin, glycopro- tein hormones). Others are more restricted to protostome lineages, with several belonging to groups with conserved amidated C-terminal amino acid sequences, like YRLamide (RLamides are known from other Trochozoans as well as from Arthropods), RGWamide (GWamides are known from annelids, molluscs, platyhelminths and arthropods) and FLRFamide (FLRFamide is known from molluscs and annelids and with N-terminal extension also from some other Protostomia, while RFamides in general can be found throughout metazoa). We investi- gated their expression pattern in embryonic and larval stages by using immunohistochemistry and in situ hybridization. Nearly all of them are expressed in the apical lobe of early and late larvae. Surprisingly a sub- set of these neuropeptides is already expressed during gastrula stages. The comparision of the neuropeptide complement and expression in brachiopods with other animals will contribute to a better understanding of nervous system evolution.