The neuropeptidomes of the sea cucumbers Stichopus cf. horrens and Holothuria scabra.

The Philippines is a renowned marine biodiversity hotspot, home to several sea cucumber species with unusual biological traits. Among these, Stichopus cf. horrens is notable for its ability to undergo rapid body wall liquefaction when stressed, coupled with remarkable regenerative abilities. In contrast, Holothuria scabra has one of the most robust body walls in sea cucumbers and thrives in many regimes in the tropics. Despite their intriguing traits, the neurobiology and chemical diversity of these species remain underexplored. Neuropeptides are important components of an animal's neurobiological toolkit that underlie various physiological and behavioral processes. Thus, the discovery of neuropeptides is a crucial step for understanding the molecular underpinnings of unique traits in sea cucumbers. Leveraging the throughput and sensitivity of tandem mass spectrometry, we obtained an unbiased view of the endogenous peptidomes of radial nerve cord tissues of non-model sea cucumber species, H. scabra and S. cf. horrens. In this work, we sequenced 60 mature peptides from S. cf. horrens that were derived from 22 precursor proteins, and 43 peptides originating from 25 precursor proteins in H. scabra nervous tissues. A total of seven previously unannotated and uncharacterized neuropeptide precursors were identified, thereby expanding the known animal neuropeptide repertoire. Furthermore, we discovered consistent structural features in mature neuropeptides based on the type of post-translational modifications while pushing forward potentially novel proteolytic processing sites during peptide maturation based on the enriched flanking amino acid residues. Collectively, our results provide preliminary data that expand our understanding of echinoderm neurobiology through neuropeptide discovery, potentially paving the way for innovative solutions to address the global demand for echinoderms.