Decoding Neuropeptide Complexity: Advancing Neurobiological Insights from Invertebrates to Vertebrates through Evolutionary Perspectives

Abstract

Neuropeptides are vital signaling molecules involved in neural communication, hormonal regulation, and stress response across diverse taxa. Despite their critical roles, neuropeptide research remains challenging due to their low abundance, complex post-translational modifications (PTMs), and dynamic expression patterns. Mass spectrometry (MS)-based neuropeptidomics has revolutionized peptide identification and quantification, enabling the high-throughput characterization of neuropeptides and their PTMs. However, the complexity of vertebrate neural networks poses significant challenges for functional studies. Invertebrate models, such as Cancer borealis, Drosophila melanogaster, and Caenorhabditis elegans, offer simplified neural circuits, well-characterized systems, and experimental tools for elucidating the functional roles of neuropeptides. These models have revealed conserved neuropeptide families, including allatostatins, RFamides, and tachykinin-related peptides, whose vertebrate homologues regulate analogous physiological functions. Recent advancements in MS techniques, including ion mobility spectrometry and MALDI MS imaging, have further enhanced the spatial and temporal resolution of neuropeptide analysis, allowing for insights into peptide signaling systems. Invertebrate neuropeptide research not only expands our understanding of conserved neuropeptide functions but also informs translational applications including the development of peptide-based therapeutics. This review highlights the utility of invertebrate models in neuropeptide discovery, emphasizing their contributions to uncovering fundamental biological principles and their relevance to vertebrate systems.

Keywords: Evolutionary Conservation; Homology; Invertebrates; Mass Spectrometry; Motifs; NPY; Neuropeptides; Neuropeptidomics; Tachykinin; Vertebrates.

Figure 1:

The process of neuropeptide generation and signaling pathways. Neuropeptides are encoded by DNA, transcribed into mRNA, and translated into preprohormones in the endoplasmic reticulum. These precursors undergo signal peptide cleavage to form proneuropeptides, followed by proteolytic processing (endonucleases and exopeptidases) and post-translational modifications (e.g., amidation, glycosylation) in the Golgi apparatus to produce bioactive neuropeptides. The mature neuropeptides are packaged into dense-core vesicles and transported along axons to release sites. Released neuropeptides act through autocrine, paracrine, or endocrine signaling pathways, targeting G protein-coupled receptors (GPCRs) or other receptors to mediate diverse physiological processes. The inset highlights the increasing complexity of neuropeptide processing and their functional diversity.

Figure 2:

General anatomy of a Jonah crab, Cancer borealis. Here, we highlight many tissues that are rich with neuropeptides. The sinus glands (SG) reside within the eyestalks. The brain is located directly above the stomatogastric nervous system (STNS), which includes stomatogastric ganglion (STG), oesophageal ganglion (OG), and the paired commissural ganglia (CoG). The STNS resides on the surface of the stomach, outlined in gray. The heart muscle lays atop the thoracic ganglion (TG), which are surrounded on each side by the pericardial organs (PO). The STNS includes key nerves such as the stomatogastric nerve (stn), inferior oesophageal nerve (ion), and pyloric dilator nerve (pdn), which connect central ganglia (e.g., CoG, OG, STG) and control rhythmic motor patterns of the gastric and pyloric systems.

Figure 3:

Conserved neuropeptide motifs between invertebrates and vertebrates are illustrated in the table, covering key families such as AST-C/Somatostatin, AST-A/Galanin, Pyrokinin/Neuromedin U, Tachykinin/TRP, RYamide/NPY, RFamide/NPFF, and Sulfakinin/CCK. Shaded motifs (e.g., PISCF, FXPR, RFamide) highlight sequence similarities, indicating evolutionary conservation and functional parallels across these taxa. X represents a variable amino acid residue.

Figure 4:

Comparison of neuropeptide families expressed in the lobster (left) and crab (right). The figure highlights the distribution of neuropeptides in key tissues: the sinus gland (SG), brain, the stomatogastric nervous system (STNS), pericardial organs (PO), and thoracic ganglia (TG). Lobster-specific neuropeptide families are in blue, and crab-specific neuropeptide families are in green. Because these two crustaceans are closely related, some peptides appearing “species-specific” may be alternative isoforms or reflect detection limits (e.g., sample preparation or instrument sensitivity). As such, caution is warranted in labeling a family as truly absent in one species. Overall, the figure illustrates both shared and potentially distinct neuropeptide distribution across two crustacean systems.

Figure 5:

Depiction of common invertebrate model organisms and their frequent areas of research. With many types of crabs serving a diverse set of research interests, an inset distinguishes these relationships.