Molecular Characterization and Signaling Mechanisms of a Corazonin-Type System in Octopus minor.

The gonadotropin-releasing hormone (GnRH) superfamily also includes corazonin-type (CRZ-type) signaling systems, yet their molecular features and transduction mechanisms remain poorly defined in cephalopods. Here, we cloned the full-length cDNAs of the CRZ-type peptide precursor OmCRZP and its cognate receptor OmCRZR from Octopus minor. OmCRZP encodes an 89-residue precursor containing a conserved dodecapeptide (pQNYHFSNGWHPG-NH₂), and OmCRZR encodes a 407-residue seven-transmembrane G protein-coupled receptor. Phylogenetic analyses placed OmCRZP within the cephalopod CRZ clade and OmCRZR within the corazonin receptor (CRZR) clade. Expression profiling showed that OmCRZP was predominantly expressed in the brain and white body, whereas OmCRZR exhibited high expression in the brain, systemic heart, branchial heart, and white body with developmental upregulation in circulatory tissues. Fluorescence in situ hybridization detected overlapping ligand and receptor signals in several brain lobes involved in sensory integration, motor control, and visceral regulation, suggesting autocrine or paracrine signaling. Strong OmCRZR signals were additionally detected in cardiac tissue. Immunofluorescence further confirmed the widespread distribution of the mature peptide in the neuropil of nearly all brain lobes examined. In HEK293T cells, synthetic OmCRZ induced receptor internalization, intracellular Ca²⁺ mobilization and transient ERK1/2 phosphorylation without activating the cAMP pathway. These results establish the molecular architecture and Ca²⁺/ERK-coupled signaling of a cephalopod CRZ-type system and provide a framework for exploring its neuromodulatory functions.