Characterization of corazonin signaling in a molluscan model species, Lymnaea stagnalis

In recent years, new concepts have emerged regarding the nomenclature, functions, and relationships of different peptide families of the gonadotropin-releasing hormone (GnRH) superfamily. One of the main driving forces for this originated from the emerging evidence that neuropeptides previously called molluscan GnRH are multifunctional and should be classified as corazonin (CRZ). However, research articles still appear that use incorrect nomenclature and attribute the same function to molluscan CRZs as vertebrate GnRHs. The aim of the present study was to further support the recent interpretation of the origin and function of the GnRH superfamily. Towards this goal, we report the characterization of CRZ signaling system in the molluscan model species, the great pond snail (Lymnaea stagnalis). We detected a CRZ-receptor-like sequence (Lym-CRZR) by homology-searching in the Lymnaea transcriptomes and the deduced amino acid sequence showed high sequence similarity to GnRH receptors and CRZ receptors. Molecular phylogenetic tree analysis demonstrated that Lym-CRZR is included in the cluster of molluscan CRZRs. Lym-CRZR transiently transfected into HEK293 cells was found to be localized at the plasma membrane, confirming that it functions as a membrane receptor, like other G protein-coupled receptors. The signaling assays revealed that the previously identified Lym-CRZ neuropeptide stimulated intracellular Ca²⁺ mobilization in a dose-dependent manner, but not cyclic AMP production, in HEK293 cells transfected with Lym-CRZR. Finally, we demonstrated a wide tissue distribution of Lym-CRZR. These results suggest that Lym-CRZ is a multifunctional peptide and provide further insights into the evolution of the GnRH neuropeptide superfamily. The present study also supports the notion that previously termed molluscan "GnRH" should be classified as "CRZ".