Calcitonin (CT) and CT gene-related peptide (CGRP) are well known to regulate blood calcium concentration and osmotic pressure in vertebrates. Although lophotrochozoan CT-like peptides and their receptors have been characterized in several model species, the presence of CT-like signaling systems in gastropods remains unknown. In this study, we identified two CT-like peptides, Hdh-CT1 and -CT2, and their receptors (CTRs), namely Hdh-CTR-L and -CTR-S, in Pacific abalone. Transcripts encoding Hdh-CT1 and Hdh-CT2 precursors were expressed mainly in neural ganglia. Molluscan CT-type peptides including Hdh-CT peptides were similar in length and showed highly conserved two Cys residues forming a disulfide bond in their N-terminal regions. A phylogenetic analysis revealed that gastropod CTRs, including Hdh-CTRs, belong to a large molluscan CTR subfamily. A luciferase reporter driven by cAMP responsive element was stimulated by Hdh-CT1 but not by Hdh-CT2 in Hdh-CTR-L-transfected human embryonic kidney 293 cells. In silico docking model using SWISS-MODEL and HPEPDOCK server showed that the N-terminal residues in Hdh-CT1 are deeply inserted into the binding pocket of Hdh-CTR-L. Taken together, the identification of the Hdh-CT system provides a comprehensive insight into the functional CT-type signaling system in marine gastropods.

Introduction
Materials and Methods
    1. Sequence analysis
    2. Reverse transcription and cDNAcloning
    3. Real-time quantitative PCR (qPCR)
    4. Luciferase reporter assay
    5. In silico docking model
    6. Statistical analysis
Results
    1. Sequence analysis of CT peptides andCTRs
    2. mRNA expression of Hdh-CT precursors
    3. Reporter assay
    4. In silico docking model
Discussion
Acknowledges
References

• Sungwoo Park(Department of Marine Bioscience, Gangneung-Wonju National University, Gangneung, Gangwon-do 25457, Korea)
• Keoho Kim(Department of Marine Bioscience, Gangneung-Wonju National University, Gangneung, Gangwon-do 25457, Korea)
• Young Chang Sohn(Department of Marine Bioscience, Gangneung-Wonju National University, Gangneung, Gangwon-do 25457, Korea) Corresponding author