Roles of Calmodulin and Calcium/Calmodulin-Dependent Protein Kinase in Flagellar Motility Regulation in the Coral Acropora Digitifera
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In the corals Acropora spp., eggs secrete substances that induce sperm motility regulation. An elevation of intracellular pH ([pH]i) and a regulation of intracellular Ca2+ concentration ([Ca2+]) are involved in the sperm motility regulation cascade. However, the detailed molecular aspects of flagellar motility regulation have not been fully demonstrated in Acropora. In this study, we determined the presence and roles of both calmodulin (CaM) and calcium/calmodulin dependent-protein kinase (CaMK) in the sperm flagellar motility regulation of Acropora. A 45Ca2+-overlay assay and an immunoblot analysis showed that sperm contain an acidic 16-kDa protein that was CaM, and an immunoblot analysis revealed the presence of CaMK in coral sperm. In addition, a specific inhibitor of CaMK, KN-93, and a CaM antagonist, W-7, inhibited sperm motility activation induced by NH4Cl treatment. NH4Cl treatment causes an increase in intracellular [pH]i of sperm, suggesting that CaM and CaMK are involved in sperm motility initiation caused by an increase in [pH]i. The involvement of CaM and CaMK in motility regulation in coral highlights the importance of these molecules throughout the animal kingdom.
KeywordsFlagellar motility Sperm Coral Chemotaxis Protein phosphorylation Calcium-binding proteins
The authors want to express gratitude to Ms. M Nakamura (University of the Ryukyus) for helpful advice on the manuscript. This study was partially supported by a grant for the 21st Century COE program “The Comprehensive Analyses on Biodiversity in Coral Reef and Island Ecosystems in Asian and Pacific Regions” from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Monbukagakusho) to MM.
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