Calmodulin/calmodulin-dependent protein kinase II mediates SAAF-induced motility activation of ascidian sperm.
Ca2+-influx and membrane hyperpolarization by sperm-activating and -attracting factor (SAAF) released from the unfertilized egg of the ascidians Ciona cause a transient increase in cAMP, which triggers activation of sperm motility. We demonstrated here the presence of Ca2+-binding protein, calmodulin (CaM), and CaM-dependent kinase II (CaMKII) in the sperm. CaM antagonist, W-7, and CaMKII inhibitor, KN-93, suppressed SAAF-induced membrane hyperpolarization, increase in cAMP, and activation of sperm motility, but inactive analogues of W-7 and KN-93, namely W-5 and KN-92, respectively, did not. Subsequent addition of K+ ionophore, valinomycin, hyperpolarized the plasma membrane, increased cAMP, and conferred motility to the immotile sperm even in the presence of W-7 and KN-93. Addition of IBMX activated motility of sperm, which has been immobilized by W-7 and KN-93. These suggest that increased [Ca2+]i through influx of Ca2+ by SAAF binds to CaM to activate CaMKII. The activated CaMKII may cause membrane hyperpolarization to increase cAMP, which triggers the activation of sperm motility in Ciona.
Nomura
Mamoru
M
Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, Miura, Japan.
Yoshida
Manabu
M
Morisawa
Masaaki
M
D000595:Amino Acid Sequence; D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002938:Ciona intestinalis / Q000201:enzymology / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D015151:Immunoblotting; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*
D002147:Calmodulin; D000242:Cyclic AMP; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases