Motility-associated and cyclic AMP-dependent protein phosphorylation in the sperm of the chum salmon, Oncorhynchus keta

Abstract

Cyclic AMP-dependent cell signaling pathway has been considered to play an essential role in the initiation of sperm motility in salmonid fishs. We showed here that inhibitors of cyclic AMP-dependent protein kinase blocked the motility of the sperm of chum salmon whose plasma membrane was removed with TritonX-100. Seven proteins, which were phosphorylated by cAMP concomitantly with motility initiation of the demembranated sperm, were identified. Among them two proteins were identified as 21 kDa light chain of the outer arm dynein and 48 kDa regulatory subunit of protein kinase-A (PKA) from their molecular masses. Five proteins had the molecular masses of 28 kDa, 33 kDa, 41 kDa, 63 kDa and 83 kDa. Phosphorylation of these proteins as well as the motility of the demembranated sperm were significantly inhibited by the PKA inhibitors. When the demembranated sperm were prepared after pre-activation, all of these 7 proteins had less labeled 32P. These results suggest that cAMP-dependent phosphorylation of multiple proteins through activation of PKA is involved in the initiation of sperm motility in the salmonid fish.