Cyclic AMP- and calmodulin-dependent phosphorylation of 21 and 26 kda proteins in axoneme is a prerequisite for SAAF-induced motile activation in ascidian spermatozoa

Dev Growth Differ. 2000 Apr;42(2):129-38. doi: 10.1046/j.1440-169x.2000.00489.x.


Sperm activating and -attracting factor (SAAF), derived from the egg of the ascidian Ciona, activates sperm motility through adenosine 3':5'-cyclic monophosphate (cAMP)-synthesis. A demembranated preparation of intact immotile sperm without SAAF was shown to require cAMP for reactivation. However, a demembranated preparation of intact motile sperm treated with SAAF did not require cAMP for reactivation, suggesting that cAMP is a prerequisite factor for SAAF-dependent activation of sperm motility. Furthermore, a cAMP-dependent protein kinase (PKA) inhibitor, H-89, was found to inhibit sperm motility. During in vivo or in vitro activation of sperm motility by SAAF or cAMP, a 26 kDa axonemal protein and 21 kDa dynein light chain were phosphorylated, respectively, suggesting the involvement of PKA-dependent phosphorylation of these proteins in sperm activation. The calmodulin antagonist, W-7, and an inhibitor of calmodulin-dependent myosin light chain kinase, ML-7, also inhibited the activation of sperm motility. Inhibition was reversed by the addition of phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Demembranated preparations of immotile sperm in the presence of W-7 or ML-7 were reactivated by cAMP, suggesting that calmodulin participated in sperm activation and that cAMP synthesis was followed by activation of a calmodulin-dependent mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calmodulin / physiology*
  • Cyclic AMP / physiology*
  • Egg Proteins / pharmacology*
  • Egg Proteins / physiology
  • Male
  • Phosphorylation
  • Signal Transduction
  • Sperm Motility / physiology*
  • Spermatozoa / cytology
  • Spermatozoa / physiology*
  • Urochordata


  • Calmodulin
  • Egg Proteins
  • Cyclic AMP