Effects of caulerpenyne, the major toxin from Caulerpa taxifolia on mechanisms related to sea urchin egg cleavage

Caulerpenyne (CYN), the major metabolite synthesized by the alga Caulerpa taxifolia (Vahl), inhibited the first cleavage of sea urchin eggs without affecting fertilization. The effect was dose-dependent with a half maximal dose of 33 mu M. Blockage of cleavage was observed when the toxin miss added within 40 min of insemination. A preliminary search for the cellular targets of this toxin showed that ionic signals involved in the cell dynamics are altered: caulerpenyne reduced the intracellular ATP-dependent Ca2+ accumulation in a dose-dependent manner but did not provoke a release of sequestered Ca2+. This effect is similar to that of thapsigargin, a specific inhibitor of reticular Ca2+-ATPase. CYN had no effect on the incorporation of S-35-methionine into proteins. H-3-thymidine incorporation into DNA was inhibited by CYN in a dose-dependent manner: an effect well correlated with cell division kinetics. A CYN concentration of 30 mu M, which delayed the first cleavage, inhibited overall protein phosphorylation but did not affect histone kinase phosphorylating activity. Thus, CYN appears to alter the main events of sea urchin egg cleavage, and may therefore constitute an ecological risk for microorganisms and eggs of pluricellular animals living close to these algae. Moreover, this compound is of potential pharmacological interest in view of its antiproliferative properties.