Acrosome reaction-related steroidal saponin, Co-ARIS, from the starfish induces structural changes in microdomains

Masahiro Naruse, Hiroyuki Suetomo, Teruhiko Matsubara, Toshinori Sato, Hiroshi Yanagawa, Motonori Hoshi, Midori Matsumoto

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Cofactor for acrosome reaction-inducing substance (Co-ARIS) is a steroidal saponin from the starfish Asterias amurensis. Saponins exist in many plants and few animals as self-defensive chemicals, but Co-ARIS has been identified as a cofactor for inducing the acrosome reaction (AR). In A. amurensis, the AR is induced by the cooperative action of egg coat components (ARIS, Co-ARIS, and asterosap); however, the mechanism of action of Co-ARIS is obscure. In this study we elucidated the membrane dynamics involved in the action of Co-ARIS. We found that cholesterol specifically inhibited the Co-ARIS activity for AR induction and detected the binding of labeled compounds with sperm using radioisotope-labeled Co-ARIS. Co-ARIS treatment did not reduce the content of sperm sterols, however, the condition was changed and localization of GM1 ganglioside on the periacrosomal region disappeared. We then developed a caveola-breaking assay, a novel method to detect the effect of chemicals on microdomains of culture cell, and confirmed the disturbance of somatic cell caveolae in the presence of Co-ARIS. Finally, by atomic force microscopy observations and surface plasmon resonance measurements using an artificial membrane, we revealed that Co-ARIS colocalized with GM1 clusters on the microdomains. Through this study, we revealed a capacitation-like event for AR in starfish sperm.

Original languageEnglish
Pages (from-to)147-153
Number of pages7
JournalDevelopmental Biology
Issue number1
Publication statusPublished - 2010 Nov 1


  • Acrosome reaction
  • Caveolae-break assay
  • GM1 ganglioside
  • Membrane microdomain
  • Sperm capacitation
  • Steroidal saponin

ASJC Scopus subject areas

  • Molecular Biology
  • Developmental Biology
  • Cell Biology


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