Cytochalasin B does not block sperm penetration into denuded starfish oocytes

Keiichiro Kyozuka, Kenzi Osanai

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


During fertilisation in starfish oocytes, the fertilisation cone develops temporarily beneath the penetrating sperm. The role of the fertilisation cone in sperm incorporation in the starfish Asterias amurensis was examined using cytochalasin B (CB). CB (2 |xM) allowed sperm acrosomal process-egg plasma membrane fusion and egg activation, but inhibited the development of the fertilisation cone containing actin microfilaments. When sperm were added to intact oocytes (with the jelly coat and vitelline coat) in seawater containing CB, the sperm head did not penetrate the fertilisation membrane. Although the acrosomal process fused with egg plasma membrane, the sperm head remained outside the fertilisation membrane. On the other hand, denuded oocytes without the jelly coat and vitelline coat allowed sperm penetration even in the presence of 2 uM CB. Electron microscopy revealed that sperm organelles, including the acrosomal process, nucleus, mitochondrion and tail, were incorporated into the slightly electron-dense cytoplasm, which was similar to the cytoplasm of the fertilisation cone. These results show that the development of the fertilisation cone/actin filament complex is not essential for incorporation of the sperm, since incorporation can occur in denuded oocytes. However, the cone is required forfertilisation of intact oocytes, suggesting that this actin-filament-containing structure is necessary for getting the sperm through the outer egg coats.

Original languageEnglish
Pages (from-to)103-109
Number of pages7
Issue number2
Publication statusPublished - 1994 May


  • Asterias amurensis
  • Egg coat
  • Fertilisation
  • Fertilisation cone
  • Microfilament

ASJC Scopus subject areas

  • Developmental Biology
  • Cell Biology


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