Novel two-step Ca2+ increase and its mechanisms and functions at fertilization in oocytes of the annelidan worm Pseudopotamilla occelata

Takeshi Nakano, Keiichiro Kyozuka, Ryusaku Deguchi

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Mature oocytes of the annelidan worm Pseudopotamilla occelata have a wide perivitelline space between the oocyte surface and the vitelline envelope and are arrested at the first metaphase (MI). We found a novel two-step Ca 2+ increase in normally fertilized oocytes. The first Ca2+ increase originated at a cortex situated underneath a fertilizing sperm on the vitelline envelope, but failed to propagate beyond the center of the oocyte. The first localized Ca2+ increase was then followed by a larger Ca 2+ increase starting from the whole oocyte cortex and spreading inwardly to the center. The first localized Ca2+ increase at fertilization was suppressed by the phospholipase C inhibitor U73122, and a similar Ca2+ change was induced by inositol 1,4,5-trisphosphate (IP3). On the other hand, the second global Ca2+ increase in fertilized oocytes was blocked by removal of external Ca2+ or the voltage-gated Ca2+ channel blocker D-600, and a similar Ca 2+ change could be mimicked by addition of excess K+ only when external Ca2+ was present. These results suggest that the first localized Ca2+ increase and the second global Ca2+ increase at fertilization are regulated by Ca2+ release from IP 3-sensitive stores and Ca2+ influx via voltage-gated Ca2+ channels, respectively. Our data also demonstrated that the localized Ca2+ increase induces the formation of large cytoplasmic protrusion, which helps the fertilizing sperm to enter the oocyte, whereas the following global Ca2+ increase is a prerequisite for the retraction of the cytoplasmic protrusion and the resumption of meiosis from MI.

Original languageEnglish
Pages (from-to)365-379
Number of pages15
JournalDevelopment Growth and Differentiation
Volume50
Issue number5
DOIs
Publication statusPublished - 2008 Jun 1

Keywords

  • Calcium influx
  • Calcium release
  • Fertilization
  • InsP
  • Polychaete

ASJC Scopus subject areas

  • Developmental Biology
  • Cell Biology

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