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During fertilization, an egg and sperm cell fuse to create a new diploid structure. In humans, the process occurs once the egg has been released from the ovary, and travels into the fallopian tubes. The process requires several key steps: 1) sperm present in the genital tract must locate the egg; 2) once there, sperm need to release enzymes to help them burrow through the protective zona pellucida of the egg; and 3) the membranes of a single sperm cell and egg must fuse, with the sperm...
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Updated: Apr 30, 2026

In Vivo Visualization of Calcium Transients during Fertilization and Early Development in C. elegans
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Polyspermy block in jellyfish eggs: collaborative controls by Ca(2+) and MAPK.

Mio Arakawa1, Noriyo Takeda2, Kazunori Tachibana1

  • 1Laboratory of Cell and Developmental Biology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.

Developmental Biology
|May 10, 2014
PubMed
Summary

Jellyfish eggs prevent multiple sperm fertilizations using a novel calcium (Ca2+) and mitogen-activated protein kinase (MAPK) pathway. This dual mechanism ensures successful reproduction by blocking additional sperm entry after the first.

Keywords:
CalciumFertilizationHydrozoan jellyfishMAP kinaseSperm–egg fusion

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Area of Science:

  • Developmental Biology
  • Cellular Biology
  • Reproductive Biology

Background:

  • Jellyfish eggs typically achieve monospermy without cortical reactions or membrane potential changes.
  • Understanding the precise mechanisms of polyspermy block in marine invertebrates is crucial for reproductive biology.

Purpose of the Study:

  • To elucidate the novel mechanism of polyspermy block in the hydrozoan jellyfish Cytaeis uchidae.
  • To investigate the collaborative roles of intracellular calcium (Ca2+) and mitogen-activated protein kinase (MAPK) in fertilization.

Main Methods:

  • Utilized transparent Cytaeis uchidae eggs for direct observation of fertilization events.
  • Manipulated intracellular Ca2+ levels using EGTA, inositol 1,5,4-trisphosphate (IP3), and excess K+.
  • Modulated MAPK activity by injecting mRNA for MAPK kinase kinase (Mos) and using MAPK kinase (MEK) inhibitors.

Main Results:

  • A Ca2+ rise following sperm-egg fusion is necessary and sufficient to block polyspermy.
  • Ca2+ elevation triggers MAPK dephosphorylation, which contributes to blocking subsequent sperm-egg fusion.
  • MAPK dephosphorylation irreversibly blocks sperm-egg fusion but reversibly suppresses sperm attraction.

Conclusions:

  • Jellyfish eggs employ a dual-component system involving Ca2+ (fast block) and MAPK (late block) to ensure monospermy.
  • This Ca2+- and MAPK-dependent mechanism represents a novel strategy for preventing polyspermy in marine invertebrate reproduction.