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Effect of Ca

Noburu Sensui1, Masaaki Morisawa1

  • 1Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, 1024 Koajiro, Misaki, Miura 238-02, Japan.

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Summary

Fertilization in ascidian eggs involves sequential calcium (Ca2+) increases essential for cortical deformation and polar body extrusion. Intracellular Ca2+ supports early events, while extracellular Ca2+ is crucial for later stages.

Keywords:
Ca2+ injectionascidian eggegg deformationmeiotic divisionpolar body extrusion

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Area of Science:

  • Reproductive Biology
  • Developmental Biology
  • Cellular Physiology

Background:

  • Cortical deformation and polar body extrusion are key events during ascidian egg fertilization.
  • Understanding the role of intracellular and extracellular calcium is crucial for deciphering these processes.

Purpose of the Study:

  • To investigate the role of intracellular Ca2+ concentration ([Ca2+ ]i) dynamics during fertilization in Ciona savignyi.
  • To determine the specific roles of intracellular and extracellular Ca2+ in cortical deformation and polar body extrusion.

Main Methods:

  • Monitoring intracellular Ca2+ ([Ca2+ ]i) levels using calcium imaging during fertilization.
  • Fertilizing eggs in Ca2+-free artificial seawater to assess extracellular Ca2+ requirements.
  • Manipulating intracellular Ca2+ levels by injecting low-Ca2+ buffers.
  • Inducing egg events by injecting varying Ca2+ concentrations.

Main Results:

  • A main Ca2+ peak and early Ca2+ spikes (1st spikes) occurred during egg deformation and before first polar body extrusion.
  • Extracellular Ca2+ was required for later Ca2+ spikes (2nd spikes) between polar body extrusions.
  • Low intracellular Ca2+ suppressed fertilization events, while specific Ca2+ concentrations induced deformation and polar body extrusion.

Conclusions:

  • Sequential increases in intracellular Ca2+ are essential for ascidian egg deformation and polar body extrusion.
  • Distinct Ca2+ sources (intracellular and extracellular) regulate different stages of fertilization.
  • Ascidian eggs exhibit latent arrest at the second meiotic metaphase, inducible by Ca2+ manipulation.