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Xenopus laevis Egg Extract Preparation and Live Imaging Methods for Visualizing Dynamic Cytoplasmic Organization
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Spindle function in Xenopus oocytes involves possible nanodomain calcium signaling.

Ruizhen Li1, Julie Leblanc1,2, Kevin He1

  • 1Ottawa Hospital Research Institute, Ottawa Hospital-General Campus, Ottawa, ON K1H 8L6, Canada.

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Calcium signaling is crucial for frog oocyte maturation and polar body emission. Localized calcium nanodomains, not global transients, regulate meiotic spindle function and ensure proper cell division.

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Area of Science:

  • Cell Biology
  • Reproductive Biology
  • Developmental Biology

Background:

  • Intracellular calcium (Ca2+) transients are vital for fertilization and egg activation.
  • The role of Ca2+ in meiotic polar body emission during oocyte maturation is unclear.
  • Previous studies show manipulating Ca2+ affects polar body emission, but mechanisms remain unknown.

Purpose of the Study:

  • To elucidate the precise role of calcium signaling in polar body formation during oocyte maturation.
  • To investigate the involvement of calcium in meiotic spindle function.

Main Methods:

  • Live-cell imaging of frog oocytes.
  • Temporally precise intracellular calcium buffering using BAPTA and EGTA.
  • Localization studies using calcium probes (Lck-GCaMP3, GCaMP3) and calmodulin immunofluorescence.

Main Results:

  • BAPTA chelation rapidly depolymerized spindle microtubules during meiosis I and II.
  • EGTA, even at higher concentrations, did not affect spindle function or polar body emission.
  • Calcium probes showed spindle enrichment, but no global calcium increase was detected during maturation.
  • Endogenous calmodulin localized to spindle microtubules throughout meiosis.

Conclusions:

  • Meiotic spindle function in frog oocytes is sensitive to specific calcium chelators, suggesting a role for localized calcium.
  • The differential effects of BAPTA and EGTA indicate that nanodomain calcium signaling, rather than bulk calcium, regulates meiotic spindle function.
  • This localized calcium signaling is critical for proper polar body emission.