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Related Experiment Videos

Parallel pathways of cell cycle control during Xenopus egg activation.

W M Bement1, D G Capco

  • 1Department of Zoology, Arizona State University, Tempe 85287-1501.

Proceedings of the National Academy of Sciences of the United States of America
|June 15, 1991
PubMed
Summary

Increased intracellular calcium ([Ca2+]i) triggers cell cycle transition. This study shows that activating protein kinase C (PKC) independently initiates interphase events, suggesting parallel calcium signaling pathways regulate the cell cycle.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Cell cycle progression from M phase to interphase in eukaryotes is often preceded by increased intracellular free calcium ([Ca2+]i).
  • Calcium-dependent enzymes are hypothesized to mediate this transition.
  • Protein kinase C (PKC), a calcium- and phospholipid-dependent enzyme, is a potential key player.

Purpose of the Study:

  • To investigate the role of protein kinase C (PKC) in the M-phase to interphase transition.
  • To determine if PKC activation alone can trigger events associated with interphase entry.
  • To elucidate the relationship between calcium signaling, PKC activation, and M-phase-promoting factor (MPF) activity.

Main Methods:

  • Activation of PKC in M-phase-arrested Xenopus eggs using phorbol 12-myristate 13-acetate (PMA) under conditions preventing a rise in [Ca2+]i.

Related Experiment Videos

  • Assessment of interphase-associated events such as sperm chromatin decondensation, Golgi and nuclear envelope reassembly, and resumption of endocytosis.
  • Measurement of M-phase-promoting factor (MPF) activity using histone H1 kinase assays and induction of meiotic resumption in oocytes.
  • Use of the inactive 4 alpha-phorbol ester isomer and a PKC pseudosubstrate peptide to confirm PKC specificity.

    • Main Results:

    • PKC activation by PMA in the absence of increased [Ca2+]i induced sperm chromatin decondensation, Golgi and nuclear envelope reassembly, and endocytosis resumption.
    • These interphase events occurred while M-phase-promoting factor (MPF) activity remained high.
    • Subsequent elevation of [Ca2+]i rapidly destroyed MPF activity, indicating a separate calcium-dependent inactivation pathway.
    • In vitro assays confirmed that PMA-treated egg lysates initiated sperm chromatin decondensation without reducing MPF activity.

    Conclusions:

    • The rise in intracellular calcium ([Ca2+]i) generates at least two parallel signaling pathways crucial for cell cycle regulation.
    • One pathway, involving PKC activation, independently drives the cellular events of interphase entry.
    • A second, distinct calcium-dependent pathway is responsible for the inactivation of M-phase-promoting factor (MPF).