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A Factor That Interrupts the Cell Cycle at G

Yutaka Sadakane1, Yasuhiro Iwao1

  • 1Biological Institute, Faculty of Science, Yamaguchi University, Yamaguchi 753, Japan.

Development, Growth & Differentiation
|June 7, 2023
PubMed

Insights

Frog oocytes contain a G2-specific cytostatic factor (G2-CSF) that halts cell cycle progression. This factor, found in germinal vesicles and cytoplasm, plays a key role in meiotic arrest and G2/M transition regulation.

Area of Science:

  • Cell Biology
  • Developmental Biology
  • Reproductive Biology

Background:

  • Full-grown amphibian oocytes naturally arrest at meiotic prophase I.
  • This arrest involves an unidentified activity preventing cell cycle progression beyond a G2-like stage.

Purpose of the Study:

  • To identify and characterize the factor responsible for cell cycle arrest in amphibian oocytes.
  • To investigate the role of this factor in meiotic arrest and early embryonic cell cycles.

Main Methods:

  • Injection of germinal vesicle (GV) contents and cytoplasm from Rana rugosa oocytes into fertilized eggs of Cynops pyrrhogaster and Bufo japonicus.
  • Monitoring of cell cycle progression, DNA synthesis, and maturation-promoting factor (MPF) cycling in injected eggs.
  • Assessing the effect of exogenous MPF on cell cycle reinitiation.
  • Investigating the inhibition of progesterone-induced oocyte maturation by injected Bufo oocyte components.

Main Results:

  • Injection of GV-content or cytoplasm prevented fertilized egg cleavage and cell cycle progression.
  • Injected eggs showed nuclear swelling with decondensed chromosomes but no MPF cycling; DNA synthesis remained unaffected.
  • Exogenous MPF injection restored cell cycle progression to M phase and cleavage.
  • Components from Bufo oocytes inhibited progesterone-induced oocyte maturation.

Conclusions:

  • A G2-specific cytostatic factor (G2-CSF) exists in the GV and cytoplasm of frog oocytes, arresting the cell cycle at G2/M or meiotic prophase I.
  • G2-CSF is crucial for physiological meiotic arrest and regulates the G2/M transition in early embryonic cells.

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