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Kinetics of MPF and histone H1 kinase activity differ during the G2- to M-phase transition in mouse oocytes
1Department of Molecular Embryology, Institute of Animal Physiology and Genetics Research, Cambridge, United Kingdom.
Abstract:
Maturation promoting factor (MPF) is universally recognized as the biological entity responsible for driving the cell cycle from G2- to M-phase. Histone H1 kinase activity is widely accepted as a biochemical indicator of p34cdc2 protein kinase complex activity and therefore MPF activity. In this paper we present results which indicate that during the G2- to M-phase transition in mouse oocytes the dynamic of p34cdc2 related histone H1 kinase activity differs markedly from the biological activity of MPF as measured by classical cell fusion procedures. MPF is activated just before germinal vesicle breakdown (GVBD) whereas histone H1 kinase is activated 5-7 h later coincident with the formation of the definitive first metaphase plate. The biological activity of MPF is merely reduced to about 50% of control levels by a short period of protein synthesis inhibition (1-2 h) and completely suppressed after a prolonged period of inhibition (4-5 h). By contrast, inhibition of protein synthesis in mouse oocytes results in a rapid and complete suppression of histone H1 kinase activity. Therefore, biological MPF and histone H1 kinase activity should not be used in an interchangeable manner during the G2- to M-phase transition in mouse oocytes.
Insights
Maturation promoting factor (MPF) drives cell cycle progression. However, in mouse oocytes, histone H1 kinase activity, a proposed MPF indicator, shows distinct dynamics and protein synthesis dependency, questioning its interchangeable use with biological MPF activity.
Area of Science:
- Cell Biology
- Molecular Biology
- Developmental Biology
Background:
- Maturation promoting factor (MPF) is critical for G2 to M-phase cell cycle transition.
- Histone H1 kinase activity is commonly used as a biochemical marker for MPF activity, specifically p34cdc2 kinase complex.
- Mouse oocytes are a key model for studying cell cycle regulation and maturation.
Purpose of the Study:
- To investigate the dynamic relationship between biological MPF activity and p34cdc2-related histone H1 kinase activity during mouse oocyte maturation.
- To determine if histone H1 kinase activity accurately reflects MPF activity throughout the G2 to M-phase transition in this model system.
- To assess the impact of protein synthesis inhibition on both biological MPF activity and histone H1 kinase activity.
Main Methods:
- Cell fusion assays to measure biological MPF activity.
- Assays to measure histone H1 kinase activity.
- Inhibition of protein synthesis for varying durations (1-5 hours) to assess its effect on MPF and histone H1 kinase activity.
- Microscopic observation of germinal vesicle breakdown (GVBD) and metaphase plate formation.
Main Results:
- Biological MPF activity initiates just before germinal vesicle breakdown (GVBD).
- Histone H1 kinase activity is significantly delayed, activating 5-7 hours later, coinciding with metaphase plate formation.
- MPF activity is only partially reduced by short-term protein synthesis inhibition, while histone H1 kinase activity is rapidly and completely suppressed.
- Prolonged protein synthesis inhibition completely suppresses biological MPF activity.
Conclusions:
- Biological MPF activity and p34cdc2-related histone H1 kinase activity exhibit distinct temporal dynamics during mouse oocyte G2 to M-phase transition.
- Histone H1 kinase activity is not a consistently interchangeable indicator of biological MPF activity in mouse oocytes.
- Protein synthesis is essential for maintaining histone H1 kinase activity, but not for the initial activation of biological MPF.