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The X-ray induced G2 arrest in mouse eggs: a maternal effect involving a lack of polypeptide phosphorylation
Simone Grinfeld1, Paul Jacquet1, Jan Gilles1
1Department of Biology, Nuclear Studies Center, CEN/SCK, Boeretang 200, B-2400, Mol, Belgium.
Abstract:
In some strains of mice, eggs when X irradiated during the pronuclear stage, undergo a mitotic block in the G2 phase of the first cell cycle and cleave when the second division takes place in controls. The importance of this effect varies considerably with the strain and depends exclusively on the maternal genotype. In previous work, two-dimensional electrophoresis showed that eggs blocked at the one-cell stage after irradiation, undergo the same modifications in polypeptide synthesis as two-cell controls of the same age, except at the time of normal first mitosis, where three polypeptide sets of 30, 35 and 45 kDa appear only in cleaving controls. In the present study, we have found phosphorylations in dividing controls, on polypeptides of 30, 35 and 45 kDa. These phosphorylations are not seen in blocked irradiated eggs.
Insights
X-irradiated mouse eggs experience a cell cycle delay, preventing early division. Phosphorylation of specific proteins occurs in normally dividing eggs but is absent in blocked, irradiated eggs, suggesting a role in cell cycle progression.
Area of Science:
- Developmental Biology
- Cell Cycle Regulation
- Radiation Biology
Background:
- X-irradiation of mouse eggs at the pronuclear stage can induce a mitotic block in G2 phase.
- This effect is strain-dependent and influenced by maternal genotype.
- Previous studies indicated altered polypeptide synthesis in blocked versus cleaving eggs.
Purpose of the Study:
- To investigate post-translational modifications, specifically phosphorylation, in X-irradiated mouse eggs.
- To compare protein phosphorylation patterns between blocked irradiated eggs and normally dividing control eggs.
Main Methods:
- Two-dimensional gel electrophoresis to analyze polypeptide synthesis.
- Phosphorylation analysis of specific polypeptides in X-irradiated and control mouse eggs.
Main Results:
- X-irradiated eggs, blocked at the G2 phase, showed similar polypeptide synthesis to two-cell controls.
- Three specific polypeptide sets (30, 35, and 45 kDa) were identified in cleaving control eggs.
- These specific polypeptides were found to be phosphorylated in dividing controls but not in blocked irradiated eggs.
Conclusions:
- The absence of phosphorylation on specific polypeptides in blocked irradiated eggs suggests a role in G2/M transition.
- Maternal genotype and its influence on protein phosphorylation may be critical for overcoming radiation-induced cell cycle arrest.
- Understanding these molecular events is crucial for assessing the impact of radiation on early embryonic development.
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