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The cyclic behavior of a cytoplasmic factor controlling nuclear membrane breakdown
Abstract:
The activity of a cytoplasmic factor (MPF), capable of inducing nuclear membrane breakdown (germinal vesicle breakdown) when injected into amphibian oocytes, has been studied during the course of early cleavage in amphibian embryos. Mature egg cytoplasm was found to contain high levels of this activity, but this was quickly lost after fertilization or artificial activation. MPF activity later reappeared in the egg cytoplasm and started to cycle with time. The peak of embryonic MPF activity during each cycle coincided with the time the embryonic nuclei were entering the G2-M transition, i.e., mitosis. However, in colchicine-arrested embryos, this activity remained at an elevated level and no longer oscillated. The timing of the appearance and disappearance of this activity appeared to be under the control of the cytoplasm because such behavior was still observed in enucleated eggs. Continued protein synthesis in the embryo was required for the reappearance, but not for the disappearance, of this activity. MPF, previously thought to be restricted to oocyte maturation, may play a more general role in controlling nuclear membrane breakdown during mitosis as well as meiosis.
Insights
Maturation-promoting factor (MPF) drives nuclear envelope breakdown in amphibian oocytes and embryos. Its activity cycles during early development, peaking at mitosis, and requires protein synthesis for reappearance.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Cytoplasmic factors regulate key cell cycle events.
- Maturation-promoting factor (MPF) induces germinal vesicle breakdown in oocytes.
- Early embryonic development involves complex regulatory mechanisms.
Purpose of the Study:
- To investigate the role and regulation of MPF during early amphibian embryonic cleavage.
- To determine if MPF activity cycles during mitosis in embryos.
- To explore the cytoplasmic control over MPF activity.
Main Methods:
- Injection of cytoplasmic factors into amphibian oocytes.
- Monitoring MPF activity during early embryonic development.
- Analysis of MPF activity in enucleated and colchicine-arrested embryos.
- Assessment of protein synthesis requirement for MPF activity.
Main Results:
- MPF activity is high in mature oocytes but lost upon fertilization.
- MPF activity reappears and cycles during early cleavage, peaking at mitosis.
- MPF activity remains elevated and non-oscillating in colchicine-arrested embryos.
- Cytoplasmic control over MPF timing is demonstrated in enucleated eggs.
- Protein synthesis is necessary for MPF reappearance but not its disappearance.
Conclusions:
- MPF plays a crucial role in nuclear membrane breakdown during both meiosis and mitosis.
- MPF activity is regulated cyclically during early embryonic development.
- Cytoplasmic factors and protein synthesis are key regulators of MPF activity in embryos.