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Multiple forms of maturation-promoting factor in unfertilized Xenopus eggs
J Kuang1, J E Penkala, C L Ashorn
1Department of Medical Oncology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Summary
Maturation-promoting factor (MPF) activity in Xenopus eggs involves at least three molecular species, not solely the cdc2 kinase complex. These distinct MPF forms regulate oocyte maturation and may be crucial for MPF autoamplification.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Maturation-promoting factor (MPF) is hypothesized to be the universal mitotic inducer in eukaryotic cells.
- The cdc2 protein kinase complex (p34cdc2-cyclin) has been identified as a potential candidate for MPF.
Purpose of the Study:
- To investigate the molecular composition and diversity of MPF activity in unfertilized Xenopus egg extracts.
- To determine if MPF activity is solely attributed to the p34cdc2-cyclin complex or if other forms exist.
Main Methods:
- Q-Sepharose chromatography was used to resolve MPF activity in Xenopus egg extracts.
- Microinjection into Xenopus oocytes was employed to assess the biological activity of different fractions.
- The mitosis-specific monoclonal antibody MPM-2 was used to differentiate MPF forms.
Main Results:
- MPF activity resolved into three fractions: a cdc2 kinase complex fraction and two other fractions lacking cdc2 kinase.
- The two novel fractions activated cdc2 kinase in oocytes and were recognized by the MPM-2 antibody, unlike the cdc2 complex fraction.
- The three MPF forms exhibited distinct molecular sizes, H1 kinase activities, and stabilities.
Conclusions:
- Unfertilized Xenopus eggs contain at least three distinct molecular species exhibiting MPF activity.
- These different MPF forms, beyond the p34cdc2-cyclin complex, play significant roles in oocyte maturation.
- The collective activity of these MPF species may be essential for the autoamplification of MPF during cell cycle regulation.