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Dynamics of maturation-promoting factor and its constituent proteins during in vitro maturation of bovine oocytes
1Department of Animal Science, Cornell University, Ithaca, New York 14853, USA.
Abstract:
Maturation-promoting factor (MPF) is known to be a key regulator of both mitotic and meiotic cell cycles. MPF is a complex of a B cyclin and the cyclin-dependent kinase cdkl (p34cdc2). Oocyte maturation and its arrest at metaphase of meiosis II (MII) are regulated by changes in MPF activity. In this study, experiments were conducted to examine the dynamics of MPF activity and its constituent proteins during in vitro maturation of bovine oocytes. Bovine oocytes displayed relatively low levels of MPF (histone H1 kinase) activity at the germinal vesicle stage during the first 8 h of maturation. MPF activity increased gradually thereafter, and its first peak of activity occurred at 12-14 h of maturation (presumptive metaphase I), which was followed by an abrupt reduction in activity at 16-18 h, during presumptive anaphase and telophase. MPF activity then increased, reaching a plateau at 20-24 h of maturation (MII stage). This high level of MPF activity was maintained for several hours but decreased gradually after 30 h of maturation and became barely detectable by 48 h of in vitro maturation (IVM) culture. At each time point, there was a significant variation among individual oocytes in histone H1 kinase activity, which was probably due to asynchronous maturation. Abundance of cdk1 increased gradually during the first 8 h and then remained relatively constant except for an apparent reduction at 18-22 h of IVM. The level of cyclin B2 increased quickly during the initial 2 h of culture, and this high level was maintained until 16 h, after which a significant reduction was observed between 18 and 22 h of IVM. The de novo synthesis of cyclin B2, however, exhibited a biphasic oscillation during maturation, with peaks before the onset of MI and of MII. These results have defined the profiles of MPF activity and its individual components during bovine oocyte maturation in vitro. We conclude that active MPF regulates bovine oocyte maturation and that de novo synthesis of cyclin B2 occurs during the process of maturation.
Insights
Maturation-promoting factor (MPF) activity and its components, cyclin B2 and cdk1, were tracked during in vitro maturation of bovine oocytes. MPF activity and cyclin B2 synthesis show dynamic changes crucial for oocyte cell cycle regulation.
Area of Science:
- Reproductive Biology
- Cell Biology
- Developmental Biology
Background:
- Maturation-promoting factor (MPF) is a key regulator of cell cycle progression in both mitotic and meiotic divisions.
- MPF comprises a B cyclin and cyclin-dependent kinase 1 (cdk1), and its activity governs oocyte maturation and arrest at metaphase II (MII).
Purpose of the Study:
- To investigate the dynamic changes in MPF activity and its constituent proteins (cdk1 and cyclin B2) during in vitro maturation (IVM) of bovine oocytes.
- To correlate these molecular dynamics with specific stages of oocyte meiotic progression.
Main Methods:
- Bovine oocytes were cultured in vitro for maturation.
- MPF activity was assessed by measuring histone H1 kinase activity at various time points.
- The abundance of cdk1 and cyclin B2 proteins was analyzed throughout the maturation process.
Main Results:
- MPF activity exhibited a biphasic pattern, with peaks preceding metaphase I and metaphase II.
- cdk1 abundance increased early and remained relatively stable, with a slight decrease during anaphase/telophase I.
- Cyclin B2 levels rose quickly and were maintained, with de novo synthesis showing biphasic oscillations tied to meiotic progression.
Conclusions:
- MPF activity and its components, particularly cyclin B2 synthesis, are dynamically regulated during bovine oocyte IVM.
- These molecular events are essential for successful oocyte maturation and progression through meiosis.