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Activation of mitogen-activated protein kinase during meiotic maturation in porcine oocytes
1Institute of Medical Science and Faculty of Agriculture, University of Tokyo, Japan.
Abstract:
To investigate the involvement of mitogen-activated protein kinase (MAP kinase) in meiotic maturation of porcine oocytes, we assayed MAP kinase activity using myelin basic protein (MBP) as a substrate. MAP kinase activity was low during the germinal vesicle stage, 0-20 h of culture. An abrupt increase was observed at metaphase I (30 h of culture), and activity remained significantly higher than that at 0 h until 50 h of culture, with a transient slight decrease at the time of first polar body extrusion (40 h). Detection of the kinase activity by an in-gel phosphorylation assay confirmed that the 42 and 44 kDa MAP kinases were significantly activated in 45 h cultured oocytes but not in 0 h oocytes, and just slightly in 20 h oocytes. In immunoblotting, however, the 42 and 44 kDa bands were detected in 0, 20 and 45 h cultured oocytes. Furthermore, the signal strength of the two bands did not change during the period of culture, but shifted up to 45 h, indicating that the activation of MAP kinase depended not on the synthesis but on the phosphorylation of this enzyme. These results suggest that the activation of MAP kinase is involved in the regulation of meiotic maturation of porcine oocytes, and especially in the regulation after germinal vesicle breakdown.
Insights
Mitogen-activated protein (MAP) kinase activation is crucial for pig oocyte maturation. This study shows MAP kinase phosphorylation, not synthesis, drives meiotic progression after germinal vesicle breakdown.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Molecular Endocrinology
Background:
- Meiotic maturation in oocytes is a complex process regulated by intracellular signaling pathways.
- Mitogen-activated protein (MAP) kinase is a key signaling molecule implicated in cell cycle progression.
Purpose of the Study:
- To investigate the role of MAP kinase activity in the meiotic maturation of porcine oocytes.
- To determine if MAP kinase activation depends on synthesis or post-translational modification.
Main Methods:
- Assaying MAP kinase activity using myelin basic protein (MBP) as a substrate.
- Employing in-gel phosphorylation assays to detect active MAP kinases (42 and 44 kDa).
- Utilizing immunoblotting to assess total MAP kinase levels during oocyte maturation.
Main Results:
- MAP kinase activity was low in germinal vesicle stage oocytes and increased significantly at metaphase I.
- Active 42 and 44 kDa MAP kinases were detected post-germinal vesicle breakdown, with activation dependent on phosphorylation, not de novo synthesis.
- Immunoblotting confirmed the presence of MAP kinases throughout maturation, but signal intensity changes indicated post-translational modification was key.
Conclusions:
- MAP kinase activation, specifically through phosphorylation, plays a critical role in regulating meiotic maturation of porcine oocytes.
- MAP kinase activation is particularly important for events occurring after germinal vesicle breakdown.