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Published on: December 28, 2021
MAP kinase, meiosis, and sperm centrosome suppression in Urechis caupo
1Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada, B.C., 22800, Mexico.
Abstract:
Although MAP kinase is an important regulatory enzyme in many somatic cells, almost nothing is known about its functions during meiosis, except in frog and mouse oocytes. We investigated MAPK activation and function in oocytes of the marine worm Urechis caupo that are fertilized at meiotic prophase. Activity was first detected at 4-6 min after fertilization in immunoblots with anti-active MAPK, prior to germinal vesicle breakdown (GVBD). MAPK activation did not require new protein synthesis and was dependent on the increases in both intracellular pH and intracellular Ca(2+) that normally occur during activation. When MAPK activation was inhibited with PD98059 or U0126, GVBD still occurred, but meiosis was abnormal and there was a dramatic premature enlargement of sperm asters, which normally do not appear until second polar body formation. Failure of polar body formation and premature sperm aster enlargement also occurred when MAPK activation was inhibited by an entirely different treatment which involved lowering the pH of external seawater to interrupt the normal cytoplasmic pH increase. Thus, in Urechis, active MAPK appears to be required for (1) normal meiotic divisions and (2) suppressing the paternal centrosome until after the egg completes meiosis, a general phenomenon whose mechanism has been unknown.
Insights
Mitogen-activated protein (MAP) kinase is crucial for normal meiosis and suppresses premature sperm aster enlargement in Urechis oocytes. This enzyme ensures proper cell division and paternal centrosome regulation during egg fertilization.
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Mitogen-activated protein (MAP) kinase regulates somatic cell functions, but its role in oocyte meiosis remains largely unknown.
- Existing knowledge is primarily limited to frog and mouse oocytes.
Purpose of the Study:
- To investigate the activation and function of MAP kinase during meiosis in Urechis caupo oocytes.
- To elucidate the role of MAP kinase in regulating meiotic progression and sperm aster development.
Main Methods:
- Immunoblotting with anti-active MAP kinase to detect enzyme activity post-fertilization.
- Inhibition of MAP kinase activation using PD98059 or U0126.
- Manipulation of intracellular pH by altering external seawater pH.
Main Results:
- MAP kinase activation was detected early after fertilization, preceding germinal vesicle breakdown (GVBD).
- Activation depended on intracellular pH and Ca(2+) increases.
- Inhibition of MAP kinase led to abnormal meiosis, premature sperm aster enlargement, and failed polar body formation.
- Lowering external seawater pH to disrupt cytoplasmic pH increase mimicked the effects of MAP kinase inhibition.
Conclusions:
- Active MAP kinase is essential for normal meiotic divisions in Urechis oocytes.
- MAP kinase plays a critical role in suppressing the paternal centrosome until after egg meiosis completion.
- These findings reveal a conserved mechanism for regulating centrosome activity during fertilization.
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