Related Experiment Videos
Mitogen-activated protein kinase activation down-regulates a mechanism that inactivates cyclin B-cdc2 kinase in
Abstract:
The G2 arrest of oocytes from frogs, clams, and starfish requires that preformed cyclin B-cdc2 complexes [prematuration-promoting factor (MPF)] be kept in an inactive form that is largely due to inhibitory phosphorylation of this pre-MPF. We have investigated the role of mitogen-activated protein (MAP) kinase in the activation of this pre-MPF. The cytoplasm of both frog and starfish oocytes contains an activity that can rapidly inactivate injected MPF. When the MAP kinase of G2-arrested starfish or Xenopus oocytes was prematurely activated by microinjection of c-mos or Ste-11 delta N fusion proteins, the rate and extent of MPF inactivation was much reduced. Both effects were suppressed by expression of the specific MAP kinase phosphatase Pyst 1. These results show that MAP kinase down-regulates a mechanism that inactivates cyclin B-cdc2 kinase in Xenopus oocytes. In starfish oocytes, however, MAP kinase activation occurs only after germinal vesicle breakdown, much after MPF activation. In this case, down-regulation of the cyclin B-cdc2 inhibiting pathway is a sensitive response to hormonal stimulation that does not require MAP kinase activation.
Insights
Mitogen-activated protein (MAP) kinase plays a key role in oocyte maturation by down-regulating MPF inactivation in Xenopus. However, in starfish, MAP kinase activation is not required for MPF inactivation during maturation.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Oocyte maturation is arrested at the G2 phase, requiring inactive cyclin B-cdc2 complexes (prematuration-promoting factor, pre-MPF).
- Inhibitory phosphorylation maintains pre-MPF in an inactive state.
- The role of mitogen-activated protein (MAP) kinase in regulating pre-MPF activation is not fully understood.
Purpose of the Study:
- To investigate the role of MAP kinase in the regulation of pre-MPF inactivation in frog and starfish oocytes.
- To determine if premature MAP kinase activation affects pre-MPF inactivation.
- To elucidate the mechanism by which MAP kinase influences oocyte maturation.
Main Methods:
- Microinjection of c-mos or Ste-11 delta N fusion proteins to prematurely activate MAP kinase in G2-arrested oocytes.
- Assessment of MPF inactivation rates and extent.
- Expression of MAP kinase phosphatase Pyst 1 to suppress MAP kinase activity.
Main Results:
- Cytoplasmic activity capable of rapidly inactivating MPF was identified in both frog and starfish oocytes.
- Premature MAP kinase activation in Xenopus oocytes significantly reduced the rate and extent of MPF inactivation.
- These effects in Xenopus were suppressed by Pyst 1, indicating MAP kinase down-regulates MPF inactivation.
- In starfish oocytes, MAP kinase activation occurred after germinal vesicle breakdown, post-MPF activation, and was not required for down-regulating MPF inactivation.
Conclusions:
- MAP kinase plays a crucial role in down-regulating the inactivation of cyclin B-cdc2 kinase (MPF) in Xenopus oocytes.
- In starfish oocytes, MAP kinase is not involved in the initial down-regulation of MPF inactivation, which is sensitive to hormonal stimulation.
- These findings highlight species-specific roles of MAP kinase in regulating oocyte maturation.