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Mos is required for MAP kinase activation and is involved in microtubule organization during meiotic maturation in
M H Verlhac1, J Z Kubiak, M Weber
1Département de Biologie du Developpement, Institut Jacques Monod, CNRS--Université Paris, France.
Abstract:
Mos is normally expressed during oocyte meiotic maturation in vertebrates. However, apart from its cytostatic factor (CSF) activity, its precise role during mouse meiosis is still unknown. First, we analyzed its role as a MAP kinase kinase kinase. Mos is synthesized concomitantly with the activation of MAP kinase in mouse oocytes. Moreover, MAP kinase is not activated during meiosis in oocytes from mos -/- mice. This result implies that Mos is necessary for MAP kinase activation in mouse oocytes. Raf-1, another MAP kinase kinase kinase, is already present in immature oocytes, but does not seem to be active when MAP kinase is activated. Moreover, the absence of MAP kinase activation in mos -/- oocytes demonstrates that Raf-1 cannot compensate for the lack of Mos. These results suggest that Raf-1 is not involved in MAP kinase activation. Second, we analyzed the organization of the microtubules and chromosomes in oocytes from mos -/- mice. We observed that during the transition between two meiotic M-phases, the microtubules and chromosomes evolve towards an interphase-like state in mos -/- oocytes, while in the control mos +/- oocytes they remain in an M-phase configuration, as in the wild type. Moreover, after spontaneous activation, the majority of mos -/- oocytes are arrested for at least 10 hours in a third meiotic M-phase where they exhibit monopolar half-spindles. These observations present the first evidence, in intact oocytes, of a role for the Mos/.../MAP kinase cascade in the control of microtubule and chromatin organization during meiosis.
Insights
Mos is essential for mouse oocyte meiosis, regulating MAP kinase activation and maintaining microtubule and chromosome organization. Its absence disrupts these processes, leading to meiotic arrest.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Mos protein is typically present during vertebrate oocyte meiotic maturation.
- The exact function of Mos during mouse meiosis, beyond its cytostatic factor activity, remains unclear.
Purpose of the Study:
- To investigate the role of Mos in MAP kinase activation during mouse oocyte meiosis.
- To examine the impact of Mos deficiency on microtubule and chromosome organization in mouse oocytes.
Main Methods:
- Analysis of MAP kinase activation in oocytes from wild-type and mos knockout mice.
- Microscopy to observe microtubule and chromosome organization in oocytes during meiotic progression and after activation.
Main Results:
- Mos is necessary for MAP kinase activation in mouse oocytes; Raf-1 cannot compensate for its absence.
- Oocytes lacking Mos transition to an interphase-like state during meiotic M-phase transitions.
- Mos-deficient oocytes arrest in a third meiotic M-phase with monopolar half-spindles after activation.
Conclusions:
- The Mos/MAP kinase cascade is crucial for controlling microtubule and chromatin organization during mouse oocyte meiosis.
- Mos plays a vital role in maintaining meiotic M-phase configuration and preventing aberrant spindle formation.