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Updated: Oct 1, 2026
Xenopus laevis as a Model to Identify Translation Impairment
Published on: September 27, 2015
Characterization of MPF and MAPK activities during meiotic maturation of Xenopus tropicalis oocytes
Jean-Francois L Bodart1, Davina V Gutierrez, Angel R Nebreda
1Van Andel Research Institute, Laboratory of Developmental Cell Biology, Special Program in Analytical, Cellular, and Molecular Microscopy, 333 Bostwick NE, Grand Rapids, Michigan 49503, USA.
Abstract:
Resumption of meiosis in oocytes of Xenopus tropicalis required translation but not transcription, and was marked by the appearance of a white spot and a dark ring, coincident with entry into metaphase I and the onset of anaphase I, respectively. Cyclin B(2)/p34(cdc2) activity increased prior to the first meiotic division, declined at the onset of anaphase I, and subsequently increased again. The capacity of egg cytoplasm to induce germinal vesicle breakdown (GVBD) was inhibited by cycloheximide, despite the fact that these oocytes contained cyclin B(2)/p34(cdc2) complexes. However, cycloheximide-treated oocytes underwent GVBD following injection of constitutively active mitogen-activated protein kinase (MAPK) kinase 2 (MEK2), p33(Ringo), or Delta 90 cyclin B. MAPK activity increased just prior to the first meiotic division and remained stable thereafter. Although injection of constitutively active MEK2 induced GVBD, treatment with the MEK inhibitors U0126 or anthrax lethal factor delayed GVBD and prevented spindle formation. Interestingly, the ability of egg cytoplasm to induce GVBD was unaffected by the inhibition of MEK activity. Our results indicate that the synthesis of a novel or short-lived protein(s) which acts in a MEK-independent fashion is required in order for egg cytoplasm to induce GVBD in X. tropicalis oocytes.
Insights
Resumption of meiosis in Xenopus tropicalis oocytes requires new protein synthesis, not transcription. This process involves specific molecular events and signaling pathways, including MAPK, for germinal vesicle breakdown (GVBD).
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Meiosis resumption in Xenopus tropicalis oocytes is a critical developmental process.
- Understanding the molecular mechanisms governing oocyte maturation is essential for reproductive biology.
Purpose of the Study:
- To investigate the translational and transcriptional requirements for meiotic resumption in Xenopus tropicalis oocytes.
- To elucidate the roles of cyclin B/p34(cdc2) and mitogen-activated protein kinase (MAPK) pathways in oocyte maturation and germinal vesicle breakdown (GVBD).
Main Methods:
- Oocytes were treated with inhibitors of translation (cycloheximide) and transcription.
- Microinjection of signaling molecules (constitutively active MEK2, p33(Ringo), Delta 90 cyclin B) and inhibitors (U0126, anthrax lethal factor) was performed.
- Cyclin B/p34(cdc2) and MAPK activities were monitored during meiotic progression.
Main Results:
- Meiosis resumption required translation but not transcription, marked by specific morphological changes.
- Cycloheximide inhibited GVBD, but this could be rescued by specific signaling molecule injections.
- MAPK activity increased prior to meiosis I, and MEK inhibition delayed GVBD and spindle formation, yet egg cytoplasm's GVBD-inducing capacity was MEK-independent.
Conclusions:
- Egg cytoplasm induces GVBD in Xenopus tropicalis oocytes via the synthesis of a novel or short-lived protein.
- This protein acts independently of the MEK pathway, highlighting a distinct mechanism in oocyte maturation.
- The findings contribute to understanding the complex regulation of meiosis and oocyte development.
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