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Updated: Feb 18, 2026
Optimized Analysis of Proteins from Xenopus Oocytes and Embryos by Immunoblotting
Published on: September 19, 2025
Proteomics of phosphorylation and protein dynamics during fertilization and meiotic exit in the Xenopus egg
Marc Presler1, Elizabeth Van Itallie1, Allon M Klein1
1Department of Systems Biology, Harvard Medical School, Boston, MA 02115.
Abstract:
Fertilization releases the meiotic arrest and initiates the events that prepare the egg for the ensuing developmental program. Protein degradation and phosphorylation are known to regulate protein activity during this process. However, the full extent of protein loss and phosphoregulation is still unknown. We examined absolute protein and phosphosite dynamics of the fertilization response by mass spectrometry-based proteomics in electroactivated eggs. To do this, we developed an approach for calculating the stoichiometry of phosphosites from multiplexed proteomics that is compatible with dynamic, stable, and multisite phosphorylation. Overall, the data suggest that degradation is limited to a few low-abundance proteins. However, this degradation promotes extensive dephosphorylation that occurs over a wide range of abundances during meiotic exit. We also show that eggs release a large amount of protein into the medium just after fertilization, most likely related to the blocks to polyspermy. Concomitantly, there is a substantial increase in phosphorylation likely tied to calcium-activated kinases. We identify putative degradation targets and components of the slow block to polyspermy. The analytical approaches demonstrated here are broadly applicable to studies of dynamic biological systems.
Insights
Fertilization triggers limited protein degradation but extensive dephosphorylation, preparing the egg for development. This study quantifies protein and phosphosite dynamics during egg activation.
Area of Science:
- Cell Biology
- Developmental Biology
- Proteomics
Background:
- Fertilization initiates egg development through complex molecular events.
- Protein activity regulation via degradation and phosphorylation is crucial.
- The precise extent of these regulatory processes remains largely unquantified.
Purpose of the Study:
- To quantify absolute protein and phosphosite dynamics during the egg fertilization response.
- To develop and apply novel mass spectrometry-based proteomics methods for dynamic phosphoregulation analysis.
- To elucidate the roles of protein degradation and phosphorylation in meiotic exit and polyspermy prevention.
Main Methods:
- Utilized mass spectrometry-based proteomics for absolute quantification of proteins and phosphosites.
- Developed a novel approach for calculating phosphosite stoichiometry in dynamic phosphorylation scenarios.
- Analyzed electroactivated eggs to capture fertilization-induced molecular changes.
Main Results:
- Identified limited degradation primarily affecting low-abundance proteins.
- Observed extensive dephosphorylation across various protein abundances during meiotic exit.
- Detected significant protein release into the medium and increased phosphorylation post-fertilization, linked to polyspermy blocks and kinases.
Conclusions:
- Protein degradation plays a targeted role, facilitating widespread dephosphorylation during meiotic resumption.
- Fertilization involves substantial extracellular protein release and kinase-mediated phosphorylation.
- The developed analytical methods offer broad applicability for studying dynamic biological systems.
