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Updated: Mar 20, 2026
Preparation of Meiotic Chromosome Spreads from Mouse Oocytes for Assessment of Synapsis and Recombination
Published on: July 18, 2025
The Pch2 AAA+ ATPase promotes phosphorylation of the Hop1 meiotic checkpoint adaptor in response to synaptonemal
Esther Herruzo1, David Ontoso1, Sara González-Arranz1
1Instituto de Biología Funcional y Genómica. Consejo Superior de Investigaciones Científicas and University of Salamanca, 37007 Salamanca, Spain.
Abstract:
Meiotic cells possess surveillance mechanisms that monitor critical events such as recombination and chromosome synapsis. Meiotic defects resulting from the absence of the synaptonemal complex component Zip1 activate a meiosis-specific checkpoint network resulting in delayed or arrested meiotic progression. Pch2 is an evolutionarily conserved AAA+ ATPase required for the checkpoint-induced meiotic block in the zip1 mutant, where Pch2 is only detectable at the ribosomal DNA array (nucleolus). We describe here that high levels of the Hop1 protein, a checkpoint adaptor that localizes to chromosome axes, suppress the checkpoint defect of a zip1 pch2 mutant restoring Mek1 activity and meiotic cell cycle delay. We demonstrate that the critical role of Pch2 in this synapsis checkpoint is to sustain Mec1-dependent phosphorylation of Hop1 at threonine 318. We also show that the ATPase activity of Pch2 is essential for its checkpoint function and that ATP binding to Pch2 is required for its localization. Previous work has shown that Pch2 negatively regulates Hop1 chromosome abundance during unchallenged meiosis. Based on our results, we propose that, under checkpoint-inducing conditions, Pch2 also possesses a positive action on Hop1 promoting its phosphorylation and its proper distribution on unsynapsed chromosome axes.
Insights
The synapsis checkpoint in meiosis relies on Pch2 protein to maintain Hop1 phosphorylation, ensuring proper chromosome axis distribution and meiotic progression. Pch2
Area of Science:
- Cell biology
- Genetics
- Molecular biology
Background:
- Meiosis involves critical events like recombination and synapsis, monitored by surveillance mechanisms.
- Meiotic defects, such as the absence of synaptonemal complex component Zip1, trigger a meiosis-specific checkpoint, delaying or arresting progression.
- Pch2, a conserved AAA+ ATPase, is crucial for this checkpoint-induced meiotic block in zip1 mutants, localizing to the ribosomal DNA array.
Purpose of the Study:
- To investigate the role of Pch2 in the synapsis checkpoint during meiosis.
- To elucidate the mechanism by which Pch2 influences checkpoint activation and meiotic progression.
- To understand the interaction between Pch2, Hop1, and the Mec1 kinase in response to meiotic defects.
Main Methods:
- Genetic analysis of zip1 and pch2 mutants in meiotic cells.
- Immunodetection of Hop1 protein localization and phosphorylation.
- Assessing Mek1 kinase activity and meiotic cell cycle progression.
- Investigating the requirement of Pch2 ATPase activity and ATP binding for its function.
Main Results:
- High levels of Hop1 protein suppress the checkpoint defect in zip1 pch2 mutants, restoring Mek1 activity and meiotic delay.
- Pch2 is essential for sustaining Mec1-dependent phosphorylation of Hop1 at threonine 318.
- Pch2's ATPase activity is critical for its checkpoint function, and ATP binding is necessary for its localization.
- Pch2 acts positively under checkpoint conditions to promote Hop1 phosphorylation and proper distribution on unsynapsed axes.
Conclusions:
- Pch2 plays a dual role: negatively regulating Hop1 during unchallenged meiosis and positively promoting Hop1 phosphorylation and distribution under checkpoint conditions.
- The phosphorylation of Hop1 by Mec1, sustained by Pch2, is a key event for the synapsis checkpoint.
- Pch2's ATPase activity and localization are essential for its function in ensuring proper meiotic progression despite synapsis defects.
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