PCH-2^TRIP13regulates spindle checkpoint strength

Abstract

Spindle checkpoint strength is dictated by three criteria: the number of unattached kinetochores, cell volume and cell fate. We show that the conserved AAA-ATPase, PCH-2/TRIP13, which remodels the checkpoint effector Mad2 from an active conformation to an inactive one, controls checkpoint strength in C. elegans. When we manipulate embryos to decrease cell volume, PCH-2 is no longer required for the spindle checkpoint or recruitment of Mad2 at unattached kinetochores. This role in checkpoint strength is not limited to large cells: the stronger checkpoint in germline precursor cells also depends on PCH-2. PCH-2 is enriched in germline precursor cells and this enrichment relies on conserved factors that induce asymmetry in the early embryo. Finally, the stronger checkpoint in germline precursor cells is regulated by CMT-1, the ortholog of p31comet, which is required for both PCH-2’s localization to unattached kinetochores and its enrichment in germline precursor cells. Thus, PCH-2, likely by regulating the availability of inactive Mad2 at and near unattached kinetochores, governs checkpoint strength. This role may be specifically relevant in scenarios where maintaining genomic stability is particularly challenging, such as in oocytes and early embryos enlarged for developmental competence and germline cells that maintain immortality.

Evolutionary Dynamics of the Spindle Assembly Checkpoint in Eukaryotes

“…The Trip13 ortholog Pch2 does not appear to be important for SAC silencing in budding yeast and p31 comet was lost very frequently, leading to its absence in most fungi, excavates and alveolates [6,71,139]. The loss of this mechanism may be related to cell volume in certain species: large but not small C. elegans cells require Pch2 to replenish 'open' Mad2 and thereby strengthen the SAC [140]. In budding yeast, Apc15-dependent ubiquitylation of Cdc20 appears to suffice for MCC disassembly.…”