Pch2 orchestrates the meiotic recombination checkpoint from the cytoplasm

Abstract

During meiosis, defects in critical events trigger checkpoint activation and restrict cell cycle progression. The budding yeast Pch2 AAA+ ATPase orchestrates the checkpoint response launched by synapsis deficiency; deletion of PCH2 or mutation of the ATPase catalytic sites suppress the meiotic block of the zip1Δ mutant lacking the central region of the synaptonemal complex. Pch2 action enables adequate levels of phosphorylation of the Hop1 axial component at threonine 318, which in turn promotes activation of the Mek1 effector kinase and the ensuing checkpoint response. In zip1Δ chromosomes, Pch2 is exclusively associated to the rDNA region, but this nucleolar fraction is not required for checkpoint activation, implying that another yet uncharacterized Pch2 population must be responsible for this function. Here, we have artificially redirected Pch2 to different subcellular compartments by adding ectopic Nuclear Export (NES) or Nuclear Localization (NLS) sequences, or by trapping Pch2 in an immobile extranuclear domain, and we have evaluated the effect on Hop1 chromosomal distribution and checkpoint activity. We have also deciphered the spatial and functional impact of Pch2 regulators including Orc1, Dot1 and Nup2. We conclude that the cytoplasmic pool of Pch2 is sufficient to support the meiotic recombination checkpoint involving the subsequent Hop1-Mek1 activation on chromosomes, whereas the nuclear accumulation of Pch2 has pathological consequences. We propose that cytoplasmic Pch2 provokes a conformational change in Hop1 that poises it for its chromosomal incorporation and phosphorylation. Our discoveries shed light into the intricate regulatory network controlling the accurate balance of Pch2 distribution among different cellular compartments, which is essential for proper meiotic outcomes.

Novel mechanistic insights into the role of Mer2 as the keystone of meiotic DNA break formation

“…The CM of Red1 (located 340–362; West et al, 2018 ) binds to Hop1 with a higher affinity than the CM of Hop1 ( West et al, 2018 ). There is mounting evidence in budding yeast and Arabidopsis , that, in addition to a chromosomal pool, a significant pool of Hop1 is non-chromosomal (in the nucleoplasm or cytoplasm) ( Herruzo et al, 2021 ; Raina and Vader, 2020 ; Yang et al, 2020 ). Once bound to its own CM, Hop1 should not be able to interact with its chromosomal axis binding partner Red1.…”

The conserved AAA-ATPase PCH-2 distributes its regulation of meiotic prophase events by remodeling multiple meiotic HORMADs inC. elegans

“…Meiotic HORMADs collaborate with cohesins and other axial proteins to organize meiotic chromosomes into linear axial elements functionally capable of undergoing interhomolog pairing, synapsis and recombination (Ur & Corbett, 2021). While PCH-2 has been implicated in remodeling meiotic HORMADs away from meiotic chromosomes to ensure their availability (Herruzo et al, 2021; Herruzo et al, 2016) and entry into the nucleus (Yang, Hu, Portheine, Chuenban, & Schnittger, 2020), its localization to meiotic chromosomes before and after synapsis (Cuacos et al, 2021; Deshong et al, 2014; Joshi et al, 2009; Lambing et al, 2015; San-Segundo & Roeder, 1999) suggests a role remodeling meiotic HORMADs on chromosomes as well. To test this, we used structured illumination microscopy to more closely investigate whether PCH-2’s localization was consistent with remodeling meiotic HORMADs on axial elements.…”

ZYP1-mediated recruitment of PCH2 to the synaptonemal complex remodels the chromosome axis leading to crossover restriction

“…PCH2 in C. elegans promotes CO assurance independent of HORMAD removal ( 43 ). Pch2 in budding yeast is required for the meiotic recombination checkpoint independent of its accumulation on the SC and Hop1 release ( 31 , 33 , 46 , 47 , 67 ). Pch2 in budding yeast also regulates proper CO levels and distribution ( 63 ), but the connection to Hop1 dynamics remains to be explored.…”

“…Recently, it has been shown in Arabidopsis that PCH2 orchestrates both the chromosomal recruitment and dissociation of ASY1/Hop1 by mediating its conformational change ( 29 , 30 ). This mechanism is likely also present in mice and budding yeast ( 28 , 31–34 ). In Arabidopsis , PCH2 requires the cofactor COMET.…”