PCH-2 collaborates with CMT-1 to proofread meiotic homolog interactions

Abstract

18 19 The conserved ATPase, PCH-2/TRIP13, is required during both the spindle checkpoint and 20 meiotic prophase. However, it's specific role in regulating meiotic homolog pairing, synapsis and 21 recombination has been enigmatic. Here, we report that this enzyme is required to proofread 22 meiotic homolog interactions. We generated a mutant version of PCH-2 in C. elegans that binds 23 ATP but cannot hydrolyze it: pch-2 E253Q . In vitro, this mutant binds its substrates but is unable to 24 remodel them. This mutation results in non-homologous synapsis and loss of crossover 25 assurance. Surprisingly, worms with a null mutation in PCH-2's adapter protein, CMT-1, the 26 ortholog of p31 comet , localize PCH-2 to meiotic chromosomes, exhibit non-homologous synapsis 27 and lose crossover assurance. The similarity in phenotypes between cmt-1 and pch-2 E253Q 28 mutants indicate that PCH-2 can bind its meiotic substrates in the absence of in 29 contrast to its role during the spindle checkpoint, but requires its adapter to hydrolyze ATP and 30 remodel them. 31Introduction 32 33 Sexual reproduction relies on meiosis, the specialized cell division that generates haploid 34 gametes, such as sperm and eggs, from diploid progenitors so that fertilization restores diploidy. 35To ensure that gametes inherit the correct number of chromosomes, meiotic chromosome 36 segregation is exquisitely choreographed: Homologous chromosomes segregate in meiosis I 37 and sister chromatids segregate in meiosis II. Having an incorrect number of chromosomes, 38 also called aneuploidy, is associated with infertility, miscarriages and birth defects, underscoring 39 the importance of understanding this process to human health. 40 41 Events in meiotic prophase ensure proper chromosome segregation. During prophase, 42 homologous chromosomes undergo progressively intimate interactions that culminate in 43 synapsis and crossover recombination (reviewed in [1]). After homologs pair, a macromolecular 44 complex, called the synaptonemal complex (SC), is assembled between them in a process 45 called synapsis. Synapsis is a prerequisite for crossover recombination to generate the 46 linkages, or chiasmata, between homologous chromosomes that direct meiotic chromosome 47 segregation. Defects in any of these events can result in chromosome missegregation during 48 the meiotic divisions and gametes, and therefore embryos, with an incorrect number of 49 chromosomes. 50 51The conserved AAA-ATPase PCH-2 (Pch2 in budding yeast, PCH2 in Arabidopsis and TRIP13 52 in mice) is crucial to coordinate these events in meiotic prophase. In vitro and cytological 53 experiments indicate that it does this by using the energy of ATP hydrolysis to remodel meiotic 54HORMADs [2][3][4][5][6], chromosomal proteins that are essential for pairing, synapsis, recombination 55 and checkpoint function [7][8][9][10][11][12][13][14][15][16][17][18]. HORMADs are a protein family defined by the ability of a 56 domain, the HORMA domain, to adopt multiple conformations that specify pr...

Pch2 orchestrates the meiotic recombination checkpoint from the cytoplasm

“…It has been proposed that Pch2 catalyzes the transition from the "closed" to the "unbuckled" conformation releasing the safety belt lock from the HORMA domain core (West et al, 2018). Contrary to what is described in plants, worms and mammals, this action of Pch2 does not involve the p31 COMET co-factor, which is absent in budding yeast (Brulotte et al, 2017;Alfieri et al, 2018;Balboni et al, 2020;Giacopazzi et al, 2020).…”

“…We envision that the emerging cytoplasmic function of Pch2 in the meiotic recombination checkpoint may be evolutionarily conserved. In C. elegans, PCH-2 localizes to pachytene chromosomes suggesting a direct local role for PCH-2 in regulating recombination, likely by unlocking HORMAD proteins in collaboration with the CMT-1 cofactor (Kim et al, 2014;Giacopazzi et al, 2020). However, worm PCH-2 is also required for the meiotic checkpoint induced in the synapsis-defective syp-1 mutant (Bhalla and Dernburg, 2005).…”