The Pif1 helicase is actively inhibited during meiotic recombination which restrains gene conversion tract length.

Dipti Vinayak Vernekar,Bertrand Llorente,Raphaël Guérois,Florent Dingli,Valérie Borde,Céline Adam,Damarys Loew,Giordano Reginato,Marie-Claude Marsolier,Lepakshi Ranjha,Petr Cejka

doi:10.1093/nar/gkab232

Abstract

Meiotic recombination ensures proper chromosome segregation to form viable gametes and results in gene conversions events between homologs. Conversion tracts are shorter in meiosis than in mitotically dividing cells. This results at least in part from the binding of a complex, containing the Mer3 helicase and the MutLβ heterodimer, to meiotic recombination intermediates. The molecular actors inhibited by this complex are elusive. The Pif1 DNA helicase is known to stimulate DNA polymerase delta (Pol δ) -mediated DNA synthesis from D-loops, allowing long synthesis required for break-induced replication. We show that Pif1 is also recruited genome wide to meiotic DNA double-strand break (DSB) sites. We further show that Pif1, through its interaction with PCNA, is required for the long gene conversions observed in the absence of MutLβ recruitment to recombination sites. In vivo, Mer3 interacts with the PCNA clamp loader RFC, and in vitro, Mer3-MutLβ ensemble inhibits Pif1-stimulated D-loop extension by Pol δ and RFC-PCNA. Mechanistically, our results suggest that Mer3-MutLβ may compete with Pif1 for binding to RFC-PCNA. Taken together, our data show that Pif1’s activity that promotes meiotic DNA repair synthesis is restrained by the Mer3-MutLβ ensemble which in turn prevents long gene conversion tracts and possibly associated mutagenesis.

Highlights

Meiosis is a specialized cell division used by sexually reproducing organisms to produce haploid gametes from a diploid parent cell
We report here that Pif1 plays a role during DNA synthesis upon programmed meiotic break repair by homologous recombination
Our results reveal that Pif1 is required for break-induced replication (BIR) in vegetative cells, where one of the double-strand break (DSB) ends is lost and a special replication bubble mediates DNA synthesis, but it is involved during meiotic recombination events, especially when longer DNA synthesis by Pol ␦ takes place

Summary

Introduction

Meiosis is a specialized cell division used by sexually reproducing organisms to produce haploid gametes from a diploid parent cell. Homologous recombination during the first meiotic division prophase forms crossovers (COs) that physically connect the homologs, which ensures their proper segregation during the reductional division. Defects in these processes result in aneuploidy and infertility. Meiotic recombination begins with genome-wide programmed DNA double-strand breaks (DSBs) catalyzed by Spo. Meiotic recombination begins with genome-wide programmed DNA double-strand breaks (DSBs) catalyzed by Spo11 These DSBs are further processed by end resection, producing 3 ends that preferably invade the homologous chromosome as a repair template, resulting in the formation of a D-loop intermediate. COs are majorly formed through the ZMM (Zip-Msh-Mer) pathway, which includes eight conserved proteins, Zip, Spo, Mer, Msh and Msh that are proposed to stabilize the D-loop intermediates [1,2]

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