The dual role of HOP2 in mammalian meiotic homologous recombination

Roberto J Pezza,Oleg N Voloshin,Alexander A Volodin,R Daniel Camerini-Otero,Alexander V Mazin,Kingsley A Boateng,Marina A Bellani

doi:10.1093/nar/gkt1234

Abstract

Deletion of Hop2 in mice eliminates homologous chromosome synapsis and disrupts double-strand break (DSB) repair through homologous recombination. HOP2 in vitro shows two distinctive activities: when it is incorporated into a HOP2–MND1 complex it stimulates DMC1 and RAD51 recombination activities and the purified HOP2 alone is proficient in promoting strand invasion. We observed that a fraction of Mnd1−/− spermatocytes, which express HOP2 but apparently have inactive DMC1 and RAD51 due to lack of the HOP2–MND1 complex, exhibits a high level of chromosome synapsis and that most DSBs in these spermatocytes are repaired. This suggests that DSB repair catalyzed solely by HOP2 supports homologous chromosome pairing and synapsis. In addition, we show that in vitro HOP2 promotes the co-aggregation of ssDNA with duplex DNA, binds to ssDNA leading to unstacking of the bases, and promotes the formation of a three-strand synaptic intermediate. However, HOP2 shows distinctive mechanistic signatures as a recombinase. Namely, HOP2-mediated strand exchange does not require ATP and, in contrast to DMC1, joint molecules formed by HOP2 are more sensitive to mismatches and are efficiently dissociated by RAD54. We propose that HOP2 may act as a recombinase with specific functions in meiosis.

Highlights

Double-strand breaks (DSBs) are a severe type of chromosomal DNA damage
We and others have previously shown that in vitro the HOP2–MND1 complex increases the stability of the DMC1/RAD51ssDNA filament found on resected DSBs and promotes capture of potential partner chromosomes to facilitate
One reasonable explanation for this is that the absence of the HOP2–MND1 heterodimer in these cells leads to deficiency in strand invasion catalyzed by DMC1 and

Summary

Introduction

Double-strand breaks (DSBs) are a severe type of chromosomal DNA damage. They arise spontaneously through exogenous and endogenous causes such as radiation or free radicals and, interestingly, occur during the course of the developmental program of meiosis. Critical functions in HR are provided by the ubiquitous RAD51 and the meiosis-specific DMC1 recombinases These enzymes repair DSB by promoting the invasion of intact double-stranded DNA (dsDNA) by singlestranded (ssDNA) ends [6]. It is currently accepted that strand invasion intermediates proceed by one of two distinct pathways [7,8,9] They can dissociate after extension of the invading 30-end with subsequent rejoining of the broken chromosome by synthesis-dependent strand annealing pathway (SDSA) to generate non-crossover (NCO). They proceed via the doublestrand break repair mechanism (DSBR) [10,11], generating CO [7,8,11]. We and others have previously shown that in vitro the HOP2–MND1 complex increases the stability of the DMC1/RAD51ssDNA filament found on resected DSBs and promotes capture of potential partner chromosomes to facilitate

Methods

Results

Conclusion