HO endonuclease-induced recombination in yeast meiosis resembles Spo11-induced events

Abstract

In meiosis, gene conversions are accompanied by higher levels of crossing over than in mitotic cells. To determine whether the special properties of meiotic recombination can be attributed to the way in which Spo11p creates double-strand breaks (DSBs) at special hot spots in Saccharomyces cerevisiae, we expressed the site-specific HO endonuclease in meiotic cells. We could therefore compare HO-induced recombination in a well-defined region both in mitosis and meiosis, as well as compare Spo11p-and HO-induced meiotic events. HO-induced gene conversions in meiosis were accompanied by crossovers at the same high level (52%) as Spo11p-induced events. Moreover, HO-induced crossovers were reduced 3-fold by a msh4⌬ mutation that similarly affects Spo11p-promoted events. In a spo11⌬ diploid, where the only DSB is made by HO, crossing over was significantly higher (27%) than in mitotic cells (<7%). This single meiotic DSB failed to induce the formation of a synaptonemal complex. We also show that HO-induced gene conversion tract lengths are shorter in meiotic than in mitotic cells. We conclude that a hallmark of meiotic recombination, the production of crossovers, is independent of the nature of Spo11p-generated DSBs at special hotspots, but some functions of Spo11p are required in trans to achieve maximum crossing over. M eiotic recombination in Saccharomyces cerevisiae differs from mitotic recombination in several respects. Beyond the fact that meiotic gene conversions occur 100 to 10,000 times more often than equivalent spontaneous mitotic events, the individual events themselves have different outcomes. Most notably, meiotic gene conversions have a higher association with crossing over than is seen in mitotic cells (reviewed in refs. 1 and 2). In addition to generating genetic diversity, crossing over is critical in ensuring accurate chromosome segregation during meiosis (3, 4).The origins of most spontaneous gene conversion events in mitosis are unknown, but they are certainly different from the way in which double strand breaks (DSBs) are induced by the meiosis-specific Spo11 protein (5, 6). DSBs created by Spo11p are generated at many nearby sites in meiotic hotspots (7,8). These hotspots represent a very special chromosomal context influenced by perhaps 10 other genes, the deletion of which abolishes or severely reduces DSB formation (reviewed in refs. 1, 3, 4, 9, and 10). Deletion of genes encoding Mre11p, Rad50p, and Xrs2p causes changes in the chromatin structure of hotspots (11). Similarly, the absence of protein components such as Hop1p that comprise the axial elements lying between sister chromatids also reduces DSB formation (12).Other mutations reduce the proportion of meiotic gene conversions accompanied by meiotic crossovers without affecting DSB formation. The zip1⌬ or zip2⌬ mutations, which eliminate formation of the central element of the synaptonemal complex (SC), have this effect (13,14), providing support for the general view that crossover regulation depends on this structure (3, 4). Deletion of ...

Local chromosome context is a major determinant of crossover pathway biochemistry during budding yeast meiosis

“…(D) Final noncrossover levels, calculated as in C, expressed as percent of wild type. Representative Southern blots are in consistent with earlier findings, that cutting both sister chromatids at a DSB site is associated with a reduced proportion of COs among repair products (Malkova et al, 2000).…”

“…However, VDE-promoted COs are substantially reduced in spo11 mutants ( Figure 5), as has been observed with HO endonuclease-induced meiotic recombination (Malkova et al, 2000). Moreover, in spo11 mutants, virtually all VDE-initiated COs are MutLg-independent ( Figure 5, Figure 5-figure supplement 2), and thus more closely resemble COs that form in mitotic cells.…”

“…Malkova and coworkers used the HO endonuclease to initiate recombination in meiotic cells at LEU2, also a 'hot' locus (Panizza et al, 2011;Wu and Lichten, 1995). The resulting COs were dependent on Msh4, a ZMM protein, to the same degree as are Spo11-induced COs, suggesting that these nuclease-induced COs at the axis enriched LEU2 locus were the products of ZMM/MutLg-dependent JM resolution (Malkova et al, 2000). Serrentino et al (2013) showed that enrichment for the budding yeast ZMM protein, Zip3, at DSB sites is correlated with interhomolog CO levels.…”

A Resurgent Phoenix‐‐A Hypothesis for the Origin of Meiosis

“…The result of Malkova et al showed that the special features of meiotic recombination can be attributed to processes occurring after the DSB is generated (19). Once generation of DSBs occurs in a cell, the recombinational repair system has therefore to be employed to eliminate the damage.…”

Spo11 and the Formation of DNA Double-Strand Breaks in Meiosis

“…A number of studies have shown that meiotic recombination can be supported by DNA damage mechanisms that do not involve Spo11. For example, DSBs made by site-specific endonucleases induce recombination that has many of the hallmarks of normal meiotic recombination (Malkova et al 2000;Neale et al 2002). Moreover, DSBs caused by ionizing radiation can at least partially suppress meiotic inviability of spo11 mutants in many organisms (Thorne and Byers 1993;Dernburg et al 1998;Celerin et al 2000;Liu et al 2002;Storlazzi et al 2003).…”