Identification of DSB-1, a Protein Required for Initiation of Meiotic Recombination in Caenorhabditis elegans, Illuminates a Crossover Assurance Checkpoint

Abstract

Meiotic recombination, an essential aspect of sexual reproduction, is initiated by programmed DNA double-strand breaks (DSBs). DSBs are catalyzed by the widely-conserved Spo11 enzyme; however, the activity of Spo11 is regulated by additional factors that are poorly conserved through evolution. To expand our understanding of meiotic regulation, we have characterized a novel gene, dsb-1, that is specifically required for meiotic DSB formation in the nematode Caenorhabditis elegans. DSB-1 localizes to chromosomes during early meiotic prophase, coincident with the timing of DSB formation. DSB-1 also promotes normal protein levels and chromosome localization of DSB-2, a paralogous protein that plays a related role in initiating recombination. Mutations that disrupt crossover formation result in prolonged DSB-1 association with chromosomes, suggesting that nuclei may remain in a DSB-permissive state. Extended DSB-1 localization is seen even in mutants with defects in early recombination steps, including spo-11, suggesting that the absence of crossover precursors triggers the extension. Strikingly, failure to form a crossover precursor on a single chromosome pair is sufficient to extend the localization of DSB-1 on all chromosomes in the same nucleus. Based on these observations we propose a model for crossover assurance that acts through DSB-1 to maintain a DSB-permissive state until all chromosome pairs acquire crossover precursors. This work identifies a novel component of the DSB machinery in C. elegans, and sheds light on an important pathway that regulates DSB formation for crossover assurance.

MEI4: a central player in the regulation of meiotic DNA double strand break formation in the mouse

“…However, in S. cerevisiae, Rec114 phosphorylation decreases DSB activity but does not lead to Rec114 depletion from axes as assayed by chromatin immunoprecipitation. The dynamics of Mei4 localization in S. cerevisiae (Li et al, 2006;Maleki et al, 2007), S. pombe (Lorenz et al, 2006) and the DSB-1 and DSB-2 proteins in C. elegans, which might play similar functions to Mei4 and Rec114 Stamper et al, 2013), share similar properties to those we have described in mice, although differences in the mechanism of regulatory pathways might operate in these species.…”

DNA Helicase HIM-6/BLM Both Promotes MutSγ-Dependent Crossovers and Antagonizes MutSγ-Independent Interhomolog Associations During Caenorhabditis elegans Meiosis

“…Markers of meiotic progression appear normal in him-6 mutants: Several recent studies have provided evidence for a checkpoint-like negative feedback network that operates during C. elegans meiosis to couple multiple aspects of meiotic prophase progression to the formation of crossovereligible recombination intermediates (Rosu et al 2011;Rosu et al 2013;Stamper et al 2013;Woglar et al 2013). These Figure 3 Timely transition in pachytene progression in the him-6 mutant.…”

“…First, they form and resect DSBs and load MutSg in a timely fashion. Second, they are competent to form later recombination intermediates that can be recognized as fulfilling the requirements of a "crossover assurance" checkpoint that couples meiotic prophase progression to formation of CO-eligible recombination intermediates Stamper et al 2013;Woglar et al 2013). Third, him-6 mutants are proficient to recruit COSA-1 to a subset of potential CO sites, to concentrate other pro-CO proteins at those sites, and to reorganize chromosome structural proteins in response (Agostinho et al 2013).…”

“…One level of regulation governs the initiation of recombination through the programmed formation of double-strand DNA breaks (DSBs), which form in substantial excess of eventual COs. Recent evidence suggests that checkpoint-like feedback mechanisms operate to ensure both that DSB formation continues until each homolog pair has at least one CO-eligible recombination intermediate and that DSB formation will shut down once this condition is met Stamper et al 2013). Following DSB formation, a subset of the initial recombination intermediates is selected to become COs, recruiting a cohort of CO-promoting (pro-CO) proteins that function to stabilize and protect these COdesignated intermediates (Baudat and De Massy 2007;Kohl and Sekelsky 2013;Lynn et al 2007).…”

Manipulation of Karyotype inCaenorhabditis elegansReveals Multiple Inputs Driving Pairwise Chromosome Synapsis During Meiosis

“…Several recent studies have converged on the conclusion that formation and repair of DSBs during meiosis are governed by a checkpoint-like negative feedback network in which germ cells monitor the formation of recombination intermediates that have the capacity to become interhomolog crossovers ("CO-eligible intermediates") and couple detection of such intermediates to progression through meiotic prophase (Rosu et al 2011Stamper et al 2013;Woglar et al 2013). If sufficient intermediates have formed to guarantee a CO for each homolog pair, the cell will be permitted to undergo a major transition affecting multiple distinct aspects of the meiotic program, including cessation of competence for DSB formation and shutting down of access to the homolog as a template for DSB repair; if the condition is not met, this transition will be delayed.…”