Data from: High throughput sequencing reveals alterations in the recombination signatures with diminishing spo11 activity

Spo11 is the topoisomerase-like enzyme responsible for the induction of the meiosis-specific double strand breaks (DSBs), which initiate the recombination events responsible for proper chromosome segregation. Nineteen PCR-induced alleles of SPO11 were identified and characterized genetically and cytologically. Recombination, spore viability and synaptonemal complex (SC) formation were decreased to varying extents in these mutants. Arrest by ndt80 restored these events in two severe hypomorphic mutants, suggesting that ndt80-arrested nuclei are capable of extended DSB activity. While crossing-over, spore viability and synaptonemal complex (SC) formation defects correlated, the extent of such defects was not predictive of the level of heteroallelic gene conversions (prototrophs) exhibited by each mutant. High throughput sequencing of tetrads from spo11 hypomorphs revealed that gene conversion tracts associated with COs are significantly longer and gene conversion tracts unassociated with COs are significantly shorter than in wild type. By modeling the extent of these tract changes, we could account for the discrepancy in genetic measurements of prototrophy and crossover association. These findings provide an explanation for the unexpectedly low prototroph levels exhibited by spo11 hypomorphs and have important implications for genetic studies that assume an unbiased recovery of prototrophs, such as measurements of CO homeostasis. Our genetic and physical data support previous observations of DSB-limited meioses, in which COs are disproportionally maintained over NCOs (CO homeostasis).

Spo11是类拓扑异构酶（topoisomerase-like enzyme），负责诱导减数分裂特异性双链断裂（double strand breaks, DSBs），而这类断裂正是启动保障染色体正确分离的重组事件的核心诱因。本研究通过遗传与细胞学分析，鉴定并表征了19个PCR诱导的SPO11等位基因突变体。结果显示，这些突变体的重组效率、孢子活力及联会复合体（synaptonemal complex, SC）形成能力均出现不同程度的受损。在两个重度功能减退的spo11低活性突变体中，经ndt80阻滞处理后，上述缺陷均得到了部分恢复，这表明经ndt80阻滞的细胞核可维持更长时间的双链断裂形成活性。尽管交叉互换（crossing-over, CO）缺陷、孢子活力下降及联会复合体形成异常三者间存在显著相关性，但各类缺陷的严重程度均无法预测每个突变体所呈现的异等位基因基因转换（heteroallelic gene conversions，即原养型prototrophs）水平。对spo11低活性突变体的四分体进行高通量测序后发现，相较于野生型，与交叉互换相关的基因转换轨迹长度显著更长，而未与交叉互换关联的基因转换轨迹则显著更短。通过对这些轨迹长度变化幅度进行建模分析，我们成功解释了原养型遗传测量值与交叉互换关联程度之间的偏差。本研究结果为spo11低活性突变体展现出的异常低下的原养型水平提供了合理解释，同时也对那些假设原养型恢复无偏性的遗传学研究（如交叉互换稳态（CO homeostasis）的相关检测）具有重要参考价值。本研究的遗传与物理数据进一步佐证了此前关于“双链断裂限制型减数分裂中，交叉互换相较于非交叉互换（non-crossover, NCO）会被优先维持”的观测结论。