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是一类拓扑异构酶样酶（topoisomerase-like enzyme），负责诱导减数分裂特异性双链断裂（meiosis-specific double strand breaks，DSBs），而这类断裂是启动确保染色体正确分离的重组事件的起始信号。研究团队通过PCR诱导获得了19个SPO11等位基因，并对其开展了遗传学与细胞学层面的表征分析。
重组效率、孢子活力以及联会复合体（synaptonemal complex，SC）的形成能力在上述突变体中均出现不同程度的下降。在两个严重的功能减弱型突变体（hypomorphic mutants）中，经ndt80阻滞后上述缺陷均得到恢复，这提示经ndt80阻滞的细胞核可维持延长的双链断裂活性。
尽管交叉互换（crossing-over，CO）、孢子活力及联会复合体形成缺陷之间存在相关性，但这类缺陷的严重程度并不能预测每个突变体所表现出的异等位基因转换（原养型prototrophs）水平。
对spo11功能减弱型突变体的四分体开展高通量测序后发现，与交叉互换相关的基因转换轨迹长度显著长于野生型（wild type），而不与交叉互换相关的基因转换轨迹则显著短于野生型。
通过对这些轨迹变化程度进行建模，我们可以解释原养型的遗传学测量结果与交叉互换关联之间的不一致性。
本研究结果为spo11功能减弱型突变体表现出的异常低水平原养型提供了合理解释，同时对那些假设原养型可无偏恢复的遗传学研究（如交叉互换稳态（CO homeostasis）相关检测）具有重要参考价值。
本研究的遗传学与物理实验数据支持了此前关于“双链断裂受限的减数分裂过程中，交叉互换相较于非交叉互换（non-crossover，NCO）会被优先维持，即交叉互换稳态”的观测结论。