Bhagat R, Manheim E A, Sherizen D E, McKim K S
Waksman Institute and Department of Genetics, Rutgers, the State University of New Jersey, Piscataway, NJ 08854, USA.
Cytogenet Genome Res. 2004;107(3-4):160-71. doi: 10.1159/000080594.
In Drosophila females, the majority of recombination events do not become crossovers and those that do occur are nonrandomly distributed. Furthermore, a group of Drosophila mutants specifically reduce crossing over, suggesting that crossovers depend on different gene products than noncrossovers. In mei-218 mutants, crossing over is reduced by approximately 90% while noncrossovers and the initiation of recombination remain unchanged. Importantly, the residual crossovers have a more random distribution than wild-type. It has been proposed that mei-218 has a role in establishing the crossover distribution by determining which recombination sites become crossovers. Surprisingly, a diverse group of genes, including those required for double strand break (DSB) formation or repair, have an effect on crossover distribution. Not all of these mutants, however, have a crossover-specific defect like mei-218 and it is not understood why some crossover-defective mutants alter the distribution of crossovers. Intragenic recombination experiments suggest that mei-218 is required for a molecular transition of the recombination intermediate late in the DSB repair pathway. We propose that the changes in crossover distribution in some crossover-defective mutants are a secondary consequence of the crossover reductions. This may be the activation of a regulatory system that ensures at least one crossover per chromosome, and which compensates for an absence of crossovers by attempting to generate them at random locations.
在果蝇雌性个体中，大多数重组事件不会形成交叉，而那些发生的交叉是随机分布的。此外，一组果蝇突变体特异性地减少了交叉，这表明交叉依赖于与非交叉不同的基因产物。在mei - 218突变体中，交叉减少了约90%，而非交叉和重组起始保持不变。重要的是，残余的交叉比野生型具有更随机的分布。有人提出，mei - 218通过确定哪些重组位点成为交叉来在建立交叉分布中发挥作用。令人惊讶的是，包括双链断裂（DSB）形成或修复所需的那些基因在内的一组不同基因，对交叉分布有影响。然而，并非所有这些突变体都具有像mei - 218那样的交叉特异性缺陷，并且不明白为什么一些交叉缺陷突变体会改变交叉的分布。基因内重组实验表明，mei - 218是DSB修复途径后期重组中间体分子转变所必需的。我们提出，一些交叉缺陷突变体中交叉分布的变化是交叉减少的次要结果。这可能是一种调节系统的激活，该系统确保每条染色体至少有一个交叉，并通过尝试在随机位置产生交叉来补偿交叉的缺失。
