School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA.
Genetics. 2023 May 26;224(2). doi: 10.1093/genetics/iyad052.
Chromosome breakage plays an important role in the evolution of karyotypes and can produce deleterious effects within a single individual, such as aneuploidy or cancer. Forces that influence how and where chromosomes break are not fully understood. In humans, breakage tends to occur in conserved hotspots called common fragile sites (CFS), especially during replication stress. By following the fate of dicentric chromosomes in Drosophila melanogaster, we find that breakage under tension also tends to occur in specific hotspots. Our experimental approach was to induce sister chromatid exchange in a ring chromosome to generate a dicentric chromosome with a double chromatid bridge. In the following cell division, the dicentric bridges may break. We analyzed the breakage patterns of 3 different ring-X chromosomes. These chromosomes differ by the amount and quality of heterochromatin they carry as well as their genealogical history. For all 3 chromosomes, breakage occurs preferentially in several hotspots. Surprisingly, we found that the hotspot locations are not conserved between the 3 chromosomes: each displays a unique array of breakage hotspots. The lack of hotspot conservation, along with a lack of response to aphidicolin, suggests that these breakage sites are not entirely analogous to CFS and may reveal new mechanisms of chromosome fragility. Additionally, the frequency of dicentric breakage and the durability of each chromosome's spindle attachment vary significantly between the 3 chromosomes and are correlated with the origin of the centromere and the amount of pericentric heterochromatin. We suggest that different centromere strengths could account for this.
染色体断裂在核型进化中起着重要作用,并可能在单个个体内产生有害影响,如非整倍体或癌症。影响染色体断裂方式和位置的力尚未完全了解。在人类中,断裂往往发生在称为常见脆弱部位(CFS)的保守热点中,尤其是在复制应激期间。通过跟踪黑腹果蝇中二联体染色体的命运,我们发现张力下的断裂也往往发生在特定的热点中。我们的实验方法是在环状染色体中诱导姐妹染色单体交换,以产生具有双染色单体桥的二联体染色体。在下一次细胞分裂中,二联体桥可能会断裂。我们分析了 3 种不同的 X 染色体环的断裂模式。这些染色体在携带异染色质的数量和质量以及它们的系统发育历史方面存在差异。对于所有 3 条染色体,断裂都优先发生在几个热点处。令人惊讶的是,我们发现这些热点的位置在 3 条染色体之间并不保守:每条染色体都显示出独特的断裂热点排列。缺乏热点保守性以及对阿非迪科林的无反应表明,这些断裂位点并非完全类似于 CFS,可能揭示了染色体脆弱性的新机制。此外,二联体断裂的频率和每条染色体纺锤体附着的耐久性在 3 条染色体之间差异很大,并且与着丝粒的起源和着丝粒周围异染色质的数量相关。我们认为不同的着丝粒强度可以解释这一点。