Center for Chromosome Stability, Department of Cellular and Molecular Medicine, University of Copenhagen, 2200 Copenhagen N, Denmark.
Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2018 Dec 18;115(51):13003-13008. doi: 10.1073/pnas.1808377115. Epub 2018 Dec 3.
The instability of chromosome fragile sites is implicated as a causative factor in several human diseases, including cancer [for common fragile sites (CFSs)] and neurological disorders [for rare fragile sites (RFSs)]. Previous studies have indicated that problems arising during DNA replication are the underlying source of this instability. Although the role of replication stress in promoting instability at CFSs is well documented, much less is known about how the fragility of RFSs arises. Many RFSs, as exemplified by expansion of a CGG trinucleotide repeat sequence in the fragile X syndrome-associated locus, exhibit fragility in response to folate deficiency or other forms of "folate stress." We hypothesized that such folate stress, through disturbing the replication program within the pathologically expanded repeats within , would lead to mitotic abnormalities that exacerbate locus instability. Here, we show that folate stress leads to a dramatic increase in missegregation of coupled with the formation of single-stranded DNA bridges in anaphase and micronuclei that contain the locus. Moreover, chromosome X aneuploidy is seen when these cells are exposed to folate deficiency for an extended period. We propose that problematic replication during interphase leads to a failure to disjoin the sister chromatids during anaphase. This generates further instability not only at itself but also of chromosome X. These data have wider implications for the effects of folate deficiency on chromosome instability in human cells.
染色体脆性位点的不稳定性被认为是几种人类疾病的致病因素，包括癌症[常见脆性位点（CFSs）]和神经紊乱[罕见脆性位点（RFSs）]。先前的研究表明，DNA 复制过程中出现的问题是这种不稳定性的根本来源。尽管复制应激在促进 CFS 不稳定性方面的作用已得到充分证明，但对于 RFS 脆弱性的产生方式知之甚少。许多 RFS，例如脆性 X 综合征相关基因座中 CGG 三核苷酸重复序列的扩展，对叶酸缺乏或其他形式的“叶酸应激”表现出脆弱性。我们假设，这种叶酸应激通过扰乱病理性扩展重复序列内的复制程序，会导致有丝分裂异常，从而加剧基因座的不稳定性。在这里，我们表明叶酸应激会导致错误分离的急剧增加，同时在后期形成单链 DNA 桥和含有基因座的微核。此外，当这些细胞暴露于叶酸缺乏时，会出现 X 染色体非整倍体。我们提出，有丝分裂期间的有问题的复制会导致后期姐妹染色单体无法分离。这不仅会导致自身的进一步不稳定性，还会导致 X 染色体的不稳定性。这些数据对叶酸缺乏对人类细胞染色体不稳定性的影响具有更广泛的意义。
