Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology, ETH Hönggerberg, Zurich, Switzerland.
Department of Biology and Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland.
Chromosome Res. 2024 Oct 10;32(4):12. doi: 10.1007/s10577-024-09756-w.
Mouse embryonic stem cells (ESCs) possess a pluripotent developmental potential and a stable karyotype. An exception is the frequent loss of one X chromosome in female ESCs derived from inbred mice. In contrast, female ESCs from crosses between different Mus musculus subspecies often maintain two X chromosomes and can model X chromosome inactivation. Here we report that combined mutations of Hira and Cdk8 induce rapid loss of one X chromosome in a Mus musculus castaneus hybrid female ESC line that originally maintains two X chromosomes. We show that MEK1 inhibition, which is used for culturing naive pluripotent ESCs is sufficient to induce X chromosome loss. In conventional ESC media, Hira and Cdk8 mutant ESCs maintain both X chromosomes. Induction of X chromosome loss by switching to naive culture media allows us to perform kinetic measurements for calculating the chromosome loss rate. Our analysis shows that X chromosome loss is not explained by selection of XO cells, but likely driven by a process of chromosome elimination. We show that elimination of the X chromosome occurs with a rate of 0.3% per cell per division, which exceeds reported autosomal loss rates by 3 orders of magnitude. We show that chromosomes 8 and 11 are stably maintained. Notably, Xist expression from one of the two X chromosomes rescues X chromosomal instability in ΔHiraΔCdk8 ESCs. Our study defines mutations of Hira and Cdk8 as molecular drivers for X chromosome elimination in naive female ESCs and describes a cell system for elucidating the underlying mechanism.
小鼠胚胎干细胞 (ESC) 具有多能性发育潜能和稳定的核型。一个例外是，来自近交系小鼠的雌性 ESC 中经常丢失一条 X 染色体。相比之下，来自不同 Mus musculus 亚种之间杂交的雌性 ESC 通常保持两条 X 染色体，并能模拟 X 染色体失活。在这里，我们报告 Hira 和 Cdk8 的联合突变会导致原本保持两条 X 染色体的 Mus musculus castaneus 杂种雌性 ESC 系迅速丢失一条 X 染色体。我们表明，用于培养原始多能 ESC 的 MEK1 抑制足以诱导 X 染色体丢失。在常规 ESC 培养基中，Hira 和 Cdk8 突变的 ESC 保持两条 X 染色体。通过切换到原始培养培养基来诱导 X 染色体丢失，使我们能够进行动力学测量以计算染色体丢失率。我们的分析表明，X 染色体丢失不是通过 XO 细胞的选择来解释的，而是可能由染色体消除过程驱动的。我们表明，X 染色体的丢失率为每个细胞每个分裂 0.3%，这比报道的常染色体丢失率高出 3 个数量级。我们表明染色体 8 和 11 稳定维持。值得注意的是，来自两条 X 染色体之一的 Xist 表达挽救了ΔHiraΔCdk8 ESC 中的 X 染色体不稳定性。我们的研究将 Hira 和 Cdk8 的突变定义为原始雌性 ESC 中 X 染色体消除的分子驱动因素，并描述了一个阐明潜在机制的细胞系统。
