Human centromere repositioning activates transcription and opens chromatin fibre structure [RNAseq]

Human centromeres appear as constrictions on mitotic chromosomes and form a platform for kinetochore assembly in mitosis. Biophysical experiments led to a suggestion that repetitive DNA at centromeric regions form a compact scaffold necessary for function, but this was revised when neocentromeres were discovered on non-repetitive DNA. To test whether centromeres have a special chromatin structure we have analysed the architecture of a neocentromere. Centromere formation is accompanied by RNA pol II recruitment and active transcription to form a decompacted, negatively supercoiled domain enriched in ‘open’ chromatin fibres. In contrast, centromerisation causes a spreading of repressive epigenetic marks to surrounding regions, delimited by H3K27me3 polycomb boundaries and divergent genes. This flanking domain is transcriptionally silent and partially remodelled to form ‘compact’ chromatin, similar to satellite-containing DNA sequences, and exhibits genomic instability. We suggest transcription disrupts chromatin to provide a foundation for kinetochore formation whilst compact pericentromeric heterochromatin generates mechanical rigidity. RNA-Seq was used to examine transcription across the neocentromere region in HybNeo3 and GM10253A cells. Two replicates for each cell line (GM10253A and HybNeo3) were processed.

人类着丝粒（centromere）在有丝分裂染色体上表现为缢痕结构，并作为有丝分裂过程中动粒（kinetochore）组装的平台。生物物理实验曾提出，着丝粒区域的重复DNA可形成维持其功能必需的紧凑支架，但这一假说在非重复DNA区域发现新着丝粒（neocentromere）后被修正。为验证着丝粒是否具有特殊的染色质结构，我们解析了新着丝粒的结构。着丝粒形成过程伴随RNA聚合酶II（RNA pol II）的招募与主动转录，进而形成富集“开放”染色质纤维的去紧凑化负超螺旋结构域。与之相反，着丝粒化会导致抑制性表观遗传标记向周边区域扩散，该扩散以H3K27me3多梳蛋白边界与双向基因为界。该侧翼结构域呈转录沉默状态，并被部分重塑为类似含卫星DNA序列的“紧凑”染色质，同时表现出基因组不稳定性。我们提出，转录过程可破坏染色质结构，为动粒形成提供基础；而紧凑的着丝粒旁异染色质则可产生机械刚性。本研究采用RNA测序（RNA-Seq）技术，检测了HybNeo3与GM10253A细胞系中新着丝粒区域的转录水平。每个细胞系均设置两组生物学重复样本。