Dicentric chromosome formation and stability in humans

描述（申请人提供）：染色体遗传确保遗传和基因组信息的传递。染色体数目异常（非整倍体）和染色体结构改变导致出生缺陷、生殖异常和癌症。着丝粒是染色体分离和基因组稳定所必需的位点。正常染色体通常有一个着丝粒，但与出生缺陷和癌症相关的基因组重排产生的染色体中，两个着丝粒是物理连接的。在大多数模式生物中，这些双心性不是自然耐受的，正如75年前芭芭拉·麦克林托克最初在玉米中所阐明的那样。在人类中，双中心染色体的出现是非随机的，并且在细胞分裂过程中非常稳定。这种稳定性归因于着丝粒失活，这是一个鲜为人知的过程，其中一个着丝粒被功能抑制。我们的目标是确定负责双中心形成和长期稳定性的分子途径。我们假设：(A)共同双中心的形成与单中心染色体的基因组特征有关，(B)着丝粒失活通常是通过基因组或表观遗传机制发生的。研究人类着丝粒失活的一个主要障碍是缺乏实验系统。为了解决这个长期存在的问题，我们已经开发出了一些检测方法来设计人类的双中心染色体，这些染色体在分子上反映了自然发生的双中心染色体。工程双着丝粒是研究正常着丝粒功能、着丝粒抑制和基因组稳定性的模型系统。利用这些实验模型，我们提出了三个具体目标：1)确定双着丝粒形成的序列依赖机制；2)定义双着丝粒稳定的分子途径，包括与着丝粒失活相关的基因组、表观遗传和时间变化；3)实验测试使用蛋白质系缚和工程基因组缺失的着丝粒失活模型。总的来说，这些研究将确定在自然发生和实验产生的染色体融合中，外中心染色体非随机参与的机制基础。我们的研究也将对评估当前着丝粒功能模型至关重要，并为人类染色体上的着丝粒的指定和维持机制提供新的见解。

DESCRIPTION (provided by applicant): Chromosome inheritance ensures transmission of genetic and genomic information. Abnormal chromosome number (aneuploidy) and altered chromosome structure cause birth defects, reproductive abnormalities, and cancer. The centromere is the locus required for chromosome segregation and genome stability. Normal chromosomes typically have one centromere, but genome rearrangements associated with birth defects and cancer produce chromosomes in which two centromeres are physically linked. These dicentrics are not naturally tolerated in most model organisms, as originally illustrated in maize by Barbara McClintock nearly 75 years ago. In humans, dicentric chromosomes occur non-randomly and can be extremely stable during cell division. Such stability has been attributed to centromere inactivation, the poorly understood process by which one centromere is functionally suppressed. Our goal is to define molecular pathways responsible for dicentric formation and long-term stability. We hypothesize that (A) formation of common dicentrics is linked to genomic features of acrocentric chromosomes, and (B) centromere inactivation routinely occurs by either genomic or epigenetic mechanisms. A major impediment in studying centromere inactivation in humans has been the absence of experimental systems. To circumvent this long-standing problem, we have developed assays to engineer dicentric human chromosomes that molecularly mirror those that occur naturally. Engineered dicentrics represented a model system to study normal centromere function, centromere repression and genome stability. Using these experimental models, we propose three specific aims: 1) To identify sequence-dependent mechanisms of dicentric formation, 2) To define the molecular pathways by which dicentric chromosomes are stabilized, including genomic, epigenetic and temporal changes associated with centromere inactivation, and 3) To experimentally test models of centromere inactivation using protein tethering and engineered genomic deletions. Collectively, these studies will define the mechanistic basis for non-random participation of acrocentric chromosomes in naturally occurring and experimentally produced chromosome fusions. Our studies will also be critical for evaluating current models of centromere function, and provide new insights into mechanisms that specify and maintain centromeres on human chromosomes.