Role of CIZ1 in maintenance of epigenetic landscape in primary differentiated cells

发育中的胚胎细胞有能力变成成人体内所有不同类型的细胞。随着它们的专门化，它们逐渐关闭不需要的基因，直到它们只产生对其功能至关重要的产品。限制它们选择的一种方式是通过修饰与要关闭的基因密切相关的特定蛋白质。一旦建立，这些修饰，或标记，必须在每次细胞分裂时复制，这样子细胞就有了与亲本相同的标记，从而获得与亲本相同的基因库。我们正在研究确保商标被忠实复制的机制；阻止细胞偏离其选择路径的“质量控制”过程。具体来说，我们感兴趣的是选择的基因和添加标记（因子）的蛋白质是如何在堆积在细胞核中的大量DNA中找到彼此的。这些因子是在细胞核周围扩散，直到它们碰巧遇到正确的基因，还是有一个传递系统确保“信件”及时到达正确的“地址”？我们的实验将着眼于，在正常细胞中，这些因子是否局限于工厂场所，限制了它们向周围扩散的能力。这意味着基因必须经过工厂才能被标记，这样就可以对整个过程进行严格的控制。到目前为止，这方面的研究很少，因为（我们的数据表明）对工厂的限制似乎在研究人员常用的大多数细胞类型（干细胞、癌细胞、培养细胞）中缺失或被覆盖。为了了解对工厂的限制是否是身体中未患病细胞的常态，有必要对新分离的未适应实验室长期生长的细胞进行研究。通常，适应的细胞经历了与癌细胞发生的变化相似的变化，似乎已经失去了将关键因素限制在工厂的能力。只有通过研究新分离的细胞，我们才能了解正常细胞如何维持它们对基因的选择，然后才能了解在癌症的早期阶段，这种选择是如何被侵蚀的。最近我们发现，在正常细胞中，测试染色体需要一种名为CIZ1的蛋白质来i)获得关键标记，ii)从细胞核的一个位置短暂地迁移到另一个位置。我们认为这两个观察结果是有联系的，通过研究CIZ1的功能，我们可以确定基因靶向递送到空间限制因子是否在体内正常细胞的细胞核内正常运作。我们的目标是利用这些结果来了解CIZ1对于保持适当的标记是多么重要，从而防止失去控制和疾病的出现。我们特别关注CIZ1改变的影响（在几种不同类型的早期癌症中常见），因为实验性去除CIZ1促进培养细胞明显倾向于放松基因和因子的空间分离。

Cells in a developing embryo have the capability to become all of the different types of cell in the adult body. As they specialize they gradually turn off genes that are not required, until they only produce products that are essential to their function. One of the ways that their choice is restricted is by modification of specific proteins that are closely associated with the genes to be shut down. Once established, these modifications, or marks, must be copied each time a cell divides so that daughter cells have the same marks as their parents, and therefore access the same repertoire of genes as their parents. We are studying the mechanism that ensures marks are faithfully copied; the 'quality control' process that stops a cell from drifting away from its chosen path.Specifically, we are interested in how the chosen genes and the proteins that add the marks (factors) find each other among the mass of DNA packed into the cell nucleus. Do the factors diffuse around the nucleus until they happen to come across the correct genes, or is there a delivery system that ensures 'letters' reach the right 'address' in good time? Our experiments will look at whether, in normal cells, the factors are confined to factory sites, restricting their ability to diffuse around. This would mean that genes must visit factories to be marked, which could afford tight control over the process. So far, there has been very little investigation of this because (our data suggest) restriction to factories appears to be absent or overridden in most of the cell types that are commonly used by researchers (stem cells, cancer cells, cultured cells). In order to understand whether restriction to factories is the norm for non-diseased cells in the body, it is necessary to work with newly isolated cells that have not been adapted to long-term growth in a laboratory. Typically, adapted cells have undergone changes that are similar to changes that take place in cancer cells, and appear to have lost the ability to restrict key factors to factories. Only by studying newly isolated cells will we understand how normal cells maintain their choice of genes, and then be able to understand how this is eroded during the early stages of cancer.Recently we showed that a protein called CIZ1 is required, in normal cells, for a test chromosome to i) acquire key marks and ii) briefly relocate from one position in the nucleus to another position. We think that these two observations are linked and that, by studying the function of CIZ1 we can establish whether targeted delivery of gene to spatially restricted factor normally operates inside the nucleus of normal cells in the body. We aim to use the results to understand how important CIZ1 is to maintain appropriate marks, and so guard against loss of control and emergence of disease. We are specifically concerned with the effect of alterations in CIZ1 (common in early stage cancers of several different types), as experimental removal of CIZ1 promotes the apparent tendency of cultured cells to loosen spatial separation of gene and factor.