Transcriptional control of cell fate decisions by chromatin remodelling proteins

一个细胞的身份是由它的基因决定的。例如，位于心脏的细胞将表达心脏基因，但不表达对肝脏或大脑功能重要的基因。相反，肝细胞表达肝脏基因，但不表达心脏或肺基因。在胚胎发育期间，动物由不同的干细胞群形成，这些干细胞能够产生在成年生物体中发现的无数不同的细胞类型。当干细胞经历分化成新细胞类型的过程时，至关重要的是它们打开适合新细胞类型的基因，但也关闭定义“干细胞”身份的基因，并阻止任何与其他细胞类型相关的基因。如果不能正确调节所有这些不同类型的基因的表达，可能会导致做出错误的决定，或者在需要时无法做出任何决定。这种失败的后果可能是发育异常或癌症。因此，毫不奇怪，我们的细胞含有许多蛋白质，它们的工作是确保基因表达的正确控制。该提案集中在两种这样的蛋白质上，称为Chd 4和Brg 1。这些蛋白质控制基因在细胞内包装的方式。虽然在机械水平上，这两种蛋白质似乎具有相似的活性，但许多研究发现它们实际上倾向于相反地工作。我们知道，任何一种蛋白质的缺失都会导致早期发育失败，而且这两种蛋白质在癌症中经常被发现缺失或突变。我们认为，正是Chd4和Brg1之间的这种对立活动的平衡，微调基因表达模式，这种平衡对于细胞成功做出发育决定至关重要。然而，这些蛋白质的生物化学活动究竟如何控制基因表达，以及这两者是否真的直接控制发育过程中相同基因的表达，目前还没有很好的了解。在本文提出的工作中，我们将使用尖端技术来非常准确地定义这些蛋白质在干细胞和早期胚胎细胞中的功能，因为它们做出了第一个决定。我们将展示一种蛋白质的缺失如何影响其他关键调控蛋白的功能，以及这如何导致发育失败。然后，我们将研究这些蛋白质如何在哺乳动物胚胎发生的第一个细胞命运决定过程中发挥作用。该项目将揭示基因表达是如何在细胞做出决定时被控制的，以及细胞如何在正常发育过程中使用这些蛋白质来精确控制细胞命运的选择。这将为创造控制哺乳动物细胞中基因表达的新方法提供信息。这些方法可能在预防癌症进展方面具有相当大的益处，并能够实现更有效和更有效的方案，以在再生医学中使用干细胞。

A cell's identity is defined by its genes. A cell located in the heart, for example, will express heart genes, but not genes important for liver or brain function. Conversely, liver cells express liver genes but not heart or lung genes. During embryonic development animals are formed by different groups of stem cells, which are able to give rise to the myriad of different cell types found in an adult organism. When stem cells undergo the process of differentiating into a new cell type, it is critically important that they turn on genes appropriate for the new cell type, but also turn off the genes that define a 'stem cell' identity and also keep off any genes associated with other cell types. Failure to properly regulate expression of all these different kinds of genes can result in the wrong decisions being made, or the inability to make any decision when required. The consequences of such failure can be developmental abnormalities or cancer. Unsurprisingly, then, our cells contain many proteins whose jobs are to ensure the proper control of gene expression. This proposal focusses on two such proteins, called Chd4 and Brg1. These proteins control the way genes get packaged within the cell. Though at a mechanistic level these two proteins appear to have similar activities, a number of studies have found that they actually tend to work in opposition. We know that loss of either protein results in failed development from very early stages, and both proteins are often found to be deleted or mutated in cancer. We propose that it is precisely this balance of opposing activities between Chd4 and Brg1 that fine tunes gene expression patterns, and that this balance is crucial for cells to successfully make developmental decisions. Yet exactly how the biochemical activities of these proteins controls gene expression, and whether the two really directly control the expression of the same genes during development is not well understood. In the work proposed herein we will use cutting edge technologies to very accurately define the function of these proteins in stem cells and in early embryonic cells as they make their very first decisions. We will show how loss of one either protein impacts the function of other key regulatory proteins, and how this leads to developmental failure. We will then examine how these proteins function during the very first cell fate decision in mammalian embryogenesis. Together this project will reveal how gene expression is controlled as cells make decisions, and how the cells use these proteins to precisely control cell fate choices during normal development. This will inform the creation of new methods for controlling gene expression in mammalian cells. Such methods could be of considerable benefit in efforts to prevent the progression of cancer, and to enable more efficient and effective protocols to use stem cells in regenerative medicine.