Mechanistic insights into priming and early gene activation processes in the haemopoietic system

所有的血细胞都来自干细胞，干细胞既能保留干细胞，又能发育成不同的血细胞。血液干细胞首先在胚胎中形成，然后在患者的余生中与其共处。在胚胎中，血细胞系统经过不同的阶段发育。在早期胚胎中，原始细胞(中胚层细胞)形成，可以发育成许多不同的细胞类型，如血细胞系统、血管系统和神经系统。当这些细胞向血细胞系统发育时，它们首先成为可以生成血管和血液干细胞的细胞，并在一段时间后才发展成血液干细胞。这些不同的发育阶段中的每一个都以精心安排的不同基因表达的开始为特征。正是这些基因的组合决定了每种细胞类型。最近研究的一个非常重要的主题是如何控制这些不同的基因，以及为什么它们在一种细胞类型中特定地被激活，而在另一种细胞类型中不被激活。现在很明显，基因是以非常不同的顺序启动的。在这个层次结构的顶端是编码蛋白质的基因，这些蛋白质与其他基因结合并控制它们的表达。我们已经证明，通过使用基于小鼠胚胎干细胞的实验系统来研究这些基因激活的非常早期的事件是可能的，该实验系统概括了体外胚胎发育。我们还能够证明，我们可以使用这个系统来调查基因启动时发生的最早事件。此外，我们已经证明，可以通过研究基因如何组织成染色质来跟踪这种早期事件。染色质是包装一米长的DNA分子以使其适合细胞核的所有蛋白质的组合。为了让基因变得活跃，这个“包装”需要打开。我们已经开发了跟随这种“开放”的技术，我们可以证明这个过程比基因表达的实际开始要早得多。在这项提议中，我们想要了解事件的顺序，染色质改变是如何发生的，以及哪些分子在驱动这种改变。我们还想确定已知的驱动染色质改变的重要因素的靶基因。这些实验对未来我们希望使用胚胎干细胞产生特定血细胞类型的实验非常重要。

All blood cells originate from stem cells which are capable of staying stem cells, but also can develop into different blood cells. Blood stem cells are first formed in the embryo and then stay with the individual for the rest of his natural life. In the embryo, the blood cell system develops via different stages. In the early embryo, primitive cells (mesoderm cells) are formed that can develop into many different cell types, such as the blood cells system, the blood vessel system and the nervous system. When these cells develop towards the blood cell system they first become cells that can make blood vessels as well as blood stem cells and only after a while develop into blood stem cells. Each of these different developmental stages is characterized by the carefully orchestrated onset of expression of different genes. It is the combination of these genes that specifies each cell type. A very important topic of recent research addresses the question of how these different genes are controlled and why they are specifically switched on in one cell type, but not in another. It is now clear that genes are switched on in a very distinct order. On top of this hierarchy are genes that encode for proteins that bind to other genes and control their expression. We have shown that it is possible to study very early events in the activation of such genes by using an experimental system based on mouse embryonic stem cells that recapitulates embryonic development in vitro. We have also been able to show that we can use this system to investigate the earliest events happening when genes are switched on. Moreover, we have shown that such early events can be followed by studying how genes are organized into chromatin. Chromatin is the combined name of all proteins that package the meter-long DNA molecule so it fits into the nucleus. In order for genes to become active, this 'packaging' needs to be opened up. We have developed techniques that follow this 'opening-up' and we could show that this process starts much earlier than the actual onset of gene expression. In this proposal we want to understand the order of events how chromatin alteration occurs and which molecules are driving such alterations. We also want to identify target genes for important factors already known to drive chromatin alterations. These experiments are important for future experiments where we want to use embryonic stem cells to generate specific blood cell types.