Epigenetic regulation of gene expression by the exoribonuclease pacman

生物体从卵到成体的发育需要一组基因在特定的时间以正确的顺序被开启和关闭。如果在必要时不关闭基因，细胞可能会继续以不受控制的方式繁殖，导致癌症。除了在癌症中的重要作用外，基因调控在控制干细胞自我更新和细胞特化途径之间的平衡方面也是至关重要的，这是形成体内特定细胞和组织所必需的。由于干细胞在再生医学中具有巨大的潜力来替代有缺陷的组织，因此了解基因控制对于利用这些细胞的潜力是至关重要的。因此，研究基因关闭(以及开启)的机制对于提供有可能导致新疗法的基础知识至关重要。以果蝇为模型生物，我们最近发现一种名为Pacman的酶参与了想象盘的生长和分化，这些盘形成了翅膀和腿等成年结构。成像盘类似于干细胞，因为它们携带着构建成人组织的信息。我们已经证明，吃豆人通常会影响一种名为Simjang的蛋白质的产生，该蛋白质反过来控制着一个基因沉默复合体(NuRD复合体)，该复合体关闭部分染色体，防止基因被激活。这种基因沉默复合体很重要，因为已知它参与了许多关键的细胞事件，包括组织再生、血细胞形成、衰老和癌细胞的扩散。这是第一次发现参与信使RNA降解的酶直接影响基因沉默复合体。这个项目的目的是了解吃豆人是如何利用Simjang来控制涉及生长和分化的特定基因集的。我们的假设是，在正常细胞中，Simjang信使RNA被以某种方式标记为要破坏，因此Simjang蛋白不会产生太多。这意味着没有足够的Simjang来打开基因沉默复合体。这些基因沉默复合体，当被激活时，通常起到阻止翼盘生长和分化的‘刹车’的作用。因此，当Simjang没有按下刹车时，这些基因就不会被启动，从而允许组织的正常生长和发育。当Pacman基因发生突变时，Simjang RNA没有(或很少)降解，导致更多的Simjang蛋白质，从而开启基因沉默复合体(即按下刹车)，从而开启阻止组织生长和发育的基因。在这个项目中，我们的目标是验证这一假说，找出这一基因控制途径的细节，并识别起到阻止生长和发育的刹车作用的基因。构成这一提议基础的基因调控机制是完全新的；到目前为止，还没有研究小组发现RNA降解和基因沉默之间的这种联系。由于所有涉及的蛋白质在果蝇和人类中都是相似的，我们发现的新的“控制模块”很可能与人类的基因调控有关。由于已知Pacman在伤口愈合、细胞膜迁移和男性生育等其他重要细胞事件中起着重要作用，这项工作也可能揭示这些过程在其他组织中的分子机制。因此，我们在这个项目中获得的见解可能有助于我们改进癌症和其他疾病的治疗，也有助于我们了解组织生长和发育的方式。因此，该项目将为基因调控的新方法提供有价值的见解，该方法可用于新疗法的开发。

Development of an organism from egg to adult requires sets of genes to be switched on and off at particular times and in the correct order. If genes are not switched off when necessary, cells can continue to multiply in an uncontrolled way leading to cancer. As well as being important in cancer, gene regulation is crucial in controlling the balance between stem cell self-renewal and pathways to cell specialisation which are required to form the particular cells and tissues in the body. Since stem cells have a vast potential in regenerative medicine for the replacement of defective tissue, the understanding of gene control is crucial for harnessing the potential of these cells. Therefore studying the mechanisms whereby genes are switched off (as well as on) is vitally important for providing basic knowledge that has potential to lead to novel therapeutics. Using the fruit fly Drosophila as a model organism, we have recently discovered that an enzyme named Pacman is involved in the growth and differentiation of imaginal discs, which form adult structures such as wings and legs. Imaginal discs are similar to stem cells in that they carry the information to build the adult tissue. We have shown that Pacman normally affects the production of a protein called Simjang (Korean for 'strong heart') which in turn controls a gene silencing complex (the NuRD complex) which shuts down parts of the chromosome, preventing genes from being turned on. This gene silencing complex is important because it is known to be involved in many critical cellular events including tissue regeneration, formation of blood cells, ageing and spread of cancer cells. This is the first time that an enzyme involved in degradation of messenger RNA has been shown to be directly affecting a gene silencing complex. The aim of this project is to understand how the Pacman uses Simjang to control particular sets of genes involved in growth and differentiation. Our hypothesis is that, in normal cells, simjang messenger RNA is somehow 'tagged' for destruction so that not much of Simjang protein is made. This means that there is not enough Simjang to turn on the gene silencing complexes. These gene silencing complexes, when activated, normally act as 'brakes' to prevent growth and differentiation of the wing disc. Therefore when the brake is not pressed by Simjang, these genes are not turned on, allowing normal growth and development of the tissue. When the pacman gene is mutated, there is no (or little) degradation of simjang RNA, resulting in more Simjang protein, which turns on the gene silencing complexes (i.e. presses the brake) therefore switching on genes that prevent tissue growth and development. In this project we aim to test this hypothesis, find out the details of this gene control pathway and identify the genes which act as brakes to prevent growth and development. The mechanism of gene regulation which forms the basis of this proposal is entirely novel; as yet no research group has found this link between RNA degradation and gene silencing. Since all the proteins involved are similar in Drosophila and humans the new 'control module' we have discovered is likely to be relevant to gene regulation in humans. Since Pacman is known to be important in other important cellular events such as wound healing, migration of cell sheets, and male fertility, this work may also shed light on the molecular mechanisms of these processes in other tissues. Therefore the insights we gain during this project may help us to improve treatment for cancer and other diseases and also help us to understand the ways that tissues grow and develop. This project will therefore provide valuable insights into a new method of gene regulation which can be used in the development of new therapeutics.