Regulation of DNA repair pathway choice during development

遗传密码（DNA）包含了一幅蓝图，用以产生细胞以程序化的方式执行其各种功能所需的所有机制。保存这种密码对于维持正常的细胞功能至关重要。然而，DNA不断受到导致遗传密码变化的因素的攻击。当细胞复制它们的DNA （DNA复制）时，通过改变DNA构建块的序列（突变），或者通过在DNA分子中产生断裂，就会发生这种情况。有趣的是，DNA损伤也发生在严格调控的环境中，在许多正常的细胞过程中，包括免疫系统的发育和遗传信息的传递，因为细胞在减数分裂过程中分离了它们的基因组。因此，细胞已经发展出一个复杂的通路网络来检测DNA损伤，并通过DNA修复来纠正这些错误。观察结果强调了DNA修复的重要性，即这些途径中的缺陷会导致各种衰弱的临床症状，包括早衰、免疫系统衰竭、发育异常和癌症风险增加。因此，了解DNA修复将提供一些基本的生物学过程的见解，以及关于许多疾病状态的分子基础的线索。DNA双螺旋双链断裂（双链断裂；DSBs）是最具毒性的DNA损伤之一。这些可以通过直接重新连接DNA断裂来修复（非同源末端连接；NHEJ），或者使用同源DNA作为模板来恢复基因组完整性（同源定向修复；HDR）。这两种途径的组成部分很好地表征了。然而，影响细胞是否通过NHEJ或HDR修复损伤的因素仍然相对不明确。DNA修复缺陷导致多种发育异常，包括抗体产生缺陷、颅面异常和神经系统变性。尽管如此，当多细胞生物发育成各种特殊组织时，这些途径是如何被调节的，这在很大程度上仍未被探索。从细菌到人类，所有生物的DNA修复都是通过类似的机制实现的。因此，在相对简单的模式生物中研究这些途径增加了我们对这些过程如何在人类中起作用的理解。不幸的是，某些常用的模式生物缺乏人类DNA DSB修复途径的关键成分，并且没有经过发育程序进入专门的细胞类型。相比之下，居住在土壤中的变形虫盘基ostelum是一种容易生长和操纵的生物，它经历了一个相对简单的发育程序。因此，它是研究细胞类型规范和分化的常用模型。此外，我们之前的工作已经表明，这种生物中的DNA DSB修复途径比其他常用的模式生物更类似于人类。本研究的目的是利用这些观察结果，并以盘基骨柱为模型，研究DNA DSB修复途径的选择是如何在生物体的生命周期和发育过程中被调节的。除了提供Dictyostelium如何调节DNA修复途径的见解外，这些研究可能适用于包括人类在内的其他高等生物如何实现这些过程。

The genetic code (DNA) contains a blueprint to produce all the machinery required for a cell to perform its various functions in a programmed manner. Preservation of this code is critical to maintain normal cellular functions. However, DNA is under continual attack from agents that cause changes in the genetic code. This can occur when cells copy their DNA (DNA replication), through changes in the sequence of DNA building blocks (mutation), or by creating breaks in the DNA molecule. Interestingly, DNA damage also occurs in a tightly regulated context during a number of normal cellular processes including development of the immune-system and transfer of genetic information as cells segregate their genomes in a process know as meiosis. Therefore, cells have developed a complex network of pathways to detect DNA damage when it occurs and correct these faults by DNA repair. The importance of DNA repair is underscored by the observations that defects in these pathways leads to a variety of debilitating clinical symptoms including premature ageing, immune-system failure, developmental abnormalities and increased cancer risk. Therefore, understanding DNA repair will provide insights into several fundamental biological processes in addition to clues regarding the molecular basis of a number of disease states. Breaks in both strands of the DNA double helix (double strand breaks; DSBs) are one of the most toxic varieties of DNA damage. These can be repaired by directly re-joining DNA breaks (non-homologous end-joining; NHEJ), or by using homologous DNA as a template to restore genome integrity (homology-directed repair; HDR). The components of these two pathways are well characterised. However, the factors that influence whether cells repair damage by NHEJ or HDR remains relatively ill defined. Defects in DNA repair lead to a variety of developmental abnormalities including defective antibody production, cranial-facial abnormalities and degeneration of the nervous system. Despite this, how these pathways are regulated as multi-cellular organisms develop into a variety of specialised tissues remains largely unexplored. DNA repair is achieved by similar mechanisms in all organisms from bacteria to humans. Therefore, studying these pathways in relatively simple model organisms has increased our understanding of how these processes work in humans. Unfortunately, certain commonly used model organisms lack key components of human DNA DSB repair pathways and do not undergo a developmental program into specialised cell types. In contrast, the soil dwelling amoeba Dictyostelium is an easily grown and manipulated organism that undergoes a relatively simple developmental program. As such, it is a commonly used model to study cell type specification and differentiation. In addition, our previous work has illustrated that DNA DSB repair pathways in this organism are more similar to humans than other commonly used model organisms. The aims of this research are to exploit these observations and use Dictyostelium as a model to study how DNA DSB repair pathway choice is regulated in the context of an organism's life cycle and developmental program. In addition to providing insights into how DNA repair pathways are regulated in Dictyostelium, these studies will likely be applicable to how these processes are achieved in other higher organisms including humans.