Resolving the basis of phenotypically variable hereditary abnormalities of eye formation

我们的眼睛是在胚胎发育早期从脑组织中长出来的。形成眼睛的细胞起源于神经板，这是中枢神经系统的前体。当神经板折叠形成大脑时，形成眼睛的细胞向外侧凸出，形成视杯，这种结构后来分化成眼睛。每个视杯都经历了形状的改变，组织融合闭合了存在于视杯一侧的间隙（视裂），从而形成了完整的球形眼睛。形成眼睛的细胞运动的复杂编排是形态发生的一个例子——胚胎细胞形成组织和器官的过程。许多调节眼睛形成的基因尚未被确定。需要解决这种知识缺乏的一个原因是，先天性眼睛畸形，如无眼症（缺少眼睛）、小眼症（小眼睛）和结肠瘤（视裂隙融合失败），与生命和生殖相适应，在人群中相对常见。由于这些都是先天性缺陷，这意味着眼睛问题从出生开始就存在。无眼症患者失明，而小眼症和结肠瘤患者可能有严重的视力障碍。例如，结肠瘤是视力问题的常见原因，可引起视网膜脱离和白内障，并经常导致失明。在这个项目中，我们将使用斑马鱼胚胎来鉴定对眼睛形成重要的基因和基因相互作用。斑马鱼胚胎体积小，透明，外部发育，便于研究完整动物的正常发育和疾病。再加上它们易于进行遗传分析，这些特征使鱼胚胎成为研究正常和病理条件下眼睛形成的良好模型系统。事实上，我们可以在健康鱼和携带一种或多种影响眼睛形成的基因突变的鱼的活胚胎中看到发育中的眼睛的所有细胞。因此，我们可以通过对鱼类的研究来确定眼睛形成所需的基因，并了解这些基因构建功能眼睛的机制。虽然一些先天性眼睛形成异常是由于单个基因的突变，但我们怀疑在许多情况下，这些缺陷是由于两个或更多基因的破坏。因此，在这个项目中，我们将使用新颖的、强大的方法，使我们能够系统地分析两个或多个基因同时被破坏的后果，这些基因是在无功能时导致眼睛缺陷的候选基因。为了促进这项研究，我们目前的MRC资金使我们能够开发携带突变的鱼类，当额外的基因被破坏时，这些突变使鱼类更有可能表现出眼睛表型。我们将移除这些“敏感”鱼线中一个或多个额外基因的功能，以识别对眼睛形成重要的新基因和基因相互作用。我们还将研究几个基因的功能，当这些基因被破坏时，会导致鱼和人类非常相似的眼睛缺陷，尽管我们知道这些基因很重要，但我们不知道它们是如何起作用的。最后，我们将研究为什么携带相同基因突变的个体会表现出截然不同的眼睛表型。为了促进这一点，我们有鱼线，我们可以进行遗传或环境干扰，影响眼睛缺陷的严重程度。总的来说，我们的研究将有助于弥合模型系统和人类疾病表型的最高质量研究之间的差距。我们将提高我们对正常眼睛发育的理解，并将使用新的人眼疾病斑马鱼模型来进一步了解遗传性眼部畸形的原因。我们的研究在先天性眼形成异常的诊断中也有很大的价值。

Our eyes start out as outpocketings of brain tissue during early embryonic development. The cells destined to form the eyes originate within the neural plate, the precursor of the central nervous system. As the neural plate folds up to form the brain, the eye-forming cells bulge out laterally forming optic cups, the structures that later differentiate as eyes. Each optic cup undergoes shape changes and tissue fusion closes a gap (the optic fissure) present on one side of the cup, leading to formation of the intact globe shaped eye. The complex orchestration of cell movements that form the eyes is an example of morphogenesis - the process by which embryonic cells form into tissues and organs. Many of the genes that regulate the formation of the eye have yet to be identified. One reason that this lack of knowledge needs to be addressed is that congenital malformations of the eye, such as anophthalmia (lack of eyes), microphthalmia (small eyes) and coloboma (a failure in optic fissure fusion), being compatible with life and reproduction, are relatively common in the human population. As these are congenital defects, this means that eye problems are present from birth. While anophthalmic patients are blind, microphthalmic and coloboma patients can have severe visual impairment. For instance, colobomas are a common cause of visual problems, can cause retinal detachment and cataracts, and often lead to blindness.In this project, we will use zebrafish embryos to identify genes and genetic interactions important for eye formation. Zebrafish embryos are small, transparent and develop externally, facilitating the study of normal development and disease in the intact animal. Together with their amenability to genetic analysis, these features make fish embryos an excellent model system to study eye formation in normal and pathological conditions. Indeed, we can visualise all of the cells in the developing eye in living embryos both in healthy fish and in fish carrying one or more genetic mutations that compromise eye formation. Consequently, we can use research in fish both to identify those genes needed for eye formation and to understand the mechanisms by which such genes build functional eyes.Although some congenital abnormalities of eye formation are due to mutations in single genes, we suspect that in many cases, such defects are due to disruption of two or more genes. Consequently, in this project, we will use novel, powerful approaches that allow us to systematically analyse the consequences of simultaneous disrupted function of two or more genes that are candidates for causing eye defects when non-functional. To facilitate this research, our current MRC funding has enabled us to develop lines of fish carrying mutations that make the fish more likely to show eye phenoytpes when additional genes are disrupted. We will remove function of one or more additional genes in these "sensitised" fish lines to identify new genes and genetic interactions important for eye formation. We will also study the function of several genes that, when disrupted, give very similar eye defects both in fish and in humans as although we know these genes to be important, we do not understand how they function. Finally, we will study why individuals carrying the same genetic mutations can show quite different eye phenotypes. To facilitate this, we have lines of fish in which we can perform genetic or environmental perturbations that affect the severity of the eye defects. Overall, our research will help to bridge the gap between the highest quality research in model systems and human disease phenotypes. We will improve our understanding of normal eye development and will use new zebrafish models of human eye diseases to gain further insights into the causes of hereditary ocular malformations. Our research also has the potential to be of great value in the diagnosis of congenital abnormalities of eye formation.