Identification and investigation of novel candidate genes for primary ciliary dyskinesia

你身体的几乎每个细胞都有一个细长的毛发状突起，叫做纤毛。纤毛可以被认为是“细胞的触角”，细胞通过它获得关于其环境的感觉信息。因此，纤毛具有许多器官发育和生理所必需的感觉功能，包括肾脏、神经系统、感觉器官、骨骼和胰腺。除了它们的感官功能，有些类型的纤毛能够弯曲或跳动，并参与液体运动。例如，在用于粘液运动的呼吸道衬里细胞和用于将新卵子飘向子宫的输卵管上就发现了这种“活动纤毛”。此外，精子细胞通过跳动的鞭毛游泳，鞭毛本质上是一种长长的可移动的纤毛。所有这些纤毛都是通过它们内部的“马达蛋白”来移动的。原发纤毛运动障碍是一种遗传性疾病，由于这些运动蛋白的失效，纤毛不活动或仅部分运动。总体而言，这是相当罕见的，但在一些社区，它的发生频率可以高达1：2200人。最明显的症状与粘液清除困难有关，例如导致频繁和破坏性的胸部感染。严重的病例还会出现内翻--器官定位紊乱(例如，心脏不再位于胸部的左侧)。如果及早诊断，那么治疗可能是有效的(例如物理治疗以清除肺部)，但诊断很困难，需要专业技术。发现PCD的遗传原因最终将有助于了解疾病，帮助诊断，并可能提供一条治疗途径。许多不同基因的突变导致PCD。一些突变存在于马达蛋白本身的基因中。然而，在大约50%-60%的PCD家族中，潜在的基因缺陷尚未被发现。我们正在解决的问题是如何加快发现导致PCD的基因突变。出人意料的是，我们的策略是观察果蝇--黑腹果蝇。果蝇很容易饲养和研究。复杂的遗传和细胞方法可以用来发现果蝇活动纤毛所需的基因。我们将研究扰乱这些基因功能的影响。这很容易实现，因为在果蝇中，运动纤毛是感觉和精子所必需的，所以运动纤毛有缺陷的果蝇很容易通过明显的感觉缺陷和雄性不育来发现。对于纤毛生物学的研究，在可能的情况下，使用果蝇比使用更复杂的生物更具成本效益和伦理上的可接受性。因此，我们的研究有助于实现减少对动物研究的依赖的目标。基因发现和分析的简便性是不够的。同样重要的是，纤毛的分子结构在昆虫和高等动物之间是完全保守的。因此，在果蝇身上发现的对纤毛运动很重要的基因很可能在人类身上也很重要。作为推论，我们在果蝇身上发现的基因是PCD病例中发生突变的主要嫌疑人。因此，尽管果蝇没有肺，但它为发现PCD的遗传原因提供了一条可能令人惊讶的途径。在我们从果蝇身上获得的证据的基础上，我们的合作者将在一组PCD家族中筛选新发现的基因突变。如果在这些家系中发现了基因变异，就会假设它们会导致这些家系中的PCD。但这一结论在成为证据之前还需要进一步的实验验证。其中一些验证将来自使用一系列分子和细胞技术对果蝇突变缺陷的进一步分析，以确定运动纤毛到底出了什么问题。

Almost every cell of your body has a thin, hair-like outgrowth called a cilium. Cilia can be thought of as the "cells' antennae", through which the cell gains sensory information about its environment. As such, the cilium performs sensory functions essential to the development and physiology of many organs, including kidney, nervous system, sense organs, bone and pancreas. In addition to their sensory functions, some types of cilia are capable of bending or beating and are involved in fluid movement. Such 'motile cilia' are found for example on cells lining the airways for mucus movement and the fallopian tubes for wafting a new egg towards the uterus. Moreover, sperm cells swim by means of a beating flagellum, which is essentially a long motile cilium. All these cilia move by means of banks of 'motor proteins' within them. Primary ciliary dyskinesia is an inherited disease in which cilia are immotile or only partially motile due to failure of these motor proteins. It is quite rare overall, but in some communities it can occur at a frequency of up to 1:2200 individuals. Most noticeable symptoms relate to difficulties in clearing mucus, leading for instance to frequent and damaging chest infections. Severe cases also have situs inversus - in which organ positioning is disrupted (e.g. the heart is no longer on the left side of the chest). If diagnosed early, then treatment can be effective (such as physiotherapy to clear lungs), but diagnosis is difficult and requires specialist techniques. Discovering the genetic causes of PCD will ultimately aid understanding of the disease, aid diagnosis, and potentially provide a route to therapy.Mutations in many different genes cause PCD. Some mutations are in genes for the motor proteins themselves. However, in some 50-60% of PCD families the underlying gene defect has not been discovered. The question we are addressing is how to accelerate the discovery of PCD-causing gene mutations. Our strategy, unexpectedly, is to look at the fruit fly, Drosophila melanogaster. The fruit fly is easy to rear and to study. Sophisticated genetic and cellular approaches can be used to discover genes that are required for motile cilia in Drosophila. We shall examine the effect of disrupting the function of these genes. This is quite straightforward to achieve because in Drosophila, motile cilia are required for senses and sperm, and so flies with defective motile cilia are easy to spot through obvious sensory deficits and male infertility. For studies into cilium biology it is cost-effective and ethically more acceptable to use Drosophila than more complex organisms where possible. Our research therefore helps to satisfy the goal of reducing reliance on animal research. Ease of gene discovery and analysis is not sufficient. Just as important is the fact that the molecular machinery of the cilium is completely conserved between insects and 'higher' animals. Therefore, genes discovered to be important for ciliary motility in Drosophila are likely to be important in humans too. As a corollary, the genes we discover in Drosophila are prime suspects to be mutated in cases of PCD. So, even though the fruit fly doesn't have lungs, it provides a perhaps surprising route to discovering the genetic causes of PCD.On the basis of the evidence we obtain in Drosophila, our collaborators will screen for mutations of newly identified genes in a panel of PCD families. If gene variants are found in such families, they would be hypothesised to cause the PCD in those families. But this conclusion would require further experimental verification before it becomes proof. Some of this verification will come from further analysis of the mutant defects in Drosophila using a range of molecular and cellular techniques, in order to define what exactly is going wrong with the motile cilia.