Transgenic approaches to sensory neuron signalling

最近在理解遗传学方面有了显著的进展。我们知道整个人类基因组的序列，并从广义上理解细胞是如何制造RNA分子和蛋白质的，这是成年生命形式正常发育和功能的基础。与我们对进化的看法一致的是，许多在人类生理学中起作用的分子系统也存在于更简单的生物体中，这一点已经变得很清楚。老鼠尤其有趣，因为它们可以进行基因改造，改变基因表达模式的后果可以在许多层面上进行检查——从细胞功能、器官功能甚至行为的角度来看。这激发了一项雄心勃勃的国际尝试，即修改所有小鼠基因的表达并检查其后果。所获得的信息对了解哺乳动物的基本生理学非常有用，因此对了解人类的健康和疾病也具有重大意义。在我们自己的实验室里，我们发现了一种蛋白质，它可以向中枢神经系统发送电信号，表明疼痛刺激的存在。当我们删除这个基因，不产生蛋白质时，老鼠基本上就没有疼痛了。在这项工作之后，一些研究小组将注意力集中在了人类遗传疼痛疾病中编码一种非常相似蛋白质的基因上。他们发现，使这种蛋白质过度活跃的基因突变导致了人类的慢性疼痛综合征。他们还发现，少数不再产生这种蛋白质功能版本的人没有疼痛。这对于决定生产新的止痛药的目标分子是很重要的。据估计，发达国家有4000万人患有慢性疼痛，目前的药物不适合或无效。因此，我们的小鼠遗传分析帮助确定了一种蛋白质，这种蛋白质可能对开发一种新的止痛药非常有用，而不是现有的止痛药。我们目前的提议利用了过去十年改进的新技术，使我们能够删除特定组织或细胞类型中的基因。我们知道，有许多不同种类的感觉神经元支配着皮肤、肌肉和内脏，并向大脑发出触摸、肌肉位置或疼痛刺激等信号。我们可以杀死由蛋白质组成的不同种类的感觉神经元，然后看看这些特殊感觉神经元的功能是什么。我们还可以通过删除这些细胞中的单个基因来识别负责对触摸、温度变化或疼痛刺激做出反应的蛋白质。我们还可以研究皮肤中的温度或压力感受器如何通过停止皮肤细胞中的蛋白质表达来间接向感觉神经元发出信号。类似的技术也可以用来检测中枢神经系统的电信号分子。一些被认为与免疫反应有关的细胞现在已被证明能够促进疼痛状态。我们还将研究它们是如何做到这一点的，通过删除编码可溶性信使的基因，这些信使是这一行动的候选者。因此，目前的项目汇集了一个由遗传学专家、测量神经系统电信号的科学家和评估老鼠行为的专家组成的团队，以了解更多关于不同种类的感觉神经元的专门功能、它们如何向中枢神经系统发出信号，以及它们可能与其他类型的细胞相互作用以感知外部环境的重要性。我们相信，我们的研究将确定疼痛检测系统的组成部分，这可能对未来的药物开发很重要。此外，我们将了解更多关于感觉神经元的功能和它们与其他细胞的相互作用。

There have been remarkable advances in understanding genetics recently. We know the sequence of the entire human genome, and understand in broad terms how cells make RNA molecules and proteins which underlie normal development and the functioning of adult life-forms. It has become clear, consistent with our ideas about evolution, that many of the molecular systems that function in human physiology also exist in simpler organisms. Mice are particularly interesting, because they can be modified genetically and the consequences of changing patterns of gene expression can then be examined at many levels - in terms of cellular function, organ function and even behaviour. This has stimulated an ambitious international attempt to modify the expression of all mouse genes and examine the consequences. The information obtained is extremely useful for understanding the basic physiology of mammals, and therefore also has enormous significance for understanding health and disease in man. In our own lab we identified a protein that sends electrical signals to the central nervous system, signaling the existence of painful stimuli. When we deleted the gene so that no protein was made, the mice were essentially pain free. After this work, a number of groups homed in on the gene that encodes a very similar protein in humans with inherited pain disorders. They found that mutations in the gene that made the protein over-active resulted in chronic pain syndromes in humans. They also found that a small number of people that no longer made a functional version of this protein were pain free. This is important in deciding what molecules to target for the production of new pain-killing drugs. Estimates suggest that 40 million people in the developed world suffer chronic pain for which present drugs are unsuitable or ineffective. Thus our mouse genetic analysis has helped identify a protein which may be very useful for the development of pain-killing drugs of a new class to those that exist at present. Our present proposal exploits new technology refined over the past decade that enables us to delete genes in specific tissues or cell types. We know that there are many different sorts of sensory neurons that innervate the skin, muscle and viscera, and signal events such as touch, muscle position or painful stimuli to the brain. We can kill different sorts of sensory neurons defined by the proteins they make, and see what the functions of these specialized sensory neurons are. We can also identify the proteins that are responsible for responding to touch, temperature changes or painful stimuli by deleting individual genes in these cells. We can also examine how temperature or pressure receptors in the skin may signal indirectly to the sensory neurons by stopping protein expression in skin cells. Similar techniques can be used to examine the molecules that underlie electrical signaling to the central nervous system. Some cells assumed to be involved with immune responses have now been shown to be able to contribute to pain states. We will also examine how they do this, by deleting genes that encode soluble messengers that are candidates for this action. The present project thus assembles a team of expert geneticists, scientist who measure electrical signaling in the nervous system, and experts in assessing mouse behaviour to learn more about the specialized function of different sorts of sensory neurons, how they signal to the central nervous system, and the importance of other cell types with which they may interact to sense the external environment. We are confident that our studies will identify components of the pain detection system that may be important for drug development in the future. In addition we will learn far more about the functioning of sensory neurons and their interactions with other cells.