Transgenic approaches to sensory neuron signalling

最近，人们在理解遗传学方面取得了显著进展。我们知道整个人类基因组的序列，并从广义上了解细胞是如何制造RNA分子和蛋白质的，这些分子和蛋白质是成人生命形式正常发育和功能的基础。与我们关于进化的观点一致的是，在人类生理学中起作用的许多分子系统也存在于更简单的生物体中，这一点已经变得清晰起来。老鼠特别有趣，因为它们可以被基因改造，然后可以在许多层面上检查基因表达模式变化的后果--从细胞功能、器官功能甚至行为方面。这激发了一项雄心勃勃的国际尝试，试图改变所有老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巨大的意义。在我们自己的实验室里，我们发现了一种蛋白质，它向中枢神经系统发送电信号，发出痛苦刺激存在的信号。当我们删除该基因，这样就不会产生蛋白质，小鼠基本上就没有疼痛了。在这项工作之后，一些研究小组找到了一种基因，该基因编码了一种与遗传性疼痛障碍患者非常相似的蛋白质。他们发现，使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，不再制造这种蛋白质功能版本的一小部分人是没有疼痛的。这对于决定生产新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，目前的药物不合适或无效。因此，我们的小鼠基因分析帮助确定了一种蛋白质，该蛋白质可能对开发现有止痛药以外的新类别止痛药非常有用。我们目前的方案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，有许多不同类型的感觉神经元支配皮肤、肌肉和内脏，并向大脑发送信号，如触摸、肌肉位置或疼痛刺激。我们可以杀死由它们制造的蛋白质定义的不同种类的感觉神经元，并了解这些专门的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个别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阻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查中枢神经系统电信号背后的分子。一些被认为与免疫反应有关的细胞现在被证明能够对疼痛状态做出贡献。我们还将通过删除编码可溶性信使的基因来研究它们是如何做到这一点的，这些基因是这一行动的候选者。因此，本项目组建了一个由专家遗传学家、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，以更多地了解不同类型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，以及它们可能与之相互作用的其他细胞类型对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件，这些组件可能对未来的药物开发具有重要意义。此外，我们还将更多地了解感觉神经元的功能及其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.