Smithies O, Maeda N
Department of Pathology, University of North Carolina at Chapel Hill 27599-7525, USA.
Proc Natl Acad Sci U S A. 1995 Jun 6;92(12):5266-72. doi: 10.1073/pnas.92.12.5266.
Gene targeting allows precise, predetermined changes to be made in a chosen gene in the mouse genome. To date, targeting has been used most often for generation of animals completely lacking the product of a gene of interest. The resulting "knockout" mice have confirmed some hypotheses, have upset others, but have rarely been uninformative. Models of several human genetic diseases have been produced by targeting--including Gaucher disease, cystic fibrosis, and the fragile X syndrome. These diseases are primarily determined by defects in single genes, and their modes of inheritance are well understood. When the disease under study has a complex etiology with multiple genetic and environmental components, the generation of animal models becomes more difficult but no less valuable. The problems associated with dissecting out the individual genetic factors also increases substantially and the distinction between causation and correlation is often difficult. To prove causation in a complex system requires rigorous adherence to the principle that the experiments must allow detection of the effects of changing only a single variable at one time. Gene targeting experiments, when properly designed, can test the effects of a precise genetic change completely free from the effects of differences in any other genes (linked or unlinked to the test gene). They therefore allow proofs of causation.
基因打靶能够对小鼠基因组中选定的基因进行精确的、预先确定的改变。到目前为止，基因打靶最常用于培育完全缺乏目标基因产物的动物。所产生的“基因敲除”小鼠证实了一些假说，推翻了另一些假说，但几乎从未没有提供信息。通过基因打靶已经建立了几种人类遗传性疾病的模型——包括戈谢病、囊性纤维化和脆性X综合征。这些疾病主要由单个基因的缺陷决定，并且它们的遗传模式已被充分了解。当所研究的疾病具有由多种遗传和环境因素组成的复杂病因时，动物模型的建立变得更加困难，但同样有价值。与剖析个体遗传因素相关的问题也大幅增加，因果关系和相关性之间的区分往往很困难。要在复杂系统中证明因果关系，需要严格遵循这样的原则：实验必须能够检测到每次仅改变一个变量所产生的影响。如果设计得当，基因打靶实验可以测试精确基因变化的影响，而完全不受任何其他基因（与测试基因连锁或不连锁）差异的影响。因此，它们能够证明因果关系。
