Can gene therapy expand sensory capacity in the adult?

成人神经系统的可塑性有多大？动物的行为能否通过传递一种编码光敏感蛋白的基因到视网膜上合适的神经元而改变？如果这个问题的答案是肯定的，那就意味着神经系统有足够的可塑性，可以重塑成人的神经回路，从而带来行为上的改变。如果这个问题的答案是肯定的，它将对我们对神经可塑性的理解产生巨大的影响，它将为人类疾病的基因治疗开辟新的前景，它将使我们能够创建一个模型系统，直接探索神经回路建立和重塑的机制。大多数新大陆灵长类动物，包括松鼠猴，在x染色体上有一个单一的视觉色素基因。然而，在这个位点上有三个等位基因，每个等位基因编码一种光谱上不同的色素。这三个等位基因对应于L和M色素基因，它们是人类红绿色觉的基础，而猴子只有一条X染色体，因此是人类男性中常见的遗传性红绿色觉缺陷的模型。人类这种形式的色觉丧失是由X染色体上除一个外的所有视觉色素基因缺失引起的。为了拥有正常的三色视觉，男性必须至少有一个L和一个M色素基因。在x连锁色素基因位点杂合的雌性松鼠猴具有与人类相似的三色视觉。因此，在这个物种中，建立三色视觉所必需的神经回路是存在的，并且当第三种视觉色素基因在发育过程中出现时，很明显被利用。我们建议通过在视网膜下注射携带人类L视蛋白基因的重组腺相关病毒，在成年雄性松鼠猴的视网膜上添加第三种锥型。这三种视锥细胞类型分别是雄性松鼠猴视网膜的内源性S和M视锥细胞，加上用rAAV病毒转导并表达人类L色素的M克隆。我们将监测视网膜下注射前后的色觉行为，以确定动物的色觉是否从二色变为三色。

How plastic is the adult nervous system? Can an animal's behavior be changed by delivering a gene encoding a light sensitive protein to the appropriate neuron in the retina. If the answer to this question is yes, it means that the nervous systems is sufficiently plastic to allow remodeling of the adult neural circuitry to the extent that it would bring about a change in behavior. If the answer to this question is yes, it will have an enormous impact on our understanding of neural plasticity, it will open new vistas for gene therapy for human disease, and i will allow us to create a model system to directly probe the mechanisms by which neural circuits are established and remodeled. Most New World primates, including squirrel monkeys, have a single visual pigment gene on the X-chromosome. However, three alleles occur at this locus and each allele encodes a spectrally distinct pigment. The three alleles correspond to the L and M pigment genes that are the basis for red-green color vision in humans, and the monkeys have a single X- chromosome, and thus are a model for a form of inherited red-green color vision deficiency common among human males. This form of color vision loss in humans is caused by deletion of all but one of the visual pigment genes on the X chromosome. To have normal, trichromatic color vision, male humans must have at least one L and ne M pigment gene. Female squirrel monkeys who are heterozygous at the X-linked pigment gene locus have trichromatic color vision similar to that of humans. Thus, the neural circuitry necessary to establish trichromatic color vision is present in this species, and is clearly utilized when a third visual pigment gene is present during development. We propose to add, by subretinal injection of recombinant adeno-associated virus carrying a human L opsin gene, a third cone type to the adult male squirrel monkey retina. The three cone types will be the endogenous S and M cones of the male squirrel monkey retina, plus M clones transduced with the rAAV virus and expressing a human L pigment. We will monitor color vision behavior both before and after subretinal injection to determine whether the animal's color vision changes from dichromatic to trichromatic.