Lem J, Krasnoperova N V, Calvert P D, Kosaras B, Cameron D A, Nicolò M, Makino C L, Sidman R L
New England Medical Center, Tufts University School of Medicine, Boston, MA 02111, USA.
Proc Natl Acad Sci U S A. 1999 Jan 19;96(2):736-41. doi: 10.1073/pnas.96.2.736.
Mutations in rod opsin, the visual pigment protein of rod photoreceptors, account for approximately 15% of all inherited human retinal degenerations. However, the physiological and molecular events underlying the disease process are not well understood. One approach to this question has been to study transgenic mice expressing opsin genes containing defined mutations. A caveat of this approach is that even the overexpression of normal opsin leads to photoreceptor cell degeneration. To overcome the problem, we have reduced or eliminated endogenous rod opsin content by targeted gene disruption. Retinas in mice lacking both opsin alleles initially developed normally, except that rod outer segments failed to form. Within months of birth, photoreceptor cells degenerated completely. Retinas from mice with a single copy of the opsin gene developed normally, and rods elaborated outer segments of normal size but with half the normal complement of rhodopsin. Photoreceptor cells in these retinas also degenerated but did so over a much slower time course. Physiological and biochemical experiments showed that rods from mice with a single opsin gene were approximately 50% less sensitive to light, had accelerated flash-response kinetics, and contained approximately 50% more phosducin than wild-type controls.
视杆视蛋白是视杆光感受器的视觉色素蛋白，其突变约占所有遗传性人类视网膜变性的15%。然而，疾病过程背后的生理和分子事件尚未得到充分了解。解决这个问题的一种方法是研究表达含有特定突变的视蛋白基因的转基因小鼠。这种方法的一个问题是，即使正常视蛋白的过度表达也会导致光感受器细胞变性。为了克服这个问题，我们通过靶向基因破坏减少或消除了内源性视杆视蛋白的含量。缺乏两个视蛋白等位基因的小鼠的视网膜最初发育正常，只是视杆外节未能形成。在出生后的几个月内，光感受器细胞完全退化。具有视蛋白基因单拷贝的小鼠的视网膜发育正常，视杆形成了正常大小的外节，但视紫红质的含量只有正常水平的一半。这些视网膜中的光感受器细胞也会退化，但退化过程要慢得多。生理和生化实验表明，具有视蛋白基因单拷贝的小鼠的视杆对光的敏感度比野生型对照低约50%，闪光反应动力学加快，磷转导蛋白的含量比野生型对照多约50%。
