Linberg Kenneth A, Fariss Robert N, Heckenlively John R, Farber Debora B, Fisher Steven K
Neuroscience Research Institute, University of California, Santa Barbara, USA.
Vis Neurosci. 2005 Nov-Dec;22(6):721-34. doi: 10.1017/S0952523805226044.
Retinal development in 3 strains of rd-3/rd-3 mutant mice, previously shown to have different rates of degeneration, was studied using light, electron, and immunofluorescence microscopy. The time course and phenotype of the degeneration as well as details on the mechanism of massive photoreceptor cell loss are compared with other known retinal degenerations in mice. Up until postnatal day (P) 10, the retinas of all three strains (RBF, 4Bnr, In-30) develop similarly to those of pigmented and nonpigmented controls. TUNEL-positive cells appear in the outer nuclear layer (ONL) by P14, and reach a maximum in all three mutant strains around P21. Scattered rods and cones form a loose, monolayered ONL by 8 weeks in the albino RBF strain, by 10 weeks in the albino 4Bnr strain, and by 16 weeks in the pigmented In-30 strain. Though the initial degeneration begins in the central retina, there is no preferred gradient of cell death between central and peripheral photoreceptors. Rods and cones are present at all ages examined. During development, stacks of outer segments (OS) form in all three strains though they never achieve full adult lengths, and often have disorganized, atypical OS. Rod opsin is expressed in the developing OS but is redistributed into plasma membrane as OS degeneration proceeds. Retinal pigment epithelial (RPE) cells of all mutant strains contain packets of phagocytosed OS, and their apical processes associate with the distal ends of the OS. At their synaptic sites, photoreceptor terminals contain ribbons apposed to apparently normal postsynaptic triads. As photoreceptors are lost, Müller cells fill in space in the ONL but they do not appear to undergo significant hypertrophy or migration, though during the degeneration, glial fibrillary acidic protein (GFAP) expression is gradually upregulated. Macrophage-like cells are found frequently in the subretinal space after the onset of photoreceptor apoptosis. As OS disappear, the RPE apical processes revert to simple microvilli. Late in the degeneration, some RPE cells die and neighboring cells appear to flatten as if to maintain confluence. In regions of RPE cell loss that happen to lie above retina where the ONL is gone, cells of the inner nuclear layer (INL), wrapped by Müller cell processes, may front directly on Bruch's membrane.
利用光学显微镜、电子显微镜和免疫荧光显微镜研究了3种rd-3/rd-3突变小鼠品系的视网膜发育情况，此前已证明这3种品系具有不同的退化速率。将退化的时间进程和表型以及大量光感受器细胞丢失机制的细节与小鼠中其他已知的视网膜退化情况进行了比较。在出生后第10天之前，所有三个品系（RBF、4Bnr、In-30）的视网膜发育与有色和无色对照的视网膜相似。到出生后第14天，TUNEL阳性细胞出现在外核层（ONL），并在所有三个突变品系中在出生后第21天左右达到最大值。在白化病RBF品系中，到8周时，散在的视杆细胞和视锥细胞形成松散的单层ONL；在白化病4Bnr品系中，到10周时形成；在有色In-30品系中，到16周时形成。尽管最初的退化始于视网膜中央，但中央和周边光感受器之间没有明显的细胞死亡梯度。在所检查的所有年龄段都存在视杆细胞和视锥细胞。在发育过程中，所有三个品系都形成了外节（OS）堆叠，尽管它们从未达到成年时的全长，并且外节常常排列紊乱、形态异常。视紫红质在发育中的外节中表达，但随着外节退化，会重新分布到质膜中。所有突变品系的视网膜色素上皮（RPE）细胞都含有吞噬的外节小体，其顶端突起与外节的远端相连。在其突触部位，光感受器终末含有与明显正常的突触后三联体相对的突触带。随着光感受器的丢失，米勒细胞填充ONL中的空间，但它们似乎没有明显的肥大或迁移，不过在退化过程中，胶质纤维酸性蛋白（GFAP）的表达逐渐上调。在光感受器凋亡开始后，视网膜下间隙中经常发现巨噬细胞样细胞。随着外节消失，RPE顶端突起恢复为简单的微绒毛。在退化后期，一些RPE细胞死亡，相邻细胞似乎变平，好像是为了保持汇合。在RPE细胞丢失且恰好位于ONL消失的视网膜上方的区域，被米勒细胞突起包裹的内核层（INL）细胞可能直接面向布鲁赫膜。
