Stone Jonathan, van Driel Diana, Valter Krisztina, Rees Sandra, Provis Jan
ARC Centre of Excellence in Visual Science and Research School of Biological Sciences, The Australian National University, Canberra ACT 2601, Australia.
Brain Res. 2008 Jan 16;1189:58-69. doi: 10.1016/j.brainres.2007.10.083. Epub 2007 Nov 7.
Adult mammalian photoreceptors are elongated cells, and their mitochondria are sequestered to the ends of the cell, to the inner segments and (in some species) to axon terminals in the outer plexiform layer (OPL). We hypothesised that mitochondria migrate to these locations towards sources of oxygen, from the choroid and (in some species) from the deep capillaries of the retinal circulation. Six mammalian species were surveyed, using electron and light microscopy, including immunohistochemistry for the mitochondrial enzyme cytochrome oxidase (CO). In all 6 species, mitochondria were absent from photoreceptor somas and were numerous in inner segments. Mitochondria were prominent in axon terminals in 3 species (mouse, rat, human) with a retinal circulation and were absent from those terminals in 3 species (wallaby, rat, guinea pig) with avascular retinas. Further, in a human developmental series, it was evident that mitochondria migrate within rods and cones, towards and eventually past the outer limiting membrane (OLM), into the inner segment. In Müller and RPE cells also, mitochondria concentrated at the external surface of the cells. Neurones located in the inner layers of avascular retinas have mitochondria, but their expression of CO is low. Mitochondrial locations in photoreceptors, Müller and RPE cells are economically explained as the result of migration within the cell towards sources of oxygen. In photoreceptors, this migration results in a separation of mitochondria from the nuclear genome; this separation may be a factor in the vulnerability of photoreceptors to mutations, toxins and environmental stresses, which other retinal neurones survive.
成年哺乳动物的光感受器是细长的细胞，其线粒体被隔离在细胞的末端、内段以及（在某些物种中）外网状层（OPL）的轴突终末。我们推测线粒体朝着氧气来源迁移至这些位置，氧气来源于脉络膜以及（在某些物种中）视网膜循环的深层毛细血管。使用电子显微镜和光学显微镜，包括对线粒体酶细胞色素氧化酶（CO）进行免疫组织化学检测，对六个哺乳动物物种进行了研究。在所有六个物种中，光感受器胞体中均没有线粒体，而在内段中大量存在。在具有视网膜循环的三个物种（小鼠、大鼠、人类）的轴突终末中，线粒体很突出，而在具有无血管视网膜的三个物种（沙袋鼠、大鼠、豚鼠）的这些终末中则没有线粒体。此外，在人类发育系列中，很明显线粒体在视杆细胞和视锥细胞内迁移，朝着并最终穿过外限制膜（OLM），进入内段。在穆勒细胞和视网膜色素上皮（RPE）细胞中，线粒体也集中在细胞的外表面。位于无血管视网膜内层的神经元有线粒体，但其CO表达较低。光感受器、穆勒细胞和RPE细胞中线粒体的位置可以从细胞内朝着氧气来源迁移的结果得到合理的解释。在光感受器中，这种迁移导致线粒体与核基因组分离；这种分离可能是光感受器易受突变、毒素和环境压力影响的一个因素，而其他视网膜神经元能够存活下来。
