Farjo Rafal, Fliesler Steven J, Naash Muna I
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
J Comp Neurol. 2007 Oct 20;504(6):619-30. doi: 10.1002/cne.21476.
We examined the molecular, structural, and functional consequences on cone photoreceptors of the neural retinal leucine zipper knockout (Nrl(-/-)) mice when only one allele of retinal degeneration slow (Rds) is present (Rds(+/-)/Nrl(-/-)). Quantitative RT-PCR and immunoblot analysis were used to assess the expression levels of several phototransduction genes; electroretinography was used to assess quantitatively the retinal responsiveness to light; and immunohistochemistry and ultrastructural analysis were used to examine retinal protein distribution and morphology, respectively. In Rds/Nrl double-null mice, S-cones form dysmorphic outer segments that lack lamellae and fail to associate properly with the cone matrix sheath and the outer limiting membrane. In Rds(+/-)/Nrl(-/-) mice, cones form oversized and disorganized outer segment lamellae; although outer limiting membrane associations are maintained, normal interactions with cone matrix sheaths are not, and photoreceptor rosette formation is observed. These retinas produce significantly higher photopic a-wave and b-wave amplitudes than do those of Rds(-/-)/Nrl(-/-) mice, and the levels of several cone phototransduction genes are significantly increased coincidently with the presence of Rds and partial lamellae formation. Thus, as in rod photoreceptors, expression of only one Rds allele is unable to support normal outer segment morphogenesis in cones. However, cone lamellae assembly, albeit disorganized, concomitantly permits outer limiting membrane association, and this appears to be linked to photoreceptor rosette formation in the rodless (cone-only) Nrl(-/-) retina. In addition, photoreceptor gene expression alterations occur in parallel with changes in Rds levels.
我们研究了在仅存在一个视网膜变性慢（Rds）等位基因（Rds(+/-)/Nrl(-/-)）时，神经视网膜亮氨酸拉链基因敲除（Nrl(-/-)）小鼠的视锥光感受器在分子、结构和功能方面的后果。采用定量逆转录聚合酶链反应（RT-PCR）和免疫印迹分析来评估几种光转导基因的表达水平；用视网膜电图定量评估视网膜对光的反应性；分别用免疫组织化学和超微结构分析来检测视网膜蛋白分布和形态。在Rds/Nrl双基因敲除小鼠中，S视锥细胞形成畸形的外节，缺乏板层结构，并且不能与视锥细胞基质鞘和外界膜正确结合。在Rds(+/-)/Nrl(-/-)小鼠中，视锥细胞形成过大且无序的外节板层；尽管与外界膜的结合得以维持，但与视锥细胞基质鞘的正常相互作用却未实现，并且观察到光感受器玫瑰花结的形成。这些视网膜产生的明视a波和b波振幅明显高于Rds(-/-)/Nrl(-/-)小鼠，并且随着Rds的存在和部分板层形成，几种视锥光转导基因的水平也显著增加。因此，与视杆光感受器一样，仅一个Rds等位基因的表达无法支持视锥细胞正常的外节形态发生。然而，视锥细胞板层组装虽然无序，但同时允许与外界膜结合，这似乎与无视杆（仅视锥）Nrl(-/-)视网膜中的光感受器玫瑰花结形成有关。此外，光感受器基因表达改变与Rds水平的变化并行发生。
