Collery Ross, McLoughlin Sarah, Vendrell Victor, Finnegan Jennifer, Crabb John W, Saari John C, Kennedy Breandán N
UCD Conway Institute and UCD School of Biomolecular and Biomedical Sciences, University College Dublin, Dublin, Ireland.
Invest Ophthalmol Vis Sci. 2008 Sep;49(9):3812-20. doi: 10.1167/iovs.08-1957. Epub 2008 May 23.
During vertebrate phototransduction 11-cis-retinal is isomerized to all-trans-retinal. Light sensitivity is restored by recombination of apo-opsin with 11-cis-retinal to regenerate visual pigments. The conversion of all-trans retinal back to 11-cis-retinal is known as the visual cycle. Within the retina, cellular retinal-binding protein (CRALBP) is abundantly expressed in the retinal pigment epithelium (RPE) and Müller glia. CRALBP expressed in the RPE is known to facilitate the rate of the rod visual cycle. Recent evidence suggests a role for Müller glia in an alternate cone visual cycle. In this study, the role of RPE- and Müller-CRALBP in cone vision was characterized.
The CRALBP orthologues rlbp1a and rlbp1b were identified in zebrafish by bioinformatic methods. The spatial and developmental expression of rlbp1a and rlbp1b was determined by in situ hybridization and immunohistochemistry. Depletion of the expression of the corresponding Cralbp a and Cralbp b proteins was achieved by microinjection of antisense morpholinos. Visual function was analyzed in 5-day post fertilization (dpf) larvae using the optokinetic response assay.
The zebrafish genome contains two CRALBP ohnologues, rlbp1a and rlbp1b. These genes have functionally diverged, exhibiting differential expression at 5 dpf in RPE and Müller glia, respectively. Depletion of CRALBP in the RPE or Müller glia results in abnormal cone visual behavior.
The results suggest that cone photoreceptors incorporate 11-cis-retinoids derived from the rod and cone visual cycles into their visual pigments and that Müller-CRALBP participates in the cone visual cycle.
在脊椎动物光转导过程中，11-顺式视黄醛异构化为全反式视黄醛。脱辅基视蛋白与11-顺式视黄醛重组以再生视觉色素，从而恢复光敏感性。全反式视黄醛转化回11-顺式视黄醛的过程称为视觉循环。在视网膜内，细胞视黄醛结合蛋白（CRALBP）在视网膜色素上皮（RPE）和Müller胶质细胞中大量表达。已知RPE中表达的CRALBP可促进视杆细胞视觉循环的速率。最近的证据表明，Müller胶质细胞在另一种视锥细胞视觉循环中发挥作用。在本研究中，对RPE和Müller-CRALBP在视锥细胞视觉中的作用进行了表征。
通过生物信息学方法在斑马鱼中鉴定出CRALBP直系同源物rlbp1a和rlbp1b。通过原位杂交和免疫组织化学确定rlbp1a和rlbp1b的空间和发育表达。通过显微注射反义吗啉代寡核苷酸来实现相应Cralbp a和Cralbp b蛋白表达的缺失。使用视动反应试验分析受精后5天（dpf）幼虫的视觉功能。
斑马鱼基因组包含两个CRALBP旁系同源物rlbp1a和rlbp1b。这些基因在功能上已经分化，分别在5 dpf的RPE和Müller胶质细胞中表现出差异表达。RPE或Müller胶质细胞中CRALBP的缺失会导致视锥细胞视觉行为异常。
结果表明，视锥光感受器将源自视杆细胞和视锥细胞视觉循环的11-顺式视黄醛纳入其视觉色素中，并且Müller-CRALBP参与视锥细胞视觉循环。
