Stenkamp D L, Cunningham L L, Raymond P A, Gonzalez-Fernandez F
Department of Anatomy and Cell Biology, University of Michigan, Ann Arbor, MI, USA.
Mol Vis. 1998 Dec 2;4:26.
Interactions between the neural retina and retinal pigment epithelium (RPE) are mediated by the interphotoreceptor matrix (IPM). The transport of retinoids across the IPM is mediated by interphotoreceptor retinoid-binding protein (IRBP). To explore the possibility that IRBP is important during retinal development, we examined its spatiotemporal expression pattern in embryonic zebrafish.
IRBP mRNA expression was examined using RT-PCR and in situ hybridization. IRBP was localized using antiserum against recombinant zebrafish IRBP. IRBP synthesis and secretion were studied by in vitro metabolic labeling of retinas and RPE-eyecups.
IRBP mRNA was first observed in the pineal at 24 hours post-fertilization (hpf) and in the ventral retina at 50 hpf. Immunoreactive IRBP was first observed at 72 hpf. Remarkably, IRBP was expressed not only by photoreceptors but also by the adult and embryonic RPE. In embryos, expression in both retina and RPE began in a ventronasal patch and spread to involve the entire eye. In general, early IRBP expression was dominated by photoreceptors, but then RPE expression spread beyond the limit of photoreceptor expression. Double in situ hybridizations suggests that cones express IRBP mRNA before they express a specific opsin, while rods may express rod opsin prior to IRBP.
The temporal and spatial patterns of IRBP expression by the RPE and retina are consistent with a role in retinal development and suggest coordination of RPE and photoreceptor differentiation.
神经视网膜与视网膜色素上皮（RPE）之间的相互作用由光感受器间基质（IPM）介导。类视黄醇跨IPM的转运由光感受器间类视黄醇结合蛋白（IRBP）介导。为了探究IRBP在视网膜发育过程中是否重要，我们检测了其在斑马鱼胚胎中的时空表达模式。
使用逆转录聚合酶链反应（RT-PCR）和原位杂交检测IRBP mRNA的表达。使用抗重组斑马鱼IRBP的抗血清对IRBP进行定位。通过对视网膜和RPE眼杯进行体外代谢标记来研究IRBP的合成和分泌。
受精后24小时（hpf），IRBP mRNA首次在松果体中被观察到，50 hpf时在腹侧视网膜中被观察到。免疫反应性IRBP在72 hpf时首次被观察到。值得注意的是，IRBP不仅由光感受器表达，还由成年和胚胎RPE表达。在胚胎中，视网膜和RPE中的表达均始于鼻腹侧斑块，并扩散至累及整个眼睛。一般来说，早期IRBP表达以光感受器为主，但随后RPE表达扩散至超出光感受器表达的范围。双重原位杂交表明，视锥细胞在表达特定视蛋白之前就表达IRBP mRNA，而视杆细胞可能在表达IRBP之前就表达视杆视蛋白。
RPE和视网膜中IRBP表达的时空模式与在视网膜发育中的作用一致，并提示RPE和光感受器分化的协调。
