Novel expression pattern of interphotoreceptor retinoid-binding protein (IRBP) in the adult and developing zebrafish retina and RPE.
ABSTRACT 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.
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ABSTRACT: The mammalian Cone-rod homeobox (Crx) gene is a divergent member of the Otx gene family known to be involved in differentiation and survival of retinal photoreceptors and photoentrainment of circadian rhythms. Zebrafish have two genes in the Otx5/crx orthology class, and we previously showed that crx can transactivate rhodopsin expression in vitro, and that otx5 (orthodenticle-related gene), but not crx, regulates expression of circadian genes in the pineal. Here, we show that zebrafish crx does not regulate expression of opsins and other photoreceptor-specific genes in the pineal. We further show that crx is expressed in proliferating retinal progenitors and may be involved in patterning the early optic primordium and in promoting the differentiation of retinal progenitors, including photoreceptors. These results suggest novel functions for zebrafish crx during retinal specification and differentiation.Developmental Biology 06/2004; 269(1):237-51. DOI:10.1016/j.ydbio.2004.01.037 · 3.64 Impact Factor
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ABSTRACT: The vertebrate brain develops from a bilaterally symmetric neural tube but later displays profound anatomical and functional asymmetries. Despite considerable progress in deciphering mechanisms of visceral organ laterality, the genetic pathways regulating brain asymmetries are unknown. In zebrafish, genes implicated in laterality of the viscera (cyclops/nodal, antivin/lefty and pitx2) are coexpressed on the left side of the embryonic dorsal diencephalon, within a region corresponding to the presumptive epiphysis or pineal organ. Asymmetric gene expression in the brain requires an intact midline and Nodal-related factors. RNA-mediated rescue of mutants defective in Nodal signaling corrects tissue patterning at gastrulation, but fails to restore left-sided gene expression in the diencephalon. Such embryos develop into viable adults with seemingly normal brain morphology. However, the pineal organ, which typically emanates at a left-to-medial site from the dorsal diencephalic roof, becomes displaced in position. Thus, a conserved signaling pathway regulating visceral laterality also underlies an anatomical asymmetry of the zebrafish forebrain.Development 01/2001; 127(23):5101-12. · 6.27 Impact Factor
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ABSTRACT: The goldfish retina displays a characteristic arrangement of cone photoreceptors that develop in a stereotyped sequence according to spectral phenotype. It has been suggested that the earliest differentiating photoreceptor in the teleost, the rod photoreceptor, might play an instructive role in development of the cone mosaic. This hypothesis was tested, first by examining the expression pattern of a cone subtype-specific marker with respect to that of rod opsin, and then by killing the cells that generate rods and examining the cone mosaic that formed in the absence of new rods. We find that, although there is potential for interactions between developing cones and immediately postmitotic rods, a role for such interactions in cone mosaic pattern formation is not likely.The Journal of Comparative Neurology 08/2000; 423(2):227-42. DOI:10.1002/1096-9861(20000724)423:2<227::AID-CNE4>3.0.CO;2-Z · 3.51 Impact Factor