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J. D. Wisard, W. Waxweiler, T. Waxweiler, C. J. Johnson, C. M. Donmoyer, G. I. Liou, J. M. Nickerson; Morphology and Development of the IRBP Knockout Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3530.
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© ARVO (1962-2015); The Authors (2016-present)
Interphotoreceptor retinoid binding protein (IRBP) is thought to protect the retina from damaging levels of retinoids and fatty acids. IRBP knockout (KO) mice experience a slow retinal degeneration that continues throughout life. We sought to identify: 1) when the reduction begins to occur, 2) which photoreceptor cells (PhRs) are reduced, and 3) by what mechanism the reduction transpires. These changes will help elucidate the role of IRBP in the developing retina.
IRBP knockout (KO) and C57BL/6 (WT) mice were sacrificed at various time points from Postnatal (P) day 2 to 300 and embedded in plastic or paraffin. For eyes from P12 to P300, number of PhR nuclei in the ONL, INL, and GCL were counted at fixed distances across the retina for a total of 41-54 counts per eye. Eyes from P2-P10 were utilized for TUNEL, rod and cone staining, BrdU labeling, microarray analysis, and developing ONL, INL, and GCL layer thicknesses. Number of PhRs was assessed using FITC conjugated peanut agglutinin for cones and a rhodopsin specific antibody for rods. Measurements and counts were obtained with Photoshop CS2 v.9.0.2 and LongBoard v.7.5.
Between P2-P10, little difference was observed in the IRBP KO in number of TUNEL positive cells, rod/cone staining, and in the thickness of the developing ONL, INL, and GCL layers. Microarray data from P2-P10 all demonstrated numerous genes that differed in expression between KO and WT mice. Plastic sections reveal that there is a decrease in the number of nuclei in the ONL of IRBP KO as early as P20 but not before P12. This reduction continues throughout the IRBP KO’s lifespan, yielding an ONL of 3-4 cells at P239. Slightly fewer cells in the INL were observed, but not to a significant level.
Morphometric analysis shows that the lack of photoreceptor development in the retina of the IRBP KO mouse was first visible by P20. This suggests that: 1) until P15, the retina displays normal developmental morphology, and 2) there is a large photoreceptor loss between P15 and P20. Microarrays indicate that the morphological degeneration is preceded by gene expression changes earlier in development.
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