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G.H. Daly, G.A. Pinzon–Duarte, V. Denes, M. Koch, D.D. Hunter, W.J. Brunken; Genetic Deletion of ß2/3 Laminin Chains Results in a Retinal Dysplasia . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2794.
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The retina expresses several laminin isoforms containing both the ß2 and γ3 chains. Genetic deletion of ß2 alone produced profound disruptions in photoreceptor morphology (Libby et al., '99). We now produced γ3 and ß2/γ3 double nulls and examined their retinal phenotypes.
Mice with all genotypes [ß2–/–, γ3–/–, and ß2γ3 –/–] were examined; all mutant lines were backcrossed to the C57/Bl6 background. Retinas from mutant and wild type animals were collected on postnatal day 20 and were examined by conventional histology, immunochemical and electron microscopy.
The ß2–/– retina had the expected disrupted phenotype (Libby et al '99) whereas γ3–/– retinae were normal. In contrast, ß2γ3 –/– retinae demonstrated gross structural abnormalities. Most obvious were the presence of numerous rosettes and a gross disruption of photoreceptor morphology. Ectopic cells were found in both the interphotoreceptor matrix and at the vitreal border. Ultrastructural disruptions of the photoreceptor include: dysmorphic outer and inner segments and floating ribbons. As laminin is the primary organizer of basement membrane (BM) assembly, we examined the organization of the retinal BMs [the ILM and Bruch's membrane (BrM)]. Staining for nidogen or perlecan, BM markers, was present in a continuous layer in the ILM of wild type and single nulls. In contrast, there was a patchy disruption of the ILM of the ß2γ3 –/– retina. Nidogen was present in BrM in all the mice. EM examination showed that the ILM was discontinuous, lacked the normal dual electron dense layers, and was pierced by frequent cell processes. BrM showed some disruptions in collagen and elastin fibrils in all genotypes; in addition, it was markedly thickened in the double null. The ILM and BrM are important attachment sites for Müller and RPE cells (respectively), so we examined the appearence of these cells. The radial organization of Müller cells was disrupted and they exhibited sprouting of processes at both apical and basal terminals. The RPE demonstrated clearly pathological features, including enlarged vacuoles and disruptions in the basal processes. In the ß2–/– animals, these processes were fused while in the double null the extracellular space between processes was expanded.
These data show that ß2γ3 containing laminins are critical for the normal organization of retinal BMs. Moreover, cells that attach to these membranes – Müller cells and the RPE – are severely disrupted in laminin–deficient mice.
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