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G. H. Daly, G. A. Pinzon-Duarte, Y. Li, D. D. Hunter, W. J. Brunken; Genetic Deletion of ß23 Laminin Chains Results in Abnormal Vasculogenesis in the Neural Retina.. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5705.
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The retina expresses ß2 and γ3 laminin chain isoforms. Genetic deletion of ß2 alone produced disruptions in photoreceptor morphology (Libby et al., '99). Deletion of laminin γ3 chains had a minimal retinal phenotype. Yet the ß2γ3 double nulls exhibited profound disruptions across the retina, including disruptions of the inner limiting membrane (ILM). Cells associated with the formation and regression of the blood vessels are closely related to the ILM. Here, we examined the expression of ß2 and γ3 laminins in retinal vasculature and then determine the effects of their deletion on retinal vascular development.
Retinas from mutant and wild type animals were collected on postnatal days 1, 7 and 15 and were examined by conventional histology, immunochemical and electron microscopy. The following markers were used: glutamine synthetase and vimentin for Müller cells; perlecan and nidogen for the basement membrane; PeCAM for endothelial cells.
Using whole mount preparations, we examined the laminin expression in retinal vasculature. ß2 immunoreactivity is found throughout the retinal vasculature but it is more pronounced on the arterial side. While γ3 immunoreactivity is absent from the arterial side, it expressed from the small caliber capillary bed through to the venous side. Vascular development takes place along the ILM, which, as we reported last year, is disrupted at all ages being marked by patchy expression of both perlecan and nidogen. Blood vessel development in the postnatal mouse retina is characterized by two main events: 1) the regression of the hyaloid blood vessel system at P10, and 2) the formation of the inner retinal blood vessels starting at P4. Both of these processes are disrupted in the ß2γ3 mice. Hyaloid vessels were present at P1, as in the control animals, yet, failed to regress and persisted throughout the life span of the mutant mice. Later, the peripheral vasculature does not form. In the central retina, distribution of blood vessel was sporadic and resulted in scattered blood vessel with enlarged diameters (~30%). Choroideal vasculature was unaffected.
These data show that ß2γ3 containing laminins, and the ILM are critical for the normal organization of retinal vasculature as well as the development of the peripheral vasculgenesis. The data suggests that ß2γ3 laminin chains’ effect is specific for the neural retina as immunoreactivity in the choroid capillaries was normal in all conditions. These disruptions are similar to those seen in vascular development in the ROP retina.
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