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Shweta Varshney, Dale Hunter, William Brunken; Laminin β2 and γ3 chains regulate proliferation and differentiation of retinal progenitor cells. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3745.
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© ARVO (1962-2015); The Authors (2016-present)
Laminin-mediated signaling regulates proliferation, differentiation and survival of cell in various tissues including CNS. The laminin β2 and γ3 chains are important structural components of the inner limiting membrane (ILM) of the retina. This study investigates the role of laminin β2 and γ3 chains in coordinating both proliferation and differentiation of the retinal progenitor cells.
Retinas were collected between embryonic day 15.5 (E15.5) to postnatal day 15 (P15) from wild type (WT), β2-/-, γ3-/- and β2-/-; γ3-/- mice for this study. The phenotypes of retinal cells were analyzed by immunohistochemistry using cell specific markers and proliferation markers. Gene expression was analyzed using real time PCR and protein expression was analyzed by immunoblots.
Retinal progenitor cells (RPC) at their basal surface adhere and interact with the ILM. Our data suggests that deletion of Lamb2 and Lamc3 leads to disruption of the ILM as early as P0. Concurrent with the ILM disruption, the distribution of two key laminin receptors: β-dystroglycan and β1-integrin is perturbed. RPCs proliferate abnormally as a consequence of these disruptions. Proliferation, assessed using markers phosH3 and PCNA, was increased in the P0 β2-/-;γ3-/- retina compared to WT. In contrast, by P5 the rate of proliferation declines by 1.5 fold in β2-/-;γ3-/- retina vs to WT. The changes in proliferation in the P5 β2-/-;γ3-/- retina are accompanied by: down-regulation of RPC markers; an up-regulation of rod markers; and down-regulation of bipolar and Müller cell markers. These results suggest that the disruption of laminin β2 and γ3 chains affect neurogenesis resulting in an overproduction of rods at the expense of other late born cell types, consistent with our previous report of the presence of rosettes in the P15 β2-/-;γ3-/- retina. Additionally, in the laminin mutants we observe a decrease in Notch effectors such as Hes1 and Hes5 by P5. These results suggest that laminin β2 and γ3 chains maintain a proliferative state of RPCs by mediating Notch signaling in the RPCs.
Our data suggests that interactions of RPCs with the ILM play important roles in regulating proliferation and differentiation of the RPCs. Furthermore, intact ILM is critical for normal retinal histogenesis and architecture.
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