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Dmitri Serjanov, galina bachay, Dale D Hunter, William J Brunken; Laminin β2 Chain Regulates Retinal Progenitor Cell Mitotic Spindle Orientation. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
Laminins are heterotrimeric molecules that are key matrix components, which regulate stem cell proliferation and spatiotemporal patterning. Laminin signaling is mediated via integrin and dystroglycan receptors. Mutations in laminins or its receptors lead to ocular and CNS dysgenesis in humans and mice. This study investigates the role of laminin β2 chain in regulation of the mitotic spindle orientation, proliferation, and laminin receptor dynamics in retinal progenitor cells (RPCs).
Retinas from P0, P3, and P5 WT and laminin β2-/- mice were used. 3D-reconstructions of dividing nuclei were used to study mitotic spindle angles, calculated by measuring the angle between a line joining opposing centrosomes and the apical retinal surface. Integrins and dystroglycans expression were assessed by IHC and quantified by digital imaging. Retinal organotypic cultures were prepared from P0 eyes. Addition of recombinant b2-containing laminin (521) was used to rescue the developmental defect caused by laminin β2 deletion ex vivo.
Deletion of the laminin β2 chain results in down-regulation of dystroglycan and β1-integrin at the retinal vitreal surface and their up-regulation in the IPL. One cell type expressing these receptors are RPCs. Laminin β2 chain deletion also results in a significant shift of the RPC mitotic spindle pole orientation towards asymmetric (neurogenic) cell divisions in P0 and P3 retinas (p≤0.01). This leads to decreased proliferation, and premature RPC pool depletion by P5 (decreased by 70%; p≤0.01), resulting in underproduction of bipolar cells (decreased by 20%; p≤0.05) and Müller glia (decreased by 47%; p≤0.001). Addition of exogenous β2-containing laminin trimers to the retinal surface ex vivo restored the normal receptor distribution and directed RPC mitotic spindle orientation towards symmetric (proliferative) cell divisions (p≤0.001), leading to increased RPC proliferation.
Together with our previous findings, these data suggest that the ILM provides developmental and orientational cues for the RPCs. Laminin β2 chain appears regulate ECM receptor expression and, thereby RPC cytokinesis dynamics and proliferation. These data suggest that b2-containing laminins regulate critical developmental patterning events at the ILM.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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