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Manuela Lahne, Rebecca Marton, David Hyde; The Role Of Rocks During Interkinetic Nuclear Migration In The Regenerating Adult Zebrafish Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1164.
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© ARVO (1962-2015); The Authors (2016-present)
In the damaged adult zebrafish retina, Müller glia are induced to proliferate and produce neuronal progenitors that further proliferate and subsequently differentiate into the lost retinal cells. During development, neuronal progenitor nuclei migrate between the basal and apical surface in phase with the cell cycle. Disrupting this process, termed interkinetic nuclear migration (INM), has been suggested to cause premature cell cycle exit. It has not been established whether a similar mechanism acts in the regenerating zebrafish retina. We present data suggesting that Müller glia undergo INM and aim to elucidate the underlying mechanism.
Dark-adapted Tg[gfap:EGFP]nt11 transgenic zebrafish, which express EGFP in Müller glia, were exposed to constant intense light for up to 96 h. For inhibition studies, zebrafish were light-damaged for 28 h and then treated with Rockout, an inhibitor of Rho-associated coiled coiled kinases (Rocks). Retinal sections from light-damaged zebrafish were immunolabeled with the proliferation marker PCNA (proliferating nuclear cellular antigen) and the mitosis marker phospho-histone 3 (pH3) to determine the position of Müller glia in relation to their phase in the cell cycle and with phalloidin to visualize filamentous(f-) actin.
At 35 h of light treatment, a few Müller glia soma had migrated from their typical basal position to an apical location within the inner nuclear layer (INL) or even into the outer nuclear layer (ONL). A subset of these Müller glia co-labeled with the mitosis marker pH3, whereas the majority of Müller glia in the basal INL were pH3-negative. At timepoints when neuronal progenitors divide, pH3-positive cells were predominantly found in the ONL. Increased f-actin accumulation was observed at the rear of migrating Müller glia at the onset of INM, suggesting that actin remodelling might be required for INM. Inhibition of Rocks, kinases that mediate the reorganization of the actin cytoskeleton, result in an increase in pH3-positive Müller glia in the basal and apical INL and a reduction in the ONL at 35 h. In addition, the number of pH3-positive (mitotic) cells was reduced, but not the number of proliferating (PCNA) cells.
During regeneration, Müller glia and neuronal progenitors undergo INM in the light-damaged adult zebrafish retina and Müller glia INM is facilitated by the action of Rocks.
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