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Fig. 2 Müller glia transiently activate the NF-κB:GFP reporter and express the NF-κB target metalloproteinase mmp9 in response to injury. (A) In homeostatic retina the NF-κB:GFP reporter is expressed in the vasculature residing below the ganglion cell layer (asterisk) and in microglial cells (arrowheads). In comparison to sham, the NF-κB:GFP reporter is activated in response to lesion in gfap:NLS-mCherry labeled Müller glia, and in photoreceptors at the outer nuclear layer (ONL), and is predominantly active in Müller cells at 4 dpl. (B) In situ hybridization of mmp9, in combination with immunohistochemistry for proliferating cell nuclear antigen (PCNA) and glial fibrillary acidic protein (GFAP/Zrf-1) labeling Müller glia, shows that mmp9 is not expressed in sham retinae. In contrast, mmp9 is transiently expressed at one and 2 dpl and returns to undetectable levels at 4 dpl. Scale bar: 50 µm, insets 10 µm. INL = inner nuclear layer; GCL = ganglion cell layer.