Inhibition of GSK3β results in delayed loss of proliferative Müller glia. Tg(gfap:GFP)mi2002 zebrafish larvae were exposed to intense-light at 6 dpf and incubated in BrdU with either DMSO as a vehicle control or 1-azakenpaullone from 1 to 5 dpl or 3 to 5 dpl. (A) Light-lesioned fish treated with DMSO from 1 to 5 dpl have BrdU-positive cells in the INL and in the ONL, and a normal distribution of GFP-labeled Müller glia in the INL. (B) In light-lesioned fish treated with 1-azakenpaullone from 1 to 5 dpl, BrdU-positive cells are only in the ONL, with few-to-none in the INL. Additionally, fewer GFP-labeled Müller glia are present compared to controls (see results). (C) Light-lesioned zebrafish treated with BrdU from 1 to 5 dpl and 1-azakenpaullone from 3 to 5 dpl also have few or no BrdU-positive cells in the INL and the number of Müller glia is reduced. (D, E) High magnification views of BrdU-positive GFP-positive cells that accumulated in the ONL at 3 dpl. (D) In fish treated with DMSO from 0 to 3 dpl, clusters of GFP-positive, BrdU-positive Müller glia and their progeny are distributed between both the ONL and the INL (dotted line indicates the outer plexiform layer separating the ONL and the INL). Arrows indicate the GFP-labeled basal processes of radial Müller glia. (E) In fish treated with 2.5 μM 1-azakenpaullone from 0 to 3 dpl, most of the BrdU-positive GFP-positive cells are in the ONL, and the radial processes of Müller glia are absent. Scale bar: A-C, 100 μm; D, E, 20 μm.