Inducible p27 inactivation results in enhanced intermediate filament GFAP expression, glial cell-cycle entry, and glial nuclear migration. (A and B) Immunostaining for p27 and the marker of glial reactivity GFAP. Micrographs of tamoxifen control (p27L-/L+) and experimental (p27L-/L-) retinas six weeks after the start of tamoxifen injections. Asterisks indicate blood vessels. (C and D) Quantitation of Müller glia becoming reactive (GFAP+) and entering cell cycle (PCNA+) as well as the total number of Müller glial nuclei (SOX9+) and stalks (GLUL+). Curves were generated using the Smooth marked scatter option in Excel™. (E-F) Bromodeoxyuridine (BrdU) injections followed by a six week chase to reveal the fate of dividing cells. (E-F insets) Higher magnification showing colocalization with glial marker GLUL. Data are expressed as the mean ± SD. Abbreviations: PCNA, Proliferating cell nuclear antigen.