Figure 7. A combination of BrdU labeling and immunohistochemistry for active Notch signaling shows Notch remains active after the Muller glia have become postmitotic and begun their differentiation.

Immunolebeling for active Notch (Notch-ICD; A,C,E, F, F′, F″″, F″″″). An injection of BrdU at postnatal day 5, followed by sacrifice 2 hours later, results in BrdU incorporation in S-phase cells in the peripheral fourth to one third of the retina (Green, C–F). (C,F) The Müller glia in the central retina have already begun their differentiation, as indicated by the strong labeling for Glast, while the progenitor cells in the peripheral retina have only a low level of Glast (C,D). The Notch pathway is active both in the peripheral retinal progenitors (BrdU+;A, C), but also in the central Müller glia (BrdU−/Glast+; A, E, and F-F′″). (G) In situ hybridization at P7 for Notch mRNA expression (H) Hes1 immunohistochemistry localizes to the Muller glia in the INL. All panels except G and H are from the same section, with the arrows and arrowheads in panels A and B pointing out the regions at higher magnification in panels C/D and E/F, respectively. Panels F-F″″″ show the region identified by the arrow in panel F, whereas the arrows in F-F″″″ point to Muller cells (Glast+) that also express Notch-ICD.