Fig. 1. Expression profile of Bhlhb5 in retinogenesis. Retinal sections from the indicated developmental stages were immunolabeled with anti-Bhlhb5 (green) and the nuclei counter-stained with Propidium Iodide (PI, red) (A-I) or probed with a Bhlhb5 in situ probe (J-O). The onset of Bhlhb5 expression starts at E11.5 in the central retina (A). At E12.5 to E15.5, Bhlhb5 expression expands toward the peripheral retina and is mostly detected in cells in the NBL (B-D,J-M). At E17.5 to P0, Bhlhb5 expression becomes localized in the inner boundary of the NBL and the GCL (E,F,N,O). Inserts in E and F show the enlarged view of the corresponding boxed regions. At P7 to P28, two rows of Bhlhb5 expression are seen in the INL and one in the GCL (arrowheads, G-I). (P-U) Bhlhb5 expression is mostly observed in post-mitotic cells of the developing retina. Anti-Bhlhb5 (green) labeling of E12.5 retina shows Bhlhb5 in nuclei of cells in the NBL (P) and anti-BrdU (red) labels the nuclei of proliferating cells at S-phase (Q). (R) Overlay image of P and Q. (S-U) Anti-Bhlhb5 (S, red) and anti-phosphorylated histone H3 (PH3) (T, green) show that Bhlhb5⁺ cells are mostly negative for PH3 labeling. Abbreviations for this and other figures: L, lens; NBL, neuroblast layer; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer. Scale bars: 100 µm.