Fig. 2. Direct transdifferentiation of or^J retinal cells into pigmented cells. (A) Schematic of the transgenic mice used for fate mapping experiments. The Chx10 BAC transgenic mouse directs expression of GFPCre and AP under control of Chx10 regulatory sequences. This reporter is integrated in the first exon of Chx10 (exons are indicated by solid vertical bars) within the Chx10 RNA (black horizontal line) such that the 5' most reporter utilizes the Chx10 start methionine (large arrow). Cre recombinase mediates recombination (curved arrows) at loxP sites (triangles) in the R26R allele. This removes a transcriptional stop cassette allowing lacZ expression from the Rosa26 promoter (small arrow). (B-I) Sections through Chx10 BAC/R26R transgenic eyes from or^J/+ (B,C,F,G) or or^J/or^J (D,E,H,I) P0 littermates. (B,G) ß-gal expression is observed throughout the retina as well as in the nonpigmented ciliary body epithelium (npcbe), but not in pigmented cells, in or^J/+ eyes as detected histochemically (B) or with anti-ß-gal antibody (G). (C) GFP reporter activity is detected in the outer neuroblastic layer (ONBL) as well as npcbe. (D,I) ß-gal expression is observed throughout the retina as well as in many pigmented cells in the peripheral pigmented regions. (E) GFP reporter activity is observed throughout the retina as well as in lightly pigmented regions (arrows in (D,E)). (J-L) Sections through Chx10 BAC transgenic or^J mutant eyes at P0 (J,K) and P17 (L,M). (K,M) GFP reporter activity is detected throughout the peripheral retina including regions of the retina that are lightly pigmented (J,L) and in pigmented cells themselves (arrows). (M) DAPI nuclear counterstaining confirms that the GFP-expressing nucleus is within a pigmented cell. (N-S) Dissociated cells from an E17.5 Chx10 BAC/R26R transgenic or^J mutant eye antibody stained for ß-gal (N) or GFP (P) with DAPI nuclear counterstaining. Arrows indicate cells that express ß-gal (N) or GFP (P) in unpigmented cells (O,Q), while arrowheads indicate pigmented cells. (Q) Inset shows higher magnification image of cell marked with arrowhead. (R,S) Histochemical ß-gal staining showing pigmented cells also expressing ß-gal. All scale bars are 100 µm.