Fig. 2. Embryonic ß-gal expression in Math5^+/- eyes. (A,B) E11.5 ß-gal expression in the developing optic cup. B shows a horizontal section through the whole-mount embryo in A. The overall pattern is identical to endogenous Math5 mRNA (see Fig. 2 of Brown et al., 1998). ß-gal staining begins in the dorsal central cup. A small number of positive cells are also visible in the diencephalon near the base of the optic stalk. (C,D) E15.5 retinal ß-gal expression. ß-gal is present in progenitors and differentiating RGCs. D shows a higher magnification. E. In situ hybridization at E15.5 showing Math5 mRNA expression solely in retinal progenitors. (F) ß-gal expression in the optic nerve at day E17.5 (arrow). (G) ß-gal-positive cells with characteristic cone morphology in the photoreceptor layer of a heterozygote at P21. Bars are 1 mm in A; 200 µm in B; 100 µm in D; 500 µm in F; and 20 µm in G.