Fig. 2. Lineage tracing of Foxg1-expressing cells in E14.5 Foxg1^Cre/+; R26RS embryos. (A) Thick horizontal section of X-gal-stained facial whole mount (the eye on the right is sectioned more ventrally). lacZ staining is uniformly intense throughout the lens (l) and nasal (n) retina but appears patchy in the temporal (t) retina. (B,C) Thick horizontal sections of the eye. (B) Medial section; (C) ventral retina. (D) Thin horizontal section through the eye showing the distribution of lacZ-stained cells. Broken lines demarcate the position occupied by nasal RGCs (nRGCs) and temporal RGCs (tRGCs). In the nasal retina, lacZ staining is uniformly strong. In the temporal retina radial columns of lacZ-expressing cells are embedded in larger areas of non-expressing cells. In B and D, these columns are viewed side-on and in C they are viewed from above. Arrows in B-D indicate examples of lacZ-stained radial stripes. on, optic nerve. Scale bars: 500 µm in A; 200 µm in B-D.