Fig. 3. The -enhancer directs expression in a subset of Pax6 positive retinal ganglion cells (RGCs) in the distal ventronasal and ventrotemporal retina. (A) Whole-mount view of E11.5 X-gal stained embryo carrying the -tau-lacZ transgene (see I) reveals specific tau-ß-gal in the nasal and temporal retina (see Fig. 2A). (B) Horizontal section through E12.5 -tau-lacZ eye (counterstained with neutral red) reveals tau-ß-gal expression in the distal nasal and temporal NR (see Fig. 2A, inset). (C) Horizontal section of P20 -tau-lacZ eye reveals tau-ß-gal mainly in the distal ganglion cell layer (gcl), as well as tau-ß-gal⁺ axons in the nerve fiber layer (nfl, see F). (D-F) Immunohistochemical detection of tau-ß-gal (green) and Pax6 (red) in P20 -tau-lacZ eye. (D) In the distal nasal NR, Pax6 is found in the nuclei of inl and gcl, while tau-ß-gal labels the cytoplasm (arrows) and axons (see F) of RGCs, as well as dendritic processes of RGCs and amacrine cells (AC) in the inner plexiform layer (ipl). (E) In the dorsal NR, tau-ß-gal is only detected in the ipl, representing long dendritic processes of nasal/temporal tau-ß- gal⁺ ACs and RGCs. (F) Nasal tau-ß-gal⁺ RGC fibers can be detected passing through the optic nerve head (onh). Note that proximal RGCs are tau-ß-gal^–, but Pax6⁺. (G) Plane of sections depicted in D,E. (H) Plane of section shown in F. (I) -tau-lacZ transgene: drives expression of tau-lacZ from the P0 promoter. inl, inner nuclear layer; D, dorsal; V, ventral; T, temporal; N, nasal.

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