Fig. 4. The -enhancer directs expression in RGCs that project to two concise domains in the lateral geniculate nucleus (LGN) and superior colliculus (SC). (A-C,E-F): Whole-mount views of P0 (A) and P20 (B-C,E-F) -tau-lacZ brains stained for tau-ß-gal activity. (A) At P0, tau-ß-gal⁺ axons can be followed from the eyes through the optic nerve (on), via the optic chiasm (oc) and optic tract (ot) up to the LGN (latter not shown in A). Ventral view of brain to reveal on, oc and ot. (B) At P20, tau-ß-gal activity allows tracing of entire extent of the ot, up to the superior colliculus (SC; lateral view of brain; overlying brain tissue was removed). (C) Ventral view of chiasm showing tau-ß-gal⁺ fibers crossing to the ot (anterior towards the top; posterior towards the bottom). (D) Schematic view of the topographic map drawn by tau-ß-gal⁺ axons in the -tau-lacZ line. tau-ß-gal⁺ axons project the distal nasal (4) and temporal (1) NR to the posterior (4) and anterior (1) LGN and superior colliculus, respectively. Proximal RGC axons (2,3) project to the remaining portions of LGN and superior colliculus. (E) Dorsal view on P20 -tau-lacZ brain showing tau-ß-gal⁺ axons terminating in two sickle shaped domains in the superior colliculus and LGN. Note that central portion of superior colliculus is devoid of staining, as is the inferior colliculus (IC) and surrounding tissue. (F) Close-up lateral view of the LGN of a P20 brain -tau-lacZ brain revealing tau-ß-gal⁺ axons terminating mainly in two domains in the ventral and dorsal LGN, respectively. (G) Sagittal section through the superior colliculus revealing tau-ß-gal⁺ axons terminating in the anterior and posterior regions, while omitting the central region (axons projecting to the posterior superior colliculus can be detected). (H) Transversal section through the -tau-lacZ diencephalon revealing tau-ß-gal⁺ axons terminating in the ventral and dorsal LGN. The additional focus of termination presumably corresponds to the binocular segment (bs). Lateral of the LGN, tau-ß-gal⁺ axons can be seen traversing the optic tract.

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