Fig. 7. (A) Schematic representation of the NR (distal is towards the left). The -enhancer () alone drives gradient expression in the distal half of the NR (red), while upon deletion of (Pax6 =Pax6^lacZ) the remaining Pax6 elements mediate evenly distributed expression throughout the proximodistal extent of the NR (pink). In the wild type NR, the composite activity of both regulatory systems lead to the full retinal expression pattern of Pax6 (Pax6^WT). (B) Nasal (red), temporal (green) and ventral (blue) characteristics are established around E9 in the wild-type optic vesicle (see OV_H) and maintained in the optic cup (E12), while dorsal characteristics (yellow) are established slightly later (shown in OV_S). In Pax6-null mutants (Pax6^–/–) the distinction between nasal and temporal optic vesicle fails to be established, while after Cre/loxP mediated inactivation (-Cre; Pax6^flox/flox) at E10.5 nasal and temporal patterning of the optic cup is lost. In addition, in the Pax6^–/– optic vesicle ventral characteristics (Vax1, Vax2) expand dorsally (dotted arrows) and, possibly as a consequence, dorsal determinants (Tbx5) are lost. See discussion for details. D, dorsal; le, lens; N, nasal; NR, neuroretina; OV_H, horizontally sectioned optic vesicle; OV_S, sectioned sagittally optic vesicle; T, temporal; V, ventral.

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