Excluding the Genomic Location of Pax2 Regulatory Elements for the Developing Mouse Eye.

The Pax2 transcription factor is activated uniformly in the optic vesicle/cup, but becomes progressively restricted to the forming optic disc and stalk. In the eye, it is not known how Pax2 expression is regulated and progressively restricted, in part because no Pax2 regulatory elements have been identified for this organ. Multiple Pax2-Cre mouse transgenic lines have been produced, but essentially none of these Cre recombinase drivers are active in the visual system. Only Tg(BAC-Pax2-cre) mice have been reported to express Cre in a subset of postnatal retinal astrocytes. We confirm this observation and demonstrate ectopic expression in branchial arches, extraocular muscles, and a subset of GABAergic amacrine cells. Our findings suggest that major eye enhancer(s) for mouse Pax2 reside outside the > 180 kb genomic segment delimited by Pax2 BAC transgenes.