The Pax2^Egfp knock-in/knockout allele has an EGFP with polyA signal upstream of the endogenous paired box gene 2 (Pax2) translational start site; both abolishing endogenous gene function and placing EGFP expression under direction of the Pax2 promoter/enhancer regions. All mice homozygous for the Pax2^Egfp allele exhibit exencephaly, complete renal agenesis, and die at birth. The donating investigator did not assess if any eye/ear abnormalities were present. Mice heterozygous for the Pax2^Egfp allele are viable, fertile, and phenotypically indistinguishable from wildtype littermate controls (do not exhibit kidney structural defects). In both heterozygous and homozygous mice, EGFP expression (direct fluorescence) is observed in a spatial and temporal pattern consistent with the expected expression of endogenous Pax2. The EGFP expression of Pax2^Egfp heterozygous mice is described in detail below.
At embryonic day (E)9.5, EGFP expression is observed in optic cup, otic vesicle, the midbrain-hindbrain junction, and developing nephric duct. By E10.5, EGFP positive cells of the intermediate mesoderm are segregated into epithelial duct cells and adjacent mesenchyme. By E11.5, EGFP is seen in the ureteric bud and condensing mesenchyme of the metanephric kidney, as well as Pax2-positive neurons that developed at this time along the entire neural tube. At later stages of development, kidney epithelia, ureters, and all the male and female specific epithelia derived from the intermediate mesoderm are EGFP positive. In newborn mice, EGFP expression is strong in the entire nephrogenic zone (nephron differentiation is still ongoing). In adult kidneys, EGFP expression is observed in the renal papilla. When comparing EGFP expression of mice heterozygous for the Pax2^Egfp knockout allele (Stock No. 018438) to mice heterozygous for the Pax2^Eneo hypomorphic allele (Stock No. 018437), there is no qualitative difference in the temporal and spatial pattern of EGFP, although the intensity of EGFP is higher in Pax2^Egfp heterozygotes compared to Pax2^Eneo heterozygotes.