PAX2 is first expressed in the intermediate mesoderm then in the nephric duct and metanephric mesenchyme of the developing kidney (inferred from the mouse homolog). Mice lacking Pax2 fail to form ureteric buds or metanephric kidneys (Torres et al. 1995, Brophy et al. 2001) due to a failure to activate expression of the signaling molecule glial cell-derived neurotrophic factor (Gdnf) (Brophy et al. 2001). In mice, expression of Pax2 in metanephric mesenchyme is activated by Six1 and absence of Six1 causes a large reduction but not a total loss of Pax2 (Xu et al. 2003).