RNA processing:RNA was extracted using Trizol reagent (Invitrogen) and purified using an RNeasy Mini kit from Qiagen. Double-stranded cDNA was generated without pooling. The Ambion MEGAscript T7 kit from Ambion was used to generate biotinylated cRNA for kidney. See Hübner et al. 2005 for additional detail. One-hundred and twenty eight samples passed RNA quality control steps.