USING GENE KNOCKOUT STRATEGIES to help define the physiological and/or pathophysiological role(s) of factors produced by specific renal cell types presents substantial challenges. Renal cell-specific gene targeting, involving a Cre recombinase (Cre)-expressing transgene (either constitutively expressed or inducible) and a loxP-flanked (floxed) target allele, has been achieved in vivo in mouse p...