We have previously reported that RA/RAR activity is physiologically confined to the collecting duct in mouse kidneys [19, 30] and that in cultured collecting duct cells, several genes implicated in the defense against kidney injury are targets of the endogenous RA/RAR activity [31], and that the RA/RAR activity in collecting duct cells is regulated differentially by AKI and CKD mediators [19]. The gene discussed is RARA; the disease is acute kidney injury.