ID1 and kidney disorder: Interestingly, the expression of agents acting as endogenous inhibitors of BMPs, such as uterine sensitization-associated gene-1 (USAG-1), was markedly upregulated in the renal cortex of the RenTg mice at the latest stages of renal disease (Fig. 4C), whereas Id-1 mRNA expression, a BMP-pathway target gene, was several folds decreased (Fig. 4D).