EPO and Ureteral obstruction: Maxwell et al. showed that REPs, which are tagged by integrated SV40 T antigen cDNA in the Epo gene locus, turn into desmin-positive myofibroblasts following ureteral obstruction injury, and that the number of T-antigen-expressing cells decreases to less than 5% of control kidneys in 9 days after the obstruction (Maxwell et al., 1997).