Cells capable of oxygen-regulated Epo expression have been reported using in vitro differentiated kidney-derived mesenchymal progenitor cells [82], and primary REP cells from kidneys of transgenic mouse lines expressing fluorescent proteins under the control of regulatory elements of the Epo locus (knock-in allele in a background of severe neonatal anemia) [78], or of the Col1a1 locus [18]. Here, EPO is linked to neonatal anemia.