Epo mRNA analysis. Total RNA was isolated from kidneys of rats receiving Epo expressing LrEpSN-transduced cells and control rats receiving LASN-transduced cells expressing human ADA. RT-PCR was performed with rat Epo-specific primers to give a 540-bp amplified segment that was subjected to electrophoresis and hybridized with a³²P-labeled Epo probe. As a control RT-PCR was performed using β-actin–specific primers to amplify a 500-bp fragment from the same cDNA preparation. Diluted aliquots of each sample were subjected to agarose electrophoresis, Southern transfer, and hybridization of the transferred DNA to a β-actin–specific ³²P-cDNA probe.