Expression of RARα mRNA in parental and RARα transfected cell lines. RT PCRM. k- – water. ATRA (5 μM) was added to cell cultures 24 h after seeding for 48 h. Then the cells were collected and processed as specified in "Methods" (RNA isolation and reverse transcriptase polymerase chain reaction (RT-PCR) analysis of RARα gene expression). This figure is representative of 2 separate experiments.