CPM expression is also suppressed on mRNA level by RA. Total RNA was isolated either from MO cultured on teflon foils with 10⁻⁷ mol/L 9-cis-RA (lane 2) or 10⁻⁹ mol/L 9-cis-RA (lane 3) or without RA (lane 1). After 4 days cells were harvested and Northern analysis was performed according to the Materials and Methods. Hybridization with an 18S rRNA oligonucleotide is shown as a loading control.