Levels of CD38 and RAR-α proteins in various tissues from normal wild-type (C) and RAR-α homozygous transgenic (T) mice. Soluble extracts from indicated tissues were prepared, and equal amounts of protein (100 μg) were resolved on SDS-PAGE. The proteins were transferred onto nitrocellulose membrane, and the membrane was probed with mouse anti-CD38 monoclonal antibody (A). The membrane was stripped and reprobed with anti–RAR-α antibody (B), as described in the Materials and Methods.