Olfactory receptors showing different expression levels. Different expression levels of one pair of olfactory receptors is due to different numbers of expressing cells and different transcript levels per cell. RNA in situ hybridization with digoxigenin-labeled probes for (a) gene A (AY318555) and (b) gene D (AY317365) on coronal sections of the olfactory turbinates of an adult mouse, shown at low magnification and inset (boxed) at high magnification. Endoturbinates II and III and ectoturbinate 3 are labeled in (b).