X-Gal histochemistry in coronal sections of a miR-21/LacZ reporter mice at three different successive rostro caudal levels each level falling between two vertical lines drawn on sagittal cartoons of the mice brain. Note the abundant X-gal labeling (blue) in the major WM bundles of the mouse brain. CC: Corpus Callosum, AC: Anterior Commissure, OT: Olfactory Tract, CuS: Corpus Striatum, Sep: Septum, IC: Internal capsule.