PCR analysis of inducible, skeletal muscle-specific, Cre-mediated recombination. (A) Schematic of the lacZ reporter gene showing the floxed (flanking loxP sites, solid arrowheads) STOP cassette prevents expression of the downstream lacZ cDNA. Following tamoxifen administration, a Cre-mediated recombination event resulted in deletion of the STOP cassette, thereby allowing expression of the lacZ cDNA. (B) Qualitative PCR analysis of genomic DNA shows Cre-mediated recombination (deleted, 0.4-kb band) occurred only in skeletal muscle samples (Gstn, gastrocnemius; Pln, plantaris; Sol, soleus; TA, tibialis anterior; Diaph, diaphragm) and not in the heart (Hrt) following tamoxifen (t) administration, with no recombination (floxed, 3.2-kb band) in vehicle-treated (v) samples. The positions of the PCR primers are indicated by half-arrows.