Generation of FKBP12 conditional knockout using Cre-loxP system. A, (a-c) Targeting vector to mutate the mouse FKBP12 gene with PGK-neo cassette and loxP sites (FKBP12loxP-neo). (d) Southern blot analysis of targeted ES cells. (e) Removal of PGKneo-loxP cassette from FKBP12loxP-neo mice. This was achieved by taking advantage of maternal expression of Cre in oocytes of Tie2-Cre transgenic females, as the oocytes have a transient presence of Cre protein from maternal Cre-mRNA. Using a PCR based genotyping strategy for PGK-Neo negative and Exon 3-loxP positive offspring, we were able to generate mice that contain only a single pair of loxP sites flanking exon 3 in FKBP12 allele (FKBP12flox). B and C, Assessment of efficiency of FKBP12 ablation using αMyHC-Cre. B, qRT-PCR analysis to determine the level of FKBP12 transcript in heart and skeletal muscle samples with indicated genotypes. C, Western blot analysis to determine the FKBP12 protein level in hearts. FKBP12 is efficiently removed from cardiac tissues in FKBP12f/f/αMyHC-Cre hearts.