Efficiency and Specificity of Tamoxifen-induced β-galactosidase Expression in Cardiomyocytes in CreLacZ Mice.

<p>(A) Generation of CreLacZ mice. CAG-CAT-LacZ mice were crossbred with the MerCreMer strain in which tamoxifen-inducible Cre recombinase expression protein was driven by the α-myosin heavy chain promoter. (B) β-galactosidase expression in cardiomyocytes detected by X-gal staining in a tamoxifen-treated CreLacZ mouse (left) and non-treated mouse (right). The bottom panels show immunofluorescence images of the same samples co-stained with sarcomeric α-actinin (SA-actinin) in green and laminin in red. Scale bar, 20 μm. (C) Frequency of X-gal-positive cardiomyocytes in the LV with or without tamoxifen administration (n = 1833 cardiomyocytes pooled from three sections from three mice and n = 1538 cardiomyocytes pooled from two sections from two mice, respectively). The mice were examined immediately after completion of tamoxifen treatment. (D) Number of X-gal-negative cardiomyocytes per area in CreLacZ mice at 1 day (n = 5), 6 months (n = 5), and 1 year (n = 4) after tamoxifen treatment. The Kruskal–Wallis test showed no significant difference among the three groups.