Mosaic expression of CAG-TAG2 due to X inactivation. Sections through the heart of an adult female (A, A', and A") and male (B, B' and B") CAG-TAG2 mouse are shown. (A, B) Td-Tomato fluorescence showing expression of the transgene. (A', B') Atto647N-phalloidin fluorescence used as a 'counter-stain' to visualise all the tissue in the field of view. (A", B") Merge of TdTomato (red) and phalloidin (green) fluorescence, illustrating the mosaic expression of the CAG-TAG transgene in females due to X inactivation, but uniform expression in males. The scale bar in (A) represents 100 μm and is applicable to all panels.