Fig. 3. Fate map of T2Cre-recombined cells in Gata4^T2del hearts. (A-D) T2Cre-mediated activation of the R26RstoplacZ reporter (blue) was mapped in E11.5 control (A,C) or Gata4^T2del (B,D) embryo hearts. Whole-mount embryos were X-gal stained, then sectioned in the sagittal plane. Sections through the AV (A,B) and OT (C,D) cushions are shown. In control hearts, T2Cre-recombined cells of endothelial origin gave rise to the AV cushion mesenchyme (asterisk), as well as the proximal tip of the OT cushion (yellow arrow). The mid- and distal OT cushions were not recombined by T2Cre (red arrows). In Gata4^T2del embryos, the corresponding regions were markedly hypocellular. Residual cells in the AV cushions were descended from T2Cre-recombined endothelium (arrowhead). Scale bar: 100 µm.