Figure 1.

Fractional ablation of embryonic CPCs by chimeric complementation. (A) Schematic diagram of the eGFP/DTA construct before and after Nkx2.5-Cre-mediated excision of the floxed eGFP transgene (upper panel). Brightfield and GFP fluorescence images of E9.5 Nkx2.5^Cre/+, ROSA26^eGFP-DTA, and Nkx2.5^Cre/+;ROSA26^eGFP-DTA transgenic embryos (lower panel). Note the absence of a heart in the compound transgenic embryo (arrow). (B) Schematic diagram of fractional ablation of CPCs by injection of Nkx2.5^Cre/+;ROSA26^eGFP-DTA ESCs into wild-type CD-1 blastocysts. (C) Generation of Nkx2.5^Cre/+;ROSA26^eGFP-DTA ESC lines. Brightfield and GFP fluorescence microscopy images are shown for the three ESC lines used. (D) Summary table demonstrating the complementation efficiency for each ESC line based upon the total number of animals collected. (E) Anticipated progression of CPC loss and regeneration in rescued embryos at approximately 50% ESC chimerism. (F) Brightfield and GFP images of E10.5 chimeric Nkx2.5^Cre/+;ROSA26^eGFP-DTA embryos with varying degrees of CPC ablation. The embryo with ~68% CPC ablation shows a pericardial effusion and developmental arrest. Arrow: heart. Scale bars: 500 μm for (A); 200 μm for (C); 1 mm for (F).