Expression of the GFPcre fusion protein in the erythroid lineage. Flow cytometric analysis of FLCs derived from (A) E13.5 wild-type (+/+) and hemizygous (GFPcre/+) or (B) E12.5 wild-type (+/+), hemizygous (GFPcre/+), and homozygous (GFPcre/GFPcre) ErGFPcre littermates. (A) To determine the lineage specificity of GFPcre expression, cells were stained either with only the secondary antibody (control) or with a Ter119-specific antibody followed by the secondary antibody (middle). A combination of CD41-, Mac-1–, Gr-1–, CD14-, Sca-1–, B220-, and YBM/42-specific antibodies was used to identify the major pool of nonerythroid cells (lin^–). (B) To determine surface marker expression of erythroid progenitor cells, cells were simultaneously stained with Sca-1– and c-kit–specific antibodies. The quadrant statistics are indicated.