Human ϵ-globin::KGFP transgenic mouse line as a model system for monitoring primitive erythroid development. (A) Cartoon of the ϵ-globin::KGFP transgenic construct. (B) Photograph of E9.5 ϵ-globin::KGFP embryo. GFP+ cells are seen throughout the circulation. (C) Flow cytometric analysis of circulating blood from E10.5 to E18.5. White area indicates cells from nontransgenic littermate. (D) Graphic representation of data from panel C and Table 2, highlighting the rapid decrease in the fraction of circulating blood cells that contains EryPs between E13.5 and E16.5. (E) Forward scatter (FSC) and side scatter (SSC) profiles of GFP+ and GFP− populations. (F) RT-PCR analysis of ϵY-, βh1-, and βmaj-globin gene transcription in FACS-sorted GFP+ and GFP− cells from E15.5 embryos. NT indicates no template (-DNA); E10.5, peripheral blood from E10.5 embryo; AdPB, adult peripheral blood.