Generation of chimeric embryos with EpoR^R129C/− ES cells.

EpoR^R129C/− ES cells were injected into the early blastocysts. X-Gal staining of chimeric embryos shows high level of chimerism in both intra-embryonic (EP, embryo proper) and extra-embryonic tissue (YS, yolk sac) (top left). No expression is apparent in maternally derived tissues such as in the ectoplacental cone (EC). Histologic sections confirmed the presence of specific blue staining in the EpoR^R129C/− embryos, especially in the YS blood islands (BI, bottom left). No X-Gal staining can be detected in stage-matched, noninjected chimeric embryos (right). Original magnifications, ×10.