Fig. 3.

Characterization of oxidant-resistant ES cells. a Morphology of ES cell colonies in culture. Parental ES cell line c7.1 and two resistant lines (1E1 and 4C11) are germline competent and also exhibit a compacted colony morphology with a tight boundary, a characteristic typical of pluripotent ES cells. Clone 5A4, however, does not retain this morphology and, indeed, this line failed to generate mice. b Fixed ES cell colonies stained with OCT4 antibody. Compared with germline-competent clones (c7.1, 1E1, and 4C11), 5A4 appears to have lower levels of the OCT4 protein. This reduced OCT4 level may correlate with the inability of the 5A4 clone to produce chimeric mice