Figure 4.

ES and EC cell tumorigenesis in immunocompromised mice. (A) Mean ± SEM teratoma weights derived from s.c. injections of TF(+/+), (+/−), and (−/−) E14 ES cells (n = 6, 15, and 20 respectively) and TF(+/+), (+/−), (−/−), and (+/−) RW4 ES cells (n = 8, 9, 19, and 16, respectively). (B) Mean teratocarcinoma weights (± SEM) derived from s.c. injections of TF(+/−) and (−/−) E14 EC cells (n = 7 and 8, respectively) or RW4 EC cells (n = 4, 8, and 4). An additional control in the RW4 (last bar) injections was included. This cell line was targeted with both constructs and survived selection with both G418 and hygromycin. However, homologous recombination was achieved only with the Neo construct; the Hyg construct was nonhomologously integrated into the genome.