Derivation of epiblast stem cells on MEFs. (A) Typical epiblast colony after 2 d of culture on fibroblast feeders. (B) The same colony after one additional day of culture. (C,D) Examples of epiblast colonies where extra-embryonic tissues were not completely removed before plating (indicated by arrows). (Reprinted with permission from Chenoweth and Tesar 2010, © Springer Science + Business Media.)