**5. Epiblast stem cells**

Epiblast stem cells are pluripotent stem cells derived from the epiblast layer of post-implan‐ tation mouse embryos [54]. Epiblast stem cells are distinct from ES cells, which are derived from the inner cell mass of blastocysts. Both ES cells and epiblast stem cells can differentiate into mesoderm, endoderm, and ectoderm. However, epiblast stem cells do not have germ-line transmission.

Rodent pluripotent stem cells are considered to have two distinct states: naïve and primed. Naïve pluripotent stem cell lines are distinguished from primed cells in their response to LIF signaling and MEK/GSK3 inhibition (LIF/2i conditions) and X chromosome activation. Human ES and iPS cells both resemble rodent primed epiblast stem cells more closely than rodent naïve ES cells. In addition, iPS cells derived from pigs can obtain the properties of primed epiblast stem cells. iPS cells derived from human, monkey, rabbit, and rat, but not mouse, can also obtain the properties of primed epiblast stem cells [55].
