Mouse ES cell culture system as a model of development.

Mouse embryonic stem (mES) cells are pluripotent stem cells derived from pre-implantation embryos. They are regarded as an essential tool for studying mouse development, as they provide a means for generating knock-out mouse lines. This, however, is not the sole utility of the mES cell system. They undergo differentiation in culture, mimicking the morphological differentiation of peri-implantation embryos from epiblast to egg-cylinder stage. Moreover, they retain the capacity to respond to triggers of differentiation toward trophectoderm and primitive endoderm by forced activation. For these reasons, mES cells can be regarded as a useful tool for analyzing molecular mechanisms underlying early mouse development.