(1) Here, human or mouse embryonic stem cells, in vitro representatives of the totipotent inner cell mass blastomeres, are placed into culture.(2) In the early stages after fertilization - immediately after a sperm and egg join together and begin dividing - stem cells are considered totipotent .(3) For the first few divisions, up to at least the 8-cell stage, all the cells of the tiny embryo are totipotent stem cells.(4) Thus, unlike totipotent single-cell embryos, pluripotent embryonic stem cells are specialized cells that have limited developmental capabilities.(5) What he showed next were a series of experiments in which they pushed cultured, totipotent mouse embryonic stem cells to desired neural fates using the various factors he had identified as significant in vivo.
