Mouse embryo stem cells: their identification, propagation and manipulation.

The early mouse embryo contains a transient population of pluripotential stem cells which are responsible for generating both the foetal primordia and extraembryonic membranes. The characterisation of murine embryo stem cells and their isolation and propagation in culture provides the first instance in which pure populations of normal stem cells are directly accessible to the researcher. This marks a considerable advance in stem cell biology which may pave the way to the dissection of general stem cell control mechanisms and the identification of key regulatory factors. In addition, the genetic manipulation of embryo stem cells affords a unique avenue for experimental intervention in mammalian development and for controlled modification of the mouse germ line.