ABSTRACT

Genetic manipulations of mammalian cells have become fundamental for our efforts to understand gene function. Embryonic stem cells (ESC) have an advantage over other cell types for performing mutagenesis studies. One reason is the easiness for introducing genetic modifi cations in the ESC genome. The effi ciency of homologous recombination in mouse ESC is high, thus enabling the generation of gene targeted alleles with desired modifi cations. The second reason is that ES cells are pluripotent and can be differentiated in vitro into all three germ layers or in the case of mESC can give rise to an entire organism after injection into preimplantation embryos. The study of the phenotype caused by a mutation is not only limited to undifferentiated ESCs but also to a variety of different cell types that can be generated downstream. In this review we will discuss the two main avenues for manipulating the ESC genome: transgenesis and gene targeting. Further we will discuss new technological developments, which enable the performance of functional studies with ES cells.