Animal Biotechnology and Modeling
ES cell transfer
ES cell culture
(a) DNA microinjection and (b) embryonic stem (ES) cell transfer are
the two most practiced methods for producing transgenic mice. Note that an
culture step is not necessary for DNA microinjection; DNA is injected
directly into the male pronucleus of fertilized one–cell ova (pronuclear zygotes).
In general, if transgenic mice (represented by black mouse) are derived by DNA
microinjection, all their cells will contain the new transgene(s). In (b), after
clonal selection of transfected ES cells, one of two techniques is used for ES cell
transfer. Ova are harvested between the eight-cell and blastocyst stages, ES cells
are either injected directly into a host blastocyst (‘‘injection’’) or cocultured with
eight-cell to morula stage ova, so that transfected ES cells are preferentially
incorporated into the inner cell mass of the developing embryo (‘‘coculture’’).
With blastocyst injection, transgenic offspring are termed
some of their cells are derived from the host blastocyst and some from
transfected ES cells (denoted by white mice with black patches). Using coculture
and tetraploid embryos, one can obtain founder mice derived completely from
the transfected ES cells (denoted as all-black mice).