The gene coding for the murine transcription factor GATA6 was inactivated
by insertion of a beta-galactosidase marker gene. The analysis of
heterozygote GATA6/lacZ mice shows two inductions of GATA6 expression
early in development. It is first expressed at the blastocyst stage in
part of the inner mass and in the trophectoderm. The second wave of
expression is in parietal endoderm (Reichert's membrane) and the mesoderm
and endoderm that form the heart and gut. Inactivation leads to a
lethality shortly after implantation (5.5 days postcoitum). Chimeric
experiments show this to be caused by an indirect effect on the epiblast
due to a defect in an extraembryonic tissue
