TARGETED MUTAGENESIS OF THE TRANSCRIPTION FACTOR GATA-4 GENE IN MOUSEEMBRYONIC STEM-CELLS DISRUPTS VISCERAL ENDODERM DIFFERENTIATION IN-VITRO

Transcription factor GATA-4 belongs to a family of zinc finger protein s involved in lineage determination, GATA-4 is first expressed in yolk sac endoderm of the developing mouse and later in cardiac tissue, gut epithelium and gonads. To delineate the role of this transcription fa ctor in differentiation and early development, we studied embryoid bod ies derived from mouse embryonic stem (ES) cells in which both copies of the Gata4 gene were disrupted. Light and electron microscopy demons trated that embryoid bodies formed from wild-type and heterozygous def icient ES cells were covered with a layer of visceral yolk sac endoder m, whereas no yolk sac endoderm was evident on the surface of the homo zygous deficient embryoid bodies. Independently selected homozygous de ficient cell lines displayed this distinctive phenotype, suggesting th at it was not an artifact of clonal variation. Biochemical markers of visceral endoderm formation, such as alpha-feto-protein, hepatocyte nu clear factor-4 and binding sites for Dolichos biflorus agglutinin, wer e absent from the homozygous deficient embryoid bodies. Examination of other differentiation markers in the mutant embryoid bodies, studies of ES cell-derived teratocarcinomas and chimeric mouse analysis demons trated that GATA-4-deficient ES cells have the capacity to differentia te along other lineages. We conclude that, under in vitro conditions, disruption of the Gata4 gene results in a specific block in visceral e ndoderm formation. These homozygous deficient cells should yield insig hts into the regulation of yolk sac endoderm development and the facto rs expressed by visceral endoderm that influence differentiation of ad joining ectoderm/mesoderm.