Novel pre- and post-gastrulation expression of Gata4 within cells of the inner cell mass and migratory neural crest cells.

GATA4 is a transcription factor known to be important for the development of many organs such as the heart, intestine, and gonads. However, information regarding the control of its expression is only now beginning to emerge. To further understand the regulation of Gata4 expression during mouse embryonic development, we have generated a novel knockin allele allowing expression of the Cre recombinase under the control of Gata4 regulatory sequences. When these Gata4(Cre/+) mice were crossed with the Cre reporter mouse R26R-YFP, we surprisingly found widespread mosaic YFP expression in e10.0 embryos. This particular expression pattern was traced back to the e5.5 stage via a cell lineage study, suggesting activation of transcription at the Gata4 locus around the blastocyst stage. In accordance with this hypothesis, we found that Gata4 is expressed in cultured embryonic stem (ES) cells and within the inner cell mass (ICM) of e4.5 blastocysts. Interestingly, such early Gata4 transcription can be recapitulated in transgenic reporter studies using 5 kb of the proximal rat Gata4 promoter. During mouse development, these 5-kb regulatory sequences were previously reported to direct reporter gene expression to Sertoli cells of the testes [Mazaud Guittot et al. (2007) Biol Reprod 76:85-95]. We now show that these regulatory sequences can also drive robust fluorescent reporter gene expression in migratory neural crest cells. Comparisons to Wnt1-Cre-mediated YFP labelling of neural crest cells suggest that most of the migratory neural crest cells are labelled in e9.5 to e11.5 Gata4p[5kb]-RFP or -GFP embryos. Analysis of GFP transcription via whole-mount in situ hybridization in e10.5 and e11.5 embryos demonstrated that the 5-kb Gata4 promoter is preferentially active in cells of the boundary caps at the dorsal root entry zone and motor exit points flanking the neural tube. RT-PCR gene expression analysis of FACS-purified GFP-positive cells from e9.5 Gata4p[5kb]-GFP embryos revealed co-expression of Gata4 with many neural crest stem cell markers. Together with sphere-forming and differentiation cell culture assays, our results indicate that the Gata4 promoter is active within at least a subset of the neural crest stem cells. Taken altogether, our studies have revealed new Gata4 expression patterns during mouse embryonic development, which are controlled by its 5-kb proximal 5' flanking sequences. (c) 2008 Wiley-Liss, Inc.