Gilbert L. Henry and Douglas A. Melton,

Howard Hughes Medical Institute, Department of Molecular and Cellular Biology,
Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA. 

"An expression cloning strategy in Xenopus laevis was used to isolate a homeobox-containing gene, Mixer, that can cause embryonic cells to form endoderm. Mixer transcripts are found specifically in the prospective endoderm of gastrula, which coincides with the time and place that endodermal cells become histologically distinct and irreversibly determined. Loss-of-function studies with a dominant inhibitory mutant demonstrate that Mixer activity is required for endoderm development. In particular, the expression of Sox17a and Sox17b, two previously identified endodermal determinants, require Mixer function. Together, these data suggest that Mixer is an embryonic transcription factor involved in specifying the endodermal germ layer."

Page 95:

"We have further assessed the effect of the Mixer-ENR fusion by assaying gene activities in endodermal explants. Vegetal pole explants dissected from embryos injected with Mixer-ENR lack IFABP and Xlhbox-8 expression (Fig. 5I). This block in gene expression is completely rescued by coinjection of wild-type Mixer RNA, which suggests that the block is specific. Mix.1 does not rescue in similar explant assays. Unlike IFABP and Xlhbox-8, Edd expression is not affected by the Mixer-ENR fusion."