Transcription Factors and Development
Generation of transgenic strains and genetic crosses does not support a critical role for Nodal in the regulation of Mixl1 during early embryonic development
L Robb, L Hartley B Borobokis, TA Wilson, AG Hart
Mixl1 is a homeobox gene required for morphogenesis and endoderm migration in the early murine embryo. In both Xenopus and zebrafish, Mixl1-like genes lie downstream of Nodal signalling. Previously, we used in vitro strategies to demonstrate a Nodal response region, containing a FoxH1 binding site, upstream of murine Mixl1. Subsequently, we analysed primary transgenic embryos to test whether this region could regulate Mixl1 expression in vivo. Constructs in which 5’ genomic sequence including the response region and 3’ intronic sequence were linked to a reporter did not recapitulate the complete expression pattern of Mixl1 at E7.5. This result was supported by lack of genetic interaction between mouse strains heterozygous for a deletion of Mixl1 and Nodal.