The transcription factor FoxH1 (FAST) mediates Nodal signaling during anterior-posterior patterning and node formation in the mouse

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Abstract
FoxH1 (FAST) is a transcription factor that mediates signaling by transforming growth factor–β, Activin, and Nodal. The role of FoxH1 in development has now been investigated by the generation and analysis of FoxH1-deficient (FoxH1 −/−) mice. TheFoxH1 −/− embryos showed various patterning defects that recapitulate most of the defects induced by the loss of Nodal signaling. A substantial proportion ofFoxH1 −/− embryos failed to orient the anterior-posterior (A-P) axis correctly, as do mice lacking Cripto, a coreceptor for Nodal. In less severely affectedFoxH1 −/− embryos, A-P polarity was established, but the primitive streak failed to elongate, resulting in the lack of a definitive node and its derivatives. Heterozygosity fornodal renders the FoxH1 −/−phenotype more severe, indicative of a genetic interaction betweenFoxH1 and nodal. The expression ofFoxH1 in the primitive endoderm rescued the A-P patterning defects, but not the midline defects, ofFoxH1 −/− mice. These results indicate that a Nodal-FoxH1 signaling pathway plays a central role in A-P patterning and node formation in the mouse.