RESUMEN
Mice with a targeted mutation of the foxj1 gene demonstrate either D- or L-looping of the embryonic cardiac tube. Foxj1 is expressed in ventral cells of the embryonic node prior to asymmetric, left-right expression of other genes. Despite an absence of 9+2 cilia in foxj1(-/-) mice, 9+0 cilia are present in the node of foxj1(-/-) embryos. In foxj1(-/-) embryos, the patterns of expression of the TGF-beta family member nodal and the homeobox family member pitx2 are randomized. No expression of the TGF-beta family member lefty-2 is observed in any foxj1(-/-) early somite stage embryos. Foxj1 thus acts early in left-right axis patterning and regulates asymmetric gene expression. This regulation does not appear to be the result of a direct interaction between Foxj1 and the genes examined.