Mice with a targeted mutation of the foxjI 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 fox j1(-/-) mice, 9 + 0 cilia are present in the node of foxjl(-/-) embryos. Infoxj1(-/-) 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. Foxjl 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 Foxjl and the genes examined. (C) 2004 Elsevier Inc. All rights reserved.