Multiple left-right asymmetry defects in Shh−/− mutant mice unveil a convergence of the Shh and retinoic acid pathways in the control of Lefty-1

Multiple left-right asymmetry defects in Shh^−/− mutant mice unveil a convergence of the Shh and retinoic acid pathways in the control of Lefty-1

^*The Salk Institute for Biological Studies, Gene Expression Laboratory, 10010 North Torrey Pines Road, La Jolla, CA 92037-1099; ^§Cardiac Molecular Biology Program, University of California, San Diego School of Medicine, 0613-C, 9500 Gilman Drive, La Jolla, CA 92093; and ^¶Retinoid Research, Departments of Chemistry and Biology, Allergan Inc., Irvine, CA 92713-9534

Contributed by Ronald M. Evans

Abstract

Asymmetric expression of Sonic hedgehog (Shh) in Hensen’s node of the chicken embryo plays a key role in the genetic cascade that controls left-right asymmetry, but its involvement in left-right specification in other vertebrates remains unclear. We show that mouse embryos lacking Shh display a variety of laterality defects, including pulmonary left isomerism, alterations of heart looping, and randomization of axial turning. Expression of the left-specific gene Lefty-1 is absent in Shh ^−/− embryos, suggesting that the observed laterality defects could be the result of the lack of Lefty-1. We also demonstrate that retinoic acid (RA) controls Lefty-1 expression in a pathway downstream or parallel to Shh. Further, we provide evidence that RA controls left-right development across vertebrate species. Thus, the roles of Shh and RA in left-right specification indeed are conserved among vertebrates, and the Shh and RA pathways converge in the control of Lefty-1.

Footnotes

↵ † T.T., J.C., and K.T. contributed equally to this work.
↵ ‡ Present address: Biological Institute, Graduate School of Science, Tohoku University, Aoba-yama Sendai, 987-8578 Japan.
↵ ‖ Present address: Department of Developmental and Cell Biology, 5209 Biosciences II, University of California, Irvine, CA 92697-2399.
↵ ** To whom reprint requests should be addressed. E-mail: belmonte{at}salk.edu.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AF179483 for chicken Lefty-1, AF181680 for chicken Raldh2, and AF181681 for zebrafish Pitx2).
ABBREVIATIONS:

E(n),

embryonic day;

LPM,

lateral plate mesoderm;

RA,

retinoic acid;

Raldh2,

retinaldehyde dehydrogenase-2;

Shh,

Sonic hedgehog