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Retinoic acid signalling links left-right asymmetric patterning and bilaterally symmetric somitogenesis in the zebrafish embryo.

Kawakami Y, Raya A, Raya RM, Rodríguez-Esteban C, Belmonte JC

Gene Expression Laboratory, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.

During embryogenesis, cells are spatially patterned as a result of highly coordinated and stereotyped morphogenetic events. In the vertebrate embryo, information on laterality is conveyed to the node, and subsequently to the lateral plate mesoderm, by a complex cascade of epigenetic and genetic events, eventually leading to a left-right asymmetric body plan. At the same time, the paraxial mesoderm is patterned along the anterior-posterior axis in metameric units, or somites, in a bilaterally symmetric fashion. Here we characterize a cascade of laterality information in the zebrafish embryo and show that blocking the early steps of this cascade (before it reaches the lateral plate mesoderm) results in random left-right asymmetric somitogenesis. We also uncover a mechanism mediated by retinoic acid signalling that is crucial in buffering the influence of the flow of laterality information on the left-right progression of somite formation, and thus in ensuring bilaterally symmetric somitogenesis.

Published 12 May 2005 in Nature, 435(7039): 165-71.
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