Cilia-Driven Leftward Flow Determines Laterality in Xenopus

Publication Type

Journal contribution

Authors

Schweickert, A.; Weber, T.; Beyer, T.; Vick, P.; Bogusch, S.; Feistel, K.; Blum, M.

Year of publication

2007

Published in

Current Biology

Pubisher

Elsevier

Band/Volume

Vol. 17/

Page (from - to)

60-66

Determination of the vertebrate left-right body axis during embryogenesis results in asymmetric development and placement of most inner organs. Although the asymmetric Nodal cascade is conserved in all vertebrates, the mechanism of symmetry breakage has remained controversial. In mammalian and fish embryos, a cilia-driven leftward flow of extracellular fluid is required for initiation of the Nodal cascade. This flow is localized at the posterior notochord ('node') and Kupffer's vesicle, respectively. In frog and chick embryos, however, molecular asymmetries are required earlier, from cleavage stages through gastrulation. The validity of a cilia-based mechanism for all vertebrates therefore has been questioned. Here we show that a cilia-driven leftward flow precedes asymmetric nodal expression in the frog Xenopus. Motile monocilia emerged on the gastrocoel roof plate during neurulation and lengthened and polarized from an initially central position to the posterior pole of cells. Concomitantly, a robust leftward fluid flow developed from stage 15 onward, significantly before asymmetric nodal transcription started in the leftlateral-plate mesoderm at stage 19. Injection of 1.5% methylcellulose into the archenteron prevented leftward flow and resulted in laterality defects, demonstrating that the flowitself was required for asymmetric gene expression and organ placement.