Right, left and cilia: How asymmetry is established

The initial breaking of left-right (L-R) symmetry in the embryo is controlled by a motile-cilia-driven leftward fluid flow in the left-right organiser (LRO), resulting in L-R asymmetric gene expression flanking the LRO. Ultimately this results in leftbut not right-sided activation of the Nodal-Pitx2 pathway in more lateral tissues. While aspects of the initial breaking event clearly vary between vertebrates, events in the Lateral Plate Mesoderm (LPM) are conserved through the vertebrate lineage. Evidence from model systems and humans highlights the role of cilia both in the initial symmetry breaking and in the ability of more lateral tissues to exhibit asymmetric gene expression. In this review we concentrate on the process of L-R determination in mouse and humans.

Automated summary

The initial breaking of left-right symmetry in the embryo is controlled by motile cilia-driven leftward fluid flow in the left-right organiser (LRO), resulting in L-R asymmetric gene expression. The activation of the Nodal-Pitx2 pathway is only on the left side in more lateral tissues. The events in the Lateral Plate Mesoderm (LPM) are conserved through the vertebrate lineage.