Roles of motile and immotile cilia in left-right symmetry breaking

Abstract

Our body possesses three body axes, anteroposterior, dorsoventral, and left-right (L-R) axes. L-R asymmetry is achieved by three consecutive steps: symmetry breaking at the node, differential patterning of the lateral plate by a signaling molecule Nodal, and finally situs-specific organogenesis. Breaking of L-R symmetry in the mouse embryo takes place in the ventral node, where two types of cilia are found. Whereas centrally located motile cilia generate a leftward fluid flow, peripherally located immotile cilia sense a flow-dependent signal. Although Ca2+ signaling is implicated in flow sensing, it is still not clear what triggers Ca2+ signaling, a determinant molecule transported by the flow or mechanical force induced by the flow.