Nodal asymmetry and hedgehog signaling during vertebrate left-right symmetry breaking.

Development of visceral left-right asymmetry in bilateria is based on initial symmetry breaking followed by subsequent asymmetric molecular patterning. An important step is the left-sided expression of transcription factor which is mediated by asymmetric expression of the morphogen in the left lateral plate mesoderm of vertebrates. Processes leading to emergence of the asymmetric domain differ depending on the mode of symmetry breaking.