title: Evolution of leftward flow.
abstract: The asymmetric Nodal signaling cascade as a prerequisite for asymmetric body plan specification is conserved among deuterostomes. In this review we argue that symmetry breakage by cilia-driven leftward flow presents an ancestral character of vertebrates, likely the chordate phylum and maybe all deuterostomes. In vertebrates, leftward flow occurs in a transient structure, a monociliated epithelium, which is derived from superficial mesoderm and localizes to the archenteron roof during gastrulation. The chick as an example for the highly derived birds lacks superficial mesoderm and flow. This loss should be secondary, as flow is present from fish and amphibians to mammals.
authors.affiliation: University of Hohenheim, Institute of Zoology, Stuttgart, Germany. mblum@uni-hohenheim.de
authors.forename: Martin
authors.initials: M
authors.lastname: Blum
authors.forename: Thomas
authors.initials: T
authors.lastname: Weber
authors.forename: Tina
authors.initials: T
authors.lastname: Beyer
authors.forename: Philipp
authors.initials: P
authors.lastname: Vick
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning; D055457:Nodal Protein
chemical_list: D055457:Nodal Protein