Regulation of anterior neurectoderm specification and differentiation by BMP signaling in ascidians.

The most anterior structure of the ascidian larva is made of three palps with sensory and adhesive functions essential for metamorphosis. They derive from the anterior neural border and their formation is regulated by FGF and Wnt. Given that they also share gene expression profiles with vertebrate anterior neural tissue and cranial placodes, their study should shed light on the emergence of the unique vertebrate telencephalon.

Highly distinct genetic programs for peripheral nervous system formation in chordates.

Background: Vertebrates develop their peripheral nervous system (PNS) from transient unique embryonic structures, the neural crest, and the ectodermal placodes that are located at the border of the forming central nervous system. By contrast, in the invertebrate chordates, amphioxus and ascidians, a large part of the PNS originates at the opposite of the embryo, in the ventral ectoderm. In both groups, a biphasic mechanism regulates ventral PNS formation: high BMP levels specify a neurogenic territory within which glutamatergic epidermal sensory neuron formation is controlled by the Notch pathway.

Conservation of peripheral nervous system formation mechanisms in divergent ascidian embryos.

Ascidians with very similar embryos but highly divergent genomes are thought to have undergone extensive developmental system drift. We compared, in four species ( and for Phlebobranchia, and for Stolidobranchia), gene expression and gene regulation for a network of six transcription factors regulating peripheral nervous system (PNS) formation in . All genes, but one in , were expressed in the PNS with some differences correlating with phylogenetic distance.