Formation of the ascidian epidermal sensory neurons: insights into the origin of the chordate peripheral nervous system.
The vertebrate peripheral nervous system (PNS) originates from neural crest and placodes. While its developmental origin is the object of intense studies, little is known concerning its evolutionary history. To address this question, we analyzed the formation of the larval tail PNS in the ascidian Ciona intestinalis. The tail PNS of Ciona is made of sensory neurons located within the epidermis midlines and extending processes in the overlying tunic median fin. We show that each midline corresponds to a single longitudinal row of epidermal cells and neurons sharing common progenitors. This simple organization is observed throughout the tail epidermis, which is made of only eight single-cell rows, each expressing a specific genetic program. We next demonstrate that the epidermal neurons are specified in two consecutive steps. During cleavage and gastrula stages, the dorsal and ventral midlines are independently induced by FGF9/16/20 and the BMP ligand ADMP, respectively. Subsequently, Delta/Notch-mediated lateral inhibition controls the number of neurons formed within these neurogenic regions. These results provide a comprehensive overview of PNS formation in ascidian and uncover surprising similarities between the fate maps and embryological mechanisms underlying formation of ascidian neurogenic epidermis midlines and the vertebrate median fin.
Pasini
Andrea
A
Institut de Biologie du Développement de Marseille-Luminy (IBDML), UMR6216, CNRS/Université de la Méditerranée, Marseille, France. pasini@ibdml.univ-mrs.fr
Amiel
Aldine
A
Rothbächer
Ute
U
Roure
Agnès
A
Lemaire
Patrick
P
Darras
Sébastien
S
D000818:Animals; D019521:Body Patterning; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D002938:Ciona intestinalis / Q000196:embryology*; D004817:Epidermis / Q000196:embryology / Q000294:innervation; D005346:Fibroblast Growth Factors / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism; D009432:Neural Crest / Q000196:embryology; D009475:Neurons, Afferent / Q000166:cytology* / Q000378:metabolism; D017933:Peripheral Nervous System / Q000196:embryology; D051880:Receptors, Notch / Q000378:metabolism; D011994:Recombinant Proteins; D015398:Signal Transduction; D014981:Xenopus
D019485:Bone Morphogenetic Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D051880:Receptors, Notch; D011994:Recombinant Proteins; C064045:delta protein; D005346:Fibroblast Growth Factors