The Notch pathway in the annelid Platynereis: insights into chaetogenesis and neurogenesis processes.
Notch is a key signalling pathway playing multiple and varied functions during development. Notch regulates the selection of cells with a neurogenic fate and maintains a pool of yet uncommitted precursors through lateral inhibition, both in insects and in vertebrates. Here, we explore the functions of Notch in the annelid Platynereis dumerilii (Lophotrochozoa). Conserved components of the pathway are identified and a scenario for their evolution in metazoans is proposed. Unexpectedly, neither Notch nor its ligands are expressed in the neurogenic epithelia of the larva at the time when massive neurogenesis begins. Using chemical inhibitors and neural markers, we demonstrate that Notch plays no major role in the general neurogenesis of larvae. Instead, we find Notch components expressed in nascent chaetal sacs, the organs that produce the annelid bristles. Impairing Notch signalling induces defects in chaetal sac formation, abnormalities in chaetae producing cells and a change of identity of chaeta growth accessory cells. This is the first bilaterian species in which the early neurogenesis processes appear to occur without a major involvement of the Notch pathway. Instead, Notch is co-opted to pattern annelid-specific organs, likely through a lateral inhibition process. These features reinforce the view that Notch signalling has been recruited multiple times in evolution due to its remarkable 'toolkit' nature.
Institut Jacques Monod, CNRS, UMR 7592, Univ Paris Diderot, Sorbonne Paris Cité, 75205 Paris, France.
Eve
0000-0002-4647-6640
E
Gazave
Institut Jacques Monod, CNRS, UMR 7592, Univ Paris Diderot, Sorbonne Paris Cité, 75205 Paris, France.
Quentin I B
QI
Lemaître
Institut Jacques Monod, CNRS, UMR 7592, Univ Paris Diderot, Sorbonne Paris Cité, 75205 Paris, France guillaume.balavoine@ijm.fr.
Guillaume
0000-0003-0880-1331
G
Balavoine
D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning; D002454:Cell Differentiation; D049109:Cell Proliferation; D018507:Gene Expression Regulation, Developmental; D055495:Neurogenesis; D010802:Phylogeny; D011077:Polychaeta / Q000254:growth & development / Q000502:physiology*; D051880:Receptors, Notch / Q000378:metabolism*; D015398:Signal Transduction
D051880:Receptors, Notch
Notch; Platynereis; chaetogenesis; lateral inhibition; neurogenesis