Neurotrophin, p75, and Trk Signaling Module in the Developing Nervous System of the Marine Annelid Platynereis dumerilii

Figure 5

Evolution of the neurotrophic signaling predated the emergence of chordates. Eumetazoa tree showing the occurrence of NT, Trk, and p75 and the possible split of Trk from an ancestral Trk/Musk/Ror ancestor gene (after Sossin, 2006). A light green “V” is given when a conserved version of the protein is found; a dark green “V” indicates the presence of less conserved molecules (see text for details). Double light green “VV” indicates expansion of the molecules due to genome duplication. A red “x” is given when a putative ortholog is not found. Evolution of the neurotrophic signaling is hypothesized to have occurred at the base of Bilateria, while expansion of the single molecules likely occurred only in the vertebrate lineage.