The action of neurotrophins, factors that modulate the differentiation, maturation and neuronal regeneration, and even death of neurons, is carried out through specific receptors. Among them, the Trk A tyrosine kinase with activity. After activation, these receptors give rise to an intracellular signaling cascade, which culminates with the expression of certain genes.

So far, these receptors were found only in vertebrates, and the search had been barren of invertebrates, made in the two most widely used models, Drosophila melanogaster and Caenorhabditis elegans, as their appearance was related to the evolution of early vertebrates. However, a paper published in Development, in collaboration between the universities of Barcelona and Lleida, has identified the Trk receptor gene in the genome of Branchiostoma floridae, an amphioxus genome equipped with a pre-archetypal gene duplication arose during the evolution of vertebrates.
The work suggests that Trk receptors originated about 550 million years before the separation between vertebrates and cefalocordados.

AmphiTrk The gene is highly genetic and functional homology with the three Trk receptors of vertebrates, their product also capable of transducing signals mediated by the neurotrophins NGF, BDNF, NT3 and NT4. The authors note from their results that is capable of activating Amphi Trk routes of differentiation, but can not do the same with the route PLCgamma, involved in synaptic plasticity in higher vertebrates. And suggest that duplication and divergence of the system neurotrophin / Trk receptor, with the incorporation of PLCgamma route would be one of the bases of the increased complexity of the nervous system in vertebrates.