During recent years, neurotrophins have increasingly become a focus of neuroscience research. These proteins are crucial for neural development, but also contribute to the function of the adult brain, particularly with respect to neural plasticity. Two articles in this issue review different aspects of the mechanisms and functions of neurotrophin signalling.
On page 615, Zweifel, Kuruvilla and Ginty discuss how the signal that is initiated when a neurotrophin binds to its receptor — often far from the cell body, perhaps on a growth cone at the tip of a developing axon — is carried retrogradely to the cell body. There are several possible mechanisms for such retrograde signalling, including the formation of a 'signalling endosome' in which the neurotrophin–receptor complex is internalized and transported within the cell; retrograde spread of signalling effector molecules; waves of receptor activation travelling back along the cell membrane; and the propagation of calcium waves, initiating from the activated receptors. There is strong evidence for the signalling endosome model, although the authors concede that the other mechanisms might also be important.
