a | Axon-derived TrkA endosomes are transported to dendrites, where they signal locally to control dendrite growth, in conjunction with autocrine bone morphogenetic protein (BMP) signalling as well as BMPs derived from neighbouring satellite glia. b | Retrograde nerve growth factor (NGF)–TrkA signalling activates transcriptional programmes to promote dendritic growth and development. c | Axon-derived TrkA endosomes influence synaptogenesis by promoting the clustering of nicotinic acetylcholine receptors (nAChRs) and postsynaptic density components, including MAGUK, GKAP and Shank. Retrograde NGF signalling also regulates preganglionic innervation by promoting secretion of brain-derived neurotrophic factor (BDNF) from postganglionic neurons. Egr3, early growth response 3.