RESUMO
During cell migration or differentiation, cell surface receptors are simultaneously exposed to different ligands. However, it is often unclear how these extracellular signals are integrated. Neogenin (NEO1) acts as an attractive guidance receptor when the Netrin-1 (NET1) ligand binds, but it mediates repulsion via repulsive guidance molecule (RGM) ligands. Here, we show that signal integration occurs through the formation of a ternary NEO1-NET1-RGM complex, which triggers reciprocal silencing of downstream signaling. Our NEO1-NET1-RGM structures reveal a "trimer-of-trimers" super-assembly, which exists in the cell membrane. Super-assembly formation results in inhibition of RGMA-NEO1-mediated growth cone collapse and RGMA- or NET1-NEO1-mediated neuron migration, by preventing formation of signaling-compatible RGM-NEO1 complexes and NET1-induced NEO1 ectodomain clustering. These results illustrate how simultaneous binding of ligands with opposing functions, to a single receptor, does not lead to competition for binding, but to formation of a super-complex that diminishes their functional outputs.
Assuntos
Moléculas de Adesão Celular Neuronais/metabolismo , Proteínas Ligadas por GPI/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Proteínas Oncogênicas/metabolismo , Animais , Moléculas de Adesão Celular Neuronais/química , Movimento Celular , Receptor DCC/deficiência , Receptor DCC/genética , Proteínas Ligadas por GPI/química , Cones de Crescimento/fisiologia , Humanos , Ventrículos Laterais/citologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas do Tecido Nervoso/antagonistas & inibidores , Proteínas do Tecido Nervoso/química , Neurônios/citologia , Neurônios/metabolismo , Proteínas Oncogênicas/química , Proteínas Oncogênicas/genética , Ligação Proteica , Multimerização Proteica , Estrutura Quaternária de Proteína , Interferência de RNA , RNA Interferente Pequeno/metabolismo , Transdução de SinaisRESUMO
The midbrain dopamine (mDA) system is composed of molecularly and functionally distinct neuron subtypes that mediate specific behaviors and show select disease vulnerability, including in Parkinson's disease. Despite progress in identifying mDA neuron subtypes, how these neuronal subsets develop and organize into functional brain structures remains poorly understood. Here we generate and use an intersectional genetic platform, Pitx3-ITC, to dissect the mechanisms of substantia nigra (SN) development and implicate the guidance molecule Netrin-1 in the migration and positioning of mDA neuron subtypes in the SN. Unexpectedly, we show that Netrin-1, produced in the forebrain and provided to the midbrain through axon projections, instructs the migration of GABAergic neurons into the ventral SN. This migration is required to confine mDA neurons to the dorsal SN. These data demonstrate that neuron migration can be controlled by remotely produced and axon-derived secreted guidance cues, a principle that is likely to apply more generally.
