Proteomic profiling across early postnatal development of midbrain dopamine axons innervating the dorsal striatum.

Precise wiring and tuning of dopamine axons in the brain is crucial for normal development of basal ganglia circuits. This process takes place both pre and postnatally, with early postnatal windows reflecting important periods of terminal maturation. Protein expression and precise localization are vital to this process, underlying changes in axon structure and function. Yet, technical hurdles have prohibited mapping protein expression and localization as dopamine axons mature to form functional release sites. Here we employ targeted proximity labeling in midbrain dopamine neurons and track isolated distal axonal proteins in the striatum across development, from the neonatal period through adolescence. Our approach enabled high-precision evaluation of the axonal proteome, supported by a combination of Cre-recombinase based restriction and spatial separation. We map co-varying subpopulations of axonal proteins differentially expressed across development. Microtubule-associated proteins decreased over time, revealing temporal dynamics of dopaminergic axon stabilization at the proteomic level. Conversely, proteins supporting coordinated action potential firing increased over time, likely contributing to the characteristic tonic firing of dopamine neurons emerging over development. Intersecting our findings with recent GWAS of psychiatric and neurological disorders provided functional confirmation of disease and disorder risk. This analysis highlighted early expression and localization of risk gene products, providing spatial-temporal points of convergence for disease-associated variants specifically to the initial stages of postnatal neurodevelopment of dopamine neurons. Together, these findings provide the essential grounding for understanding postnatal dopaminergic axon development and contextualize neurodevelopmental functions for numerous risk gene products.