Cell type-specific metabolic labelling of nascent proteomes in vivo

Changes in protein expression drive both the acute responses and long-lasting adaptation of cells to internal and external stimuli. While advances in labelling strategies have made it possible to examine general proteome dynamics, it is still not possible to access the proteomes of specific cell types in vivo in vertebrates. Here we describe a transgenic mouse line where Cre-recombinase-induced expression of a mutant methionyl-tRNA synthetase (L274G) enables the cell type-specific labelling of nascent proteins with a non-canonical amino-acid and click chemistry. Using immunoblotting, imaging and mass spectrometry, we demonstrate the metabolic labelling of proteins in genetically-targeted neurons in brain slices and in vivo. Moreover, we discover over 200 proteins that are regulated in hippocampal excitatory neurons by exposing mice to an enriched environment. As such, this approach opens new avenues for the isolation, analysis and quantitative comparison of cell type-specific proteomes and their dynamics in healthy and diseased tissues.