© GEORGE RETSECK
FOLLOW THE mRNA
To determine where in the mouse brain individual neurons have axon terminals, researchers inject a library of viral vectors in the vicinity of cell bodies. The viruses contain plasmids each encoding a unique
RNA barcode and a presynaptic protein called MAPP-nλ that will shuttle the barcoded mRNA to the ends of the axon. Typically, each cell takes up only one virus, giving that cell an RNA identifier. Dissecting brain regions and sequencing the RNAs reveals which cells project where.
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