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. Author manuscript; available in PMC: 2016 May 21.
Published in final edited form as: Cell. 2015 May 21;161(5):1202–1214. doi: 10.1016/j.cell.2015.05.002

Figure 1. Molecular barcoding of cellular transcriptomes in droplets.

Figure 1

(A) Drop-Seq barcoding schematic. A complex tissue is dissociated into individual cells, which are then encapsulated in droplets together with microparticles (gray circles) that deliver barcoded primers. Each cell is lysed within a droplet; its mRNAs bind to the primers on its companion microparticle. The mRNAs are reverse-transcribed into cDNAs, generating a set of beads called “single-cell transcriptomes attached to microparticles” (STAMPs). The barcoded STAMPs can then be amplified in pools for high-throughput mRNA-seq to analyze any desired number of individual cells.

(B) Sequence of primers on the microparticle. The primers on all beads contain a common sequence (“PCR handle”) to enable PCR amplification after STAMP formation. Each microparticle contains more than 108 individual primers that share the same “cell barcode” (panel C) but have different unique molecular identifiers (UMIs), enabling mRNA transcripts to be digitally counted (panel D). A 30 bp oligo dT sequence is present at the end of all primer sequences for capture of mRNAs.

(C) Split-and-pool synthesis of the cell barcode. To generate the cell barcode, the pool of microparticles is repeatedly split into four equally sized oligonucleotide synthesis reactions, to which one of the four DNA bases is added, and then pooled together after each cycle, in a total of 12 split-pool cycles. The barcode synthesized on any individual bead reflects that bead’s unique path through the series of synthesis reactions. The result is a pool of microparticles, each possessing one of 412 (16,777,216) possible sequences on its entire complement of primers (see also Figure S1).

(D) Synthesis of a unique molecular identifier (UMI). Following the completion of the “split-and-pool” synthesis cycles, all microparticles are together subjected to eight rounds of degenerate synthesis with all four DNA bases available during each cycle, such that each individual primer receives one of 48 (65,536) possible sequences (UMIs).