The present invention provides a method of identifying mRNA transcripts in the 
transcriptome of a 
cell comprising i) delivering into the 
cell a donor 
expression vector comprising nucleotides in a sequence encoding a trans-splicing 
barcode cassette, wherein the trans-splicing 
barcode cassette comprises a) a first portion, the 
nucleotide sequence of which encodes an 
intron comprising as part of its 3′ end, or followed at its 3′ end by a splice-site 
nucleotide sequence; followed at its 3′ end by, b) a second portion, the 
nucleotide sequence of which encodes a 
barcode polynucleotide; followed at its 3′ end by c) a third portion, which encodes a nucleotide identification element sequence, ii) exposing the 
cell to conditions such that the cell produces multiple copies of the trans-splicing barcode cassette encoded by the donor 
expression vector, which multiple copies of the trans-splicing barcode cassette each splice the barcode 
polynucleotide onto a mRNA transcript of the cell, thereby forming multiple mRNA transcripts of the cell, each spliced to the barcode 
polynucleotide; and iii) identifying the multiple mRNA transcripts that are spliced to the barcode polynucleotides, thereby identifying mRNA transcripts in the 
transcriptome of the cell.