Total RNA sequencing has been used to reveal poly(A) and non-poly(A) RNA expression, RNA processing and enhancer activity. To date, no method for full-length total RNA sequencing of single cells has been developed despite the potential of this technology for single-cell biology. Here RIKEN institute researchers describe random displacement amplification sequencing (RamDA-seq), the first full-length total RNA-sequencing method for single cells. Compared with other methods, RamDA-seq shows high sensitivity to non-poly(A) RNA and near-complete full-length transcript coverage. Using RamDA-seq with differentiation time course samples of mouse embryonic stem cells, the researchers reveal hundreds of dynamically regulated non-poly(A) transcripts, including histone transcripts and long noncoding RNA Neat1. Moreover, RamDA-seq profiles recursive splicing in >300-kb introns. RamDA-seq also detects enhancer RNAs and their cell type-specific activity in single cells. Taken together, they demonstrate that RamDA-seq could help investigate the dynamics of gene expression, RNA-processing events and transcriptional regulation in single cells.
Overview of RT-RamDA and single-cell RamDA-seq
a Schematic diagram of RT-RamDA. 1. RT primers (oligo-dT and not-so-random primers) anneal to a RNA template. 2. Complementary DNA (cDNA) is synthesized by the RNA-dependent DNA polymerase activity of RNase H minus reverse transcriptase (RTase). 3. Endonuclease (DNase I) selectively nicks the cDNA of the RNA:cDNA hybrid strand. 4. The 3′ cDNA strand is displaced by the strand displacement activity of RTase mediated by the T4 gene 32 protein (gp32), starting from the nick randomly introduced by DNase I. cDNA is amplified as a displaced strand and protected by gp32 from DNase I. b Relative yield of cDNA molecules using RT-qPCR (n = 4). Mouse ESC total RNA (10 pg) was used as a template, and 1/10 the amount of cDNA was used for qPCR. The relative yield was calculated by averaging the amplification efficiency of four mESC (Nanog, Pou5f1, Zfp42, and Sox2) and three housekeeping (Gnb2l1, Atp5a1, and Tubb5) genes using a conventional method (−) as a standard. c Schematic diagram of RamDA-seq and C1-RamDA-seq. For details, please refer to the Methods section. d Number of detected transcripts with twofold or lower expression changes against rdRNA-seq (count ≥ 10). For the boxplots in b and d, the center line, and lower and upper bounds of each box represent the median, and first and third quartiles, respectively. The lower (upper) whisker extends to smallest (largest) values no further than 1.5 × interquartile range (IQR) from the first (third) quartile. e Squared coefficient of variation of the read count. All conditions were adjusted, and 10 million reads were used in d and e. Transcripts were annotated by GENCODE gene annotation (vM9)