Smart-Seq2

Switch Mechanism at the 5′ End of RNA Templates

Smart-Seq was developed as a single-cell sequencing protocol with improved read coverage across transcripts (Ramskold et al., 2012). Complete coverage across the genome allows the detection of alternative transcript isoforms and SNPs. There are 2 versions of Smart-Seq: Smart-Seq and Smart-seq2. Smart-seq2 includes several improvements over the original Smart-Seq protocol (Picelli et al., 2013) (Picelli et al., 2014). The new protocol includes a locked nucleic acid (LNA), an increased MgCl2 concentration, betaine, and elimination of the purification step to improve the yield significantly.

Smart-seq2: Single cells are lysed in a buffer that contains free dNTPs and oligo(dT)-tailed oligonucleotides with a universal 5′-anchor sequence. RT is performed, which adds 2_5 untemplated nucleotides to the cDNA 3′ end. A template-switching oligo (TSO) is added, carrying 2 riboguanosines and a modified guanosine to produce a LNA as the last base at the 3_ end. After the first-strand reaction, the cDNA is amplified using a limited number of cycles. Next, tagmentation is used to construct sequencing libraries quickly and efficiently from the amplified cDNA.

Advantages:

  • As little as 50 pg of starting material can be used
  • mRNA sequence does not have to be known
  • Improved coverage across transcripts
  • High level of mappable reads

Disadvantages:

  • Not strand-specific
  • No early multiplexing (Shapiro et al., 2013)
  • Transcript length bias, with inefficient transcription of reads over 4 Kb (Bhargava et al., 2014)
  • Preferential amplification of high-abundance transcripts
  • Purification step may lead to loss of material
  • Could be subject to strand-invasion bias (Tang et al., 2013)


Reagents:

Illumina Library prep and Array Kit Selector



Reviews:

This method has been widely integrated into various sequencing techniques due to its high versatility.

References:

This method has been widely integrated into various sequencing techniques due to its high versatility.