Chemical capping improves template switching and enhances sequencing of small RNAs
Madalee G. Wulf, Sean Maguire, Nan Dai, Alice Blondel, Dora Posfai, Keerthana Krishnan, Zhiyi Sun, Shengxi Guan, Ivan R. Corrêa
Abstract
Template-switching reverse transcription is widely used in RNA sequencing for low-input and low-quality samples, including RNA from single cells or formalin-fixed paraffin-embedded (FFPE) tissues. Previously, we identified the native eukaryotic mRNA 5' cap as a key structural element for enhancing template switching efficiency. Here, we introduce CapTS-seq, a new strategy for sequencing small RNAs that combines chemical capping and template switching. We probed a variety of non-native synthetic cap structures and found that an unmethylated guanosine triphosphate cap led to the lowest bias and highest efficiency for template switching. Through cross-examination of different nucleotides at the cap position, our data provided unequivocal evidence that the 5' cap acts as a template for the first nucleotide in reverse transcriptase-mediated post-templated addition to the emerging cDNA-a key feature to propel template switching. We deployed CapTS-seq for sequencing synthetic miRNAs, human total brain and liver FFPE RNA, and demonstrated that it consistently improves library quality for miRNAs in comparison with a gold standard template switching-based small RNA-seq kit.