Unambiguous detection of SARS-CoV-2 subgenomic mRNAs with single cell RNA sequencing

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiologic agent responsible for the ongoing pandemic of coronavirus disease 2019 (COVID-19). Single cell RNA sequencing (scRNAseq) studies have been valuable for studying SARS-CoV-2 pathogenesis, but the performance of these methods to detect and quantify viral RNAs has not been evaluated. Here we develop an analysis pipeline, single cell coronavirus sequencing (scCoVseq), to quantify unambiguous reads derived from coronavirus genomic (gRNA) and subgenomic mRNAs (sgmRNAs). We use this method to compare the ability of scRNAseq methods developed by 10X Genomics to detect and quantify SARS-CoV-2 RNAs, with particular focus on sgmRNAs. We find that while sequencing libraries from 10X Genomics Chromium Next Gem Single Cell V(D)J (10X 5') contain more unambiguous reads derived from sgmRNAs due to the presence of reads spanning junctions between the viral 5' leader and sgmRNA open reading frames. We demonstrate that by extending read 1 (R1) of 10X 5' leaders we can further increase the number of unambiguous reads from SARS-CoV-2 sgmRNA resulting in more UMIs per sgmRNA per cell. Using this method, which we call 10X 5' Extended R1, we are able quantify viral sgmRNA production per cell, which we believe will improve understanding regarding the dynamics of coronavirus RNA biogenesis over time and across cell types and viruses. We believe this will improve our understanding of coronavirus pathogenesis. Overall design: Single cell RNA sequencing of mock and SARS-CoV-2 infected Vero E6 cells performed with either 10X Genomics Chromium Next GEM Single Cell 3' (10X 3') or 10X Genomics Chromium Next GEM Single Cell V(D)J (10X 5').