Hannah Dueck1, Mugdha Khaladkar2, Tae Kyung Kim34, Jennifer M. Spaethling3, Chantal Francis2, Sangita Suresh56, Stephen Fisher2, Patrick Seale7, Sheryl G. Beck8, Tamas Bartfai9, Bernhard Kuhn1056, Jim Eberwine3† and Junhyong Kim2*†
† Equal contributors
1 Department of Genomics and Computational Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
2 Department of Biology, School of Arts and Sciences, University of Pennsylvania, 103I Lynch Laboratory, 433 S University Avenue, Philadelphia 19104, PA, USA
3 Department of Pharmacology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
4 Current address: Allen Institute for Brain Science, Seattle, WA, USA
5 Department of Pediatrics, Harvard Medical School, Boston, MA, USA
6 Department of Cardiology, Boston Children¿s Hospital, Boston, MA, USA
7 Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
8 Department of Anesthesiology, The Children¿s Hospital of Philadelphia Research Institute, Philadelphia, PA, USA
9 The Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA
10 Current address: Richard King Mellon Institute for Pediatric Research, Children¿s Hospital of Pittsburgh of UPMC, Pittsburgh, USA
* Corresponding author: Junhyong Kim
Abstract (provisional)
Background Differentiation of metazoan cells requires execution of different gene expression programs but recent single-cell transcriptome profiling has revealed considerable variation within cells of seeming identical phenotype. This brings into question the relationship between transcriptome states and cell phenotypes. Additionally, single-cell transcriptomics presents unique analysis challenges that need to be addressed to answer this question. Results We present high quality deep read-depth single-cell RNA sequencing for 91 cells from five mouse tissues and 18 cells from two rat tissues, along with 30 control samples of bulk RNA diluted to single-cell levels. We find that transcriptomes differ globally across tissues with regard to the number of genes expressed, the average expression patterns, and within-cell-type variation patterns. We develop methods to filter genes for reliable quantification and to calibrate biological variation. All cell types include genes with high variability in expression, in a tissue-specific manner. We also find evidence that single-cell variability of neuronal genes in mice is correlated with that in rats consistent with the hypothesis that levels of variation may be conserved. Conclusions Single-cell RNA-sequencing data provide a unique view of transcriptome function; however, careful analysis is required in order to use single-cell RNA-sequencing measurements for this purpose. Technical variation must be considered in single-cell RNA-sequencing studies of expression variation. For a subset of genes, biological variability within each cell type appears to be regulated in order to perform dynamic functions, rather than solely molecular noise.