Arjun Raj, Ph.D.

Professor of Bioengineering, School of Engineering and Applied Sciences;Professor of Genetics, PSOM

University of Pennsylvania
The School of Engineering and Applied Science
Department of Bioengineering and Genetics
415/420 Clinical Research Building
415 Curie Boulevard
Philadelphia, PA 19104
Lab: 215-821-7394

We have contributed to the understanding of mechanisms that create and control cell-to-cell variability in gene expression. In particular, our work was amongst the first to use quantitative single molecule RNA detection techniques to describe the phenomenon of transcriptional bursts, in which we found that transcription is a pulsatile process consisting of pulses of activity interspersed with periods when the gene is completely inactive (Raj et al. PLOS Bio 2006, Leveque and Raj Nat Meth 2013a). We also contributed to the mathematical modeling of this field (Raj et al. PLOS Bio 2006). We have now shown how these pulses relate to homeostatic mechanisms that maintain transcript concentration despite changes in cell volume and DNA content (Padovan-Merhar et al. Mol Cell 2015). We have also shown that variability can be used as a tool for dissecting mechanisms of transcriptional control of molecules such as long non-coding RNA (Maamar et al. Genes and Dev. 2013).

Raj A, Peskin CS, Tranchina D, Vargas DY, Tyagi S. Stochastic mRNA synthesis in mammalian cells.PLoS Biol. 2006 Oct;4(10):e309. PubMed PMID: 17048983; PubMed Central PMCID: PMC1563489.
Levesque MJ, Raj A. Single-chromosome transcriptional profiling reveals chromosomal gene expression regulation. Nat Methods. 2013 Mar;10(3):246-8. doi: 10.1038/nmeth.2372. Epub 2013 Feb 17. Erratum in: Nat Methods. 2013 May;10(5):445. PubMed PMID: 23416756; PubMed Central PMCID: PMC4131260.
Maamar H, Cabili MN, Rinn J, Raj A. linc-HOXA1 is a noncoding RNA that represses Hoxa1 transcription in cis. Genes Dev. 2013 Jun 1;27(11):1260-71. doi: 10.1101/gad.217018.113. Epub 2013 May 30. PubMed PMID: 23723417; PubMed Central PMCID: PMC3690399.
Padovan-Merhar O, Nair GP, Biaesch AG, Mayer A, Scarfone S, Foley SW, Wu AR, Churchman LS, Singh A, Raj A. Single Mammalian Cells Compensate for Differences in Cellular Volume and DNA Copy Number through Independent Global Transcriptional Mechanisms. Mol Cell. 2015 Apr 16;58(2):339-52. doi: 10.1016/j.molcel.2015.03.005. Epub 2015 Apr 9. PubMed PMID: 25866248; PubMed Central PMCID: PMC4402149.

We have contributed to the understanding of how cell-to-cell variability can lead to phenotypic consequences. Specifically, we showed that variability in transcription can lead to random cell fate decisions in bacteria (Maamar and Raj et al. Science 2008), and that variability in gene expression can lead to phenotypic variability in metazoan development (Raj and Rifkin et al. Nature 2010). More recently, we have linked gene expression variability to single cell non-genetic resistance mechanisms in melanoma (Shaffer et al. Nature, in press).

Maamar H, Raj A, Dubnau D. Noise in gene expression determines cell fate in Bacillus subtilis. Science. 2007 Jul 27;317(5837):526-9. Epub 2007 Jun 14. PubMed PMID: 17569828; PubMed Central PMCID: PMC3828679.
Raj A, Rifkin SA, Andersen E, van Oudenaarden A. Variability in gene expression underlies incomplete penetrance. Nature. 2010 Feb 18;463(7283):913-8. doi: 10.1038/nature08781. PubMed PMID: 20164922; PubMed Central PMCID: PMC2836165.
Shaffer SM, Dunagin M, Torborg S, Torre EA, Emert T, Krepler C, Beqiri M, Sproesser K, Brafford P, Xiao M, Eggan E, Anastopoulos IN, Vargas-Garcia CA, Singh A, Nathanson K, Heryn M, Raj A. Rare cell variability and drug-induced reprogramming as a mode of cancer drug resistance. Nature, in press.

We have contributed to methodological approaches to measuring expression and transcription in single cells via RNA fluorescence in situ hybridization (RNA FISH). First, we developed a method that greatly simplifies the detection of individual RNA molecules by RNA FISH (Raj et al. Nat Meth 2008). We have since pushed the method to high multiplexing in the detection of chromosome structure and gene expression simultaneously (Levesque and Raj, Nat Meth 2013a). We also have enabled the detection of single nucleotide variants on individual RNA molecules (Levesque et al. Nat Meth 2013b), which allows for mutation detection and measurements of allele-specific expression. Further, we have developed an ultra-fast variant of RNA FISH that enables use in diagnostic and point of care settings (Shaffer et al. PLOS ONE 2013).

Raj A, van den Bogaard P, Rifkin SA, van Oudenaarden A, Tyagi S. Imaging individual mRNA molecules using multiple singly labeled probes. Nat Methods. 2008 Oct;5(10):877-9. doi: 10.1038/nmeth.1253. Epub 2008 Sep 21. PubMed PMID: 18806792; PubMed Central PMCID: PMC3126653.
Levesque MJ, Raj A. Single-chromosome transcriptional profiling reveals chromosomal gene expression regulation. Nat Methods. 2013 Mar;10(3):246-8. doi: 10.1038/nmeth.2372. Epub 2013 Feb 17. Erratum in: Nat Methods. 2013 May;10(5):445. PubMed PMID: 23416756; PubMed Central PMCID: PMC4131260.
Levesque MJ, Ginart P, Wei Y, Raj A. Visualizing SNVs to quantify allele-specific expression in single cells. Nat Methods. 2013 Sep;10(9):865-7. doi: 10.1038/nmeth.2589. Epub 2013 Aug 4. PubMed PMID: 23913259; PubMed Central PMCID: PMC3771873.
Shaffer SM, Wu MT, Levesque MJ, Raj A. Turbo FISH: a method for rapid single molecule RNA FISH. PLoS One. 2013 Sep 16;8(9):e75120. doi: 10.1371/journal.pone.0075120. eCollection 2013. PubMed PMID: 24066168; PubMed Central PMCID: PMC3774626.

Research Interest

Our lab aims to develop a quantitative understanding of the molecular biology of the cell. Interests include chromosome structure and gene expression, non-coding RNA, and global regulation of gene expression. Applications include genetics, cancer and stem cells.

Lab Members

VinayAyyappanMD/PhD Student
MargaretDunaginLab Manager
NaveenJainMD/PhD Student
SamReffsinPhD Student