Linking transcriptional and genetic tumor heterogeneity through allele analysis of single-cell RNA-seq data
Jean Fan*, Hae-Ock Lee*, Soohyun Lee, Da-eun Ryu, Semin Lee, Catherine Xue, Seok Jin Kim, Kihyun Kim, Nikolas Barkas, Peter J Park, Woong-Yang Park and Peter V Kharchenko
Abstract: Characterization of intratumoral heterogeneity is critical to cancer therapy, as presence of phenotypically diverse cell populations commonly fuels relapse and resistance to treatment. Although genetic variation is a well-studied source of intratumoral heterogeneity, the functional impact of most genetic alterations remains unclear. Even less understood is the relative importance of other factors influencing heterogeneity, such as epigenetic state or tumor microenvironment. To investigate the relationship between genetic and transcriptional heterogeneity in a context of cancer progression, we devised a computational approach called HoneyBADGER to identify copy number variation and loss-of-heterozygosity in individual cells from single-cell RNA-sequencing data. By integrating allele and normalized expression information, HoneyBADGER is able to identify and infer the presence of subclone-specific alterations in individual cells and reconstruct underlying subclonal architecture. Examining several tumor types, we show that HoneyBADGER is effective at identifying deletion, amplifications, and copy-neutral loss-of-heterozygosity events, and is capable of robustly identifying subclonal focal alterations as small as 10 megabases. We further apply HoneyBADGER to analyze single cells from a progressive multiple myeloma patient to identify major genetic subclones that exhibit distinct transcriptional signatures relevant to cancer progression. Surprisingly, other prominent transcriptional subpopulations within these tumors did not line up with the genetic subclonal structure, and were likely driven by alternative, non-clonal mechanisms. These results highlight the need for integrative analysis to understand the molecular and phenotypic heterogeneity in cancer.
Integrative single-cell analysis of transcriptional and epigenetic states in the human adult brain
Blue B Lake*, Song Chen*, Brandon C Sos*, Jean Fan*, Gwendolyn E Kaeser, Yun C Yung, Thu E Duong, Derek Gao, Jerold Chun, Peter V Kharchenko, Kun Zhang
Abstract: Detailed characterization of the cell types in the human brain requires scalable experimental approaches to examine multiple aspects of the molecular state of individual cells, as well as computational integration of the data to produce unified cell-state annotations. Here we report improved high-throughput methods for single-nucleus droplet-based sequencing (snDrop-seq) and single-cell transposome hypersensitive site sequencing (scTHS-seq). We used each method to acquire nuclear transcriptomic and DNA accessibility maps for >60,000 single cells from human adult visual cortex, frontal cortex, and cerebellum. Integration of these data revealed regulatory elements and transcription factors that underlie cell-type distinctions, providing a basis for the study of complex processes in the brain, such as genetic programs that coordinate adult remyelination. We also mapped disease-associated risk variants to specific cellular populations, which provided insights into normal and pathogenic cellular processes in the human brain. This integrative multi-omics approach permits more detailed single-cell interrogation of complex organs and tissues.
Integrated single-cell genetic and transcriptional analysis suggests novel drivers of chronic lymphocytic leukemia
Lili Wang*, Jean Fan*, Joshua M. Francis, George Georghiou, Sarah Hergert, Shuqiang Li, Rutendo Gambe, Chensheng W. Zhou, Chunxiao Yang, Sheng Xiao, Paola Dal Cin, Michaela Bowden, Dylan Kotliar, Sachet A. Shukla, Jennifer R. Brown, Donna Neuberg, Dario R. Alessi, Cheng-Zhong Zhang, Peter V. Kharchenko, Kenneth J. Livak, Catherine J. Wu
Abstract: Intra-tumoral genetic heterogeneity has been characterized across cancers by genome sequencing of bulk tumors, including chronic lymphocytic leukemia (CLL). In order to more accurately identify subclones, define phylogenetic relationships, and probe genotype–phenotype relationships, we developed methods for targeted mutation detection in DNA and RNA isolated from thousands of single cells from five CLL samples. By clearly resolving phylogenic relationships, we uncovered mutated LCP1 and WNK1 as novel CLL drivers, supported by functional evidence demonstrating their impact on CLL pathways. Integrative analysis of somatic mutations with transcriptional states prompts the idea that convergent evolution generates phenotypically similar cells in distinct genetic branches, thus creating a cohesive expression profile in each CLL sample despite the presence of genetic heterogeneity. Our study highlights the potential for single-cell RNA-based targeted analysis to sensitively determine transcriptional and mutational profiles of individual cancer cells, leading to increased understanding of driving events in malignancy.
Integrative single-cell analysis of transcriptional and epigenetic states in the human adult brain
Lili Wang*, Angela N. Brooks*, Jean Fan*, Youzhong Wan*, Rutendo Gambe, Shuqiang Li, Sarah Hergert, Shanye Yin, Samuel S. Freeman, Joshua Z. Levin, Lin Fan, Michael Seiler, Silvia Buonamici, Peter G. Smith, Kevin F. Chau, Carrie L. Cibulskis, Wandi Zhang, Laura Z. Rassenti, Emanuela M. Ghia, Thomas J. Kipps, Stacey Fernandes, Donald B. Bloch, Dylan Kotliar, Dan A. Landau, Sachet A. Shukla, Jon C. Aster, Robin Reed, David S. DeLuca, Jennifer R. Brown, Donna Neuberg, Gad Getz, Kenneth J. Livak, Matthew M. Meyerson, Peter V. Kharchenko, Catherine J. Wu16,’Correspondence information about the author Catherine J. Wu
Abstract: Mutations in SF3B1, which encodes a spliceosome component, are associated with poor outcome in chronic lymphocytic leukemia (CLL), but how these contribute to CLL progression remains poorly understood. We undertook a transcriptomic characterization of primary human CLL cells to identify transcripts and pathways affected by SF3B1 mutation. Splicing alterations, identified in the analysis of bulk cells, were confirmed in single SF3B1-mutated CLL cells and also found in cell lines ectopically expressing mutant SF3B1. SF3B1 mutation was found to dysregulate multiple cellular functions including DNA damage response, telomere maintenance, and Notch signaling (mediated through KLF8 upregulation, increased TERC and TERT expression, or altered splicing of DVL2 transcript, respectively). SF3B1 mutation leads to diverse changes in CLL-related pathways.
Cell-Type-Specific Alternative Splicing Governs Cell Fate in the Developing Cerebral Cortex
Xiaochang Zhang, Ming Hui Chen, Xuebing Wu, Andrew Kodani, Jean Fan, Ryan Doan, Manabu Ozawa, Jacqueline Ma, Nobuaki Yoshida, Jeremy F. Reiter, Douglas L. Black, Peter V. Kharchenko, Phillip A. Sharp, Christopher A. Walsh
Abstract: Alternative splicing is prevalent in the mammalian brain. To interrogate the functional role of alternative splicing in neural development, we analyzed purified neural progenitor cells (NPCs) and neurons from developing cerebral cortices, revealing hundreds of differentially spliced exons that preferentially alter key protein domains—especially in cytoskeletal proteins—and can harbor disease-causing mutations. We show that Ptbp1 and Rbfox proteins antagonistically govern the NPC-to-neuron transition by regulating neuron-specific exons. Whereas Ptbp1 maintains apical progenitors partly through suppressing a poison exon of Flna in NPCs, Rbfox proteins promote neuronal differentiation by switching Ninein from a centrosomal splice form in NPCs to a non-centrosomal isoform in neurons. We further uncover an intronic human mutation within a PTBP1-binding site that disrupts normal skipping of the FLNA poison exon in NPCs and causes a brain-specific malformation. Our study indicates that dynamic control of alternative splicing governs cell fate in cerebral cortical development.
Clonal evolution in patients with chronic lymphocytic leukaemia developing resistance to BTK inhibition
Jan A. Burger*, Dan A. Landau*, Amaro Taylor-Weiner*, Ivana Bozic*, Huidan Zhang*, Kristopher Sarosiek, Lili Wang, Chip Stewart, Jean Fan, Julia Hoellenriegel, Mariela Sivina, Adrian M. Dubuc, Cameron Fraser, Yulong Han, Shuqiang Li, Kenneth J. Livak, Lihua Zou, Youzhong Wan, Sergej Konoplev, Carrie Sougnez, Jennifer R. Brown, Lynne V. Abruzzo, Scott L. Carter, Michael J. Keating, Matthew S. Davids, William G. Wierda, Kristian Cibulskis, Thorsten Zenz, Lillian Werner, Paola Dal Cin, Peter Kharchencko, Donna Neuberg, Hagop Kantarjian, Eric Lander, Stacey Gabriel, Susan O’Brien, Anthony Letai, David A. Weitz, Martin A. Nowak, Gad Getz, Catherine J. Wu
Abstract: Resistance to the Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib has been attributed solely to mutations in BTK and related pathway molecules. Using whole-exome and deep-targeted sequencing, we dissect evolution of ibrutinib resistance in serial samples from five chronic lymphocytic leukaemia patients. In two patients, we detect BTK-C481S mutation or multiple PLCG2 mutations. The other three patients exhibit an expansion of clones harbouring del(8p) with additional driver mutations (EP300, MLL2 and EIF2A), with one patient developing trans-differentiation into CD19-negative histiocytic sarcoma. Using droplet-microfluidic technology and growth kinetic analyses, we demonstrate the presence of ibrutinib-resistant subclones and estimate subclone size before treatment initiation. Haploinsufficiency of TRAIL-R, a consequence of del(8p), results in TRAIL insensitivity, which may contribute to ibrutinib resistance. These findings demonstrate that the ibrutinib therapy favours selection and expansion of rare subclones already present before ibrutinib treatment, and provide insight into the heterogeneity of genetic changes associated with ibrutinib resistance.
Characterizing transcriptional heterogeneity through pathway and gene set overdispersion analysis
Jean Fan, Neeraj Salathia, Rui Liu, Gwendolyn E Kaeser, Yun C Yung, Joseph L Herman, Fiona Kaper, Jian-Bing Fan, Kun Zhang, Jerold Chun, Peter V Kharchenko
Abstract: The transcriptional state of a cell reflects a variety of biological factors, from cell-type-specific features to transient processes such as the cell cycle, all of which may be of interest. However, identifying such aspects from noisy single-cell RNA-seq data remains challenging. We developed pathway and gene set overdispersion analysis (PAGODA) to resolve multiple, potentially overlapping aspects of transcriptional heterogeneity by testing gene sets for coordinated variability among measured cells.
Locally Disordered Methylation Forms the Basis of Intratumor Methylome Variation in Chronic Lymphocytic Leukemia
Dan A. Landau*, Kendell Clement*, Michael J. Ziller, Patrick Boyle, Jean Fan, Hongcang Gu, Kristen Stevenson, Carrie Sougnez, Lili Wang, Shuqiang Li, Dylan Kotliar, Wandi Zhang, Mahmoud Ghandi, Levi Garraway, Stacey M. Fernandes, Kenneth J. Livak, Stacey Gabriel, Andreas Gnirke, Eric S. Lander, Jennifer R. Brown, Donna Neuberg, Peter V. Kharchenko, Nir Hacohen, Gad Getz14, Alexander Meissner, Catherine J. Wu
Abstract: Intratumoral heterogeneity plays a critical role in tumor evolution. To define the contribution of DNA methylation to heterogeneity within tumors, we performed genome-scale bisulfite sequencing of 104 primary chronic lymphocytic leukemias (CLLs). Compared with 26 normal B cell samples, CLLs consistently displayed higher intrasample variability of DNA methylation patterns across the genome, which appears to arise from stochastically disordered methylation in malignant cells. Transcriptome analysis of bulk and single CLL cells revealed that methylation disorder was linked to low-level expression. Disordered methylation was further associated with adverse clinical outcome. We therefore propose that disordered methylation plays a similar role to that of genetic instability, enhancing the ability of cancer cells to search for superior evolutionary trajectories.