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Cahan, Patrick

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Cahan

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Patrick

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Cahan, Patrick

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2006 - 200912010 - 20142

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Author's Publications: search.filters.isAuthorOfPublication.eb1a7d19-e230-4764-8e93-c138cb322178

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Now showing 1 - 3 of 3
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    Deconstructing transcriptional heterogeneity in pluripotent stem cells
    (2014) Kumar, Roshan M.; Cahan, Patrick; Shalek, Alex K.; Satija, Rahul; DaleyKeyser, AJay; Li, Hu; Zhang, Jin; Pardee, Keith; Gennert, David; Trombetta, John J.; Ferrante, Thomas; Regev, Aviv; Daley, George; Collins, James
    SUMMARY Pluripotent stem cells (PSCs) are capable of dynamic interconversion between distinct substates, but the regulatory circuits specifying these states and enabling transitions between them are not well understood. We set out to characterize transcriptional heterogeneity in PSCs by single-cell expression profiling under different chemical and genetic perturbations. Signaling factors and developmental regulators show highly variable expression, with expression states for some variable genes heritable through multiple cell divisions. Expression variability and population heterogeneity can be influenced by perturbation of signaling pathways and chromatin regulators. Strikingly, either removal of mature miRNAs or pharmacologic blockage of signaling pathways drives PSCs into a low-noise ground state characterized by a reconfigured pluripotency network, enhanced self-renewal, and a distinct chromatin state, an effect mediated by opposing miRNA families acting on the c-myc / Lin28 / let-7 axis. These data illuminate the nature of transcriptional heterogeneity in PSCs.
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    Chromatin Modifying Enzymes as Modulators of Reprogramming
    (Nature Publishing Group, 2012) Onder, Tamer T.; Kara, Nergis; Sinha, Amit U.; Bernt, Kathrin M.; Mancarci, Ogan. B.; Gupta, Piyush B.; Cherry, Anne Blanche Cresswell; Zhu, Nan; Cahan, Patrick; Unternaehrer, Juli; Lander, Eric; Armstrong, Scott A.; Daley, George
    Generation of induced pluripotent stem cells (iPSCs) by somatic cell reprogramming involves global epigenetic remodeling. While several proteins are known to regulate chromatin marks associated with the distinct epigenetic states of cells before and after reprogramming, the role of specific chromatin modifying enzymes in reprogramming remains to be determined. To address how chromatin-modifying proteins influence reprogramming, we used shRNAs to target genes in DNA and histone methylation pathways, and have identified positive and negative modulators of iPSC generation. While inhibition of the core components of the polycomb repressive complex 1 and 2, including the histone 3 lysine 27 methyltransferase Ezh2, reduced reprogramming efficiency, suppression of SUV39H1, YY1, and Dot1L enhanced reprogramming. Specifically, inhibition of the H3K79 histone methyltransferase Dot1L by shRNA or a small molecule accelerated reprogramming, significantly increased the yield of iPSC colonies, and substituted for Klf4 and c-Myc. Inhibition of Dot1L early in the reprogramming process is associated with a marked increase in two alternative factors, Nanog and Lin28, which play essential functional roles in the enhancement of reprogramming. Genome-wide analysis of H3K79me2 distribution revealed that fibroblast-specific genes associated with the epithelial to mesenchymal transition lose H3K79me2 in the initial phases of reprogramming. Dot1L inhibition facilitates the loss of this mark from genes that are fated to be repressed in the pluripotent state. These findings implicate specific chromatin-modifying enzymes as barriers to or facilitators of reprogramming, and demonstrate how modulation of chromatin-modifying enzymes can be exploited to more efficiently generate iPSCs with fewer exogenous transcription factors.
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    A High-Resolution Map of Segmental DNA Copy Number Variation in the Mouse Genome
    (Public Library of Science, 2006) Graubert, Timothy A; Edwin, Deepa; Selzer, Rebecca R; Richmond, Todd A; Eis, Peggy S; Shannon, William D; McLeod, Howard L; Cheverud, James M; Ley, Timothy J; Cahan, Patrick; Li, Xia
    Submicroscopic (less than 2 Mb) segmental DNA copy number changes are a recently recognized source of genetic variability between individuals. The biological consequences of copy number variants (CNVs) are largely undefined. In some cases, CNVs that cause gene dosage effects have been implicated in phenotypic variation. CNVs have been detected in diverse species, including mice and humans. Published studies in mice have been limited by resolution and strain selection. We chose to study 21 well-characterized inbred mouse strains that are the focus of an international effort to measure, catalog, and disseminate phenotype data. We performed comparative genomic hybridization using long oligomer arrays to characterize CNVs in these strains. This technique increased the resolution of CNV detection by more than an order of magnitude over previous methodologies. The CNVs range in size from 21 to 2,002 kb. Clustering strains by CNV profile recapitulates aspects of the known ancestry of these strains. Most of the CNVs (77.5%) contain annotated genes, and many (47.5%) colocalize with previously mapped segmental duplications in the mouse genome. We demonstrate that this technique can identify copy number differences associated with known polymorphic traits. The phenotype of previously uncharacterized strains can be predicted based on their copy number at these loci. Annotation of CNVs in the mouse genome combined with sequence-based analysis provides an important resource that will help define the genetic basis of complex traits.