UpSET recruits HDAC complexes and restricts chromatin accessibility and acetylation at promoter regions.

Developmental gene expression results from the orchestrated interplay between genetic and epigenetic mechanisms. Here, we describe upSET, a transcriptional regulator encoding a SET domain-containing protein recruited to active and inducible genes in Drosophila. However, unlike other Drosophila SET proteins associated with gene transcription, UpSET is part of an Rpd3/Sin3-containing complex that restricts chromatin accessibility and histone acetylation to promoter regions. In the absence of UpSET, active chromatin marks and chromatin accessibility increase and spread to genic and flanking regions due to destabilization of the histone deacetylase complex. Consistent with this, transcriptional noise increases, as manifest by activation of repetitive elements and off-target genes. Interestingly, upSET mutant flies are female sterile due to upregulation of key components of Notch signaling during oogenesis. Thus UpSET defines a class of metazoan transcriptional regulators required to fine tune transcription by preventing the spread of active chromatin.

Tumor-Specific T Cell Dysfunction Is a Dynamic Antigen-Driven Differentiation Program Initiated Early during Tumorigenesis.

CD8(+) T cells recognizing tumor-specific antigens are detected in cancer patients but are dysfunctional. Here we developed a tamoxifen-inducible liver cancer mouse model with a defined oncogenic driver antigen (SV40 large T-antigen) to follow the activation and differentiation of naive tumor-specific CD8(+) T (TST) cells after tumor initiation. Early during the pre-malignant phase of tumorigenesis, TST cells became dysfunctional, exhibiting phenotypic, functional, and transcriptional features similar to dysfunctional T cells isolated from late-stage human tumors. Thus, T cell dysfunction seen in advanced human cancers may already be established early during tumorigenesis. Although the TST cell dysfunctional state was initially therapeutically reversible, it ultimately evolved into a fixed state. Persistent antigen exposure rather than factors associated with the tumor microenvironment drove dysfunction. Moreover, the TST cell differentiation and dysfunction program exhibited features distinct from T cell exhaustion in chronic infections. Strategies to overcome this antigen-driven, cell-intrinsic dysfunction may be required to improve cancer immunotherapy.

Autocrine insulin pathway signaling regulates actin dynamics in cell wound repair.

Cells are exposed to frequent mechanical and/or chemical stressors that can compromise the integrity of the plasma membrane and underlying cortical cytoskeleton. The molecular mechanisms driving the immediate repair response launched to restore the cell cortex and circumvent cell death are largely unknown. Using microarrays and drug-inhibition studies to assess gene expression, we find that initiation of cell wound repair in the Drosophila model is dependent on translation, whereas transcription is required for subsequent steps. We identified 253 genes whose expression is up-regulated (80) or down-regulated (173) in response to laser wounding. A subset of these genes were validated using RNAi knockdowns and exhibit aberrant actomyosin ring assembly and/or actin remodeling defects. Strikingly, we find that the canonical insulin signaling pathway controls actin dynamics through the actin regulators Girdin and Chickadee (profilin), and its disruption leads to abnormal wound repair. Our results provide new insight for understanding how cell wound repair proceeds in healthy individuals and those with diseases involving wound healing deficiencies.

Heme exporter FLVCR is required for T cell development and peripheral survival.

All aerobic cells and organisms must synthesize heme from the amino acid glycine and the tricarboxylic acid cycle intermediate succinyl CoA for incorporation into hemoproteins, such as the cytochromes needed for oxidative phosphorylation. Most studies on heme regulation have been done in erythroid cells or hepatocytes; however, much less is known about heme metabolism in other cell types. The feline leukemia virus subgroup C receptor (FLVCR) is a 12-transmembrane domain surface protein that exports heme from cells, and it was shown to be required for erythroid development. In this article, we show that deletion of Flvcr in murine hematopoietic precursors caused a complete block in αß T cell development at the CD4(+)CD8(+) double-positive stage, although other lymphoid lineages were not affected. Moreover, FLVCR was required for the proliferation and survival of peripheral CD4(+) and CD8(+) T cells. These studies identify a novel and unexpected role for FLVCR, a major facilitator superfamily metabolite transporter, in T cell development and suggest that heme metabolism is particularly important in the T lineage.

Degringolade, a SUMO-targeted ubiquitin ligase, inhibits Hairy/Groucho-mediated repression.

Transcriptional cofactors are essential for proper embryonic development. One such cofactor in Drosophila, Degringolade (Dgrn), encodes a RING finger/E3 ubiquitin ligase. Dgrn and its mammalian ortholog RNF4 are SUMO-targeted ubiquitin ligases (STUbLs). STUbLs bind to SUMOylated proteins via their SUMO interaction motif (SIM) domains and facilitate substrate ubiquitylation. In this study, we show that Dgrn is a negative regulator of the repressor Hairy and its corepressor Groucho (Gro/transducin-like enhancer (TLE)) during embryonic segmentation and neurogenesis, as dgrn heterozygosity suppresses Hairy mutant phenotypes and embryonic lethality. Mechanistically Dgrn functions as a molecular selector: it targets Hairy for SUMO-independent ubiquitylation that inhibits the recruitment of its corepressor Gro, without affecting the recruitment of its other cofactors or the stability of Hairy. Concomitantly, Dgrn specifically targets SUMOylated Gro for sequestration and antagonizes Gro functions in vivo. Our findings suggest that by targeting SUMOylated Gro, Dgrn serves as a molecular switch that regulates cofactor recruitment and function during development. As Gro/TLE proteins are conserved universal corepressors, this may be a general paradigm used to regulate the Gro/TLE corepressors in other developmental processes.

Multiplexed functional genomic analysis of 5' untranslated region mutations across the spectrum of prostate cancer.

The functional consequences of genetic variants within 5' untranslated regions (UTRs) on a genome-wide scale are poorly understood in disease. Here we develop a high-throughput multi-layer functional genomics method called PLUMAGE (Pooled full-length UTR Multiplex Assay on Gene Expression) to quantify the molecular consequences of somatic 5' UTR mutations in human prostate cancer. We show that 5' UTR mutations can control transcript levels and mRNA translation rates through the creation of DNA binding elements or RNA-based cis-regulatory motifs. We discover that point mutations can simultaneously impact transcript and translation levels of the same gene. We provide evidence that functional 5' UTR mutations in the MAP kinase signaling pathway can upregulate pathway-specific gene expression and are associated with clinical outcomes. Our study reveals the diverse mechanisms by which the mutational landscape of 5' UTRs can co-opt gene expression and demonstrates that single nucleotide alterations within 5' UTRs are functional in cancer.

Calf-thymus topoisomerase I equilibrates metastable secondary structure subsequent to relaxation of superhelical stress.

After relaxation of superhelical stress by various methods not involving topoisomerases, a long-lived metastable secondary structure with an anomalously low torsion elastic constant commonly prevails. The aim here is to ascertain whether such metastable secondary structure also results from the action of calf-thymus topoisomerase I (CT Topo I) on a native supercoiled DNA and, if so, whether the enzyme catalyzes its subsequent equilibration. The action of CT Topo I on supercoiled p30delta DNA was examined over a range of times from 10 min to 6 h. We verify that the enzyme operates in an almost completely processive manner, and at each time point determine the twist energy parameter, E(T), that governs the supercoiling free energy. E(T) is initially low, 533 +/- 60, and remains essentially constant up to at least 360 min, when no further CT Topo I is added. The activity of the rather dilute enzyme dies within approximately 60 min. During the 60 min after a second addition of fresh enzyme at either 60 or 120 min, E(T) rises up to a plateau at approximately 1100, which lies within the consensus equilibrium range, 1000 +/- 100. Over that same time period, the average peak spacing between the gel bands (corresponding to individual topoisomers) decreases somewhat with increasing time of exposure to active CT Topo I. After a third addition of fresh CT Topo I at 240 min, there is no further change in either E(T) or the average gel spacing. These and other observations indicate that active CT Topo I catalyzes the equilibration of a metastable secondary structure with abnormally low torsion and bending elastic constants that prevails after the initial release of superhelical stress. An observed temporal lag of this structural equilibration behind the relaxation of native superhelical DNAs suggests that it may require cleavage and religation events at multiple sites on the DNA. A novel analysis of the unwinding kinetics using literature data accounts for the almost complete processivity of the enzyme. The action of CT Topo I was also examined in the presence of 20 and 40 w/v% ethylene glycol (EG), which shift a secondary structure equilibrium toward an alternative state with altered torsion and bending elastic constants. The present results suggest that the usual metastable state coexists with the EG-induced state, and is equilibrated more rapidly than in the absence of EG.

The temporal program of chromosome replication: genomewide replication in clb5{Delta} Saccharomyces cerevisiae.

Temporal regulation of origin activation is widely thought to explain the pattern of early- and late-replicating domains in the Saccharomyces cerevisiae genome. Recently, single-molecule analysis of replication suggested that stochastic processes acting on origins with different probabilities of activation could generate the observed kinetics of replication without requiring an underlying temporal order. To distinguish between these possibilities, we examined a clb5Delta strain, where origin firing is largely limited to the first half of S phase, to ask whether all origins nonspecifically show decreased firing (as expected for disordered firing) or if only some origins ("late" origins) are affected. Approximately half the origins in the mutant genome show delayed replication while the remainder replicate largely on time. The delayed regions can encompass hundreds of kilobases and generally correspond to regions that replicate late in wild-type cells. Kinetic analysis of replication in wild-type cells reveals broad windows of origin firing for both early and late origins. Our results are consistent with a temporal model in which origins can show some heterogeneity in both time and probability of origin firing, but clustering of temporally like origins nevertheless yields a genome that is organized into blocks showing different replication times.

Correction to: NSAID use and somatic exomic mutations in Barrett's esophagus.

It was highlighted that in the original article [1] the Availability of data and materials section was incorrect.

Expansion of primitive human hematopoietic stem cells by culture in a zwitterionic hydrogel.

The ability to expand hematopoietic stem and progenitor cells (HSPCs) ex vivo is critical to fully realize the potential of HSPC-based therapies. In particular, the application of clinically effective therapies, such as cord blood transplantation, has been impeded because of limited HSPC availability. Here, using 3D culture of human HSPCs in a degradable zwitterionic hydrogel, we achieved substantial expansion of phenotypically primitive CD34+ cord blood and bone-marrow-derived HSPCs. This culture system led to a 73-fold increase in long-term hematopoietic stem cell (LT-HSC) frequency, as demonstrated by limiting dilution assays, and the expanded HSPCs were capable of hematopoietic reconstitution for at least 24 weeks in immunocompromised mice. Both the zwitterionic characteristics of the hydrogel and the 3D format were important for HSPC self-renewal. Mechanistically, the impact of 3D zwitterionic hydrogel culture on mitigating HSPC differentiation and promoting self-renewal might result from an inhibition of excessive reactive oxygen species (ROS) production via suppression of O2-related metabolism. HSPC expansion using zwitterionic hydrogels has the potential to facilitate the clinical application of hematopoietic-stem-cell therapies.

N6-methyladenosine mRNA marking promotes selective translation of regulons required for human erythropoiesis.

Many of the regulatory features governing erythrocyte specification, maturation, and associated disorders remain enigmatic. To identify new regulators of erythropoiesis, we utilize a functional genomic screen for genes affecting expression of the erythroid marker CD235a/GYPA. Among validating hits are genes coding for the N6-methyladenosine (m6A) mRNA methyltransferase (MTase) complex, including, METTL14, METTL3, and WTAP. We demonstrate that m6A MTase activity promotes erythroid gene expression programs through selective translation of ~300 m6A marked mRNAs, including those coding for SETD histone methyltransferases, ribosomal components, and polyA RNA binding proteins. Remarkably, loss of m6A marks results in dramatic loss of H3K4me3 marks across key erythroid-specific KLF1 transcriptional targets (e.g., Heme biosynthesis genes). Further, each m6A MTase subunit and a subset of their mRNAs targets are required for human erythroid specification in primary bone-marrow derived progenitors. Thus, m6A mRNA marks promote the translation of a network of genes required for human erythropoiesis.

A virus-packageable CRISPR screen identifies host factors mediating interferon inhibition of HIV.

Interferon (IFN) inhibits HIV replication by inducing antiviral effectors. To comprehensively identify IFN-induced HIV restriction factors, we assembled a CRISPR sgRNA library of Interferon Stimulated Genes (ISGs) into a modified lentiviral vector that allows for packaging of sgRNA-encoding genomes in trans into budding HIV-1 particles. We observed that knockout of Zinc Antiviral Protein (ZAP) improved the performance of the screen due to ZAP-mediated inhibition of the vector. A small panel of IFN-induced HIV restriction factors, including MxB, IFITM1, Tetherin/BST2 and TRIM5alpha together explain the inhibitory effects of IFN on the CXCR4-tropic HIV-1 strain, HIV-1LAI, in THP-1 cells. A second screen with a CCR5-tropic primary strain, HIV-1Q23.BG505, described an overlapping, but non-identical, panel of restriction factors. Further, this screen also identifies HIV dependency factors. The ability of IFN-induced restriction factors to inhibit HIV strains to replicate in human cells suggests that these human restriction factors are incompletely antagonized. Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

NSAID use and somatic exomic mutations in Barrett's esophagus.

BACKGROUND: Use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) has been shown to protect against tetraploidy, aneuploidy, and chromosomal alterations in the metaplastic condition Barrett's esophagus (BE) and to lower the incidence and mortality of esophageal adenocarcinoma (EA). The esophagus is exposed to both intrinsic and extrinsic mutagens resulting from gastric reflux, chronic inflammation, and exposure to environmental carcinogens such as those found in cigarettes. Here we test the hypothesis that NSAID use inhibits accumulation of point mutations/indels during somatic genomic evolution in BE. METHODS: Whole exome sequences were generated from 82 purified epithelial biopsies and paired blood samples from a cross-sectional study of 41 NSAID users and 41 non-users matched by sex, age, smoking, and continuous time using or not using NSAIDs. RESULTS: NSAID use reduced overall frequency of point mutations across the spectrum of mutation types, lowered the frequency of mutations even when adjusted for both TP53 mutation and smoking status, and decreased the prevalence of clones with high variant allele frequency. Never smokers who consistently used NSAIDs had fewer point mutations in signature 17, which is commonly found in EA. NSAID users had, on average, a 50% reduction in functional gene mutations in nine cancer-associated pathways and also had less diversity in pathway mutational burden compared to non-users. CONCLUSIONS: These results indicate NSAID use functions to limit overall mutations on which selection can act and supports a model in which specific mutant cell populations survive or expand better in the absence of NSAIDs.

Hairy transcriptional repression targets and cofactor recruitment in Drosophila.

Members of the widely conserved Hairy/Enhancer of split family of basic Helix-Loop-Helix repressors are essential for proper Drosophila and vertebrate development and are misregulated in many cancers. While a major step forward in understanding the molecular mechanism(s) surrounding Hairy-mediated repression was made with the identification of Groucho, Drosophila C-terminal binding protein (dCtBP), and Drosophila silent information regulator 2 (dSir2) as Hairy transcriptional cofactors, the identity of Hairy target genes and the rules governing cofactor recruitment are relatively unknown. We have used the chromatin profiling method DamID to perform a global and systematic search for direct transcriptional targets for Drosophila Hairy and the genomic recruitment sites for three of its cofactors: Groucho, dCtBP, and dSir2. Each of the proteins was tethered to Escherichia coli DNA adenine methyltransferase, permitting methylation proximal to in vivo binding sites in both Drosophila Kc cells and early embryos. This approach identified 40 novel genomic targets for Hairy in Kc cells, as well as 155 loci recruiting Groucho, 107 loci recruiting dSir2, and wide genomic binding of dCtBP to 496 loci. We also adapted DamID profiling such that we could use tightly gated collections of embryos (2-6 h) and found 20 Hairy targets related to early embryogenesis. As expected of direct targets, all of the putative Hairy target genes tested show Hairy-dependent expression and have conserved consensus C-box-containing sequences that are directly bound by Hairy in vitro. The distribution of Hairy targets in both the Kc cell and embryo DamID experiments corresponds to Hairy binding sites in vivo on polytene chromosomes. Similarly, the distributions of loci recruiting each of Hairy's cofactors are detected as cofactor binding sites in vivo on polytene chromosomes. We have identified 59 putative transcriptional targets of Hairy. In addition to finding putative targets for Hairy in segmentation, we find groups of targets suggesting roles for Hairy in cell cycle, cell growth, and morphogenesis, processes that must be coordinately regulated with pattern formation. Examining the recruitment of Hairy's three characterized cofactors to their putative target genes revealed that cofactor recruitment is context-dependent. While Groucho is frequently considered to be the primary Hairy cofactor, we find here that it is associated with only a minority of Hairy targets. The majority of Hairy targets are associated with the presence of a combination of dCtBP and dSir2. Thus, the DamID chromatin profiling technique provides a systematic means of identifying transcriptional target genes and of obtaining a global view of cofactor recruitment requirements during development.

ZNF131 suppresses centrosome fragmentation in glioblastoma stem-like cells through regulation of HAUS5.

Zinc finger domain genes comprise ~3% of the human genome, yet many of their functions remain unknown. Here we investigated roles for the vertebrate-specific BTB domain zinc finger gene ZNF131 in the context of human brain tumors. We report that ZNF131 is broadly required for Glioblastoma stem-like cell (GSC) viability, but dispensable for neural progenitor cell (NPC) viability. Examination of gene expression changes after ZNF131 knockdown (kd) revealed that ZNF131 activity notably promotes expression of Joubert Syndrome ciliopathy genes, including KIF7, NPHP1, and TMEM237, as well as HAUS5, a component of Augmin/HAUS complex that facilitates microtubule nucleation along the mitotic spindle. Of these genes only kd of HAUS5 displayed GSC-specific viability loss. Critically, HAUS5 ectopic expression was sufficient to suppress viability defects of ZNF131 kd cells. Moreover, ZNF131 and HAUS5 kd phenocopied each other in GSCs, each causing: mitotic arrest, centrosome fragmentation, loss of Augmin/HAUS complex on the mitotic spindle, and loss of GSC self-renewal and tumor formation capacity. In control NPCs, we observed centrosome fragmentation and lethality only when HAUS5 kd was combined with kd of HAUS2 or HAUS4, demonstrating that the complex is essential in NPCs, but that GSCs have heightened requirement. Our results suggest that GSCs differentially rely on ZNF131-dependent expression of HAUS5 as well as the Augmin/HAUS complex activity to maintain the integrity of centrosome function and viability.

The eIF2-alpha kinase HRI is a novel therapeutic target in multiple myeloma.

Dexamethasone (dex) induces apoptosis in multiple myeloma (MM) cells and is a frontline treatment for this disease. However resistance to dex remains a major challenge and novel treatment approaches are needed. We hypothesized that dex utilizes translational pathways to promote apoptosis in MM and that specific targeting of these pathways could overcome dex-resistance. Global unbiased profiling of mRNA translational profiles in MM cells treated with or without dex revealed that dex significantly repressed eIF2 signaling, an important pathway for regulating ternary complex formation and protein synthesis. We demonstrate that dex induces the phosphorylation of eIF2α resulting in the translational upregulation of ATF4, a known eIF2 regulated mRNA. Pharmacologic induction of eIF2α phosphorylation via activation of the heme-regulated eIF2α kinase (HRI) induced apoptosis in MM cell lines and in primary MM cells from patients with dex-resistant disease. In addition, co-culture with marrow stroma failed to protect MM cells from apoptosis induced by targeting the eIF2 pathway. Combination therapy with rapamycin, an mTOR inhibitor, and BTdCPU, an activator of HRI, demonstrated additive effects on apoptosis in dex-resistant cells. Thus, specific activation of the eIF2α kinase HRI is a novel therapeutic target in MM that can augment current treatment strategies.

Array comparative genomic hybridization analysis of genomic alterations in breast cancer subtypes.

In this study, we performed high-resolution array comparative genomic hybridization with an array of 4153 bacterial artificial chromosome clones to assess copy number changes in 44 archival breast cancers. The tumors were flow sorted to exclude non-tumor DNA and increase our ability to detect gene copy number changes. In these tumors, losses were more frequent than gains, and gains in 1q and loss in 16q were the most frequent alterations. We compared gene copy number changes in the tumors based on histologic subtype and estrogen receptor (ER) status, i.e., ER-negative infiltrating ductal carcinoma, ER-positive infiltrating ductal carcinoma, and ER-positive infiltrating lobular carcinoma. We observed a consistent association between loss in regions of 5q and ER-negative infiltrating ductal carcinoma, as well as more frequent loss in 4p16, 8p23, 8p21, 10q25, and 17p11.2 in ER-negative infiltrating ductal carcinoma compared with ER-positive infiltrating ductal carcinoma (adjusted P values < or = 0.05). We also observed high-level amplifications in ER-negative infiltrating ductal carcinoma in regions of 8q24 and 17q12 encompassing the c-myc and c-erbB-2 genes and apparent homozygous deletions in 3p21, 5q33, 8p23, 8p21, 9q34, 16q24, and 19q13. ER-positive infiltrating ductal carcinoma showed a higher frequency of gain in 16p13 and loss in 16q21 than ER-negative infiltrating ductal carcinoma. Correlation analysis highlighted regions of change commonly seen together in ER-negative infiltrating ductal carcinoma. ER-positive infiltrating lobular carcinoma differed from ER-positive infiltrating ductal carcinoma in the frequency of gain in 1q and loss in 11q and showed high-level amplifications in 1q32, 8p23, 11q13, and 11q14. These results indicate that array comparative genomic hybridization can identify significant differences in the genomic alterations between subtypes of breast cancer.

Cells Comprising the Prostate Cancer Microenvironment Lack Recurrent Clonal Somatic Genomic Aberrations.

UNLABELLED: Prostate cancer-associated stroma (CAS) plays an active role in malignant transformation, tumor progression, and metastasis. Molecular analyses of CAS have demonstrated significant changes in gene expression; however, conflicting evidence exists on whether genomic alterations in benign cells comprising the tumor microenvironment (TME) underlie gene expression changes and oncogenic phenotypes. This study evaluates the nuclear and mitochondrial DNA integrity of prostate carcinoma cells, CAS, matched benign epithelium and benign epithelium-associated stroma by whole-genome copy-number analyses, targeted sequencing of TP53, and FISH. Array comparative genomic hybridization (aCGH) of CAS revealed a copy-neutral diploid genome with only rare and small somatic copy-number aberrations (SCNA). In contrast, several expected recurrent SCNAs were evident in the adjacent prostate carcinoma cells, including gains at 3q, 7p, and 8q, and losses at 8p and 10q. No somatic TP53 mutations were observed in CAS. Mitochondrial DNA (mtDNA) extracted from carcinoma cells and stroma identified 23 somatic mtDNA mutations in neoplastic epithelial cells, but only one mutation in stroma. Finally, genomic analyses identified no SCNAs, LOH, or copy-neutral LOH in cultured cancer-associated fibroblasts, which are known to promote prostate cancer progression in vivo IMPLICATIONS: The gene expression changes observed in prostate cancer-adjacent stroma and the attendant contribution of the stroma to the development and progression of prostate cancer are not due to frequent or recurrent genomic alterations in the TME.

Wash interacts with lamin and affects global nuclear organization.

The cytoplasmic functions of Wiskott-Aldrich syndrome family (WAS) proteins are well established and include roles in cytoskeleton reorganization and membrane-cytoskeletal interactions important for membrane/vesicle trafficking, morphogenesis, immune response, and signal transduction. Misregulation of these proteins is associated with immune deficiency and metastasis [1-4]. Cytoplasmic WAS proteins act as effectors of Rho family GTPases and polymerize branched actin through the Arp2/3 complex [1, 5]. Previously, we identified Drosophila washout (wash) as a new member of the WAS family with essential cytoplasmic roles in early development [6, 7]. Studies in mammalian cells and Dictyostelium suggest that WASH functions primarily in a multiprotein complex that regulates endosome shape and trafficking in an Arp2/3-dependent manner [8-11]. However, roles for classically cytoplasmic proteins in the nucleus are beginning to emerge, in particular, as participants in the regulation of gene expression [12, 13]. Here, we show that Drosophila Wash is present in the nucleus, where it plays a key role in global nuclear organization. wash mutant and knockdown nuclei disrupt subnuclear structures/organelles and exhibit the abnormal wrinkled morphology reminiscent of those observed in diverse laminopathies [14-16]. We find that nuclear Wash interacts with B-type Lamin (Lamin Dm0), and, like Lamin, Wash associates with constitutive heterochromatin. Wash knockdown increases chromatin accessibility of repressive compartments and results in a global redistribution of repressive histone modifications. Thus, our results reveal a novel role for Wash in modulating nucleus morphology and in the organization of both chromatin and non-chromatin nuclear sub-structures.

Functional analysis of a chromosomal deletion associated with myelodysplastic syndromes using isogenic human induced pluripotent stem cells.

Chromosomal deletions associated with human diseases, such as cancer, are common, but synteny issues complicate modeling of these deletions in mice. We use cellular reprogramming and genome engineering to functionally dissect the loss of chromosome 7q (del(7q)), a somatic cytogenetic abnormality present in myelodysplastic syndromes (MDS). We derive del(7q)- and isogenic karyotypically normal induced pluripotent stem cells (iPSCs) from hematopoietic cells of MDS patients and show that the del(7q) iPSCs recapitulate disease-associated phenotypes, including impaired hematopoietic differentiation. These disease phenotypes are rescued by spontaneous dosage correction and can be reproduced in karyotypically normal cells by engineering hemizygosity of defined chr7q segments in a 20-Mb region. We use a phenotype-rescue screen to identify candidate haploinsufficient genes that might mediate the del(7q)- hematopoietic defect. Our approach highlights the utility of human iPSCs both for functional mapping of disease-associated large-scale chromosomal deletions and for discovery of haploinsufficient genes.