Broad applications of zinc finger nuclease (ZFN) technology-which allows targeted genome editing-in research, medicine, and biotechnology are hampered by the lack of a convenient, rapid, and publicly available method for the synthesis of functional ZFNs. Here we describe an efficient and easy-to-practice modular-assembly method using publicly available zinc fingers to make ZFNs that can modify the DNA sequences of predetermined genomic sites in human cells. We synthesized and tested hundreds of ZFNs to target dozens of different sites in the human CCR5 gene-a co-receptor required for HIV infection-and found that many of these nucleases induced site-specific mutations in the CCR5 sequence.

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Introduction Transposable element (TE) derived sequences comprise half of our genome and DNA methylome, and are presumed densely methylated and inactive. Examination of the genome-wide DNA methylation status within 928 TE subfamilies in human embryonic and adult tissues revealed unexpected tissue-specific and subfamily-specific hypomethylation signatures. Genes proximal to tissue-specific hypomethylated TE sequences were enriched for functions important for the tissue type and their expression correlated strongly with hypomethylation of the TEs. When hypomethylated, these TE sequences gained tissue-specific enhancer marks including H3K4me1 and occupancy by p300, and a majority exhibited enhancer activity in reporter gene assays. Many such TEs also harbored binding sites for transcription factors that are important for tissue-specific functions and exhibited evidence for evolutionary selection. These data suggest that sequences derived from TEs may be responsible for wiring tissue type-specific regulatory networks, and have acquired tissue-specific epigenetic regulation.

We present a novel approach for generating targeted deletions of genomic segments in human and other eukaryotic cells using engineered zinc finger nucleases (ZFNs). We found that ZFNs designed to target two different sites in a human chromosome could introduce two concurrent DNA double-strand breaks (DSBs) in the chromosome and give rise to targeted deletions of the genomic segment between the two sites. Using this method in human cells, we were able to delete predetermined genomic DNA segments in the range of several-hundred base pairs (bp) to 15 mega-bp at frequencies of 10 -3 to 10 -1. These high frequencies allowed us to isolate clonal populations of cells, in which the target chromosomal segments were deleted, by limiting dilution. Sequence analysis revealed that many of the deletion junctions contained small insertions or deletions and microhomologies, indicative of DNA repair via nonhomologous end-joining. Unlike other genome engineering tools such as recombinases and meganucleases, ZFNs do not require preinsertion of target sites into the genome and allow precise manipulation of endogenous genomic scripts in animal and plant cells. Thus, ZFN-induced genomic deletions should be broadly useful as a novel method in biomedical research, biotechnology, and gene therapy.[Supplemental material is available online at http://www.genome.org.]The ability to generate targeted deletions of genomic DNA greater than 10 kilobase pairs (kbp) in length could expand genetic and genomic studies in new dimensions by allowing the selective removal of gene clusters, intergenic regions, exons, and introns from a genome and may have broad applications in research, biotechnology, and gene therapy, but it has been difficult, if not impossible, to achieve this aim in higher eukaryotic cells and organisms. Recombinase systems such as Flp/FRT (Ryder et al. 2007) and Cre/loxP (Ramirez-Solis et al. 1995) and bacterial artificial chromosome (BAC)-based gene targeting (Valenzuela et al. 2003) have been used to delete large genomic DNA segments; however, practically, these approaches are limited to murine embryonic stem (ES) cells, which are more amenable to genetic manipulation via homologous recombination (HR) than are other cells. Furthermore, recombinase systems require two rounds of FRT or loxP insertion into the genome via HR, isolation of cells in which two target sites are inserted in the same chromosome but not in different homologous chromosomes, and subsequent treatment with Flp or Cre recombinases, respectively, to delete the intervening DNA segment, a process that still leaves a single FRT or loxP site behind in the genome. BAC-based gene targeting also has limitations associated with the preparation of BAC vectors and the screening of recombinant clones because of the huge size of these vectors. In addition, false positive clones are often isolated, which results from the breakage and partial integration of BAC vectors (Gomez-Rodriguez et al. 2008). Thus, these approaches are highly laborious and time-consuming even in murin...

1-15 [Author affiliations appear at the end of the paper.]DNA methylation plays key roles in diverse biological processes such as X chromosome inactivation, transposable element repression, genomic imprinting, and tissue-specific gene expression. Sequencing-based DNA methylation profiling provides an unprecedented opportunity to map and compare complete DNA methylomes. This includes one of the most widely applied technologies for measuring DNA methylation: methylated DNA immunoprecipitation followed by sequencing (MeDIP-seq), coupled with a complementary method, methylation-sensitive restriction enzyme sequencing (MRE-seq). A computational approach that integrates data from these two different but complementary assays and predicts methylation differences between samples has been unavailable. Here, we present a novel integrative statistical framework M&M (for integration of MeDIP-seq and MRE-seq) that dynamically scales, normalizes, and combines MeDIPseq and MRE-seq data to detect differentially methylated regions. Using sample-matched whole-genome bisulfite sequencing (WGBS) as a gold standard, we demonstrate superior accuracy and reproducibility of M&M compared to existing analytical methods for MeDIP-seq data alone. M&M leverages the complementary nature of MeDIP-seq and MREseq data to allow rapid comparative analysis between whole methylomes at a fraction of the cost of WGBS. Comprehensive analysis of nineteen human DNA methylomes with M&M reveals distinct DNA methylation patterns among different tissue types, cell types, and individuals, potentially underscoring divergent epigenetic regulation at different scales of phenotypic diversity. We find that differential DNA methylation at enhancer elements, with concurrent changes in histone modifications and transcription factor binding, is common at the cell, tissue, and individual levels, whereas promoter methylation is more prominent in reinforcing fundamental tissue identities.