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The vertebrate adaptive immune system modifies the genome of individual B cells to encode antibodies that bind particular antigens1. In most mammals, antibodies are composed of heavy and light chains that are generated sequentially by recombination of V, D (for heavy chains), J and C gene segments. Each chain contains three complementarity-determining regions (CDR1–CDR3), which contribute to antigen specificity. Certain heavy and light chains are preferred for particular antigens2–22. Here we consider pairs of B cells that share the same heavy chain V gene and CDRH3 amino acid sequence and were isolated from different donors, also known as public clonotypes23,24. We show that for naive antibodies (those not yet adapted to antigens), the probability that they use the same light chain V gene is around 10%, whereas for memory (functional) antibodies, it is around 80%, even if only one cell per clonotype is used. This property of functional antibodies is a phenomenon that we call light chain coherence. We also observe this phenomenon when similar heavy chains recur within a donor. Thus, although naive antibodies seem to recur by chance, the recurrence of functional antibodies reveals surprising constraint and determinism in the processes of V(D)J recombination and immune selection. For most functional antibodies, the heavy chain determines the light chain.Among naturally occurring antibodies that have adapted to antigen, those with similar heavy chains usually have similar light chains. [ABSTRACT FROM AUTHOR]

Complete knowledge of the genetic variation in individual human genomes is a crucial foundation for understanding the etiology of disease. Genetic variation is typically characterized by sequencing individual genomes and comparing reads to a reference. Existing methods do an excellent job of detecting variants in approximately 90% of the human genome; however, calling variants in the remaining 10% of the genome (largely low-complexity sequence and segmental duplications) is challenging. To improve variant calling, we developed a new algorithm, DISCOVAR, and examined its performance on improved, low-cost sequence data. Using a newly created reference set of variants from the finished sequence of 103 randomly chosen fosmids, we find that some standard variant call sets miss up to 25% of variants. We show that the combination of new methods and improved data increases sensitivity by several fold, with the greatest impact in challenging regions of the human genome. [ABSTRACT FROM AUTHOR]

Cichlid fishes are famous for large, diverse and replicated adaptive radiations in the Great Lakes of East Africa. To understand the molecular mechanisms underlying cichlid phenotypic diversity, we sequenced the genomes and transcriptomes of five lineages of African cichlids: the Nile tilapia (Oreochromis niloticus), an ancestral lineage with low diversity; and four members of the East African lineage: Neolamprologus brichardi/pulcher (older radiation, Lake Tanganyika), Metriaclima zebra (recent radiation, Lake Malawi), Pundamilia nyererei (very recent radiation, Lake Victoria), and Astatotilapia burtoni (riverine species around Lake Tanganyika). We found an excess of gene duplications in the East African lineage compared to tilapia and other teleosts, an abundance of non-coding element divergence, accelerated coding sequence evolution, expression divergence associated with transposable element insertions, and regulation by novel microRNAs. In addition, we analysed sequence data from sixty individuals representing six closely related species from Lake Victoria, and show genome-wide diversifying selection on coding and regulatory variants, some of which were recruited from ancient polymorphisms. We conclude that a number of molecular mechanisms shaped East African cichlid genomes, and that amassing of standing variation during periods of relaxed purifying selection may have been important in facilitating subsequent evolutionary diversification. [ABSTRACT FROM AUTHOR]

Although genetic lesions responsible for some mendelian disorders can be rapidly discovered through massively parallel sequencing of whole genomes or exomes, not all diseases readily yield to such efforts. We describe the illustrative case of the simple mendelian disorder medullary cystic kidney disease type 1 (MCKD1), mapped more than a decade ago to a 2-Mb region on chromosome 1. Ultimately, only by cloning, capillary sequencing and de novo assembly did we find that each of six families with MCKD1 harbors an equivalent but apparently independently arising mutation in sequence markedly under-represented in massively parallel sequencing data: the insertion of a single cytosine in one copy (but a different copy in each family) of the repeat unit comprising the extremely long (∼1.5-5 kb), GC-rich (>80%) coding variable-number tandem repeat (VNTR) sequence in the MUC1 gene encoding mucin 1. These results provide a cautionary tale about the challenges in identifying the genes responsible for mendelian, let alone more complex, disorders through massively parallel sequencing. [ABSTRACT FROM AUTHOR]

Detection of somatic point substitutions is a key step in characterizing the cancer genome. However, existing methods typically miss low-allelic-fraction mutations that occur in only a subset of the sequenced cells owing to either tumor heterogeneity or contamination by normal cells. Here we present MuTect, a method that applies a Bayesian classifier to detect somatic mutations with very low allele fractions, requiring only a few supporting reads, followed by carefully tuned filters that ensure high specificity. We also describe benchmarking approaches that use real, rather than simulated, sequencing data to evaluate the sensitivity and specificity as a function of sequencing depth, base quality and allelic fraction. Compared with other methods, MuTect has higher sensitivity with similar specificity, especially for mutations with allelic fractions as low as 0.1 and below, making MuTect particularly useful for studying cancer subclones and their evolution in standard exome and genome sequencing data. [ABSTRACT FROM AUTHOR]

Background: Computer-based endoscopy simulators have been developed to enable trainees to learn and gain technical endoscopic skills before operating on patients. However, these simulators have not been validated as models of patient-based endoscopy. This study aimed to determine whether a computer-based simulator can accurately represent an actual esophagogastroduodenoscopy (EGD) and colonoscopy and to evaluate its ability to discriminate between varying levels of expertise in performing endoscopic procedures based on objective parameters. Methods: In a prospective, observational trial, five first-year gastroenterology fellows and six gastroenterology attendings from a single academic center completed six endoscopy cases on the Simbionix GI Mentor II endoscopy simulator. The cases were selected to represent common clinical scenarios. The performance parameters were collected by the simulator. The 13 performance parameters measured by the endoscopy simulator were compared between the two study groups. After the simulator cases, the participants completed a survey evaluating the realism of the simulator. Results: Novices and experts were able to complete the tasks in the simulated cases with no significant overall differences between the two groups. The computer-based simulator was able to discriminate levels of expertise only for parameters related to the time spent on the procedure (total time, time to reach the second duodenum, time to reach the cecum, and efficiency of screening). No statistically significant differences were found for the other nine performance parameters measured by the simulator. Based on the survey data, expert opinion concluded that the simulator does not offer a realistic simulation of human endoscopy. Conclusions: The computer-based endoscopy simulator displays a lack of ability to discriminate between novices and experts in terms of endoscopic skills based on measured objective performance parameters. The findings of this study suggest that the computer-based simulator lacks fidelity and that upgrades are necessary to increase the simulator's ability to reproduce human endoscopy more accurately. [ABSTRACT FROM AUTHOR]

Background and Aims: There is limited data on the impact of capsule endoscopy (CE) findings on patient outcomes. The aim of our study is to evaluate the impact of CE findings on further diagnostic work-up, treatment, and symptom resolution.Methods: A retrospective chart review of patients who underwent CE at a single tertiary care center over a 3-year period was performed. CE findings were classified as positive, suspicious, or negative. Therapeutic interventions were medical, endoscopic, surgical, other, or none. Symptoms were considered resolved when the patient had cessation of symptoms for at least 6 months post-CE.Results: A total of 193 patients were studied. The overall diagnostic yield of CE was 37%. There were 97 (50%) patients who had further diagnostic testing following CE; (40 with positive, 22 with suspicious, 35 with negative CE findings). There were 76% patients who received treatment post-CE (59% with positive, 43% with suspicious, 49% with negative CE findings). Overall symptom resolution was seen in 71% of patients (59% with positive, 68% with suspicious, 70% with negative CE findings). There was no statistically significant difference in diagnostic work-up, treatment, and symptom resolution between patients with positive, suspicious, and negative findings. Patients with obscure overt GI bleeding were less likely to have further diagnostic work-up (P = 0.001), and had the highest rate of symptom resolution as compared to other indications (P < 0.001).Conclusions: There is no significant difference in outcomes amongst patients with positive, suspicious, and negative CE findings. Patients with obscure overt GI bleeding had more favorable outcomes as compared to other indications. [ABSTRACT FROM AUTHOR]

Targeting genomic loci by massively parallel sequencing requires new methods to enrich templates to be sequenced. We developed a capture method that uses biotinylated RNA 'baits' to fish targets out of a 'pond' of DNA fragments. The RNA is transcribed from PCR-amplified oligodeoxynucleotides originally synthesized on a microarray, generating sufficient bait for multiple captures at concentrations high enough to drive the hybridization. We tested this method with 170-mer baits that target >15,000 coding exons (2.5 Mb) and four regions (1.7 Mb total) using Illumina sequencing as read-out. About 90% of uniquely aligning bases fell on or near bait sequence; up to 50% lay on exons proper. The uniformity was such that ∼60% of target bases in the exonic 'catch', and ∼80% in the regional catch, had at least half the mean coverage. One lane of Illumina sequence was sufficient to call high-confidence genotypes for 89% of the targeted exon space. [ABSTRACT FROM AUTHOR]

Cancer results from somatic alterations in key genes, including point mutations, copy-number alterations and structural rearrangements. A powerful way to discover cancer-causing genes is to identify genomic regions that show recurrent copy-number alterations (gains and losses) in tumor genomes. Recent advances in sequencing technologies suggest that massively parallel sequencing may provide a feasible alternative to DNA microarrays for detecting copy-number alterations. Here we present: (i) a statistical analysis of the power to detect copy-number alterations of a given size; (ii) SegSeq, an algorithm to segment equal copy numbers from massively parallel sequence data; and (iii) analysis of experimental data from three matched pairs of tumor and normal cell lines. We show that a collection of ∼14 million aligned sequence reads from human cell lines has comparable power to detect events as the current generation of DNA microarrays and has over twofold better precision for localizing breakpoints (typically, to within ∼1 kilobase). [ABSTRACT FROM AUTHOR]

DNA methylation is essential for normal development and has been implicated in many pathologies including cancer. Our knowledge about the genome-wide distribution of DNA methylation, how it changes during cellular differentiation and how it relates to histone methylation and other chromatin modifications in mammals remains limited. Here we report the generation and analysis of genome-scale DNA methylation profiles at nucleotide resolution in mammalian cells. Using high-throughput reduced representation bisulphite sequencing and single-molecule-based sequencing, we generated DNA methylation maps covering most CpG islands, and a representative sampling of conserved non-coding elements, transposons and other genomic features, for mouse embryonic stem cells, embryonic-stem-cell-derived and primary neural cells, and eight other primary tissues. Several key findings emerge from the data. First, DNA methylation patterns are better correlated with histone methylation patterns than with the underlying genome sequence context. Second, methylation of CpGs are dynamic epigenetic marks that undergo extensive changes during cellular differentiation, particularly in regulatory regions outside of core promoters. Third, analysis of embryonic-stem-cell-derived and primary cells reveals that ‘weak’ CpG islands associated with a specific set of developmentally regulated genes undergo aberrant hypermethylation during extended proliferation in vitro, in a pattern reminiscent of that reported in some primary tumours. More generally, the results establish reduced representation bisulphite sequencing as a powerful technology for epigenetic profiling of cell populations relevant to developmental biology, cancer and regenerative medicine. [ABSTRACT FROM AUTHOR]

We report the application of single-molecule-based sequencing technology for high-throughput profiling of histone modifications in mammalian cells. By obtaining over four billion bases of sequence from chromatin immunoprecipitated DNA, we generated genome-wide chromatin-state maps of mouse embryonic stem cells, neural progenitor cells and embryonic fibroblasts. We find that lysine 4 and lysine 27 trimethylation effectively discriminates genes that are expressed, poised for expression, or stably repressed, and therefore reflect cell state and lineage potential. Lysine 36 trimethylation marks primary coding and non-coding transcripts, facilitating gene annotation. Trimethylation of lysine 9 and lysine 20 is detected at satellite, telomeric and active long-terminal repeats, and can spread into proximal unique sequences. Lysine 4 and lysine 9 trimethylation marks imprinting control regions. Finally, we show that chromatin state can be read in an allele-specific manner by using single nucleotide polymorphisms. This study provides a framework for the application of comprehensive chromatin profiling towards characterization of diverse mammalian cell populations. [ABSTRACT FROM AUTHOR]

Chromosome 11, although average in size, is one of the most gene- and disease-rich chromosomes in the human genome. Initial gene annotation indicates an average gene density of 11.6 genes per megabase, including 1,524 protein-coding genes, some of which were identified using novel methods, and 765 pseudogenes. One-quarter of the protein-coding genes shows overlap with other genes. Of the 856 olfactory receptor genes in the human genome, more than 40% are located in 28 single- and multi-gene clusters along this chromosome. Out of the 171 disorders currently attributed to the chromosome, 86 remain for which the underlying molecular basis is not yet known, including several mendelian traits, cancer and susceptibility loci. The high-quality data presented here—nearly 134.5 million base pairs representing 99.8% coverage of the euchromatic sequence—provide scientists with a solid foundation for understanding the genetic basis of these disorders and other biological phenomena. [ABSTRACT FROM AUTHOR]

Here we report a high-quality draft genome sequence of the domestic dog (Canis familiaris), together with a dense map of single nucleotide polymorphisms (SNPs) across breeds. The dog is of particular interest because it provides important evolutionary information and because existing breeds show great phenotypic diversity for morphological, physiological and behavioural traits. We use sequence comparison with the primate and rodent lineages to shed light on the structure and evolution of genomes and genes. Notably, the majority of the most highly conserved non-coding sequences in mammalian genomes are clustered near a small subset of genes with important roles in development. Analysis of SNPs reveals long-range haplotypes across the entire dog genome, and defines the nature of genetic diversity within and across breeds. The current SNP map now makes it possible for genome-wide association studies to identify genes responsible for diseases and traits, with important consequences for human and companion animal health. [ABSTRACT FROM AUTHOR]

Accurate and comprehensive sequence coverage for large genomes has been restricted to only a few species of specific interest. Lower sequence coverage (survey sequencing) of related species can yield a wealth of information about gene content and putative regulatory elements. But survey sequences lack long-range continuity and provide only a fragmented view of a genome. Here we show the usefulness of combining survey sequencing with dense radiation-hybrid (RH) maps for extracting maximum comparative genome information from model organisms. Based on results from the canine system, we propose that from now on all low-pass sequencing projects should be accompanied by a dense, gene-based RH map-construction effort to extract maximum information from the genome with a marginal extra cost. [ABSTRACT FROM AUTHOR]

Tetraodon nigroviridis is a freshwater puffer fish with the smallest known vertebrate genome. Here, we report a draft genome sequence with long-range linkage and substantial anchoring to the 21 Tetraodon chromosomes. Genome analysis provides a greatly improved fish gene catalogue, including identifying key genes previously thought to be absent in fish. Comparison with other vertebrates and a urochordate indicates that fish proteins have diverged markedly faster than their mammalian homologues. Comparison with the human genome suggests~900 previously unannotated human genes. Analysis of the Tetraodon and human genomes shows that whole-genome duplication occurred in the teleost fish lineage, subsequent to its divergence from mammals. The analysis also makes it possible to infer the basic structure of the ancestral bony vertebrate genome, which was composed of 12 chromosomes, and to reconstruct much of the evolutionary history of ancient and recent chromosome rearrangements leading to the modern human karyotype. [ABSTRACT FROM AUTHOR]

Neurospora crassa is a central organism in the history of twentieth-century genetics, biochemistry and molecular biology. Here, we report a high-quality draft sequence of the N. crassa genome. The approximately 40-megabase genome encodes about 10,000 protein-coding genes-more than twice as many as in the fission yeast Schizosaccharomyces pombe and only about 25% fewer than in the fruitfly Drosophila melanogaster. Analysis of the gene set yields insights into unexpected aspects of Neurospora biology including the identification of genes potentially associated with red light photobiology, genes implicated in secondary metabolism, and important differences in Ca2+ signalling as compared with plants and animals. Neurospora possesses the widest array of genome defence mechanisms known for any eukaryotic organism, including a process unique to fungi called repeat-induced point mutation (RIP). Genome analysis suggests that RIP has had a profound impact on genome evolution, greatly slowing the creation of new genes through genomic duplication and resulting in a genome with an unusually low proportion of closely related genes. [ABSTRACT FROM AUTHOR]

The 2-rank of any 2-(28,4,1) design (unital on 28 points) is known to be between 19 and 27. It is shown by the enumeration and analysis of certain binary linear codes that there are no unitals of 2-rank 20, and that there are exactly 4 isomorphism classes of unitals of 2-rank 21. Combined with previous results, this completes the classification of unitals on 28 points of 2-rank less than 22. [ABSTRACT FROM AUTHOR]

We obtain results concerning the existence of smooth curves on the cone over a (possibly singular) plane curve. As an application, these results are used to prove the existence of certain smooth space curves which are the set-theoretic complete intersection of a cone with some other surface. [ABSTRACT FROM AUTHOR]

Our variant ascertainment algorithm, VAAL, uses massively parallel DNA sequence data to identify differences between bacterial genomes with high sensitivity and specificity. VAAL detected ∼98% of differences (including large insertion-deletions) between pairs of strains from three species while calling no false positives. VAAL also pinpointed a single mutation between Vibrio cholerae genomes, identifying an antibiotic's site of action by identifying sequence differences between drug-sensitive strains and drug-resistant derivatives. [ABSTRACT FROM AUTHOR]

Placement of a transjugular intrahepatic portosystemic shunt is a well accepted treatment in the management of gastroesophageal variceal bleeding. Although morbidity and mortality associated with the use of transjugular intrahepatic portosystemic shunts have dramatically decreased, complications still occur. We report a case of fatal fungemia resulting from an infected transjugular intrahepatic portosystemic shunt stent. [ABSTRACT FROM AUTHOR]

An abstract of the article "Ursodeoxycholic Acid for Chemoprevention in Ulcerative Colitis and Primary Sclerosing Cholangitis: A Retrospectove Cohort Study," by Thomas A. Ullman, Victoria Croog, and Leon Maracthi is presented.