Position effects at the FGF8 locus are associated with femoral hypoplasia.

Copy-number variations (CNVs) are a common cause of congenital limb malformations and are interpreted primarily on the basis of their effect on gene dosage. However, recent studies show that CNVs also influence the 3D genome chromatin organization. The functional interpretation of whether a phenotype is the result of gene dosage or a regulatory position effect remains challenging. Here, we report on two unrelated families with individuals affected by bilateral hypoplasia of the femoral bones, both harboring de novo duplications on chromosome 10q24.32. The ∼0.5 Mb duplications include FGF8, a key regulator of limb development and several limb enhancer elements. To functionally characterize these variants, we analyzed the local chromatin architecture in the affected individuals' cells and re-engineered the duplications in mice by using CRISPR-Cas9 genome editing. We found that the duplications were associated with ectopic chromatin contacts and increased FGF8 expression. Transgenic mice carrying the heterozygous tandem duplication including Fgf8 exhibited proximal shortening of the limbs, resembling the human phenotype. To evaluate whether the phenotype was a result of gene dosage, we generated another transgenic mice line, carrying the duplication on one allele and a concurrent Fgf8 deletion on the other allele, as a control. Surprisingly, the same malformations were observed. Capture Hi-C experiments revealed ectopic interaction with the duplicated region and Fgf8, indicating a position effect. In summary, we show that duplications at the FGF8 locus are associated with femoral hypoplasia and that the phenotype is most likely the result of position effects altering FGF8 expression rather than gene dosage effects.

Non-coding deletions identify Maenli lncRNA as a limb-specific En1 regulator.

Long non-coding RNAs (lncRNAs) can be important components in gene-regulatory networks1, but the exact nature and extent of their involvement in human Mendelian disease is largely unknown. Here we show that genetic ablation of a lncRNA locus on human chromosome 2 causes a severe congenital limb malformation. We identified homozygous 27-63-kilobase deletions located 300 kilobases upstream of the engrailed-1 gene (EN1) in patients with a complex limb malformation featuring mesomelic shortening, syndactyly and ventral nails (dorsal dimelia). Re-engineering of the human deletions in mice resulted in a complete loss of En1 expression in the limb and a double dorsal-limb phenotype that recapitulates the human disease phenotype. Genome-wide transcriptome analysis in the developing mouse limb revealed a four-exon-long non-coding transcript within the deleted region, which we named Maenli. Functional dissection of the Maenli locus showed that its transcriptional activity is required for limb-specific En1 activation in cis, thereby fine-tuning the gene-regulatory networks controlling dorso-ventral polarity in the developing limb bud. Its loss results in the En1-related dorsal ventral limb phenotype, a subset of the full En1-associated phenotype. Our findings demonstrate that mutations involving lncRNA loci can result in human Mendelian disease.

Enhancer hijacking determines extrachromosomal circular MYCN amplicon architecture in neuroblastoma.

MYCN amplification drives one in six cases of neuroblastoma. The supernumerary gene copies are commonly found on highly rearranged, extrachromosomal circular DNA (ecDNA). The exact amplicon structure has not been described thus far and the functional relevance of its rearrangements is unknown. Here, we analyze the MYCN amplicon structure using short-read and Nanopore sequencing and its chromatin landscape using ChIP-seq, ATAC-seq and Hi-C. This reveals two distinct classes of amplicons which explain the regulatory requirements for MYCN overexpression. The first class always co-amplifies a proximal enhancer driven by the noradrenergic core regulatory circuit (CRC). The second class of MYCN amplicons is characterized by high structural complexity, lacks key local enhancers, and instead contains distal chromosomal fragments harboring CRC-driven enhancers. Thus, ectopic enhancer hijacking can compensate for the loss of local gene regulatory elements and explains a large component of the structural diversity observed in MYCN amplification.

The mole genome reveals regulatory rearrangements associated with adaptive intersexuality.

Linking genomic variation to phenotypical traits remains a major challenge in evolutionary genetics. In this study, we use phylogenomic strategies to investigate a distinctive trait among mammals: the development of masculinizing ovotestes in female moles. By combining a chromosome-scale genome assembly of the Iberian mole, Talpa occidentalis, with transcriptomic, epigenetic, and chromatin interaction datasets, we identify rearrangements altering the regulatory landscape of genes with distinct gonadal expression patterns. These include a tandem triplication involving CYP17A1, a gene controlling androgen synthesis, and an intrachromosomal inversion involving the pro-testicular growth factor gene FGF9, which is heterochronically expressed in mole ovotestes. Transgenic mice with a knock-in mole CYP17A1 enhancer or overexpressing FGF9 showed phenotypes recapitulating mole sexual features. Our results highlight how integrative genomic approaches can reveal the phenotypic impact of noncoding sequence changes.

Hi-C Identifies Complex Genomic Rearrangements and TAD-Shuffling in Developmental Diseases.

Genome-wide analysis methods, such as array comparative genomic hybridization (CGH) and whole-genome sequencing (WGS), have greatly advanced the identification of structural variants (SVs) in the human genome. However, even with standard high-throughput sequencing techniques, complex rearrangements with multiple breakpoints are often difficult to resolve, and predicting their effects on gene expression and phenotype remains a challenge. Here, we address these problems by using high-throughput chromosome conformation capture (Hi-C) generated from cultured cells of nine individuals with developmental disorders (DDs). Three individuals had previously been identified as harboring duplications at the SOX9 locus and six had been identified with translocations. Hi-C resolved the positions of the duplications and was instructive in interpreting their distinct pathogenic effects, including the formation of new topologically associating domains (neo-TADs). Hi-C was very sensitive in detecting translocations, and it revealed previously unrecognized complex rearrangements at the breakpoints. In several cases, we observed the formation of fused-TADs promoting ectopic enhancer-promoter interactions that were likely to be involved in the disease pathology. In summary, we show that Hi-C is a sensible method for the detection of complex SVs in a clinical setting. The results help interpret the possible pathogenic effects of the SVs in individuals with DDs.

CRUP: a comprehensive framework to predict condition-specific regulatory units.

We present the software Condition-specific Regulatory Units Prediction (CRUP) to infer from epigenetic marks a list of regulatory units consisting of dynamically changing enhancers with their target genes. The workflow consists of a novel pre-trained enhancer predictor that can be reliably applied across cell types and species, solely based on histone modification ChIP-seq data. Enhancers are subsequently assigned to different conditions and correlated with gene expression to derive regulatory units. We thoroughly test and then apply CRUP to a rheumatoid arthritis model, identifying enhancer-gene pairs comprising known disease genes as well as new candidate genes.

Preformed chromatin topology assists transcriptional robustness of Shh during limb development.

Long-range gene regulation involves physical proximity between enhancers and promoters to generate precise patterns of gene expression in space and time. However, in some cases, proximity coincides with gene activation, whereas, in others, preformed topologies already exist before activation. In this study, we investigate the preformed configuration underlying the regulation of the Shh gene by its unique limb enhancer, the ZRS, in vivo during mouse development. Abrogating the constitutive transcription covering the ZRS region led to a shift within the Shh-ZRS contacts and a moderate reduction in Shh transcription. Deletion of the CTCF binding sites around the ZRS resulted in the loss of the Shh-ZRS preformed interaction and a 50% decrease in Shh expression but no phenotype, suggesting an additional, CTCF-independent mechanism of promoter-enhancer communication. This residual activity, however, was diminished by combining the loss of CTCF binding with a hypomorphic ZRS allele, resulting in severe Shh loss of function and digit agenesis. Our results indicate that the preformed chromatin structure of the Shh locus is sustained by multiple components and acts to reinforce enhancer-promoter communication for robust transcription.

Serial genomic inversions induce tissue-specific architectural stripes, gene misexpression and congenital malformations.

Balanced chromosomal rearrangements such as inversions and translocations can cause congenital disease or cancer by inappropriately rewiring promoter-enhancer contacts1,2. To study the potentially pathogenic consequences of balanced chromosomal rearrangements, we generated a series of genomic inversions by placing an active limb enhancer cluster from the Epha4 regulatory domain at different positions within a neighbouring gene-dense region and investigated their effects on gene regulation in vivo in mice. Expression studies and high-throughput chromosome conformation capture from embryonic limb buds showed that the enhancer cluster activated several genes downstream that are located within asymmetric regions of contact, the so-called architectural stripes3. The ectopic activation of genes led to a limb phenotype that could be rescued by deleting the CCCTC-binding factor (CTCF) anchor of the stripe. Architectural stripes appear to be driven by enhancer activity, because they do not form in mouse embryonic stem cells. Furthermore, we show that architectural stripes are a frequent feature of developmental three-dimensional genome architecture often associated with active enhancers. Therefore, balanced chromosomal rearrangements can induce ectopic gene expression and the formation of asymmetric chromatin contact patterns that are dependent on CTCF anchors and enhancer activity.

Dynamic 3D chromatin architecture contributes to enhancer specificity and limb morphogenesis.

The regulatory specificity of enhancers and their interaction with gene promoters is thought to be controlled by their sequence and the binding of transcription factors. By studying Pitx1, a regulator of hindlimb development, we show that dynamic changes in chromatin conformation can restrict the activity of enhancers. Inconsistent with its hindlimb-restricted expression, Pitx1 is controlled by an enhancer (Pen) that shows activity in forelimbs and hindlimbs. By Capture Hi-C and three-dimensional modeling of the locus, we demonstrate that forelimbs and hindlimbs have fundamentally different chromatin configurations, whereby Pen and Pitx1 interact in hindlimbs and are physically separated in forelimbs. Structural variants can convert the inactive into the active conformation, thereby inducing Pitx1 misexpression in forelimbs, causing partial arm-to-leg transformation in mice and humans. Thus, tissue-specific three-dimensional chromatin conformation can contribute to enhancer activity and specificity in vivo and its disturbance can result in gene misexpression and disease.

Composition and dosage of a multipartite enhancer cluster control developmental expression of Ihh (Indian hedgehog).

Copy number variations (CNVs) often include noncoding sequences and putative enhancers, but how these rearrangements induce disease is poorly understood. Here we investigate CNVs involving the regulatory landscape of IHH (encoding Indian hedgehog), which cause multiple, highly localized phenotypes including craniosynostosis and synpolydactyly. We show through transgenic reporter and genome-editing studies in mice that Ihh is regulated by a constellation of at least nine enhancers with individual tissue specificities in the digit anlagen, growth plates, skull sutures and fingertips. Consecutive deletions, resulting in growth defects of the skull and long bones, showed that these enhancers function in an additive manner. Duplications, in contrast, caused not only dose-dependent upregulation but also misexpression of Ihh, leading to abnormal phalanges, fusion of sutures and syndactyly. Thus, precise spatiotemporal control of developmental gene expression is achieved by complex multipartite enhancer ensembles. Alterations in the composition of such clusters can result in gene misexpression and disease.

A likelihood ratio-based method to predict exact pedigrees for complex families from next-generation sequencing data.

MOTIVATION: Next generation sequencing technology considerably changed the way we screen for pathogenic mutations in rare Mendelian disorders. However, the identification of the disease-causing mutation amongst thousands of variants of partly unknown relevance is still challenging and efficient techniques that reduce the genomic search space play a decisive role. Often segregation- or linkage analysis are used to prioritize candidates, however, these approaches require correct information about the degree of relationship among the sequenced samples. For quality assurance an automated control of pedigree structures and sample assignment is therefore highly desirable in order to detect label mix-ups that might otherwise corrupt downstream analysis. RESULTS: We developed an algorithm based on likelihood ratios that discriminates between different classes of relationship for an arbitrary number of genotyped samples. By identifying the most likely class we are able to reconstruct entire pedigrees iteratively, even for highly consanguineous families. We tested our approach on exome data of different sequencing studies and achieved high precision for all pedigree predictions. By analyzing the precision for varying degrees of relatedness or inbreeding we could show that a prediction is robust down to magnitudes of a few hundred loci. AVAILABILITY AND IMPLEMENTATION: A java standalone application that computes the relationships between multiple samples as well as a Rscript that visualizes the pedigree information is available for download as well as a web service at www.gene-talk.de CONTACT: heinrich@molgen.mpg.deSupplementary information: Supplementary data are available at Bioinformatics online.

Characterization of hundreds of regulatory landscapes in developing limbs reveals two regimes of chromatin folding.

Complex regulatory landscapes control the pleiotropic transcriptional activities of developmental genes. For most genes, the number, location, and dynamics of their associated regulatory elements are unknown. In this work, we characterized the three-dimensional chromatin microarchitecture and regulatory landscape of 446 limb-associated gene loci in mouse using Capture-C, ChIP-seq, and RNA-seq in forelimb, hindlimb at three developmental stages, and midbrain. The fine mapping of chromatin interactions revealed a strong preference for functional genomic regions such as repressed or active domains. By combining chromatin marks and interaction peaks, we annotated more than 1000 putative limb enhancers and their associated genes. Moreover, the analysis of chromatin interactions revealed two regimes of chromatin folding, one producing interactions stable across tissues and stages and another one associated with tissue and/or stage-specific interactions. Whereas stable interactions associate strongly with CTCF/RAD21 binding, the intensity of variable interactions correlates with changes in underlying chromatin modifications, specifically at the viewpoint and at the interaction site. In conclusion, this comprehensive data set provides a resource for the characterization of hundreds of limb-associated regulatory landscapes and a framework to interpret the chromatin folding dynamics observed during embryogenesis.

Formation of new chromatin domains determines pathogenicity of genomic duplications.

Chromosome conformation capture methods have identified subchromosomal structures of higher-order chromatin interactions called topologically associated domains (TADs) that are separated from each other by boundary regions. By subdividing the genome into discrete regulatory units, TADs restrict the contacts that enhancers establish with their target genes. However, the mechanisms that underlie partitioning of the genome into TADs remain poorly understood. Here we show by chromosome conformation capture (capture Hi-C and 4C-seq methods) that genomic duplications in patient cells and genetically modified mice can result in the formation of new chromatin domains (neo-TADs) and that this process determines their molecular pathology. Duplications of non-coding DNA within the mouse Sox9 TAD (intra-TAD) that cause female to male sex reversal in humans, showed increased contact of the duplicated regions within the TAD, but no change in the overall TAD structure. In contrast, overlapping duplications that extended over the next boundary into the neighbouring TAD (inter-TAD), resulted in the formation of a new chromatin domain (neo-TAD) that was isolated from the rest of the genome. As a consequence of this insulation, inter-TAD duplications had no phenotypic effect. However, incorporation of the next flanking gene, Kcnj2, in the neo-TAD resulted in ectopic contacts of Kcnj2 with the duplicated part of the Sox9 regulatory region, consecutive misexpression of Kcnj2, and a limb malformation phenotype. Our findings provide evidence that TADs are genomic regulatory units with a high degree of internal stability that can be sculptured by structural genomic variations. This process is important for the interpretation of copy number variations, as these variations are routinely detected in diagnostic tests for genetic disease and cancer. This finding also has relevance in an evolutionary setting because copy-number differences are thought to have a crucial role in the evolution of genome complexity.

Strategies to improve the performance of rare variant association studies by optimizing the selection of controls.

MOTIVATION: When analyzing a case group of patients with ultra-rare disorders the ethnicities are often diverse and the data quality might vary. The population substructure in the case group as well as the heterogeneous data quality can cause substantial inflation of test statistics and result in spurious associations in case-control studies if not properly adjusted for. Existing techniques to correct for confounding effects were especially developed for common variants and are not applicable to rare variants. RESULTS: We analyzed strategies to select suitable controls for cases that are based on similarity metrics that vary in their weighting schemes. We simulated different disease entities on real exome data and show that a similarity-based selection scheme can help to reduce false positive associations and to optimize the performance of the statistical tests. Especially when data quality as well as ethnicities vary a lot in the case group, a matching approach that puts more weight on rare variants shows the best performance. We reanalyzed collections of unrelated patients with Kabuki make-up syndrome, Hyperphosphatasia with Mental Retardation syndrome and Catel-Manzke syndrome for which the disease genes were recently described. We show that rare variant association tests are more sensitive and specific in identifying the disease gene than intersection filters and should thus be considered as a favorable approach in analyzing even small patient cohorts. AVAILABILITY AND IMPLEMENTATION: Datasets used in our analysis are available at ftp://ftp.1000genomes.ebi.ac.uk./vol1/ftp/ CONTACT: : peter.krawitz@charite.de SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Continuing harmonization of terminology and innovations for methodologies in developmental toxicology: Report of the 8th Berlin Workshop on Developmental Toxicity, 14-16 May 2014.

This article is a report of the 8th Berlin Workshop on Developmental Toxicity held in May 2014. The main aim of the workshop was the continuing harmonization of terminology and innovations for methodologies used in the assessment of embryo- and fetotoxic findings. The following main topics were discussed: harmonized categorization of external, skeletal, visceral and materno-fetal findings into malformations, variations and grey zone anomalies, aspects of developmental anomalies in humans and laboratory animals, and innovations for new methodologies in developmental toxicology. The application of Version 2 terminology in the DevTox database was considered as a useful improvement in the categorization of developmental anomalies. Participants concluded that initiation of a project for comparative assessments of developmental anomalies in humans and laboratory animals could support regulatory risk assessment and university-based training. Improvement of new methodological approaches for alternatives to animal testing should be triggered for a better understanding of developmental outcomes.

Disruptions of topological chromatin domains cause pathogenic rewiring of gene-enhancer interactions.

Mammalian genomes are organized into megabase-scale topologically associated domains (TADs). We demonstrate that disruption of TADs can rewire long-range regulatory architecture and result in pathogenic phenotypes. We show that distinct human limb malformations are caused by deletions, inversions, or duplications altering the structure of the TAD-spanning WNT6/IHH/EPHA4/PAX3 locus. Using CRISPR/Cas genome editing, we generated mice with corresponding rearrangements. Both in mouse limb tissue and patient-derived fibroblasts, disease-relevant structural changes cause ectopic interactions between promoters and non-coding DNA, and a cluster of limb enhancers normally associated with Epha4 is misplaced relative to TAD boundaries and drives ectopic limb expression of another gene in the locus. This rewiring occurred only if the variant disrupted a CTCF-associated boundary domain. Our results demonstrate the functional importance of TADs for orchestrating gene expression via genome architecture and indicate criteria for predicting the pathogenicity of human structural variants, particularly in non-coding regions of the human genome.

Non-invasive spectroscopic determination of the antioxidative status of gravidae and neonates.

Pregnancy and postpartum adaptation cause an increased formation of free radicals. This is associated with various perinatological diseases, e.g. necrotising enterocolitis. The human body has developed a protective system in the form of the antioxidative potential. The present study was the first to investigate the kinetics of the cutaneous antioxidative status in pregnant women and newborns using a non-invasive spectroscopic method. Eighteen pregnant women and their babies took part in the study. A light-emitting diode-based compact scanner system was used for quick non-invasive measurements of carotenoid antioxidants in human skin based on reflection spectroscopy. It could be shown that the antioxidative status of the expectant mothers significantly declined during labour (p < 0.001) and on day 1 after delivery (p < 0.01). Compared to the mothers, the newborns exhibited a significantly higher cutaneous carotenoid concentration on both day 1 (p < 0.01) and 5 (p < 0.01) after delivery. These results suggest that the oxidative stress due to postpartum adaptation is counteracted by an enhanced reservoir of carotenoid antioxidants in the subcutaneous fatty tissue. The peripartum cutaneous carotenoid level of mothers declines continuously, whereas term newborns show very high cutaneous antioxidant values.

Somatic neurofibromatosis type 1 (NF1) inactivation events in cutaneous neurofibromas of a single NF1 patient.

Neurofibromatosis type 1 (NF1) (MIM#162200) is a relatively frequent genetic condition that predisposes to tumor formation. The main types of tumors occurring in NF1 patients are cutaneous and subcutaneous neurofibromas, plexiform neurofibromas, optic pathway gliomas, and malignant peripheral nerve sheath tumors. To search for somatic mutations in cutaneous (dermal) neurofibromas, whole-exome sequencing (WES) was performed on seven spatially separated tumors and two reference tissues (blood and unaffected skin) from a single NF1 patient. Validation of WES findings was done using routine Sanger sequencing or Sequenom IPlex SNP genotyping. Exome sequencing confirmed the existence of a known familial splice-site mutation NM_000267.3:c.3113+1G>A in exon 23 of NF1 gene (HGMD ID CS951480) in blood, unaffected skin, and all tumor samples. In five out of seven analyzed tumors, we additionally detected second-hit mutations in the NF1 gene. Four of them were novel and one was previously observed. Each mutation was distinct, demonstrating the independent origin of each tumor. Only in two of seven tumors we detected an additional somatic mutation that was not associated with NF1. Our study demonstrated that somatic mutations of NF1 are likely the main drivers of cutaneous tumor formation. The study provides evidence for the rareness of single base pair level alterations in the exomes of benign NF1 cutaneous tumors.

Homozygous and compound-heterozygous mutations in TGDS cause Catel-Manzke syndrome.

Catel-Manzke syndrome is characterized by Pierre Robin sequence and a unique form of bilateral hyperphalangy causing a clinodactyly of the index finger. We describe the identification of homozygous and compound heterozygous mutations in TGDS in seven unrelated individuals with typical Catel-Manzke syndrome by exome sequencing. Six different TGDS mutations were detected: c.892A>G (p.Asn298Asp), c.270_271del (p.Lys91Asnfs(∗)22), c.298G>T (p.Ala100Ser), c.294T>G (p.Phe98Leu), c.269A>G (p.Glu90Gly), and c.700T>C (p.Tyr234His), all predicted to be disease causing. By using haplotype reconstruction we showed that the mutation c.298G>T is probably a founder mutation. Due to the spectrum of the amino acid changes, we suggest that loss of function in TGDS is the underlying mechanism of Catel-Manzke syndrome. TGDS (dTDP-D-glucose 4,6-dehydrogenase) is a conserved protein belonging to the SDR family and probably plays a role in nucleotide sugar metabolism.

Screening for single nucleotide variants, small indels and exon deletions with a next-generation sequencing based gene panel approach for Usher syndrome.

Usher syndrome is an autosomal recessive disorder characterized both by deafness and blindness. For the three clinical subtypes of Usher syndrome causal mutations in altogether 12 genes and a modifier gene have been identified. Due to the genetic heterogeneity of Usher syndrome, the molecular analysis is predestined for a comprehensive and parallelized analysis of all known genes by next-generation sequencing (NGS) approaches. We describe here the targeted enrichment and deep sequencing for exons of Usher genes and compare the costs and workload of this approach compared to Sanger sequencing. We also present a bioinformatics analysis pipeline that allows us to detect single-nucleotide variants, short insertions and deletions, as well as copy number variations of one or more exons on the same sequence data. Additionally, we present a flexible in silico gene panel for the analysis of sequence variants, in which newly identified genes can easily be included. We applied this approach to a cohort of 44 Usher patients and detected biallelic pathogenic mutations in 35 individuals and monoallelic mutations in eight individuals of our cohort. Thirty-nine of the sequence variants, including two heterozygous deletions comprising several exons of USH2A, have not been reported so far. Our NGS-based approach allowed us to assess single-nucleotide variants, small indels, and whole exon deletions in a single test. The described diagnostic approach is fast and cost-effective with a high molecular diagnostic yield.