DIXDC1 contributes to psychiatric susceptibility by regulating dendritic spine and glutamatergic synapse density via GSK3 and Wnt/ß-catenin signaling.

Mice lacking DIX domain containing-1 (DIXDC1), an intracellular Wnt/ß-catenin signal pathway protein, have abnormal measures of anxiety, depression and social behavior. Pyramidal neurons in these animals' brains have reduced dendritic spines and glutamatergic synapses. Treatment with lithium or a glycogen synthase kinase-3 (GSK3) inhibitor corrects behavioral and neurodevelopmental phenotypes in these animals. Analysis of DIXDC1 in over 9000 cases of autism, bipolar disorder and schizophrenia reveals higher rates of rare inherited sequence-disrupting single-nucleotide variants (SNVs) in these individuals compared with psychiatrically unaffected controls. Many of these SNVs alter Wnt/ß-catenin signaling activity of the neurally predominant DIXDC1 isoform; a subset that hyperactivate this pathway cause dominant neurodevelopmental effects. We propose that rare missense SNVs in DIXDC1 contribute to psychiatric pathogenesis by reducing spine and glutamatergic synapse density downstream of GSK3 in the Wnt/ß-catenin pathway.

Rare disruptive variants in the DISC1 Interactome and Regulome: association with cognitive ability and schizophrenia.

Schizophrenia (SCZ), bipolar disorder (BD) and recurrent major depressive disorder (rMDD) are common psychiatric illnesses. All have been associated with lower cognitive ability, and show evidence of genetic overlap and substantial evidence of pleiotropy with cognitive function and neuroticism. Disrupted in schizophrenia 1 (DISC1) protein directly interacts with a large set of proteins (DISC1 Interactome) that are involved in brain development and signaling. Modulation of DISC1 expression alters the expression of a circumscribed set of genes (DISC1 Regulome) that are also implicated in brain biology and disorder. Here we report targeted sequencing of 59 DISC1 Interactome genes and 154 Regulome genes in 654 psychiatric patients and 889 cognitively-phenotyped control subjects, on whom we previously reported evidence for trait association from complete sequencing of the DISC1 locus. Burden analyses of rare and singleton variants predicted to be damaging were performed for psychiatric disorders, cognitive variables and personality traits. The DISC1 Interactome and Regulome showed differential association across the phenotypes tested. After family-wise error correction across all traits (FWERacross), an increased burden of singleton disruptive variants in the Regulome was associated with SCZ (FWERacross P=0.0339). The burden of singleton disruptive variants in the DISC1 Interactome was associated with low cognitive ability at age 11 (FWERacross P=0.0043). These results identify altered regulation of schizophrenia candidate genes by DISC1 and its core Interactome as an alternate pathway for schizophrenia risk, consistent with the emerging effects of rare copy number variants associated with intellectual disability.

De novo mutations in schizophrenia implicate chromatin remodeling and support a genetic overlap with autism and intellectual disability.

Schizophrenia is a serious psychiatric disorder with a broadly undiscovered genetic etiology. Recent studies of de novo mutations (DNMs) in schizophrenia and autism have reinforced the hypothesis that rare genetic variation contributes to risk. We carried out exome sequencing on 57 trios with sporadic or familial schizophrenia. In sporadic trios, we observed a ~3.5-fold increase in the proportion of nonsense DNMs (0.101 vs 0.031, empirical P=0.01, Benjamini-Hochberg-corrected P=0.044). These mutations were significantly more likely to occur in genes with highly ranked probabilities of haploinsufficiency (P=0.0029, corrected P=0.006). DNMs of potential functional consequence were also found to occur in genes predicted to be less tolerant to rare variation (P=2.01 × 10(-)(5), corrected P=2.1 × 10(-)(3)). Genes with DNMs overlapped with genes implicated in autism (for example, AUTS2, CHD8 and MECP2) and intellectual disability (for example, HUWE1 and TRAPPC9), supporting a shared genetic etiology between these disorders. Functionally CHD8, MECP2 and HUWE1 converge on epigenetic regulation of transcription suggesting that this may be an important risk mechanism. Our results were consistent in an analysis of additional exome-based sequencing studies of other neurodevelopmental disorders. These findings suggest that perturbations in genes, which function in the epigenetic regulation of brain development and cognition, could have a central role in the susceptibility to, pathogenesis and treatment of mental disorders.

Next-generation sequencing of endoscopic biopsies identifies ARID1A as a tumor-suppressor gene in Barrett's esophagus.

The incidence of Barrett's esophagus (BE)-associated esophageal adenocarcinoma (EAC) is increasing. Next-generation sequencing (NGS) provides an unprecedented opportunity to uncover genomic alterations during BE pathogenesis and progression to EAC, but treatment-naive surgical specimens are scarce. The objective of this study was to establish the feasibility of using widely available endoscopic mucosal biopsies for successful NGS, using samples obtained from a BE 'progressor'. Paired-end whole-genome NGS was performed on the Illumina platform using libraries generated from mucosal biopsies of normal squamous epithelium (NSE), BE and EAC obtained from a patient who progressed to adenocarcinoma during endoscopic surveillance. Selective validation studies, including Sanger sequencing, immunohistochemistry and functional assays, were performed to confirm the NGS findings. NGS identified somatic nonsense mutations of AT-rich interactive domain 1A (SWI like) (ARID1A) and PPIE and an additional 37 missense mutations in BE and/or EAC, which were confirmed by Sanger sequencing. ARID1A mutations were detected in 15% (3/20) high-grade dysplasia (HGD)/EAC patients. Immunohistochemistry performed on an independent archival cohort demonstrated ARID1A protein loss in 0% (0/76), 4.9% (2/40), 14.3% (4/28), 16.0% (8/50) and 12.2% (12/98) of NSE, BE, low-grade dysplasia, HGD and EAC tissues, respectively, and was inversely associated with nuclear p53 accumulation (P=0.028). Enhanced cell growth, proliferation and invasion were observed on ARID1A knockdown in EAC cells. In addition, genes downstream of ARID1A that potentially contribute to the ARID1A knockdown phenotype were identified. Our studies establish the feasibility of using mucosal biopsies for NGS, which should enable the comparative analysis of larger 'progressor' versus 'non-progressor' cohorts. Further, we identify ARID1A as a novel tumor-suppressor gene in BE pathogenesis, reiterating the importance of aberrant chromatin in the metaplasia-dysplasia sequence.

708 Common and 2010 rare DISC1 locus variants identified in 1542 subjects: analysis for association with psychiatric disorder and cognitive traits.

A balanced t(1;11) translocation that transects the Disrupted in schizophrenia 1 (DISC1) gene shows genome-wide significant linkage for schizophrenia and recurrent major depressive disorder (rMDD) in a single large Scottish family, but genome-wide and exome sequencing-based association studies have not supported a role for DISC1 in psychiatric illness. To explore DISC1 in more detail, we sequenced 528 kb of the DISC1 locus in 653 cases and 889 controls. We report 2718 validated single-nucleotide polymorphisms (SNPs) of which 2010 have a minor allele frequency of <1%. Only 38% of these variants are reported in the 1000 Genomes Project European subset. This suggests that many DISC1 SNPs remain undiscovered and are essentially private. Rare coding variants identified exclusively in patients were found in likely functional protein domains. Significant region-wide association was observed between rs16856199 and rMDD (P=0.026, unadjusted P=6.3 × 10(-5), OR=3.48). This was not replicated in additional recurrent major depression samples (replication P=0.11). Combined analysis of both the original and replication set supported the original association (P=0.0058, OR=1.46). Evidence for segregation of this variant with disease in families was limited to those of rMDD individuals referred from primary care. Burden analysis for coding and non-coding variants gave nominal associations with diagnosis and measures of mood and cognition. Together, these observations are likely to generalise to other candidate genes for major mental illness and may thus provide guidelines for the design of future studies.

Distinct p53 genomic binding patterns in normal and cancer-derived human cells.

We report here genome-wide analysis of the tumor suppressor p53 binding sites in normal human cells. 743 high-confidence ChIP-seq peaks representing putative genomic binding sites were identified in normal IMR90 fibroblasts using a reference chromatin sample. More than 40% were located within 2 kb of a transcription start site (TSS), a distribution similar to that documented for individually studied, functional p53 binding sites and, to date, not observed by previous p53 genome-wide studies. Nearly half of the high-confidence binding sites in the IMR90 cells reside in CpG islands, in marked contrast to sites reported in cancer-derived cells. The distinct genomic features of the IMR90 binding sites do not reflect a distinct preference for specific sequences, since the de novo developed p53 motif based on our study is similar to those reported by genome-wide studies of cancer cells. More likely, the different chromatin landscape in normal, compared with cancer-derived cells, influences p53 binding via modulating availability of the sites. We compared the IMR90 ChIPseq peaks to the recently published IMR90 methylome and demonstrated that they are enriched at hypomethylated DNA. Our study represents the first genome-wide, de novo mapping of p53 binding sites in normal human cells and reveals that p53 binding sites reside in distinct genomic landscapes in normal and cancer-derived human cells.

EST analysis in Ginkgo biloba: an assessment of conserved developmental regulators and gymnosperm specific genes.

BACKGROUND: Ginkgo biloba L. is the only surviving member of one of the oldest living seed plant groups with medicinal, spiritual and horticultural importance worldwide. As an evolutionary relic, it displays many characters found in the early, extinct seed plants and extant cycads. To establish a molecular base to understand the evolution of seeds and pollen, we created a cDNA library and EST dataset from the reproductive structures of male (microsporangiate), female (megasporangiate), and vegetative organs (leaves) of Ginkgo biloba. RESULTS: RNA from newly emerged male and female reproductive organs and immature leaves was used to create three distinct cDNA libraries from which 6,434 ESTs were generated. These 6,434 ESTs from Ginkgo biloba were clustered into 3,830 unigenes. A comparison of our Ginkgo unigene set against the fully annotated genomes of rice and Arabidopsis, and all available ESTs in Genbank revealed that 256 Ginkgo unigenes match only genes among the gymnosperms and non-seed plants--many with multiple matches to genes in non-angiosperm plants. Conversely, another group of unigenes in Gingko had highly significant homology to transcription factors in angiosperms involved in development, including MADS box genes as well as post-transcriptional regulators. Several of the conserved developmental genes found in Ginkgo had top BLAST homology to cycad genes. We also note here the presence of ESTs in G. biloba similar to genes that to date have only been found in gymnosperms and an additional 22 Ginkgo genes common only to genes from cycads. CONCLUSION: Our analysis of an EST dataset from G. biloba revealed genes potentially unique to gymnosperms. Many of these genes showed homology to fully sequenced clones from our cycad EST dataset found in common only with gymnosperms. Other Ginkgo ESTs are similar to developmental regulators in higher plants. This work sets the stage for future studies on Ginkgo to better understand seed and pollen evolution, and to resolve the ambiguous phylogenetic relationship of G. biloba among the gymnosperms.

Evolution and microsynteny of the apyrase gene family in three legume genomes.

Apyrases have been suggested to play important roles in plant nutrition, photomorphogenesis, and nodulation. To help trace the evolution of these genes in the legumes--and possibly, the acquisition of new functions for nodulation--apyrase-containing BACs were sequenced from three legume genomes. Genomic sequences from Medicago truncatula, Glycine max and Lotus japonicus were compared to one another and to corresponding regions in Arabidopsis thaliana. A phylogenetic analysis of apyrase homologs from these regions and sequences from other legume species, as well as other plant families, identified a potentially legume-specific clade that contains a well-characterized soybean ( G. soja) apyrase, Gs52, as well as homologs from Dolichos, Lotus, Medicago and Pisum. Sister clades contain homologs from members of Brassicaceae, Solanaceae, Poaceae and Fabaceae. Comparisons of rates of change at synonymous and nonsynonymous sites in the Gs52 and sister clades show rapid evolution in the potentially legume-specific Gs52 clade. The genomic organization of the apyrase-containing BACs shows evidence of gene duplication, genomic rearrangement, and gene conversion among Gs52 homologs. Taken together, these results suggest a scenario of local apyrase gene duplication in an ancestor of the legumes, followed by functional diversification and increased rates of change in the new genes, and further duplications in the Galegae (which include the genera Medicago and Pisum). The study also provides a detailed comparison of genomic regions between two model genomes which are now being sequenced ( M. truncatulaand L. japonicus), and a genome from an economically important legume species ( G. max).

A survey of canine expressed sequence tags and a display of their annotations through a flexible web-based interface.

We have initially sequenced approximately 8,000 canine expressed sequence tags (ESTs) from several complementary DNA (cDNA) libraries: testes, whole brain, and Madin-Darby canine kidney (MDCK) cells. Analysis of these sequences shows that they provide partial sequence information for about 5%-10% of the canine genes. An analysis pipeline has been created to cluster the ESTs and to map individual ESTs as well as clustered ESTs to both the human genome and the human proteome. Gene ontology (GO) terms have been assigned to the ESTs and clusters based on their top matches to the International Protein Index (IPI) set of human proteins. The data generated is stored in a MySQL relational database for analysis and display. A Web-based Perl script has been written to display the analyzed data to the scientific community.

Identification of mesoderm development (mesd) candidate genes by comparative mapping and genome sequence analysis.

The proximal albino deletions identify several functional regions on mouse Chromosome 7 critical for differentiation of mesoderm (mesd), development of the hypothalamus neuroendocrine lineage (nelg), and function of the liver (hsdr1). Using comparative mapping and genomic sequence analysis, we have identified four novel genes and Il16 in the mesd deletion interval. Two of the novel genes, mesdc1 and mesdc2, are located within the mesd critical region defined by BAC transgenic rescue. We have investigated the fetal role of genes located outside the mesd critical region using BAC transgenic complementation of the mesd early embryonic lethality. Using human radiation hybrid mapping and BAC contig construction, we have identified a conserved region of human chromosome 15 homologous to the mesd, nelg, and hsdr1 functional regions. Three human diseases cosegregate with microsatellite markers used in construction of the human BAC/YAC physical map, including autosomal dominant nocturnal frontal lobe epilepsy (ENFL2; also known as ADNFLE), a syndrome of mental retardation, spasticity, and tapetoretinal degeneration (MRST); and a pyogenic arthritis, pyoderma gangrenosum, and acne syndrome (PAPA).

Differential methylation of genes and retrotransposons facilitates shotgun sequencing of the maize genome.

The genomes of higher plants and animals are highly differentiated, and are composed of a relatively small number of genes and a large fraction of repetitive DNA. The bulk of this repetitive DNA constitutes transposable, and especially retrotransposable, elements. It has been hypothesized that most of these elements are heavily methylated relative to genes, but the evidence for this is controversial. We show here that repeat sequences in maize are largely excluded from genomic shotgun libraries by the selection of an appropriate host strain because of their sensitivity to bacterial restriction-modification systems. In contrast, unmethylated genic regions are preserved in these genetically filtered libraries if the insert size is less than the average size of genes. The representation of unique maize sequences not found in plant reference genomes is also greatly enriched. This demonstrates that repeats, and not genes, are the primary targets of methylation in maize. The use of restrictive libraries in genome shotgun sequencing in plant genomes should allow significant representation of genes, reducing the number of reactions required.

The Arabidopsis SKP1-LIKE1 gene is essential for male meiosis and may control homologue separation.

The yeast and human SKP1 genes regulate the mitotic cell cycle but are not yet known to be required for meiosis. Nine Arabidopsis SKP1 homologues have been uncovered and are named ASK1 through ASK9. Here, we report the isolation and characterization of a male sterile Arabidopsis mutant and show that the mutant defect was caused by a Ds transposon insertion into the ASK1 gene. In the ask1-1 mutant, abnormal microspores exhibit a range of sizes. Furthermore, during mutant male meiosis, although homologous chromosome pairing appeared normal at metaphase I, chromosome segregation at anaphase I is unequal, and some chromosomes are abnormally extended. Therefore, in ask1-1, at least some homologues remain associated after metaphase I. In addition, immunofluorescence microscopy indicates that the mutant spindle morphology at both metaphase I and early anaphase I is normal; thus, the abnormal chromosome segregation is not likely caused by a spindle defect. Because the yeast Skp1p is required for targeting specific proteins for ubiquitin-mediated proteolysis, we propose that ASK1 controls homologue separation by degrading or otherwise removing a protein that is required directly or indirectly for homologue association before anaphase I.

zA map for sequence analysis of the Arabidopsis thaliana genome.

Arabidopsis thaliana has emerged as a model system for studies of plant genetics and development, and its genome has been targeted for sequencing by an international consortium (the Arabidopsis Genome Initiative; http://genome-www. stanford.edu/Arabidopsis/agi.html). To support the genome-sequencing effort, we fingerprinted more than 20,000 BACs (ref. 2) from two high-quality publicly available libraries, generating an estimated 17-fold redundant coverage of the genome, and used the fingerprints to nucleate assembly of the data by computer. Subsequent manual revision of the assemblies resulted in the incorporation of 19,661 fingerprinted BACs into 169 ordered sets of overlapping clones ('contigs'), each containing at least 3 clones. These contigs are ideal for parallel selection of BACs for large-scale sequencing and have supported the generation of more than 5.8 Mb of finished genome sequence submitted to GenBank; analysis of the sequence has confirmed the integrity of contigs constructed using this fingerprint data. Placement of contigs onto chromosomes can now be performed, and is being pursued by groups involved in both sequencing and positional cloning studies. To our knowledge, these data provide the first example of whole-genome random BAC fingerprint analysis of a eucaryote, and have provided a model essential to efforts aimed at generating similar databases of fingerprint contigs to support sequencing of other complex genomes, including that of human.

Genetic definition and sequence analysis of Arabidopsis centromeres.

High-precision genetic mapping was used to define the regions that contain centromere functions on each natural chromosome in Arabidopsis thaliana. These regions exhibited dramatic recombinational repression and contained complex DNA surrounding large arrays of 180-base pair repeats. Unexpectedly, the DNA within the centromeres was not merely structural but also encoded several expressed genes. The regions flanking the centromeres were densely populated by repetitive elements yet experienced normal levels of recombination. The genetically defined centromeres were well conserved among Arabidopsis ecotypes but displayed limited sequence homology between different chromosomes, excluding repetitive DNA. This investigation provides a platform for dissecting the role of individual sequences in centromeres in higher eukaryotes.

Kaleidaseq: a Web-based tool to monitor data flow in a high throughput sequencing facility.

Tracking data flow in high throughput sequencing is important in maintaining a consistent number of successfully sequenced samples, making decisions on scheduling the flow of sequencing steps, resolving problems at various steps and tracking the status of different projects. This is especially critical when the laboratory is handling a multitude of projects. We have built a Web-based data flow tracking package, called Kaleidaseq, which allows us to monitor the flow and quality of sequencing samples through the steps of preparation of library plates, plaque-picking, preparation of templates, conducting sequencing reactions, loading of samples on gels, base-calling the traces, and calculating the quality of the sequenced samples. Kaleidaseq's suite of displays allows for outstanding monitoring of the production sequencing process. The online display of current information that Kaleidaseq provides on both project status and process queues sorted by project enables accurate real-time assessment of the necessary samples that must be processed to complete the project. This information allows the process manager to allocate future resources optimally and schedule tasks according to scientific priorities. Quality of the sequenced samples can be tracked on a daily basis, which allows the sequencing laboratory to maintain a steady performance level and quickly resolve dips in quality. Kaleidaseq has a simple easy-to-use interface that allows access to all major functions and process queues from one Web page. This software package is modular and designed to allow additional processing steps and new monitoring variables to be added and tracked with ease. Access to the underlying relational database is through the Perl DBI interface, which allows for the use of different relational databases. Kaleidaseq is available for free use by the academic community from http://www.cshl.org/kaleidaseq.

Molecular cloning and functional expression of a serotonin receptor from Caenorhabditis elegans.

A cDNA encoding a serotonin receptor has been isolated from a Caenorhabditis elegans mixed stage cDNA library. The nematode serotonin receptor, designated 5HT-Ce, was permanently expressed in murine Ltk-cells, where it mediates adenylate cyclase attenuation. Sequence analysis and the pharmacological profiles demonstrate its relatedness not only to Drosophila and Lymnae 5HT receptors but also to mammalian 5HT1a receptors. The 5HT-Ce-gene does not map close to the position of any known serotonergic mutations.

Fluorescence-based sequencing of double-stranded DNA by hexamer string priming.

A fluorescence-based, T7 (Sequenase) dye terminator method for sequencing double-stranded DNA using strings of three contiguous hexamers as primers and single-stranded binding protein is described. In this method, the circular, supercoiled DNA vector pUC19 is first linearized with a restriction enzyme to create a sequenceable template. Sequencing is then accomplished using three cycles of "denaturation," annealing, and extension/termination. Twenty-two of 33 hexamer strings tested in a controlled study produced acceptable sequence, with read lengths varying from the mid 300s to the low 400s and a base-calling accuracy of at least 97%. To test its potential utility in directed DNA sequencing, the protocol was then used to completely sequence both strands of pUC19. For this test project, a total of 28 hexamer strings was used with an overall successful priming rate of 75%. The current protocol appears to be sufficiently robust to be used in the finishing phase of a shotgun sequencing project and is amenable to semiautomation. Prospects for using the protocol for full-scale directed sequencing as well as for full automation are discussed.

High-quality automated DNA sequencing primed with hexamer strings.

The finishing phase of genome sequencing projects is expensive, in part, because of the cost of de novo synthesis of custom primers and the management burden associated with obtaining and using them for primer walking. One approach to reduce these high costs is the use of a presynthesized library of short oligonucleotides (8-10 bases) rather than long primers. The use of such a library eliminates the need for custom synthesis of oligonucleotides, providing the convenience of priming from any site by combining two to three short oligonucleotides to form a string with the required specificity. The first practical implementation of this strategy presented a robust protocol for using hexamer strings with radioisotopic labelling. Whereas versions of this technique have subsequently been implemented on fluorescent sequencers we felt that there was a need to develop and extensively test a protocol that consistently gave read lengths comparable to dye-terminator sequencing with longer primers. We have developed a new two-cycle fluorescent Sequenase terminator procedure for using hexamer strings. We tested this procedure using a set of 32 different 3 hexamer primer strings, each known to be functional to some degree in radioisotopic sequencing, on single-stranded M13mp18 template and ABI 373 DNA sequencers. The overall success rate of priming with these hexamer primer strings is 97% with the failure of only one string. In this case, the corresponding 18-mer primer also failed to produce usable sequence from M13mp18 template. The average read length from reactions successfully primed with the 31 different hexamer strings was 461 bases with > 99% base-calling accuracy. The current protocol is robust enough to be used in virtually any situation where primer walking on single-stranded templates is used. The success rate and read lengths make it universally applicable to the sequencing of single-stranded templates on automated sequencers. It is also amenable to automation.