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PubMed2003

Chicken genome sequence: a centennial gift to poultry genetics.

A draft sequence of the chicken genome will be available by early 2004. This event conveniently marks the start of the second century of poultry genetics, coming 100 years after the use of the chicken to demonstrate Mendelian inheritance in animals by William Bateson. How will the second, post-genomic century of poultry genetics differ from the first? A whole genome shotgun (WGS) approach is being used to obtain the chicken sequence, with the goal of generating approximately six-fold coverage of the genome. Bacterial artificial chromosome (BAC) and fosmid clone end sequences, along with a BAC contig map integrated with genetic linkage and radiation hybrid maps, will form the platform for assembly of the WGS data. Rapid progress in global analysis of chicken gene expression patterns is also being made. Comparative genomics will link these new discoveries to the knowledge base for all other animal species. It's hoped that the genome sequence will also provide common ground on which to unite studies of the chicken as a model species with those aimed at agriculturally-relevant applications. The current status of chicken genomics will be assessed with projections for its near and long term future.

Animals↗

PubMed1999

A complete BAC-based physical map of the Arabidopsis thaliana genome.

Arabidopsis thaliana is a small flowering plant that serves as the major model system in plant molecular genetics. The efforts of many scientists have produced genetic maps that provide extensive coverage of the genome (http://genome-www. stanford.edu/Arabidopsis/maps.html). Recently, detailed YAC, BAC, P1 and cosmid-based physical maps (that is, representations of genomic regions as sets of overlapping clones of corresponding libraries) have been established that extend over wide genomic areas ranging from several hundreds of kilobases to entire chromosomes. These maps provide an entry to gain deeper insight into the A. thaliana genome structure. A. thaliana has been chosen as the subject of the first large-scale project intended to determine the full genome sequence of a plant. This sequencing project, together with the increasing interest in map-based gene cloning, has highlighted the requirement for a complete and accurate physical map of this plant species. To supply the scientific community with a high-quality resource, we present here a complete physical map of A. thaliana using essentially the IGF BAC library. The map consists of 27 contigs that cover the entire genome, except for the presumptive centromeric regions, nucleolar organization regions (NOR) and telomeric areas. This is the first reported map of a complex organism based entirely on BAC clones and it represents the most homogeneous and complete physical map established to date for any plant genome. Furthermore, the analysis performed here serves as a model for an efficient physical mapping procedure using BAC clones that can be applied to other complex genomes.

Arabidopsis↗

PubMed2006

High-resolution genome-wide array-based comparative genome hybridization reveals cryptic chromosome changes in AML and MDS cases with trisomy 8 as the sole cytogenetic aberration.

Although trisomy 8 as the sole chromosome aberration is the most common numerical abnormality in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), little is known about its pathogenetic effects. Considering that +8 is a frequent secondary change in AML/MDS, cryptic--possibly primary--genetic aberrations may occur in cases with trisomy 8 as the apparently single anomaly. However, no such hidden anomalies have been reported. We performed a high-resolution genome-wide array-based comparative genome hybridization (array CGH) analysis of 10 AML/MDS cases with isolated +8, utilizing a 32K bacterial artificial chromosome array set, providing >98% coverage of the genome with a resolution of 100 kb. Array CGH revealed intrachromosomal imbalances, not corresponding to known genomic copy number polymorphisms, in 4/10 cases, comprising nine duplications and hemizygous deletions ranging in size from 0.5 to 2.2 Mb. A 1.8 Mb deletion at 7p14.1, which had occurred prior to the +8, was identified in MDS transforming to AML. Furthermore, a deletion including ETV6 was present in one case. The remaining seven imbalances involved more than 40 genes. The present results show that cryptic genetic abnormalities are frequent in trisomy 8-positive AML/MDS cases and that +8 as the sole cytogenetic aberration is not always the primary genetic event.

Acute Disease↗

PubMed2025

Genetic analysis of three patients from two unrelated Chinese families with autosomal recessive spastic ataxia of Charlevoix-Saguenay.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a rare early-onset neurodegenerative disorder characterized by progressive cerebellar ataxia, spasticity, and sensorimotor peripheral neuropathy. This disorder is caused by homozygous or compound heterozygous variants in the sacsin (SACS) gene on chromosome 13q12.12. Three patients with ARSACS from two unrelated Chinese families were recruited for this study. Patient #1 was an 18-year-old male who had been walking unstably for 12 years. Patient #2, the younger sister of Patient #1, was a 5-year-old girl who had been walking unstably for 2 years. Patient #3 was a 19-year-old female who had been walking unstably and a tendency to fall for 17 years. For Patient #1, whole-exome sequencing (WES) identified a hemizygous variant c.8310_8313delAGAT (p.Asp2771fs4*) in SACS (NM_014363.6), with the father being heterozygous, the mother wild-type, and Patient #2 hemizygous, as verified by Sanger sequencing. Additional copy number variant analysis of the WES data indicated that Patient #1 had a heterozygous gross deletion of chr13q12.12 (chr13:23,808,732 - 24,890,322). Low-coverage whole-genome sequencing results revealed that Patient #2 carried a chr13q12.12 deletion (chr13:23,520,000-24,940,000). Together with Sanger sequencing results, this gross deletion was speculated to have been inherited from the mother, further explaining the hemizygous state of c.8310_8313delAGAT (p.Asp2771fs4*) in Patients #1 and #2. Through WES, Patient #3 was identified as having suspected compound heterozygous variants of c.2881 C > T (p.Arg961*) and c.6409 C > T (p.Gln2137*), inherited from the father and mother, respectively, as confirmed by Sanger sequencing. This study identified three variants in SACS. The c.8310_8313delAGAT (p.Asp2771fs4*) is novel, whereas c.2881 C > T (p.Arg961*) and c.6409 C > T (p.Gln2137*) have been reported previously. Moreover, this study highlights the growing trend that ARSACS has become increasingly prevalent worldwide rather than being localized to a specific region or race. As an increasing number of patients with ARSACS are diagnosed, the genetic spectrum of ARSACS will gradually broaden, providing an accurate genetic basis for prenatal diagnosis of mothers in the years ahead, if possible.

Adolescent↗

PubMed2001

A bacterial artificial chromosome (BAC) library for sunflower, and identification of clones containing genes for putative transmembrane receptors.

Sunflower (Helianthus annuus L.) is an economically important oil seed crop with an estimated genome size of 3000 Mb. We have constructed a bacterial artificial chromosome (BAC) library for sunflower, which represents an estimated 4- to 5-fold coverage of the genome. Nuclei isolated from young leaves were used as a source of high-molecular-weight DNA and a partial restriction endonuclease digestion protocol was used to cleave the DNA. A random sample of 60 clones indicated an average insert size of 80 kb, implying a 95% probability of recovering any specific sequence of interest. The library was screened with chloroplast DNA probes. Only 0.1% of the clones were identified to be of chloroplast origin, indicating that contamination with organellar DNAs is very low. The utility of the library was evaluated by screening for the presence of genes for putative transmembrane receptors sharing epidermal growth factor (EGF) and integrin-like domains. First, a homologous sunflower EST (HaELP1) was obtained by degenerate RT-PCR cloning, using Arabidopsis thaliana genes (AtELP) as a source of consensus sequences. Three different BACs yielded positive hybridization signals when HaELP1 was used as a probe. BAC subcloning and sequencing demonstrated the presence of two different loci putatively homologous to genes for transmembrane proteins with EGF- and integrin-like domains from sunflower. This work demonstrates the suitability of the library for homology map-based cloning of sunflower genes and physical mapping of the sunflower genome.

Amino Acid Sequence↗

PubMed2004

Insight into Trichoderma reesei's genome content, organization and evolution revealed through BAC library characterization.

Trichoderma reesei is an important industrial fungus known for its ability to efficiently secrete large quantities of protein as well as its wide variety of biomass degrading enzymes. Past research on this fungus has primarily focused on extending its protein production capabilities, leaving the structure of its 33 Mb genome essentially a mystery. To begin to address these deficiencies and further our knowledge of T. reesei's secretion and cellulolytic potential, we have created a genomic framework for this fungus. We constructed a BAC library containing 9216 clones with an average insert size of 125 kb which provides a coverage of 28 genome equivalents. BAC ends were sequenced and annotated using publicly available software which identified a number of genes not seen in previously sequenced EST datasets. Little evidence was found for repetitive sequence in T. reesei with the exception of several copies of an element with similarity to the Podospora anserina transposon, PAT. Hybridization of 34 genes involved in biomass degradation revealed five groups of co-located genes in the genome. BAC clones were fingerprinted and analyzed using fingerprinted contigs (FPC) software resulting in 334 contigs covering 28 megabases of the genome. The assembly of these FPC contigs was verified by congruence with hybridization results.

Chromosome Mapping↗

PubMed2026

Mitogenome assembly and phylogenetic relationships of Phalaris arundinacea.

INTRODUCTION: As a perennial herb of Poaceae, Phalaris arundinacea plays key roles in grazing, production, and soil and water conservation because of its well-developed rhizomes and seed dispersal. We assembled and annotated the first mitogenome of P. arundinacea to support evolutionary and taxonomic research. METHODS: We assembled and annotated the first complete mitochondrial genome of P. arundinacea by integrating Illumina short reads with Nanopore long reads via a hybrid assembly strategy. The genome architecture was comprehensively characterized, encompassing codon usage bias, repetitive sequence organization, and inter-organellar genetic exchange with the chloroplast genome. RESULTS AND DISCUSSION: Assembly of the P. arundinacea mitogenome revealed two circular structures with a combined length of 526,717 bp. The genome comprised a set of 37 protein-coding genes (PCGs), 27 tRNAs, and 8 rRNAs, with the rRNA genes exhibiting full assembly (100% coverage). The mitochondrial genome contained 154 forward and 164 palindromic repeats, along with 25 tandem repeats and 124 simple sequence repeats (SSRs). Notably, 102 SSRs were distributed on contig1, predominantly in tetrameric form. Furthermore, 376 RNA editing sites were predicted. A total of 104 fragments were integrated into the mitochondrial genome from the chloroplast, amounting to 55,866 bp of transferred sequence. Finally, phylogenetic analysis of 28 plant mitogenomes placed P. arundinacea closest to species within the genus Poa (P. chaixii and P. pratensis). Comparative analysis of non-synonymous-to-synonymous substitution rate (Ka/Ks) ratios across divergent species revealed that the mitochondrial genome of P. arundinacea underwent stabilizing evolutionary dynamics, characterized by predominant purifying selection with several lineage-specific variations in selective pressure. Our findings support the close phylogenetic relationship between P. arundinacea and species of the genus Poa and provide a reference mitochondrial genome resource for future comparative studies within Phalaris that incorporate broader taxon sampling. These results support deeper phylogenetic investigations of P. arundinacea and facilitate future work on its germplasm characterization and applied use.

Phalaris arundinacea↗

PubMed2003

The COG database: an updated version includes eukaryotes.

BACKGROUND: The availability of multiple, essentially complete genome sequences of prokaryotes and eukaryotes spurred both the demand and the opportunity for the construction of an evolutionary classification of genes from these genomes. Such a classification system based on orthologous relationships between genes appears to be a natural framework for comparative genomics and should facilitate both functional annotation of genomes and large-scale evolutionary studies. RESULTS: We describe here a major update of the previously developed system for delineation of Clusters of Orthologous Groups of proteins (COGs) from the sequenced genomes of prokaryotes and unicellular eukaryotes and the construction of clusters of predicted orthologs for 7 eukaryotic genomes, which we named KOGs after eukaryotic orthologous groups. The COG collection currently consists of 138,458 proteins, which form 4873 COGs and comprise 75% of the 185,505 (predicted) proteins encoded in 66 genomes of unicellular organisms. The eukaryotic orthologous groups (KOGs) include proteins from 7 eukaryotic genomes: three animals (the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster and Homo sapiens), one plant, Arabidopsis thaliana, two fungi (Saccharomyces cerevisiae and Schizosaccharomyces pombe), and the intracellular microsporidian parasite Encephalitozoon cuniculi. The current KOG set consists of 4852 clusters of orthologs, which include 59,838 proteins, or approximately 54% of the analyzed eukaryotic 110,655 gene products. Compared to the coverage of the prokaryotic genomes with COGs, a considerably smaller fraction of eukaryotic genes could be included into the KOGs; addition of new eukaryotic genomes is expected to result in substantial increase in the coverage of eukaryotic genomes with KOGs. Examination of the phyletic patterns of KOGs reveals a conserved core represented in all analyzed species and consisting of approximately 20% of the KOG set. This conserved portion of the KOG set is much greater than the ubiquitous portion of the COG set (approximately 1% of the COGs). In part, this difference is probably due to the small number of included eukaryotic genomes, but it could also reflect the relative compactness of eukaryotes as a clade and the greater evolutionary stability of eukaryotic genomes. CONCLUSION: The updated collection of orthologous protein sets for prokaryotes and eukaryotes is expected to be a useful platform for functional annotation of newly sequenced genomes, including those of complex eukaryotes, and genome-wide evolutionary studies.

Animals↗

PubMed2003

Gene discovery in the Entamoeba invadens genome.

Entamoeba invadens, a parasite of reptiles, is a model for the study of encystation by the human enteric pathogen Entamoeba histolytica, because E. invadens form cysts in axenic culture. With approximately 0.5-fold sequence coverage of the genome, we were able to get insights into E. invadens gene and genome features. Overall, the E. invadens genome displays many of the features that are emerging from ongoing genome sequencing efforts in E. histolytica. At the nucleotide level the E. invadens genome has on average 60% sequence identity with that of E. histolytica. The presence of introns in E. invadens was predicted with similar consensus (GTTTGT em leader A/TAG) sequences to those identified in E. histolytica and Entamoeba dispar. Sequences highly repeated in the genome of E. histolytica (rRNAs, tRNAs, CXXC-rich proteins, and Leu-rich repeat proteins) were found to be highly repeated in the E. invadens genome. Numerous proteins homologous to those implicated in amoebic virulence, (Gal/GalNAc lectins, amoebapores, and cysteine proteinases) and drug resistance (p-glycoproteins) were identified. Homologs of proteins involved in cell cycle, vesicular trafficking and signal transduction were identified, which may be involved in en/excystation and cell growth of E. invadens. Finally, multiple copies of a number of E. invadens genes coding for predicted enzymes involved in core metabolism and the targets of anti-amoebic drugs were identified.

Amino Acid Sequence↗

PubMed2026

Comprehensive evaluation of new sequencer T20 and well-established T7 with 507 human samples.

The DNBSEQ-T20×2 (T20) sequencer, developed by MGI Tech, enables cost-effective human whole-genome sequencing (WGS) at 30× coverage for less than $100 per genome. Here, we evaluate the sequencing performance and data quality of the T20 platform by benchmarking it against the established DNBSEQ-T7 (T7) sequencer using 507 samples derived from blood (N = 75), stool (N = 242), and saliva (N = 190). The T20 exhibited lower sequencing quality metrics compared with the T7, with Q20 scores of 95.76%-95.83% and Q30 scores of 87.25%-87.40%, compared with 97.81%-97.93% and 93.26%-93.60%, respectively, for T7 data. Quality differences were more evident toward the end of reads, and PCR-free libraries sequenced on the T20 showed similar reductions in quality scores. The median empirical base error rate estimated from 102 ZymoBIOMICS samples was 0.33%. The T20 demonstrated comparable coverage uniformity to the T7 and showed high concordance in microbiome composition analysis, with a median Bray-Curtis dissimilarity of 0.02. Variant calling performance was highly consistent between the two platforms. Among variants with non-missing genotype calls on both platforms, 94.92% of SNPs and 87.20% of InDels showed concordant genotypes between T20 and T7. Overall, the T20 delivers reliable sequencing accuracy and reproducibility for large-scale genomic and microbiome studies, providing a cost-effective alternative for high-throughput sequencing applications.

Metagenomics↗

PubMed2002

Construction of BAC libraries derived from the ascidian Ciona intestinalis.

Large insert genomic bacterial artificial chromosome (BAC) libraries were constructed from a basal chordate, the ascidian Ciona intestinalis. Insert analyses of randomly selected clones indicated that in the first library the mean insert size was 135 kb and predicted a 15-fold coverage of the Ciona genome, and in the second library the mean insert size was 165 kb and predicted a 5-fold coverage of the genome. These first large insert genomic libraries of the ascidian should increase the speed of genomic analyses of basal chordates.

Animals↗

PubMed1999

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.

Arabidopsis↗

PubMed2004

Fosmid-based physical mapping of the Histoplasma capsulatum genome.

A fosmid library representing 10-fold coverage of the Histoplasma capsulatum G217B genome was used to construct a restriction-based physical map. The data obtained from three restriction endonuclease fingerprints, generated from each clone using BamHI, HindIII, and PstI endonucleases, were combined and used in FPC for automatic and manual contig assembly builds. Concomitantly, a whole-genome shotgun (WGS) sequencing of paired-end reads from plasmids and fosmids were assembled with PCAP, providing a predicted genome size of up to 43.5 Mbp and 17% repetitive DNA. Fosmid paired-end sequences in the WGS assembly provide anchoring information to the physical map and result in joining of existing physical map contigs into 84 clusters containing 9551 fosmid clones. Here, we detail mapping the Histoplasma capsulatum genome comprehensively in fosmids, resulting in an efficient paradigm for de novo sequencing that uses a map-assisted whole genome shotgun approach.

Contig Mapping↗

PubMed2006

Are GC-rich isochores vanishing in mammals?

Several studies of nucleotide substitution patterns in mammalian species suggested that GC-rich isochores might be vanishing in mammalian genomes. However, the number of genes and the number of genomes included in these studies might not have given a reliable broad view of the trend in GC change in mammals. It is therefore worth exploiting this issue with a broader coverage of mammalian genomes using a reliable approach, the maximum likelihood approach. We have applied two maximum likelihood methods to infer the ancestral GC contents of 176 mammalian genes from representative eutherian species and at least one marsupial species. Except for a large GC decrease in marsupial genes, we found no general decreasing trend in GC content in GC-rich genes or in other genes among eutherian mammals; indeed, the GC content of GC-rich genes appears to have increased in recent times in some genomes, e.g., the rabbit. For the large GC decrease in marsupials, it could be mainly due to the great reduction in chromosome number, which could lead to a large reduction in recombination rate and thus also a large reduction in the rate of gene conversion. Since many eutherian mammals still maintain a fairly large number of chromosomes, it is unlikely that GC-rich isochores are vanishing in these mammals.

Animals↗

PubMed2004

Integrated and sequence-ordered BAC- and YAC-based physical maps for the rat genome.

As part of the effort to sequence the genome of Rattus norvegicus, we constructed a physical map comprised of fingerprinted bacterial artificial chromosome (BAC) clones from the CHORI-230 BAC library. These BAC clones provide approximately 13-fold redundant coverage of the genome and have been assembled into 376 fingerprint contigs. A yeast artificial chromosome (YAC) map was also constructed and aligned with the BAC map via fingerprinted BAC and P1 artificial chromosome clones (PACs) sharing interspersed repetitive sequence markers with the YAC-based physical map. We have annotated 95% of the fingerprint map clones in contigs with coordinates on the version 3.1 rat genome sequence assembly, using BAC-end sequences and in silico mapping methods. These coordinates have allowed anchoring 358 of the 376 fingerprint map contigs onto the sequence assembly. Of these, 324 contigs are anchored to rat genome sequences localized to chromosomes, and 34 contigs are anchored to unlocalized portions of the rat sequence assembly. The remaining 18 contigs, containing 54 clones, still require placement. The fingerprint map is a high-resolution integrative data resource that provides genome-ordered associations among BAC, YAC, and PAC clones and the assembled sequence of the rat genome.

Animals↗

PubMed2000

Single nucleotide polymorphism and linkage disequilibrium within the TCR alpha/delta locus.

Much attention is being given to the identification of common disease genes through whole-genome linkage disequilibrium (LD) screens with single nucleotide polymorphisms (SNPs). Simulation studies have suggested that useful LD is unlikely to extend beyond 3 kb, and that > 500,000 SNPs may be needed for comprehensive coverage of the genome. The TCR alpha/delta locus on chromosome 14q contains many V, J and D segments that combine with constant domains to produce either an alpha or a delta chain of the T cell receptor. Multiple SNPs have been recognized within the V segments, and it has been suggested that variation within the locus may modify the course of autoimmune and allergic diseases. We have examined LD within an 850 kb section of the TCR alpha/delta locus on chromosome 14q by typing 24 V gene segment SNPs and two microsatellites. One hundred and fifty-nine nuclear and extended families were genotyped in order to derive haplotypes, and the pair-wise LD between SNPs was investigated in 600 haplotypes from unrelated individuals (the parents). The mean extent of useful LD was much greater than suggested by simulations: significant LD was relatively common at 250 kb and was detectable beyond 500 kb. The mean extent of LD was twice as far between alleles of low frequency than between common alleles. The distribution of LD was highly irregular and concentrated in three distinct islands. The results differ from those obtained by simulation, and if they are typical of other genomic regions, suggest that the minimum number of markers necessary for comprehensive LD mapping may be reduced by at least an order of magnitude.

Alleles↗

PubMed1990

A 3.5 genome equivalent multi access YAC library: construction, characterisation, screening and storage.

The construction of a yeast artificial chromosome (YAC) primary gridded library of 35,000 clones from human lymphoblastoid (48,XXXX) cell line DNA is described. The average YAC size is approximately 350kb representing a greater than 3.5 times coverage of the genome. The library is stored at -70 degrees C as gridded clones on nylon filters impregnated with 20% glycerol and as glycerol suspensions of individual clones in microtitre plates providing a prolonged multi-user potential. To date we have used 14 single copy probes to screen this library by colony hybridisation as well as PCR and have isolated between 1 and 5 YAC clones for every probe.

Cell Line↗

PubMed2006

GENOMIZER: an integrated analysis system for genome-wide association data.

Genome-wide association analysis appears to be a promising way to identify heritable susceptibility factors for complex human disorders. However, the feasibility of large-scale genotyping experiments is currently limited by an incomplete marker coverage of the genome, a restricted understanding of the functional role of given genomic regions, and the small sample sizes used. Thus, genome-wide association analysis will be a screening tool to facilitate subsequent gene discovery rather than a means to completely resolve individual genetic risk profiles. The validation of association findings will continue to rely upon the replication of "leads" in independent samples from either the same or different populations. Even under such pragmatic conditions, the timely analysis of the large data sets in question poses serious technical challenges. We have therefore developed public-domain software, GENOMIZER, that implements the workflow of an association experiment, including data management, single-point and haplotype analysis, "lead" definition, and data visualization. GENOMIZER (www.ikmb.uni-kiel.de/genomizer) comes with a complete user manual, and is open-source software licensed under the GNU Lesser General Public License. We suggest that the use of this software will facilitate the handling and interpretation of the currently emerging genome-wide association data.

Chromosome Mapping↗