June 1, 2021  |  

HLA sequencing using SMRT Technology – High resolution and high throughput HLA genotyping in a clinical setting

Sequence based typing (SBT) is considered the gold standard method for HLA typing. Current SBT methods are rather laborious and are prone to phase ambiguity problems and genotyping uncertainties. As a result, the NGS community is rapidly seeking to remedy these challenges, to produce high resolution and high throughput HLA sequencing conducive to a clinical setting. Today, second generation NGS technologies are limited in their ability to yield full length HLA sequences required for adequate phasing and identification of novel alleles. Here we present the use of single molecule real time (SMRT) sequencing as a means of determining full length/long HLA sequences. Moreover we reveal the scalability of this method through multiplexing approches and determine HLA genotyping calls through the use of third party Gendx NGSengine® software.

April 21, 2020  |  

Combinations of Spok genes create multiple meiotic drivers in Podospora.

Meiotic drive is the preferential transmission of a particular allele during sexual reproduction. The phenomenon is observed as spore killing in multiple fungi. In natural populations of Podospora anserina, seven spore killer types (Psks) have been identified through classical genetic analyses. Here we show that the Spok gene family underlies the Psks. The combination of Spok genes at different chromosomal locations defines the spore killer types and creates a killing hierarchy within a population. We identify two novel Spok homologs located within a large (74-167 kbp) region (the Spok block) that resides in different chromosomal locations in different strains. We confirm that the SPOK protein performs both killing and resistance functions and show that these activities are dependent on distinct domains, a predicted nuclease and kinase domain. Genomic and phylogenetic analyses across ascomycetes suggest that the Spok genes disperse through cross-species transfer, and evolve by duplication and diversification within lineages. © 2019, Vogan et al.

April 21, 2020  |  

Complete Genome Sequence of the Marine Hydrocarbon Degrader Alcaligenes aquatilis QD168, Isolated from Crude Oil-Polluted Sediment of Quintero Bay, Central Chile.

Alcaligenes aquatilis strain QD168 (= CCUG 69566) is a marine hydrocarbon-degrading bacterium isolated from crude oil-polluted sediment from Quintero Bay, Central Chile. Here, we present the 4.32-Mb complete genome sequence of strain QD168, with 3,892 coding sequences, 58 tRNAs, and a 56.3% G+C content.

April 21, 2020  |  

Extended insight into the Mycobacterium chelonae-abscessus complex through whole genome sequencing of Mycobacterium salmoniphilum outbreak and Mycobacterium salmoniphilum-like strains.

Members of the Mycobacterium chelonae-abscessus complex (MCAC) are close to the mycobacterial ancestor and includes both human, animal and fish pathogens. We present the genomes of 14 members of this complex: the complete genomes of Mycobacterium salmoniphilum and Mycobacterium chelonae type strains, seven M. salmoniphilum isolates, and five M. salmoniphilum-like strains including strains isolated during an outbreak in an animal facility at Uppsala University. Average nucleotide identity (ANI) analysis and core gene phylogeny revealed that the M. salmoniphilum-like strains are variants of the human pathogen Mycobacterium franklinii and phylogenetically close to Mycobacterium abscessus. Our data further suggested that M. salmoniphilum separates into three branches named group I, II and III with the M. salmoniphilum type strain belonging to group II. Among predicted virulence factors, the presence of phospholipase C (plcC), which is a major virulence factor that makes M. abscessus highly cytotoxic to mouse macrophages, and that M. franklinii originally was isolated from infected humans make it plausible that the outbreak in the animal facility was caused by a M. salmoniphilum-like strain. Interestingly, M. salmoniphilum-like was isolated from tap water suggesting that it can be present in the environment. Moreover, we predicted the presence of mutational hotspots in the M. salmoniphilum isolates and 26% of these hotspots overlap with genes categorized as having roles in virulence, disease and defense. We also provide data about key genes involved in transcription and translation such as sigma factor, ribosomal protein and tRNA genes.

September 22, 2019  |  

Increasing sorghum yields by seed treatment with an aqueous extract of the plant Eclipta alba may involve a dual mechanism of hydropriming and suppression of fungal pathogens

Background Soaking of sorghum seeds for six hours in an aqueous extract of Eclipta alba has been shown to increase the yield of sorghum in field experiments. The effect on yield is known to depend on field location and a mechanism involving pathogen suppression has been proposed. However, it has not been clear to which extent the same effect can be obtained by soaking of seeds in pure water (hydropriming). To address this question, fifty eight field tests were conducted comparing no treatment of seeds, hydropriming and treatment with plant extract. Experiments were distributed over three years in Burkina Faso on three locations previously showing a positive yield response to the plant extract. Results Despite strong variation across locations and years, a mean yield increase of 19.6% was found for hydropriming compared to no treatment (p?

September 22, 2019  |  

Revertant mosaicism repairs skin lesions in a patient with keratitis-ichthyosis-deafness syndrome by second-site mutations in connexin 26.

Revertant mosaicism (RM) is a naturally occurring phenomenon where the pathogenic effect of a germline mutation is corrected by a second somatic event. Development of healthy-looking skin due to RM has been observed in patients with various inherited skin disorders, but not in connexin-related disease. We aimed to clarify the underlying molecular mechanisms of suspected RM in the skin of a patient with keratitis-ichthyosis-deafness (KID) syndrome. The patient was diagnosed with KID syndrome due to characteristic skin lesions, hearing deficiency and keratitis. Investigation of GJB2 encoding connexin (Cx) 26 revealed heterozygosity for the recurrent de novo germline mutation, c.148G?>?A, p.Asp50Asn. At age 20, the patient developed spots of healthy-looking skin that grew in size and number within widespread erythrokeratodermic lesions. Ultra-deep sequencing of two healthy-looking skin biopsies identified five somatic nonsynonymous mutations, independently present in cis with the p.Asp50Asn mutation. Functional studies of Cx26 in HeLa cells revealed co-expression of Cx26-Asp50Asn and wild-type Cx26 in gap junction channel plaques. However, Cx26-Asp50Asn with the second-site mutations identified in the patient displayed no formation of gap junction channel plaques. We argue that the second-site mutations independently inhibit Cx26-Asp50Asn expression in gap junction channels, reverting the dominant negative effect of the p.Asp50Asn mutation. To our knowledge, this is the first time RM has been reported to result in the development of healthy-looking skin in a patient with KID syndrome. © The Author 2017. Published by Oxford University Press.

September 22, 2019  |  

Functional metagenomics reveals a novel carbapenem-hydrolyzing mobile beta-lactamase from Indian river sediments contaminated with antibiotic production waste.

Evolution has provided environmental bacteria with a plethora of genes that give resistance to antibiotic compounds. Under anthropogenic selection pressures, some of these genes are believed to be recruited over time into pathogens by horizontal gene transfer. River sediment polluted with fluoroquinolones and other drugs discharged from bulk drug production in India constitute an environment with unprecedented, long-term antibiotic selection pressures. It is therefore plausible that previously unknown resistance genes have evolved and/or are promoted here. In order to search for novel resistance genes, we therefore analyzed such river sediments by a functional metagenomics approach. DNA fragments providing resistance to different antibiotics in E. coli were sequenced using Sanger and PacBio RSII platforms. We recaptured the majority of known antibiotic resistance genes previously identified by open shot-gun metagenomics sequencing of the same samples. In addition, seven novel resistance gene candidates (six beta-lactamases and one amikacin resistance gene) were identified. Two class A beta-lactamases, blaRSA1 and blaRSA2, were phylogenetically close to clinically important ESBLs like blaGES, blaBEL and blaL2, and were further characterized for their substrate spectra. The blaRSA1 protein, encoded as an integron gene cassette, efficiently hydrolysed penicillins, first generation cephalosporins and cefotaxime, while blaRSA2 was an inducible class A beta-lactamase, capable of hydrolyzing carbapenems albeit with limited efficiency, similar to the L2 beta-lactamase from Stenotrophomonas maltophilia. All detected novel genes were associated with plasmid mobilization proteins, integrons, and/or other resistance genes, suggesting a potential for mobility. This study provides insight into a resistome shaped by an exceptionally strong and long-term antibiotic selection pressure. An improved knowledge of mobilized resistance factors in the external environment may make us better prepared for the resistance challenges that we may face in clinics in the future. Copyright © 2017 Elsevier Ltd. All rights reserved.

September 22, 2019  |  

Targeted long-read sequencing of a locus under long-term balancing selection in Capsella.

Rapid advances in short-read DNA sequencing technologies have revolutionized population genomic studies, but there are genomic regions where this technology reaches its limits. Limitations mostly arise due to the difficulties in assembly or alignment to genomic regions of high sequence divergence and high repeat content, which are typical characteristics for loci under strong long-term balancing selection. Studying genetic diversity at such loci therefore remains challenging. Here, we investigate the feasibility and error rates associated with targeted long-read sequencing of a locus under balancing selection. For this purpose, we generated bacterial artificial chromosomes (BACs) containing the Brassicaceae S-locus, a region under strong negative frequency-dependent selection which has previously proven difficult to assemble in its entirety using short reads. We sequence S-locus BACs with single-molecule long-read sequencing technology and conduct de novo assembly of these S-locus haplotypes. By comparing repeated assemblies resulting from independent long-read sequencing runs on the same BAC clone we do not detect any structural errors, suggesting that reliable assemblies are generated, but we estimate an indel error rate of 5.7×10-5 A similar error rate was estimated based on comparison of Illumina short-read sequences and BAC assemblies. Our results show that, until de novo assembly of multiple individuals using long-read sequencing becomes feasible, targeted long-read sequencing of loci under balancing selection is a viable option with low error rates for single nucleotide polymorphisms or structural variation. We further find that short-read sequencing is a valuable complement, allowing correction of the relatively high rate of indel errors that result from this approach. Copyright © 2018 Bachmann et al.

September 22, 2019  |  

Exploring benzimidazole resistance in Haemonchus contortus by next generation sequencing and droplet digital PCR.

Anthelmintic resistance in gastrointestinal nematode (GIN) parasites of grazing ruminants is on the rise in countries across the world. Haemonchus contortus is one of most frequently encountered drug-resistant GINs in small ruminants. This blood-sucking abomasal nematode contributes to massive treatment costs and poses a serious threat to farm animal health. To prevent the establishment of resistant strains of this parasite, up-to-date molecular techniques need to be proposed which would allow for quick, cheap and accurate identification of individuals infected with resistant worms. The effort has been made in the previous decade, with the development of the pyrosequencing method to detect resistance-predicting alleles. Here we propose a novel droplet digital PCR (ddPCR) assay for rapid and precise identification of H. contortus strains as being resistant or susceptible to benzimidazole drugs based on the presence or absence of the most common resistance-conferring mutation F200Y (TAC) in the ß tubulin isotype 1 gene. The newly developed ddPCR assay was first optimized and validated utilizing DNA templates from single-worm samples, which were previously sequenced using the next generation PacBio RSII Sequencing (NGS) platform. Subsequent NGS results for faecal larval cultures were then used as a reference to compare the obtained values for fractional abundances of the resistance-determining mutant allele between ddPCR and NGS techniques in each sample. Both methods managed to produce highly similar results and ddPCR proved to be a reliable tool which, when utilized at full capacity, can be used to create a powerful mutation detection and quantification assay. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

July 19, 2019  |  

Large deletions at the SHOX locus in the pseudoautosomal region are associated with skeletal atavism in Shetland ponies.

Skeletal atavism in Shetland ponies is a heritable disorder characterized by abnormal growth of the ulna and fibula that extend the carpal and tarsal joints, respectively. This causes abnormal skeletal structure, impaired movements, and affected foals are usually euthanized. In order to identify the causal mutation we subjected six confirmed Swedish cases and a DNA pool consisting of 21 control individuals to whole genome resequencing. We screened for polymorphisms where the cases and the control pool were fixed for opposite alleles and observed this signature for only 25 SNPs, most of which were scattered on genome assembly unassigned scaffolds. Read depth analysis at these loci revealed homozygosity or compound heterozygosity for two partially overlapping large deletions in the pseudoautosomal region (PAR) of chromosome X/Y in cases but not in the control pool. One of these deletions removes the entire coding region of the SHOX gene and both deletions remove parts of the CRLF2 gene located downstream of SHOX. The horse reference assembly of the PAR is highly fragmented, and in order to characterize this region we sequenced bacterial artificial chromosome (BAC) clones by single-molecule real-time (SMRT) sequencing technology. This considerably improved the assembly and enabled size estimations of the two deletions to 160-180 kb and 60-80 kb, respectively. Complete association between the presence of these deletions and disease status was verified in eight other affected horses. The result of the present study is consistent with previous studies in humans showing crucial importance of SHOX for normal skeletal development. Copyright © 2016 Author et al.

July 19, 2019  |  

A novel approach using long-read sequencing and ddPCR to investigate gonadal mosaicism and estimate recurrence risk in two families with developmental disorders.

De novo mutations contribute significantly to severe early-onset genetic disorders. Even if the mutation is apparently de novo, there is a recurrence risk due to parental germ line mosaicism, depending on in which gonadal generation the mutation occurred.We demonstrate the power of using SMRT sequencing and ddPCR to determine parental origin and allele frequencies of de novo mutations in germ cells in two families whom had undergone assisted reproduction.In the first family, a TCOF1 variant c.3156C>T was identified in the proband with Treacher Collins syndrome. The variant affects splicing and was determined to be of paternal origin. It was present in <1% of the paternal germ cells, suggesting a very low recurrence risk. In the second family, the couple had undergone several unsuccessful pregnancies where a de novo mutation PTPN11 c.923A>C causing Noonan syndrome was identified. The variant was present in 40% of the paternal germ cells suggesting a high recurrence risk.Our findings highlight a successful strategy to identify the parental origin of mutations and to investigate the recurrence risk in couples that have undergone assisted reproduction with an unknown donor or in couples with gonadal mosaicism that will undergo preimplantation genetic diagnosis.© 2017 The Authors Prenatal Diagnosis published by John Wiley & Sons Ltd.

July 19, 2019  |  

De novo assembly of two Swedish genomes reveals missing segments from the human GRCh38 reference and improves variant calling of population-scale sequencing data.

The current human reference sequence (GRCh38) is a foundation for large-scale sequencing projects. However, recent studies have suggested that GRCh38 may be incomplete and give a suboptimal representation of specific population groups. Here, we performed a de novo assembly of two Swedish genomes that revealed over 10 Mb of sequences absent from the human GRCh38 reference in each individual. Around 6 Mb of these novel sequences (NS) are shared with a Chinese personal genome. The NS are highly repetitive, have an elevated GC-content, and are primarily located in centromeric or telomeric regions. Up to 1 Mb of NS can be assigned to chromosome Y, and large segments are also missing from GRCh38 at chromosomes 14, 17, and 21. Inclusion of NS into the GRCh38 reference radically improves the alignment and variant calling from short-read whole-genome sequencing data at several genomic loci. A re-analysis of a Swedish population-scale sequencing project yields > 75,000 putative novel single nucleotide variants (SNVs) and removes > 10,000 false positive SNV calls per individual, some of which are located in protein coding regions. Our results highlight that the GRCh38 reference is not yet complete and demonstrate that personal genome assemblies from local populations can improve the analysis of short-read whole-genome sequencing data.

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