CRISPR-Cas9-targeted fragmentation and selective sequencing enable massively parallel microsatellite analysis

CRISPR-Cas technology in forensic investigations: Principles, applications, and ethical considerations

CRISPR-Cas (Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated proteins) systems are adaptive immune systems originally present in bacteria, where they are essential to protect against external genetic elements, including viruses and plasmids. Taking advantage of this system, CRISPR-Cas-based technologies have emerged as incredible tools for precise genome editing, thus significantly advancing several research fields. Forensic sciences represent a multidisciplinary field that explores scientific methods to investigate and resolve legal issues, particularly criminal investigations and subject identification. Consequently, it plays a critical role in the justice system, providing scientific evidence to support judicial investigations. Although less explored, CRISPR-Cas-based methodologies demonstrate strong potential in the field of forensic sciences due to their high accuracy and sensitivity, including DNA profiling and identification, interpretation of crime scene investigations, detection of food contamination or fraud, and other aspects related to environmental forensics. However, using CRISPR-Cas-based methodologies in human samples raises several ethical issues and concerns regarding the potential misuse of individual genetic information. In this manuscript, we provide an overview of potential applications of CRISPR-Cas-based methodologies in several areas of forensic sciences and discuss the legal implications that challenge their routine implementation in this research field.

Applications of CRISPR-Cas9 for advancing precision medicine in oncology: from target discovery to disease modeling

The clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) (CRISPR/Cas9) system is a powerful tool that enables precise and efficient gene manipulation. In a relatively short time, CRISPR has risen to become the preferred gene-editing system due to its high efficiency, simplicity, and programmability at low costs. Furthermore, in the recent years, the CRISPR toolkit has been rapidly expanding, and the emerging advancements have shown tremendous potential in uncovering molecular mechanisms and new therapeutic strategies for human diseases. In this review, we provide our perspectives on the recent advancements in CRISPR technology and its impact on precision medicine, ranging from target identification, disease modeling, and diagnostics. We also discuss the impact of novel approaches such as epigenome, base, and prime editing on preclinical cancer drug discovery.

Short tandem repeat profiling via next-generation sequencing for cell line authentication

Cell lines are indispensable models for modern biomedical research. A large part of their usefulness derives from the ability of a cell line to proliferate over multiple passages (often indefinitely), allowing multiple experiments to be performed. However, over time, cell line identity and purity can be compromised by human errors. Cross-contamination from other cell lines and complete misidentification are both possible. Routine cell line authentication is a necessary preventive measure and has become a requirement for many funding applications and publications. Short tandem repeat (STR) profiling is the most common method for cell line authentication and is usually carried out using standard polymerase chain reaction-capillary electrophoresis analysis (STR-CE). Here, we evaluated next-generation sequencing (NGS)-based STR profiling of human and mouse cell lines at 18 and 15 loci, respectively, in a high-throughput format. Using the Python program STRight, we demonstrate that NGS-based analysis (STR-NGS) is superior to standard STR-CE in terms of the ability to report the sequence context of repeat motifs, sensitivity and flexible multiplexing capability. STR-NGS is thus a valuable alternative for cell line authentication.

Viral vectors and extracellular vesicles: innate delivery systems utilized in CRISPR/Cas-mediated cancer therapy

Gene editing-based therapeutic strategies grant the power to override cell machinery and alter faulty genes contributing to disease development like cancer. Nowadays, the principal tool for gene editing is the clustered regularly interspaced short palindromic repeats-associated nuclease 9 (CRISPR/Cas9) system. In order to bring this gene-editing system from the bench to the bedside, a significant hurdle remains, and that is the delivery of CRISPR/Cas to various target cells in vivo and in vitro. The CRISPR-Cas system can be delivered into mammalian cells using various strategies; among all, we have reviewed recent research around two natural gene delivery systems that have been proven to be compatible with human cells. Herein, we have discussed the advantages and limitations of viral vectors, and extracellular vesicles (EVs) in delivering the CRISPR/Cas system for cancer therapy purposes.

CRISPR-Cas9 Targeted Enrichment and Next-Generation Sequencing for Mutation Detection

Despite the rapid application of next-generation sequencing (NGS) technologies, target sequencing in regions of the genome is often required to diagnose many genetic diseases. Target enrichment can be an effective factor in reducing the cost of sequencing and the duration of sequencing. Recently, several clustered system regularly interspaced short palindromic repeats (CRISPR)-based methods (amplification-free sequencing) have been developed to target enrichment in combination with one of the NGS platforms. CRISPR-based target enrichment strategies act as an auxiliary tool to improve NGS analytical performance, thereby indirectly facilitating nucleic acid detection. The direct DNA cleavage approach by CRISPR-Cas at genome-specific sites enhances the possibility of separating native large fragments from disease-related genomic regions. The CRISPR-Cas can isolate the target region without any amplification; subsequently, long-read sequencing technologies were also implemented. These methods, as promising tools, have the ability to assess genetic and epigenetic composition for clinical application and treatment responses in cancer precision medicine. By modifying CRISPR-based enrichment protocols, it was possible to identify different types of mutations, including structural variants, short tandem repeats, fusion genes, and mobile elements. The Cas9 can specifically eliminate wild-type sequences, and it also enables the enrichment and detection of small amounts of tumor DNA fragments among the highly heterogeneous fragments of wild-type DNA.

Cas12a-Capture: A Novel, Low-Cost, and Scalable Method for Targeted Sequencing

Targeted sequencing remains a valuable technique for clinical and research applications. However, many existing technologies suffer from pervasive guanine-cytosine (GC) sequence content bias, high input DNA requirements, and high cost for custom panels. We have developed Cas12a-Capture, a low-cost and highly scalable method for targeted sequencing. The method utilizes preprogrammed guide RNAs to direct CRISPR-Cas12a cleavage of double-stranded DNA in vitro and then takes advantage of the resulting four to five nucleotide overhangs for selective ligation with a custom sequencing adapter. Addition of a second sequencing adapter and enrichment for ligation products generates a targeted sequence library. We first performed a pilot experiment with 7176 guides targeting 3.5 Mb of DNA. Using these data, we modeled the sequence determinants of Cas12a-Capture efficiency, then designed an optimized set of 11,438 guides targeting 3.0 Mb. The optimized guide set achieves an average 64-fold enrichment of targeted regions with minimal GC bias. Cas12a-Capture variant calls had strong concordance with Illumina Platinum Genome calls, especially for single nucleotide variants, which could be improved by applying basic variant quality heuristics. We believe Cas12a-Capture has a wide variety of potential clinical and research applications and is amendable for selective enrichment for any double-stranded DNA template or genome.

CRISPR-CasB technology in forensic DNA analysis: challenges and solutions

CRISPR-Cas technology has revolutionized the field of biotechnology with its precise therapeutic use from genetic as well as infectious diseases point of view. This technology is rapidly evolving to single tool enabling site-directed cut in the genome and highly specific activation or inhibition of gene expression or the exchange of single bases. Besides clinical applications, CRISPR-Cas technology has also shown promising use in the field of forensic DNA analysis. Enrichment of targeted genetic marker for identification followed by sequencing and non-PCR-dependent technique ensures the use of CRISPR-Cas technology in challenging forensic biological samples. The use of this advanced technology is also deemed helpful in mixed profile attribution, mostly in LCN contributors and the generation of a useful DNA profile in degraded samples. Besides its useful applications in forensic DNA analysis, CRISPR-Cas technology poses a huge threat from the generation of ghost DNA profiles by modification/alteration of target genetic markers. Forensic DNA analysts should carry out analysis of additional markers such as non-CODIS markers, Y-, X-chromosome markers, and mitochondrial DNA sequencing in a suspected ghost DNA profile case. KEY POINTS: • CRISPR-Cas9 technique is useful in analyzing LCN, mixed and degraded samples • Alteration of DNA using this technique can lead to generation of ghost DNA profiles • Alternative genetic markers and methylation pattern may detect a ghost DNA profile.

CRISPR in cancer biology and therapy

Over the past decade, CRISPR has become as much a verb as it is an acronym, transforming biomedical research and providing entirely new approaches for dissecting all facets of cell biology. In cancer research, CRISPR and related tools have offered a window into previously intractable problems in our understanding of cancer genetics, the noncoding genome and tumour heterogeneity, and provided new insights into therapeutic vulnerabilities. Here, we review the progress made in the development of CRISPR systems as a tool to study cancer, and the emerging adaptation of these technologies to improve diagnosis and treatment.

New approaches to moderate CRISPR-Cas9 activity: Addressing issues of cellular uptake and endosomal escape

CRISPR-Cas9 is rapidly entering molecular biology and biomedicine as a promising gene-editing tool. A unique feature of CRISPR-Cas9 is a single-guide RNA directing a Cas9 nuclease toward its genomic target. Herein, we highlight new approaches for improving cellular uptake and endosomal escape of CRISPR-Cas9. As opposed to other recently published works, this review is focused on non-viral carriers as a means to facilitate the cellular uptake of CRISPR-Cas9 through endocytosis. The majority of non-viral carriers, such as gold nanoparticles, polymer nanoparticles, lipid nanoparticles, and nanoscale zeolitic imidazole frameworks, is developed with a focus toward optimizing the endosomal escape of CRISPR-Cas9 by taking advantage of the acidic environment in the late endosomes. Among the most broadly used methods for in vitro and ex vivo ribonucleotide protein transfection are electroporation and microinjection. Thus, other delivery formats are warranted for in vivo delivery of CRISPR-Cas9. Herein, we specifically revise the use of peptide and nanoparticle-based systems as platforms for CRISPR-Cas9 delivery in vivo. Finally, we highlight future perspectives of the CRISPR-Cas9 gene-editing tool and the prospects of using non-viral vectors to improve its bioavailability and therapeutic potential.

Revisiting tandem repeats in psychiatric disorders from perspectives of genetics, physiology, and brain evolution

Genome-wide association studies (GWASs) have revealed substantial genetic components comprised of single nucleotide polymorphisms (SNPs) in the heritable risk of psychiatric disorders. However, genetic risk factors not covered by GWAS also play pivotal roles in these illnesses. Tandem repeats, which are likely functional but frequently overlooked by GWAS, may account for an important proportion in the "missing heritability" of psychiatric disorders. Despite difficulties in characterizing and quantifying tandem repeats in the genome, studies have been carried out in an attempt to describe impact of tandem repeats on gene regulation and human phenotypes. In this review, we have introduced recent research progress regarding the genomic distribution and regulatory mechanisms of tandem repeats. We have also summarized the current knowledge of the genetic architecture and biological underpinnings of psychiatric disorders brought by studies of tandem repeats. These findings suggest that tandem repeats, in candidate psychiatric risk genes or in different levels of linkage disequilibrium (LD) with psychiatric GWAS SNPs and haplotypes, may modulate biological phenotypes related to psychiatric disorders (e.g., cognitive function and brain physiology) through regulating alternative splicing, promoter activity, enhancer activity and so on. In addition, many tandem repeats undergo tight natural selection in the human lineage, and likely exert crucial roles in human brain evolution. Taken together, the putative roles of tandem repeats in the pathogenesis of psychiatric disorders is strongly implicated, and using examples from previous literatures, we wish to call for further attention to tandem repeats in the post-GWAS era of psychiatric disorders.

Comparing Phylogenetic Approaches to Reconstructing Cell Lineage From Microsatellites With Missing Data

Due to the imperfect fidelity of DNA replication, somatic cells acquire DNA mutations at each division which record their lineage history. Microsatellites, tandem repeats of DNA nucleotide motifs, mutate more frequently than other genomic regions and by observing microsatellite lengths in single cells and implementing suitable inference procedures, the cell lineage tree of an organism can be reconstructed. Due to recent advances in single cell Next Generation Sequencing (NGS) and the phylogenetic methods used to infer lineage trees, this work investigates which computational approaches best exploit the lineage information found in single cell NGS data. We simulated trees representing cell division with mutating microsatellites, and tested a range of available phylogenetic algorithms to reconstruct cell lineage. We found that distance-based approaches are fast and accurate with fully observed data. However, Maximum Parsimony and the computationally intensive probabilistic methods are more robust to missing data and therefore better suited to reconstructing cell lineage from NGS datasets. We also investigated how robust reconstruction algorithms are to different tree topologies and mutation generation models. Our results show that the flexibility of Maximum Parsimony and the probabilistic approaches mean they can be adapted to allow good reconstruction across a range of biologically relevant scenarios.

Profiling diverse sequence tandem repeats in colorectal cancer reveals co-occurrence of microsatellite and chromosomal instability involving Chromosome 8

We developed a sensitive sequencing approach that simultaneously profiles microsatellite instability, chromosomal instability, and subclonal structure in cancer. We assessed diverse repeat motifs across 225 microsatellites on colorectal carcinomas. Our study identified elevated alterations at both selected tetranucleotide and conventional mononucleotide repeats. Many colorectal carcinomas had a mix of genomic instability states that are normally considered exclusive. An MSH3 mutation may have contributed to the mixed states. Increased copy number of chromosome arm 8q was most prevalent among tumors with microsatellite instability, including a case of translocation involving 8q. Subclonal analysis identified co-occurring driver mutations previously known to be exclusive.

PolyG-DS: An ultrasensitive polyguanine tract-profiling method to detect clonal expansions and trace cell lineage

Polyguanine tracts (PolyGs) are short guanine homopolymer repeats that are prone to accumulating mutations when cells divide. This feature makes them especially suitable for cell lineage tracing, which has been exploited to detect and characterize precancerous and cancerous somatic evolution. PolyG genotyping, however, is challenging because of the inherent biochemical difficulties in amplifying and sequencing repetitive regions. To overcome this limitation, we developed PolyG-DS, a next-generation sequencing (NGS) method that combines the error-correction capabilities of duplex sequencing (DS) with enrichment of PolyG loci using CRISPR-Cas9-targeted genomic fragmentation. PolyG-DS markedly reduces technical artifacts by comparing the sequences derived from the complementary strands of each original DNA molecule. We demonstrate that PolyG-DS genotyping is accurate, reproducible, and highly sensitive, enabling the detection of low-frequency alleles (<0.01) in spike-in samples using a panel of only 19 PolyG markers. PolyG-DS replicated prior results based on PolyG fragment length analysis by capillary electrophoresis, and exhibited higher sensitivity for identifying clonal expansions in the nondysplastic colon of patients with ulcerative colitis. We illustrate the utility of this method for resolving the phylogenetic relationship among precancerous lesions in ulcerative colitis and for tracing the metastatic dissemination of ovarian cancer. PolyG-DS enables the study of tumor evolution without prior knowledge of tumor driver mutations and provides a tool to perform cost-effective and easily scalable ultra-accurate NGS-based PolyG genotyping for multiple applications in biology, genetics, and cancer research.

Engineering CRISPR/Cas9 to mitigate abundant host contamination for 16S rRNA gene-based amplicon sequencing

BACKGROUND

High-throughput sequencing of bacterial 16S rRNA gene (16S-seq) is a useful and common method for studying bacterial community structures. However, contamination of the 16S rRNA genes from the mitochondrion and plastid hinders the sensitive bacterial 16S-seq in plant microbiota profiling, especially for some plant species such as rice. To date, efficiently mitigating such host contamination without a bias is challenging in 16S rRNA gene-based amplicon sequencing.

RESULTS

We developed Cas-16S-seq method to reduce abundant host contamination for plant microbiota profiling. This method utilizes the Cas9 nuclease and specific guide RNA (gRNA) to cut 16S rRNA targets during library construction, thereby removing host contamination in 16S-seq. We used rice as an example to validate the feasibility and effectiveness of Cas-16S-seq. We established a bioinformatics pipeline to design gRNAs that specifically target rice 16S rRNA genes without bacterial 16S rRNA off-targets. We compared the effectiveness of Cas-16S-seq with that of the commonly used 16S-seq method for artificially mixed 16S rRNA gene communities, paddy soil, rice root, and phyllosphere samples. The results showed that Cas-16S-seq substantially reduces the fraction of rice 16S rRNA gene sequences from 63.2 to 2.9% in root samples and from 99.4 to 11.6% in phyllosphere samples on average. Consequently, Cas-16S-seq detected more bacterial species than the 16S-seq in plant samples. Importantly, when analyzing soil samples, Cas-16S-seq and 16S-seq showed almost identical bacterial communities, suggesting that Cas-16S-seq with host-specific gRNAs that we designed has no off-target in rice microbiota profiling.

CONCLUSION

Our Cas-16S-seq can efficiently remove abundant host contamination without a bias for 16S rRNA gene-based amplicon sequencing, thereby enabling deeper bacterial community profiling with a low cost and high flexibility. Thus, we anticipate that this method would be a useful tool for plant microbiomics. Video Abstract.

Transforming ecology and conservation biology through genome editing

As the conservation challenges increase, new approaches are needed to help combat losses in biodiversity and slow or reverse the decline of threatened species. Genome-editing technology is changing the face of modern biology, facilitating applications that were unimaginable only a decade ago. The technology has the potential to make significant contributions to the fields of evolutionary biology, ecology, and conservation, yet the fear of unintended consequences from designer ecosystems containing engineered organisms has stifled innovation. To overcome this gap in the understanding of what genome editing is and what its capabilities are, more research is needed to translate genome-editing discoveries into tools for ecological research. Emerging and future genome-editing technologies include new clustered regularly interspaced short palindromic repeats (CRISPR) targeted sequencing and nucleic acid detection approaches as well as species genetic barcoding and somatic genome-editing technologies. These genome-editing tools have the potential to transform the environmental sciences by providing new noninvasive methods for monitoring threatened species or for enhancing critical adaptive traits. A pioneering effort by the conservation community is required to apply these technologies to real-world conservation problems.

Effects of electroporation treatment using different concentrations of Cas9 protein with gRNA targeting Myostatin (MSTN) genes on the development and gene editing of porcine zygotes

This study was conducted to investigate the effect of seven concentrations of Cas9 protein (0, 25, 50, 100, 200, 500, and 1,000 ng/µl) on the development and gene editing of porcine embryos. This included the target editing and off-target effect of embryos developed from zygotes that were edited via electroporation of the Cas9 protein with guide RNA targeting Myostatin genes. We found that the development to blastocysts of electroporated zygotes was not affected by the concentration of Cas9 protein. Although the editing rate, which was defined as the ratio of edited blastocysts to total examined blastocysts, did not differ with Cas9 protein concentration, the editing efficiency, which was defined as the frequency of indel mutations in each edited blastocyst, was significantly decreased in the edited blastocysts from zygotes electroporated with 25 ng/µl of Cas9 protein compared with that of blastocysts from zygotes electroporated with higher Cas9 protein concentrations. Moreover the frequency of indel events at the two possible off-target sites was not significantly different with different concentrations of Cas9 protein. These results indicate that the concentration of Cas9 protein affects gene editing efficiency in embryos but not the embryonic development, gene editing rate, and non-specific cleavage of off-target sites.

Targeted short read sequencing and assembly of re-arrangements and candidate gene loci provide megabase diplotypes

The human genome is composed of two haplotypes, otherwise called diplotypes, which denote phased polymorphisms and structural variations (SVs) that are derived from both parents. Diplotypes place genetic variants in the context of cis-related variants from a diploid genome. As a result, they provide valuable information about hereditary transmission, context of SV, regulation of gene expression and other features which are informative for understanding human genetics. Successful diplotyping with short read whole genome sequencing generally requires either a large population or parent-child trio samples. To overcome these limitations, we developed a targeted sequencing method for generating megabase (Mb)-scale haplotypes with short reads. One selects specific 0.1-0.2 Mb high molecular weight DNA targets with custom-designed Cas9-guide RNA complexes followed by sequencing with barcoded linked reads. To test this approach, we designed three assays, targeting the BRCA1 gene, the entire 4-Mb major histocompatibility complex locus and 18 well-characterized SVs, respectively. Using an integrated alignment- and assembly-based approach, we generated comprehensive variant diplotypes spanning the entirety of the targeted loci and characterized SVs with exact breakpoints. Our results were comparable in quality to long read sequencing.

Multi-individual microsatellite identification: A multiple genome approach to microsatellite design (MiMi)

Bespoke microsatellite marker panels are increasingly affordable and tractable to researchers and conservationists. The rate of microsatellite discovery is very high within a shotgun genomic data set, but extensive laboratory testing of markers is required for confirmation of amplification and polymorphism. By incorporating shotgun next-generation sequencing data sets from multiple individuals of the same species, we have developed a new method for the optimal design of microsatellite markers. This new tool allows us to increase the rate at which suitable candidate markers are selected by 58% in direct comparisons and facilitate an estimated 16% reduction in costs associated with producing a novel microsatellite panel. Our method enables the visualisation of each microsatellite locus in a multiple sequence alignment allowing several important quality checks to be made. Polymorphic loci can be identified and prioritised. Loci containing fragment-length-altering mutations in the flanking regions, which may invalidate assumptions regarding the model of evolution underlying variation at the microsatellite, can be avoided. Priming regions containing point mutations can be detected and avoided, helping to reduce sample-site-marker specificity arising from genetic isolation, and the likelihood of null alleles occurring. We demonstrate the utility of this new approach in two species: an echinoderm and a bird. Our method makes a valuable contribution towards minimising genotyping errors and reducing costs associated with developing a novel marker panel. The Python script to perform our method of multi-individual microsatellite identification (MiMi) is freely available from GitHub (https://github.com/graemefox/mimi).

Clinical sequencing: From raw data to diagnosis with lifetime value

High-throughput sequencing (HTS) has revolutionized genetics by enabling the detection of sequence variants at hitherto unprecedented large scale. Despite these advances, however, there are still remaining challenges in the complete coverage of targeted regions (genes, exome or genome) as well as in HTS data analysis and interpretation. Moreover, it is easy to get overwhelmed by the plethora of available methods and tools for HTS. Here, we review the step-by-step process from the generation of sequence data to molecular diagnosis of Mendelian diseases. Highlighting advantages and limitations, this review addresses the current state of (1) HTS technologies, considering targeted, whole-exome, and whole-genome sequencing on short- and long-read platforms; (2) read alignment, variant calling and interpretation; as well as (3) regulatory issues related to genetic counseling, reimbursement, and data storage.

CRISPR/Cas9-targeted removal of unwanted sequences from small-RNA sequencing libraries

In small RNA (smRNA) sequencing studies, highly abundant molecules such as adapter dimer products and tissue-specific microRNAs (miRNAs) inhibit accurate quantification of lowly expressed species. We previously developed a method to selectively deplete highly abundant miRNAs. However, this method does not deplete adapter dimer ligation products that, unless removed by gel-separation, comprise most of the library. Here, we have adapted and modified recently described methods for CRISPR/Cas9-based Depletion of Abundant Species by Hybridization ('DASH') to smRNA-seq, which we have termed miRNA and Adapter Dimer-DASH (MAD-DASH). In MAD-DASH, Cas9 is complexed with single guide RNAs (sgRNAs) targeting adapter dimer ligation products, alongside highly expressed tissue-specific smRNAs, for cleavage in vitro. This process dramatically reduces adapter dimer and targeted smRNA sequences, can be multiplexed, shows minimal off-target effects, improves the quantification of lowly expressed miRNAs from human plasma and tissue derived RNA, and obviates the need for gel-separation, greatly increasing sample throughput. Additionally, the method is fully customizable to other smRNA-seq preparation methods. Like depletion of ribosomal RNA for mRNA-seq and mitochondrial DNA for ATAC-seq, our method allows for greater proportional read-depth of non-targeted sequences.

CRISPR-Cap: multiplexed double-stranded DNA enrichment based on the CRISPR system

Existing methods to enrich target regions of genomic DNA based on PCR, hybridization capture, or molecular inversion probes have various drawbacks, including long experiment times and low throughput and/or enrichment quality. We developed CRISPR-Cap, a simple and scalable CRISPR-based method to enrich target regions of dsDNA, requiring only two short experimental procedures that can be completed within two hours. We used CRISPR-Cap to enrich 10 target genes 355.7-fold on average from Escherichia coli genomic DNA with a maximum on-target ratio of 81% and high enrichment uniformity. We also used CRISPR-Cap to measure gene copy numbers and detect rare alleles with frequencies as low as 1%. Finally, we enriched coding sequence regions of 20 genes from the human genome. We envision that CRISPR-Cap can be used as an alternative to other widely used target-enrichment methods, which will broaden the scope of CRISPR applications to the field of target enrichment field.

Real-Time Selective Sequencing with RUBRIC: Read Until with Basecall and Reference-Informed Criteria

The Oxford MinION, the first commercial nanopore sequencer, is also the first to implement molecule-by-molecule real-time selective sequencing or “Read Until”. As DNA transits a MinION nanopore, real-time pore current data can be accessed and analyzed to provide active feedback to that pore. Fragments of interest are sequenced by default, while DNA deemed non-informative is rejected by reversing the pore bias to eject the strand, providing a novel means of background depletion and/or target enrichment. In contrast to the previously published pattern-matching Read Until approach, our RUBRIC method is the first example of real-time selective sequencing where on-line basecalling enables alignment against conventional nucleic acid references to provide the basis for sequence/reject decisions. We evaluate RUBRIC performance across a range of optimizable parameters, apply it to mixed human/bacteria and CRISPR/Cas9-cut samples, and present a generalized model for estimating real-time selection performance as a function of sample composition and computing configuration.

CRISPR/CAS9 targeted CAPTURE of mammalian genomic regions for characterization by NGS

The robust detection of structural variants in mammalian genomes remains a challenge. It is particularly difficult in the case of genetically unstable Chinese hamster ovary (CHO) cell lines with only draft genome assemblies available. We explore the potential of the CRISPR/Cas9 system for the targeted capture of genomic loci containing integrated vectors in CHO-K1-based cell lines followed by next generation sequencing (NGS), and compare it to popular target-enrichment sequencing methods and to whole genome sequencing (WGS). Three different CRISPR/Cas9-based techniques were evaluated; all of them allow for amplification-free enrichment of target genomic regions in the range from 5 to 60 fold, and for recovery of ~15 kb-long sequences with no sequencing artifacts introduced. The utility of these protocols has been proven by the identification of transgene integration sites and flanking sequences in three CHO cell lines. The long enriched fragments helped to identify Escherichia coli genome sequences co-integrated with vectors, and were further characterized by Whole Genome Sequencing (WGS). Other advantages of CRISPR/Cas9-based methods are the ease of bioinformatics analysis, potential for multiplexing, and the production of long target templates for real-time sequencing.

Covalent "Click Chemistry"-Based Attachment of DNA onto Solid Phase Enables Iterative Molecular Analysis

Molecular analysis of DNA samples with limited quantities can be challenging. Repeatedly sequencing the original DNA molecules from a given sample would overcome many issues related to accurate genetic analysis and mitigate issues with processing small amounts of DNA analyte. Moreover, an iterative, replicated analysis of the same DNA molecule has the potential to improve genetic characterization. Herein, we demonstrate that the use of "click"-based attachment of DNA sequencing libraries onto an agarose bead support enables repetitive primer extension assays for specific genomic DNA targets such as gene exons. We validated the performance of this assay for evaluating specific genetic alterations in both normal and cancer reference standard DNA samples. We demonstrate the stability of conjugated DNA libraries and related sequencing results over the course of independent serial assays spanning several months from the same set of samples. Finally, we finally applied this method to DNA derived from a tumor sample and demonstrated improved mutation detection accuracy.

Class 2 CRISPR/Cas: an expanding biotechnology toolbox for and beyond genome editing

Artificial nuclease-dependent DNA cleavage systems (zinc-finger nuclease, ZFN; transcription activator like effectors, TALENs) and exogenous nucleic acid defense systems (CRISPR/Cas) have been used in the new era for genome modification. The most widely used toolbox for genome editing, modulation and detection contains Types II, V and VI of CRISPR/Cas Class 2 systems, categorized and characterized by Cas9, Cas12a and Cas13 respectively. In this review, we (1) elaborate on the definition, classification, structures of CRISPR/Cas Class 2 systems; (2) advance our understanding of new molecular mechanisms and recent progress in their applications, especially beyond genome-editing applications; (3) provide the insights on the specificity, efficiency and versatility of each tool; (4) elaborate the enhancement on specificity and efficiency of the CRISPR/Cas toolbox. The expanding and concerted usage of the CRISPR/Cas tools is making them more powerful in genome editing and other biotechnology applications.

Association Analysis of a Microsatellite Repeat in the TRIB1 Gene With Prostate Cancer Risk, Aggressiveness and Survival

With an estimated 1.1 million men worldwide diagnosed with prostate cancer yearly, effective and more specific biomarkers for early diagnosis could lead to better patient outcome. As such, novel genetic markers are sought for this purpose. The tribbles homologue 1 gene (TRIB1) has recently shown to have a role in prostate tumorigenesis and data-mining of prostate cancer expression data confirmed clinical significance of TRIB1 in prostate cancer. For the first time, a polymorphic microsatellite in this gene was studied for its potential association with prostate cancer risk and aggressiveness. Genomic DNA was extracted from a cohort of 1,152 prostate cancer patients and 1,196 cancer-free controls and the TTTTG-TRIB1 microsatellite was genotyped. The socio-demographic and clinical characteristics were analyzed using the non-parametric t-test and two-way ANOVA. Association of the TTTTG-TRIB1 microsatellite and prostate cancer risk and aggressiveness were analyzed by binary logistic regression and confirmed by bootstrapping. Total and prostate cancer mortality was analyzed using the Kaplan Meier test. Genotype and allele correlation with TRIB1 mRNA levels was analyzed using the non-parametric Kolmogorov-Smirnov test. To predict the effect that the TTTTG-TRIB1 polymorphisms had on the mRNA structure, the in silico RNA folding predictor tool, mfold, was used. By analyzing the publicly available data, we confirmed a significant over-expression of TRIB1 in prostate cancer compared to other cancer types, and an over-expression in prostate cancerous tissue compared to adjacent benign. Three alleles (three-five repeats) were observed for TTTTG-TRIB1. The three-repeat allele was associated with prostate cancer risk at the allele (OR = 1.16; P = 0.044) and genotypic levels (OR = 1.70; P = 0.006) and this association was age-independent. The four-repeat allele was inversely associated with prosatet cancer risk (OR = 0.57; P < 0.0001). TRIB1 expression was upregulated in tumors when compared to adjacent cancer-free tissue but was not allele specific. In silico analysis suggested that the TTTTG-TRIB1 alleles may alter TRIB1 mRNA structure. In summary, the three-repeat allele was significantly associated with prostate cancer risk, suggesting a biomarker potential for this microsatellite to predict prostate cancer. Further studies are needed to elucidate the functional role of this microsatellite in regulating TRIB1 expression, perhaps by affecting the TRIB1 mRNA structure and stability.

Targeted genome fragmentation with CRISPR/Cas9 enables fast and efficient enrichment of small genomic regions and ultra-accurate sequencing with low DNA input (CRISPR-DS)

Next-generation sequencing methods suffer from low recovery, uneven coverage, and false mutations. DNA fragmentation by sonication is a major contributor to these problems because it produces randomly sized fragments, PCR amplification bias, and end artifacts. In addition, oligonucleotide-based hybridization capture, a common target enrichment method, has limited efficiency for small genomic regions, contributing to low recovery. This becomes a critical problem in clinical applications, which value cost-effective approaches focused on the sequencing of small gene panels. To address these issues, we developed a targeted genome fragmentation approach based on CRISPR/Cas9 digestion that produces DNA fragments of similar length. These fragments can be enriched by a simple size selection, resulting in targeted enrichment of up to approximately 49,000-fold. Additionally, homogenous length fragments significantly reduce PCR amplification bias and maximize read usability. We combined this novel target enrichment approach with Duplex Sequencing, which uses double-strand molecular tagging to correct for sequencing errors. The approach, termed CRISPR-DS, enables efficient target enrichment of small genomic regions, even coverage, ultra-accurate sequencing, and reduced DNA input. As proof of principle, we applied CRISPR-DS to the sequencing of the exonic regions of TP53 and performed side-by-side comparisons with standard Duplex Sequencing. CRISPR-DS detected previously reported pathogenic TP53 mutations present as low as 0.1% in peritoneal fluid of women with ovarian cancer, while using 10- to 100-fold less DNA than standard Duplex Sequencing. Whether used as standalone enrichment or coupled with high-accuracy sequencing methods, CRISPR-based fragmentation offers a simple solution for fast and efficient small target enrichment.

A broad genomic panel of microsatellite loci from Brycon orbignyanus (Characiformes: Bryconidae) an endangered migratory Neotropical fish

A broad panel of tens of thousands of microsatellite loci is unveiled for an endangered piracema (i.e. migratory) South American fish, Brycon orbignyanus. Once one of the main fisheries resources in the Platine Basin, it is now almost extinct in nature and focus of intense aquaculture activity. A total of 178.2 million paired-end reads (90 bases long) were obtained through the use of sequencing-by-synthesis (from a primary genomic library of 500 bp DNA fragments) and is made available through NCBI’s Sequence Read Archive, SRA accession SRX3350440. Short reads were assembled de novo and screening for perfect microsatellite motifs revealed more than 81 thousands unique microsatellite loci, for which primer pairs were proposed. A total of 29 polymorphic microsatellite markers were already previously validated for this panel. A partial genomic assembly is hereby presented and these genomic resources are publicly made available. These data will foster the rapid development of hundreds of new DNA markers for genetic diversity studies, conservation initiatives and management practices for this important and depleted species. The availability of such preliminary genomic data will also be of use in the areas of bioinformatics, ecology, genetics and evolution.

Genome-scale portrait and evolutionary significance of human-specific core promoter tri- and tetranucleotide short tandem repeats

BACKGROUND

While there is an ongoing trend to identify single nucleotide substitutions (SNSs) that are linked to inter/intra-species differences and disease phenotypes, short tandem repeats (STRs)/microsatellites may be of equal (if not more) importance in the above processes. Genes that contain STRs in their promoters have higher expression divergence compared to genes with fixed or no STRs in the gene promoters. In line with the above, recent reports indicate a role of repetitive sequences in the rise of young transcription start sites (TSSs) in human evolution.

RESULTS

Following a comparative genomics study of all human protein-coding genes annotated in the GeneCards database, here we provide a genome-scale portrait of human-specific short- and medium-size (≥ 3-repeats) tri- and tetranucleotide STRs and STR motifs in the critical core promoter region between - 120 and + 1 to the TSS and evidence of skewing of this compartment in reference to the STRs that are not human-specific (Levene's test p < 0.001). Twenty-five percent and 26% enrichment of human-specific transcripts was detected in the tri and tetra human-specific compartments (mid-p < 0.00002 and mid-p < 0.002, respectively).

CONCLUSION

Our findings provide the first evidence of genome-scale skewing of STRs at a specific region of the human genome and a link between a number of these STRs and TSS selection/transcript specificity. The STRs and genes listed here may have a role in the evolution and development of characteristics and phenotypes that are unique to the human species.

A Comparison of Microsatellites in Phytopathogenic Aspergillus Species in Order to Develop Markers for the Assessment of Genetic Diversity among Its Isolates

The occurrence of Microsatellites (SSRs) has been witnessed in most of the fungal genomes however its abundance varies across species. In the present study, we analyzed the frequency of SSRs in the whole genome and transcripts of two phyto-pathogenic (Aspergillus niger and Aspergillus terreus) and compared them with two non-pathogenic (Aspergillus nidulans and Aspergillus oryzae) Aspergillus. Higher relative abundance and relative density of SSRs were observed in the whole genome and transcript sequences of the pathogenic Aspergillus when compared to the non-pathogenic. The relative abundance and density of SSRs were positively correlated with the G+C content of transcripts. Among the different classes of SSR, the percentage of tetra-nucleotide SSRs were maximum in A. niger (36.7%) and A. oryzae (35.9%) whereas A. nidulans and A. terreus preferred tri-nucleotide SSRs (38.2 and 42.1%) in whole genome sequences. In transcripts, tri-nucleotide SSRs were the most abundant whereas di-nucleotide SSRs were the least favored. Motif conservation study among the transcripts revealed conservation of only 27% motif within Aspergillus species. Furthermore, a similar relationship among the Ascomycetes was obtained on the basis of motif conservation and conserved genes (rDNA). To analyze the diversity present within the Indian isolates of Aspergillus, primers were successfully designed for 692 motifs in A. niger and A. terreus of which 20 were selected for diversity analysis. Among all the markers amplified, 10 markers (83.3%) were polymorphic, whereas remaining two markers (16.6%) were monomorphic. Ten polymorphic markers acquired in this investigation showed the utility of recently created SSR markers in the assessment of genetic diversity among various isolates of Aspergillus.

Functional Mechanisms of Microsatellite DNA in Eukaryotic Genomes

Microsatellite repeat DNA is best known for its length mutability, which is implicated in several neurological diseases and cancers, and often exploited as a genetic marker. Less well-known is the body of work exploring the widespread and surprisingly diverse functional roles of microsatellites. Recently, emerging evidence includes the finding that normal microsatellite polymorphism contributes substantially to the heritability of human gene expression on a genome-wide scale, calling attention to the task of elucidating the mechanisms involved. At present, these are underexplored, but several themes have emerged. I review evidence demonstrating roles for microsatellites in modulation of transcription factor binding, spacing between promoter elements, enhancers, cytosine methylation, alternative splicing, mRNA stability, selection of transcription start and termination sites, unusual structural conformations, nucleosome positioning and modification, higher order chromatin structure, noncoding RNA, and meiotic recombination hot spots.