PCR amplification of repetitive DNA: a limitation to genome editing technologies and many other applications

Genetic therapies and potential therapeutic applications of CRISPR activators in the eye

Conventional gene therapy involving supplementation only treats loss-of-function diseases and is limited by viral packaging sizes, precluding therapy of large genes. The discovery of CRISPR/Cas has led to a paradigm shift in the field of genetic therapy, with the promise of precise gene editing, thus broadening the range of diseases that can be treated. The initial uses of CRISPR/Cas have focused mainly on gene editing or silencing of abnormal variants via utilising Cas endonuclease to trigger the target cell endogenous non-homologous end joining. Subsequently, the technology has evolved to modify the Cas enzyme and even its guide RNA, leading to more efficient editing tools in the form of base and prime editing. Further advancements of this CRISPR/Cas technology itself have expanded its functional repertoire from targeted editing to programmable transactivation, shifting the therapeutic focus to precise endogenous gene activation or upregulation with the potential for epigenetic modifications. In vivo experiments using this platform have demonstrated the potential of CRISPR-activators (CRISPRa) to treat various loss-of-function diseases, as well as in regenerative medicine, highlighting their versatility to overcome limitations associated with conventional strategies. This review summarises the molecular mechanisms of CRISPRa platforms, the current applications of this technology in vivo, and discusses potential solutions to translational hurdles for this therapy, with a focus on ophthalmic diseases.

The mitochondrial genome of Bottapotamon fukienense (Brachiura: Potamidae) is fragmented into two chromosomes

BACKGROUND

China is the hotspot of global freshwater crab diversity, but their wild populations are facing severe pressures associated with anthropogenic factors, necessitating the need to map their taxonomic and genetic diversity and design conservation policies.

RESULTS

Herein, we sequenced the mitochondrial genome of a Chinese freshwater crab species Bottapotamon fukienense, and found that it is fragmented into two chromosomes. We confirmed that fragmentation was not limited to a single specimen or population. Chromosome 1 comprised 15,111 base pairs (bp) and there were 26 genes and one pseudogene (pseudo-nad1) encoded on it. Chromosome 2 comprised 8,173 bp and there were 12 genes and two pseudogenes (pseudo-trnL2 and pseudo-rrnL) encoded on it. Combined, they comprise the largest mitogenome (23,284 bp) among the Potamidae. Bottapotamon was the only genus in the Potamidae dataset exhibiting rearrangements of protein-coding genes. Bottapotamon fukienense exhibited average rates of sequence evolution in the dataset and did not differ in selection pressures from the remaining Potamidae.

CONCLUSIONS

This is the first experimentally confirmed fragmentation of a mitogenome in crustaceans. While the mitogenome of B. fukienense exhibited multiple signs of elevated mitogenomic architecture evolution rates, including the exceptionally large size, duplicated genes, pseudogenisation, rearrangements of protein-coding genes, and fragmentation, there is no evidence that this is matched by elevated sequence evolutionary rates or changes in selection pressures.

A rapid and scalable approach to build synthetic repetitive hormone-responsive promoters

Advancement of DNA-synthesis technologies has greatly facilitated the development of synthetic biology tools. However, high-complexity DNA sequences containing tandems of short repeats are still notoriously difficult to produce synthetically, with commercial DNA synthesis companies usually rejecting orders that exceed specific sequence complexity thresholds. To overcome this limitation, we developed a simple, single-tube reaction method that enables the generation of DNA sequences containing multiple repetitive elements. Our strategy involves commercial synthesis and PCR amplification of padded sequences that contain the repeats of interest, along with random intervening sequence stuffers that include type IIS restriction enzyme sites. GoldenBraid molecular cloning technology is then employed to remove the stuffers, rejoin the repeats together in a predefined order, and subclone the tandem(s) in a vector using a single-tube digestion-ligation reaction. In our hands, this new approach is much simpler, more versatile and efficient than previously developed solutions to this problem. As a proof of concept, two different phytohormone-responsive, synthetic, repetitive proximal promoters were generated and tested in planta in the context of transcriptional reporters. Analysis of transgenic lines carrying the synthetic ethylene-responsive promoter 10x2EBS-S10 fused to the GUS reporter gene uncovered several developmentally regulated ethylene response maxima, indicating the utility of this reporter for monitoring the involvement of ethylene in a variety of physiologically relevant processes. These encouraging results suggest that this reporter system can be leveraged to investigate the ethylene response to biotic and abiotic factors with high spatial and temporal resolution.

Disruption of mitochondrial pyruvate oxidation in dorsal root ganglia drives persistent nociceptive sensitization and causes pervasive transcriptomic alterations

ABSTRACT

Metabolism is inextricably linked to every aspect of cellular function. In addition to energy production and biosynthesis, metabolism plays a crucial role in regulating signal transduction and gene expression. Altered metabolic states have been shown to maintain aberrant signaling and transcription, contributing to diseases like cancer, cardiovascular disease, and neurodegeneration. Metabolic gene polymorphisms and defects are also associated with chronic pain conditions, as are increased levels of nerve growth factor (NGF). However, the mechanisms by which NGF may modulate sensory neuron metabolism remain unclear. This study demonstrated that intraplantar NGF injection reprograms sensory neuron metabolism. Nerve growth factor suppressed mitochondrial pyruvate oxidation and enhanced lactate extrusion, requiring 24 hours to increase lactate dehydrogenase A and pyruvate dehydrogenase kinase 1 (PDHK1) expression. Inhibiting these metabolic enzymes reversed NGF-mediated effects. Remarkably, directly disrupting mitochondrial pyruvate oxidation induced severe, persistent allodynia, implicating this metabolic dysfunction in chronic pain. Nanopore long-read sequencing of poly(A) mRNA uncovered extensive transcriptomic changes upon metabolic disruption, including altered gene expression, splicing, and poly(A) tail lengths. By linking metabolic disturbance of dorsal root ganglia to transcriptome reprogramming, this study enhances our understanding of the mechanisms underlying persistent nociceptive sensitization. These findings imply that impaired mitochondrial pyruvate oxidation may drive chronic pain, possibly by impacting transcriptomic regulation. Exploring these metabolite-driven mechanisms further might reveal novel therapeutic targets for intractable pain.

AutoESDCas: A Web-Based Tool for the Whole-Workflow Editing Sequence Design for Microbial Genome Editing Based on the CRISPR/Cas System

Genome editing is the basis for the modification of engineered microbes. In the process of genome editing, the design of editing sequences, such as primers and sgRNA, is very important for the accurate positioning of editing sites and efficient sequence editing. The whole process of genome editing involves multiple rounds and types of editing sequence design, while the development of related whole-workflow design tools for high-throughput experimental requirements lags. Here, we propose AutoESDCas, an online tool for the end-to-end editing sequence design for microbial genome editing based on the CRISPR/Cas system. This tool facilitates all types of genetic manipulation covering diverse experimental requirements and design scenarios, enables biologists to quickly and efficiently obtain all editing sequences needed for the entire genome editing process, and empowers high-throughput strain modification. Notably, with its off-target risk assessment function for editing sequences, the usability of the design results is significantly improved. AutoESDCas is freely available at https://autoesdcas.biodesign.ac.cn/with the source code at https://github.com/tibbdc/AutoESDCas/.

Combining CRISPR-Cas-mediated terminal resolution with a novel genetic workflow to achieve high-diversity adenoviral libraries

While recombinant adenoviruses (rAds) are widely used in both laboratory and medical gene transfer, library-based applications using this vector platform are not readily available. Recently, we developed a new method, the CRISPR-Cas9 mediated in vivo terminal resolution aiding high-efficiency rescue of rAds from recombinant DNA. Here we report on a genetic workflow that allows construction of bacterial artificial chromosome-based rAd libraries reconstituted using highly efficient terminal resolution. We utilized frequent, pre-existing genomic sequences to allow the insertion of a selection marker, complementing two selected target sites into novel endonuclease recognition sites. In the second step, this selection marker is replaced with a transgene or mutation of interest via Gibson assembly. Our approach does not cause unwanted genomic off-target mutations while providing substantial flexibility for the site and nature of the genetic modification. This new genetic workflow, which we termed half site-directed fragment replacement (HFR) allows the introduction of more than 106 unique modifications into rAd encoding BACs using laboratory scale methodology. To demonstrate the power of HFR, we rescued barcoded viral vector libraries yielding a diversity of approximately 2.5 × 104 unique rAds per cm2 of transfected cell culture.

Applications of Synthetic Pentatricopeptide Repeat Proteins

RNA-binding proteins play integral roles in the regulation of essential processes in cells and as such are attractive targets for engineering to manipulate gene expression at the RNA level. Expression of transcripts in chloroplasts and mitochondria is heavily regulated by pentatricopeptide repeat (PPR) proteins. The diverse roles of PPR proteins and their naturally modular architecture make them ideal candidates for engineering. Synthetic PPR proteins are showing great potential to become valuable tools for controlling the expression of plastid and mitochondrial transcripts. In this review, by 'synthetic', we mean both rationally modified natural PPR proteins and completely novel proteins designed using the principles learned from their natural counterparts. We focus on the many different applications of synthetic PPR proteins, covering both their use in basic research to learn more about protein-RNA interactions and their use to achieve specific outcomes in RNA processing and the control of gene expression. We describe the challenges associated with the design, construction and deployment of synthetic PPR proteins and provide perspectives on how they might be assembled and used in future biotechnology applications.

High-throughput DNA synthesis for data storage

With the explosion of digital world, the dramatically increasing data volume is expected to reach 175 ZB (1 ZB = 1012 GB) in 2025. Storing such huge global data would consume tons of resources. Fortunately, it has been found that the deoxyribonucleic acid (DNA) molecule is the most compact and durable information storage medium in the world so far. Its high coding density and long-term preservation properties make itself one of the best data storage carriers for the future. High-throughput DNA synthesis is a key technology for "DNA data storage", which encodes binary data stream (0/1) into quaternary long DNA sequences consisting of four bases (A/G/C/T). In this review, the workflow of DNA data storage and the basic methods of artificial DNA synthesis technology are outlined first. Then, the technical characteristics of different synthesis methods and the state-of-the-art of representative commercial companies, with a primary focus on silicon chip microarray-based synthesis and novel enzymatic DNA synthesis are presented. Finally, the recent status of DNA storage and new opportunities for future development in the field of high-throughput, large-scale DNA synthesis technology are summarized.

Synthetic intrinsically disordered protein fusion tags that enhance protein solubility

We report the de novo design of small (<20 kDa) and highly soluble synthetic intrinsically disordered proteins (SynIDPs) that confer solubility to a fusion partner with minimal effect on the activity of the fused protein. To identify highly soluble SynIDPs, we create a pooled gene-library utilizing a one-pot gene synthesis technology to create a large library of repetitive genes that encode SynIDPs. We identify three small (<20 kDa) and highly soluble SynIDPs from this gene library that lack secondary structure and have high solvation. Recombinant fusion of these SynIDPs to three known inclusion body forming proteins rescue their soluble expression and do not impede the activity of the fusion partner, thereby eliminating the need for removal of the SynIDP tag. These findings highlight the utility of SynIDPs as solubility tags, as they promote the soluble expression of proteins in E. coli and are small, unstructured proteins that minimally interfere with the biological activity of the fused protein.

DeGenPrime provides robust primer design and optimization unlocking the biosphere

Motivation

Polymerase chain reaction (PCR) is the world's most important molecular diagnostic with applications ranging from medicine to ecology. PCR can fail because of poor primer design. The nearest-neighbor thermodynamic properties, picking conserved regions, and filtration via penalty of oligonucleotides form the basis for good primer design.

Results

DeGenPrime is a console-based high-quality PCR primer design tool that can utilize MSA formats and degenerate bases expanding the target range for a single primer set. Our software utilizes thermodynamic properties, filtration metrics, penalty scoring, and conserved region finding of any proposed primer. It has degeneracy, repeated k-mers, relative GC content, and temperature range filters. Minimal penalty scoring is included according to secondary structure self-dimerization metrics, GC clamping, tri- and tetra-loop hairpins, and internal repetition. We compared PrimerDesign-M, DegePrime, ConsensusPrimer, and DeGenPrime on acceptable primer yield. PrimerDesign-M, DegePrime, and ConsensusPrimer provided 0%, 11%, and 17% yield, respectively, for the alternative iron nitrogenase (anfD) gene target. DeGenPrime successfully identified quality primers within the conserved regions of the T4-like phage major capsid protein (g23), conserved regions of molybdenum-based nitrogenase (nif), and its alternatives vanadium (vnf) and iron (anf) nitrogenase. DeGenPrime provides a universal and scalable primer design tool for the entire tree of life.

Availability and implementation

DeGenPrime is written in C++ and distributed under a BSD-3-Clause license. The source code for DeGenPrime is freely available on www.github.com/raw-lab/degenprime.

Novel genotype-phenotype correlations, differential cerebellar allele-specific methylation, and a common origin of the (ATTTC)n insertion in spinocerebellar ataxia type 37

Spinocerebellar ataxia subtype 37 (SCA37) is a rare disease originally identified in ataxia patients from the Iberian Peninsula with a pure cerebellar syndrome. SCA37 patients carry a pathogenic intronic (ATTTC)n repeat insertion flanked by two polymorphic (ATTTT)n repeats in the Disabled-1 (DAB1) gene leading to cerebellar dysregulation. Herein, we determine the precise configuration of the pathogenic 5'(ATTTT)n-(ATTTC)n-3'(ATTTT)n SCA37 alleles by CRISPR-Cas9 and long-read nanopore sequencing, reveal their epigenomic signatures in SCA37 lymphocytes, fibroblasts, and cerebellar samples, and establish new molecular and clinical correlations. The 5'(ATTTT)n-(ATTTC)n-3'(ATTTT)n pathogenic allele configurations revealed repeat instability and differential methylation signatures. Disease age of onset negatively correlated with the (ATTTC)n, and positively correlated with the 3'(ATTTT)n. Geographic origin and gender significantly correlated with age of onset. Furthermore, significant predictive regression models were obtained by machine learning for age of onset and disease evolution by considering gender, the (ATTTC)n, the 3'(ATTTT)n, and seven CpG positions differentially methylated in SCA37 cerebellum. A common 964-kb genomic region spanning the (ATTTC)n insertion was identified in all SCA37 patients analysed from Portugal and Spain, evidencing a common origin of the SCA37 mutation in the Iberian Peninsula originating 859 years ago (95% CI 647-1378). In conclusion, we demonstrate an accurate determination of the size and configuration of the regulatory 5'(ATTTT)n-(ATTTC)n-3'(ATTTT)n repeat tract, avoiding PCR bias amplification using CRISPR/Cas9-enrichment and nanopore long-read sequencing, resulting relevant for accurate genetic diagnosis of SCA37. Moreover, we determine novel significant genotype-phenotype correlations in SCA37 and identify differential cerebellar allele-specific methylation signatures that may underlie DAB1 pathogenic dysregulation.

A high-performance cell-phone based polarized microscope for malaria diagnosis

We present a cell-phone based polarized microscope for diagnosing malaria through hemozoin recognition over a wide field-of-view (FOV) accompanied with decent image performance. The system is constructed based on attachment method using a lens assembly as objective, two mobile phones and two linear polarizers. A ~0.92 μm resolution across a FOV of ~3.27 mm × 3.27 mm with high imaging quality is realized, demonstrating an increased resolving power, four times improvement in FOV and better imaging quality over mobile-optical-polarization imaging device. Importantly, we also demonstrate it has capability of recognizing hemozoin within the sample for malaria diagnosis by imaging malaria-infected blood samples with similar sensitivity comparable to Leica microscopy. It is more compact, portable, and insensitive to alignment, making it highly suitable for malaria detection in a portable, easy to setup and use way in low-resource areas.

Novel mitochondrial genome rearrangements including duplications and extensive heteroplasmy could underlie temperature adaptations in Antarctic notothenioid fishes

Mitochondrial genomes are known for their compact size and conserved gene order, however, recent studies employing long-read sequencing technologies have revealed the presence of atypical mitogenomes in some species. In this study, we assembled and annotated the mitogenomes of five Antarctic notothenioids, including four icefishes (Champsocephalus gunnari, C. esox, Chaenocephalus aceratus, and Pseudochaenichthys georgianus) and the cold-specialized Trematomus borchgrevinki. Antarctic notothenioids are known to harbor some rearrangements in their mt genomes, however the extensive duplications in icefishes observed in our study have never been reported before. In the icefishes, we observed duplications of the protein coding gene ND6, two transfer RNAs, and the control region with different copy number variants present within the same individuals and with some ND6 duplications appearing to follow the canonical Duplication-Degeneration-Complementation (DDC) model in C. esox and C. gunnari. In addition, using long-read sequencing and k-mer analysis, we were able to detect extensive heteroplasmy in C. aceratus and C. esox. We also observed a large inversion in the mitogenome of T. borchgrevinki, along with the presence of tandem repeats in its control region. This study is the first in using long-read sequencing to assemble and identify structural variants and heteroplasmy in notothenioid mitogenomes and signifies the importance of long-reads in resolving complex mitochondrial architectures. Identification of such wide-ranging structural variants in the mitogenomes of these fishes could provide insight into the genetic basis of the atypical icefish mitochondrial physiology and more generally may provide insights about their potential role in cold adaptation.

Sexing of cattle embryos using RNA-sequencing data or polymerase chain reaction based on a complete sequence of cattle chromosome Y

When necessary, RNA-sequencing data or polymerase chain reaction (PCR) assays can be used to determine the presence of the chromosome Y (ChrY) in samples. This information allows for biological variation due to sexual dimorphism to be studied. A prime example is when researchers conduct RNA-sequencing of single embryos, or conceptuses, prior to the development of gonads. A recent publication of a complete sequence of the ChrY has removed limitations for the development of these procedures in cattle, otherwise imposed by the absence of a ChrY in the reference genome. Using the sequence of the cattle ChrY and transcriptome data, we conducted a systematic search for genes in the ChrY that are exclusively expressed in male tissues. The genes ENSBIXG00000029763, ENSBIXG00000029774, ENSBIXG00000029788, and ENSBIXG00000029892 were consistently expressed across male tissues and lowly expressed or absent in female samples. We observed that the cumulative values of counts per million were 2688-fold greater in males than the equivalent values in female samples. Thus, we deemed these genes suitable for the sexing of samples using RNA-sequencing data. We successfully used this set of genes to infer the sex of 22 cattle blastocysts (8 females and 14 males). Additionally, the completed sequence of the cattle ChrY has segments in the male-specific region that are not repeated. We designed a pair of oligonucleotides that targets one of these non-repeated regions in the male-specific sequence of the ChrY. Using this pair of oligonucleotides, in a multiplexed PCR assay with oligonucleotides that anneal to an autosome chromosome, we accurately identified the sex of cattle blastocysts. We developed efficient procedures for the sexing of samples in cattle using either transcriptome data or their DNA. The procedures using RNA-sequencing will greatly benefit researchers who work with samples limited in cell numbers which are only sufficient to produce transcriptome data. The oligonucleotides used for the accurate sexing of samples using PCR are transferable to other cattle tissue samples.

Multivalent forms of the ribonuclease H1 hybrid binding domain are high-affinity binders of RNA-DNA hybrids

The hybrid binding domain (HBD) is a conserved fold present in ribonucleases H1 that selectively recognizes RNA-DNA hybrids, which are structures present in cellular R-loops and participate in diverse biological processes. We engineered multivalent HBD proteins to create high-affinity hybrid binders. Using EMSA- and SPR-based analyses, we showed that the triple-HBD protein exhibits a ~ 22 000-fold increase in hybrid affinity (K_D 370 pm) relative to the single HBD (K_D 8.29 μm), with the length and sequence of the linkers enabling optimal function. These findings provide a framework for testing models that correlate multivalency and affinity to understand how multivalent proteins function and also can serve to guide applications that exploit multivalency as a strategy to enhance binding affinity.

LPA disruption with AAV-CRISPR potently lowers plasma apo(a) in transgenic mouse model: A proof-of-concept study

Lipoprotein(a) (Lp(a)) represents a unique subclass of circulating lipoprotein particles and consists of an apolipoprotein(a) (apo(a)) molecule covalently bound to apolipoprotein B-100. The metabolism of Lp(a) particles is distinct from that of low-density lipoprotein (LDL) cholesterol, and currently approved lipid-lowering drugs do not provide substantial reductions in Lp(a), a causal risk factor for cardiovascular disease. Somatic genome editing has the potential to be a one-time therapy for individuals with extremely high Lp(a). We generated an LPA transgenic mouse model expressing apo(a) of physiologically relevant size. Adeno-associated virus (AAV) vector delivery of CRISPR-Cas9 was used to disrupt the LPA transgene in the liver. AAV-CRISPR nearly completely eliminated apo(a) from the circulation within a week. We performed genome-wide off-target assays to determine the specificity of CRISPR-Cas9 editing within the context of the human genome. Interestingly, we identified intrachromosomal rearrangements within the LPA cDNA in the transgenic mice as well as in the LPA gene in HEK293T cells, due to the repetitive sequences within LPA itself and neighboring pseudogenes. This proof-of-concept study establishes the feasibility of using CRISPR-Cas9 to disrupt LPA in vivo, and highlights the importance of examining the diverse consequences of CRISPR cutting within repetitive loci and in the genome globally.

A comparative analysis of mitochondrial ORFs provides new insights on expansion of mitochondrial genome size in Arcidae

BACKGROUND

Arcidae, comprising about 260 species of ark shells, is an ecologically and economically important lineage of bivalve mollusks. Interestingly, mitochondrial genomes of several Arcidae species are 2-3 times larger than those of most bilaterians, and are among the largest bilaterian mitochondrial genomes reported to date. The large mitochondrial genome size is mainly due to expansion of unassigned regions (regions that are functionally unassigned). Previous work on unassigned regions of Arcidae mtDNA genomes has focused on nucleotide-level analyses to observe sequence characteristics, however the origin of expansion remains unclear.

RESULTS

We assembled six new mitogenomes and sequenced six transcriptomes of Scapharca broughtonii to identify conserved functional ORFs that are transcribed in unassigned regions. Sixteen lineage-specific ORFs with different copy numbers were identified from seven Arcidae species, and 11 of 16 ORFs were expressed and likely biologically active. Unassigned regions of 32 Arcidae mitogenomes were compared to verify the presence of these novel mitochondrial ORFs and their distribution. Strikingly, multiple structural analyses and functional prediction suggested that these additional mtDNA-encoded proteins have potential functional significance. In addition, our results also revealed that the ORFs have a strong connection to the expansion of Arcidae mitochondrial genomes and their large-scale duplication play an important role in multiple expansion events. We discussed the possible origin of ORFs and hypothesized that these ORFs may originate from duplication of mitochondrial genes.

CONCLUSIONS

The presence of lineage-specific mitochondrial ORFs with transcriptional activity and potential functional significance supports novel features for Arcidae mitochondrial genomes. Given our observation and analyses, these ORFs may be products of mitochondrial gene duplication. These findings shed light on the origin and function of novel mitochondrial genes in bivalves and provide new insights into evolution of mitochondrial genome size in metazoans.

Characterization of full-length CNBP expanded alleles in myotonic dystrophy type 2 patients by Cas9-mediated enrichment and nanopore sequencing

Myotonic dystrophy type 2 (DM2) is caused by CCTG repeat expansions in the CNBP gene, comprising 75 to >11,000 units and featuring extensive mosaicism, making it challenging to sequence fully expanded alleles. To overcome these limitations, we used PCR-free Cas9-mediated nanopore sequencing to characterize CNBP repeat expansions at the single-nucleotide level in nine DM2 patients. The length of normal and expanded alleles can be assessed precisely using this strategy, agreeing with traditional methods, and revealing the degree of mosaicism. We also sequenced an entire ~50 kbp expansion, which has not been achieved previously for DM2 or any other repeat-expansion disorders. Our approach precisely counted the repeats and identified the repeat pattern for both short interrupted and uninterrupted alleles. Interestingly, in the expanded alleles, only two DM2 samples featured the expected pure CCTG repeat pattern, while the other seven presented also TCTG blocks at the 3′ end, which have not been reported before in DM2 patients, but confirmed hereby with orthogonal methods. The demonstrated approach simultaneously determines repeat length, structure/motif, and the extent of somatic mosaicism, promising to improve the molecular diagnosis of DM2 and achieve more accurate genotype–phenotype correlations for the better stratification of DM2 patients in clinical trials.

Target residence of Cas9-sgRNA influences DNA double-strand break repair pathway choices in CRISPR/Cas9 genome editing

BACKGROUND

Due to post-cleavage residence of the Cas9-sgRNA complex at its target, Cas9-induced DNA double-strand breaks (DSBs) have to be exposed to engage DSB repair pathways. Target interaction of Cas9-sgRNA determines its target binding affinity and modulates its post-cleavage target residence duration and exposure of Cas9-induced DSBs. This exposure, via different mechanisms, may initiate variable DNA damage responses, influencing DSB repair pathway choices and contributing to mutational heterogeneity in genome editing. However, this regulation of DSB repair pathway choices is poorly understood.

RESULTS

In repair of Cas9-induced DSBs, repair pathway choices vary widely at different target sites and classical nonhomologous end joining (c-NHEJ) is not even engaged at some sites. In mouse embryonic stem cells, weakening the target interaction of Cas9-sgRNA promotes bias towards c-NHEJ and increases target dissociation and reduces target residence of Cas9-sgRNAs in vitro. As an important strategy for enhancing homology-directed repair, inactivation of c-NHEJ aggravates off-target activities of Cas9-sgRNA due to its weak interaction with off-target sites. By dislodging Cas9-sgRNA from its cleaved targets, DNA replication alters DSB end configurations and suppresses c-NHEJ in favor of other repair pathways, whereas transcription has little effect on c-NHEJ engagement. Dissociation of Cas9-sgRNA from its cleaved target by DNA replication may generate three-ended DSBs, resulting in palindromic fusion of sister chromatids, a potential source for CRISPR/Cas9-induced on-target chromosomal rearrangements.

CONCLUSIONS

Target residence of Cas9-sgRNA modulates DSB repair pathway choices likely through varying dissociation of Cas9-sgRNA from cleaved DNA, thus widening on-target and off-target mutational spectra in CRISPR/Cas9 genome editing.

Characterization of the mitochondrial genomes of Bradysia hygida, Phytosciara flavipes and Trichosia splendens (Diptera: Sciaridae) and novel insights on the control region of sciarid mitogenomes

Sciarids, also called "fungus gnats" are small, almost entirely dark-coloured insects. Sciarid larvae feed on different substrates and can infest agricultural crops and mushroom nurseries, causing economic losses. Of the 2174 Diptera mitogenome sequences currently available in GenBank, only eight are from the Sciaridae family, none of which are complete circular molecules. Here we describe the mitogenome sequences of three sciarid species: Phytosciara flavipes, Trichosia splendens and Bradysia hygida and provide novel insights on the control region of sciarid mitogenomes. The assembled mitogenomes range from 16,062 bp in P. flavipes to 17,095 bp in B. hygida. All 13 protein coding genes, 22 tRNAs and 2 rRNAs characteristic of insect mitogenomes were identified, but the sequence of the control region could not be determined. Experimental results suggest that the B. hygida control region is about 21 kb long resulting in a 37 kb long mitogenome which constitutes the largest insect mitochondrial genome described so far. Phylogenetic analysis using all Bibionomorpha mitogenome sequences available in GenBank strongly supports the Sciaridae monophyly and led to the identification of species and subfamily specific gene rearrangements. Our study extends the knowledge of this large and diverse insect family that includes agricultural pest species.

Population Scale Analysis of Centromeric Satellite DNA Reveals Highly Dynamic Evolutionary Patterns and Genomic Organization in Long-Tailed and Rhesus Macaques

Centromeric satellite DNA (cen-satDNA) consists of highly divergent repeat monomers, each approximately 171 base pairs in length. Here, we investigated the genetic diversity in the centromeric region of two primate species: long-tailed (Macaca fascicularis) and rhesus (Macaca mulatta) macaques. Fluorescence in situ hybridization and bioinformatic analysis showed the chromosome-specific organization and dynamic nature of cen-satDNAsequences, and their substantial diversity, with distinct subfamilies across macaque populations, suggesting increased turnovers. Comparative genomics identified high level polymorphisms spanning a 120 bp deletion region and a remarkable interspecific variability in cen-satDNA size and structure. Population structure analysis detected admixture patterns within populations, indicating their high divergence and rapid evolution. However, differences in cen-satDNA profiles appear to not be involved in hybrid incompatibility between the two species. Our study provides a genomic landscape of centromeric repeats in wild macaques and opens new avenues for exploring their impact on the adaptive evolution and speciation of primates.

The Utility of Repetitive Cell-Free DNA in Cancer Liquid Biopsies

Liquid biopsy is a broad term that refers to the testing of body fluids for biomarkers that correlate with a pathological condition. While a variety of body-fluid components (e.g., circulating tumor cells, extracellular vesicles, RNA, proteins, and metabolites) are studied as potential liquid biopsy biomarkers, cell-free DNA (cfDNA) has attracted the most attention in recent years. The total cfDNA population in a typical biospecimen represents an immensely rich source of biological and pathological information and has demonstrated significant potential as a versatile biomarker in oncology, non-invasive prenatal testing, and transplant monitoring. As a significant portion of cfDNA is composed of repeat DNA sequences and some families (e.g., pericentric satellites) were recently shown to be overrepresented in cfDNA populations vs their genomic abundance, it holds great potential for developing liquid biopsy-based biomarkers for the early detection and management of patients with cancer. By outlining research that employed cell-free repeat DNA sequences, in particular the ALU and LINE-1 elements, we highlight the clinical potential of the repeat-element content of cfDNA as an underappreciated marker in the cancer liquid biopsy repertoire.

Detection of Peripheral Malarial Parasites in Blood Smears Using Deep Learning Models

Due to the plasmodium parasite, malaria is transmitted mostly through red blood cells. Manually counting blood cells is extremely time consuming and tedious. In a recommendation for the advanced technology stage and analysis of malarial disease, the performance of the XG-Boost, SVM, and neural networks is compared. In comparison to machine learning models, convolutional neural networks provide reliable results when analyzing and recognizing the same datasets. To reduce discrepancies and improve robustness and generalization, we developed a model that analyzes blood samples to determine whether the cells are parasitized or not. Experiments were conducted on 13,750 parasitized and 13,750 parasitic samples. Support vector machines achieved 94% accuracy, XG-Boost models achieved 90% accuracy, and neural networks achieved 80% accuracy. Among these three models, the support vector machine was the most accurate at distinguishing parasitized cells from uninfected ones. An accuracy rate of 97% was achieved by the convolution neural network in recognizing the samples. The deep learning model is useful for decision making because of its better accuracy.

Unamplified, Long-Read Metagenomic Sequencing Approach to Close Endosymbiont Genomes of Low-Biomass Insect Populations

With the current advancements in DNA sequencing technology, the limiting factor in long-read metagenomic assemblies is now the quantity and quality of input DNA. Although these requirements can be met through the use of axenic bacterial cultures or large amounts of biological material, insect systems that contain unculturable bacteria or that contain a low amount of available DNA cannot fully utilize the benefits of third-generation sequencing. The citrus greening disease insect vector Diaphorina citri is an example that exhibits both of these limitations. Although endosymbiont genomes have mostly been closed after the short-read sequencing of amplified template DNA, creating de novo long-read genomes from the unamplified DNA of an insect population may benefit communities using bioinformatics to study insect pathosystems. Here all four genomes of the infected D. citri microbiome were sequenced to closure using unamplified template DNA and two long-read sequencing technologies. Avoiding amplification bias and using long reads to assemble the bacterial genomes allowed for the circularization of the Wolbachia endosymbiont of Diaphorina citri for the first time and paralleled the annotation context of all four reference genomes without utilizing a traditional hybrid assembly. The strategies detailed here are suitable for the sequencing of other insect systems for which the input DNA, time, and cost are an issue.

Primer Designing for Amplifying an AT-Rich Promoter from Arabidopsis thaliana

The aim of the present study is to optimize the PCR conditions required to amplify the promoter sequence of an amino acid transporter having an AT-rich base composition with a high number of tandem repeats. The present study also covers the key parameters that need to be kept in mind while designing primers. Results show that successful can be achieved by performing a 2-step PCR reaction at a lower extension temperature of 65 ̊C for an increased extension period of 1.5 min/kb, with MgCl2 concentration ranging from 2.5 to 3.0mM. The results also suggest that the DNA concentration of around 25-30 ng/µl was essential to achieve this amplification.

Advancing genomic technologies and clinical awareness accelerates discovery of disease-associated tandem repeat sequences

Expansions of gene-specific DNA tandem repeats (TRs), first described in 1991 as a disease-causing mutation in humans, are now known to cause >60 phenotypes, not just disease, and not only in humans. TRs are a common form of genetic variation with biological consequences, observed, so far, in humans, dogs, plants, oysters, and yeast. Repeat diseases show atypical clinical features, genetic anticipation, and multiple and partially penetrant phenotypes among family members. Discovery of disease-causing repeat expansion loci accelerated through technological advances in DNA sequencing and computational analyses. Between 2019 and 2021, 17 new disease-causing TR expansions were reported, totaling 63 TR loci (>69 diseases), with a likelihood of more discoveries, and in more organisms. Recent and historical lessons reveal that properly assessed clinical presentations, coupled with genetic and biological awareness, can guide discovery of disease-causing unstable TRs. We highlight critical but underrecognized aspects of TR mutations. Repeat motifs may not be present in current reference genomes but will be in forthcoming gapless long-read references. Repeat motif size can be a single nucleotide to kilobases/unit. At a given locus, repeat motif sequence purity can vary with consequence. Pathogenic repeats can be "insertions" within nonpathogenic TRs. Expansions, contractions, and somatic length variations of TRs can have clinical/biological consequences. TR instabilities occur in humans and other organisms. TRs can be epigenetically modified and/or chromosomal fragile sites. We discuss the expanding field of disease-associated TR instabilities, highlighting prospects, clinical and genetic clues, tools, and challenges for further discoveries of disease-causing TR instabilities and understanding their biological and pathological impacts-a vista that is about to expand.

A simple and sensitive detection of the binding ligands by using the receptor aggregation and NMR spectroscopy: a test case of the maltose binding protein

Protein-ligand interaction is one of the highlights of molecular recognition. The most popular application of this type of interaction is drug development which requires a high throughput screening of a ligand that binds to the target protein. Our goal was to find a binding ligand with a simple detection, and once this type of ligand was found, other methods could then be used to measure the detailed kinetic or thermodynamic parameters. We started with the idea that the ligand NMR signal would disappear if it was bound to the non-tumbling mass. In order to create the non-tumbling mass, we tried the aggregates of a target protein, which was fused to the elastin-like polypeptide. We chose the maltose binding proteinas a test case, and we tried it with several sugars, which included maltose, glucose, sucrose, lactose, galactose, maltotriose, and β-cyclodextrin. The maltose signal in the H-1 NMR spectrum disappeared completely as hoped around the protein to ligand ratio of 1:3 at 298 K where the proteins aggregated. The protein signals also disappeared upon aggregation except for the fast-moving part, which resulted in a cleaner background than the monomeric form. Since we only needed to look for a disappearing signal amongst those from the mixture, it should be useful in high throughput screening. Other types of sugars except for the maltotriose and β-cyclodextrin, which are siblings of the maltose, did not seem to bind at all. We believe that our system would be especially more effective when dealing with a smaller target protein, so both the protein and the bound ligand would lose their signals only when the aggregates formed. We hope that our proposed method would contribute to accelerating the development of the potent drug candidates by simultaneously identifying several binders directly from a mixture.

SCRAMBLER: A Tool for De Novo CRISPR Array Reconstruction and Its Application for Analysis of the Structure of Prokaryotic Populations

CRISPR arrays are prokaryotic genomic loci consisting of repeat sequences alternating with unique spacers acquired from foreign nucleic acids. As one of the fastest-evolving parts of the genome, CRISPR arrays can be used to differentiate closely related prokaryotic lineages and track individual strains in prokaryotic communities. However, the assembly of full-length CRISPR arrays sequences remains a problem. Here, we developed SCRAMBLER, a tool that includes several pipelines for assembling CRISPR arrays from high-throughput short-read sequencing data. We assessed its performance with model data sets (Escherichia coli strains containing different CRISPR arrays and imitating prokaryotic communities of different complexities) and intestinal microbiomes of extant and extinct pachyderms. Evaluation of SCRAMBLER's performance using model data sets demonstrated its ability to assemble CRISPR arrays correctly from reads containing pairs of spacers, yielding a precision rate of >80% and a recall rate of 60-85% when checked against ground-truth data. Likewise, SCRAMBLER successfully assembled CRISPR arrays from the environmental samples, as attested by their matching with database entries. SCRAMBLER, an open-source software (github.com/biolab-tools/SCRAMBLER), can facilitate analysis of the composition and dynamics of CRISPR arrays in complex communities.

Application of PCR-HRM method for microsatellite polymorphism genotyping in the LDHA gene of pigeons (Columba livia)

High-resolution melting (HRM) is a post-PCR method that allows to discriminate genotypes based on fluorescence changes during the melting phase. HRM is used to detect mutations or polymorphisms (e.g. microsatellites, SNPs, indels). Here, the (TTTAT)_3-5 microsatellite polymorphism within intron 6 of the LDHA gene in pigeons was analysed using the HRM method. Individuals (123 homing pigeons) were genotyped using conventional PCR. Birds were classified into groups based on genotype type and the results were tested by qPCR-HRM and verified using sequencing. Based on the evaluated protocol, five genotypes were identified that vary in the number of TTTAT repeat units (3/3, 4/4, 3/4, 4/5, and 5/5). Sequencing have confirmed the results obtained with qPCR-HRM and verified that HRM is a suitable method for identification of three-allele microsatellite polymorphisms. It can be concluded that the high-resolution melting (HRM) method can be effectively used for rapid (one-step) discrimination of the (TTTAT)_3-5 microsatellite polymorphism in the pigeon’s LDHA gene.

A recombineering pipeline to clone large and complex genes in Chlamydomonas

The ability to clone genes has greatly advanced cell and molecular biology research, enabling researchers to generate fluorescent protein fusions for localization and confirm genetic causation by mutant complementation. Most gene cloning is polymerase chain reaction (PCR)�or DNA synthesis-dependent, which can become costly and technically challenging as genes increase in size, particularly if they contain complex regions. This has been a long-standing challenge for the Chlamydomonas reinhardtii research community, as this alga has a high percentage of genes containing complex sequence structures. Here we overcame these challenges by developing a recombineering pipeline for the rapid parallel cloning of genes from a Chlamydomonas bacterial artificial chromosome collection. To generate fluorescent protein fusions for localization, we applied the pipeline at both batch and high-throughput scales to 203 genes related to the Chlamydomonas CO2 concentrating mechanism (CCM), with an overall cloning success rate of 77%. Cloning success was independent of gene size and complexity, with cloned genes as large as 23 kb. Localization of a subset of CCM targets confirmed previous mass spectrometry data, identified new pyrenoid components, and enabled complementation of mutants. We provide vectors and detailed protocols to facilitate easy adoption of this technology, which we envision will open up new possibilities in algal and plant research.

An ERF121 transcription factor from Brassica oleracea is a target for the conserved TAL-effectors from different Xanthomonas campestris pv. campestris strains

Transcription activator-like effectors (TALEs), which induce the expression of specific plant genes to promote infection, are the main pathogenic determinants of various Xanthomonas bacteria. However, investigation of TALEs from Xanthomonas campestris pv. campestris, which causes black rot disease of crucifers, received little attention. In this study, we used PCR-based amplification followed by SMRT amplicon sequencing to identify TALE genes in several X. campestris pv. campestris strains. Computational prediction in conjunction with quantitative reverse transcription PCR analysis was used to find their targets in the Brassica oleracea genome. Transcription factor ERF121, from the AP2/ERF family, was identified as target gene for the conserved TALEs from multiple X. campestris pv. campestris strains. Several members of this family from diverse plants were previously identified as targets of TALEs from different Xanthomonas species. We propose that TALE-dependent activation of AP2/ERF transcription factors promotes susceptibility to Xanthomonas through the misregulation of plant defence pathways.

Nanopore Sequencing Resolves Elusive Long Tandem-Repeat Regions in Mitochondrial Genomes

Long non-coding, tandem-repetitive regions in mitochondrial (mt) genomes of many metazoans have been notoriously difficult to characterise accurately using conventional sequencing methods. Here, we show how the use of a third-generation (long-read) sequencing and informatic approach can overcome this problem. We employed Oxford Nanopore technology to sequence genomic DNAs from a pool of adult worms of the carcinogenic parasite, Schistosoma haematobium, and used an informatic workflow to define the complete mt non-coding region(s). Using long-read data of high coverage, we defined six dominant mt genomes of 33.4 kb to 22.6 kb. Although no variation was detected in the order or lengths of the protein-coding genes, there was marked length (18.5 kb to 7.6 kb) and structural variation in the non-coding region, raising questions about the evolution and function of what might be a control region that regulates mt transcription and/or replication. The discovery here of the largest tandem-repetitive, non-coding region (18.5 kb) in a metazoan organism also raises a question about the completeness of some of the mt genomes of animals reported to date, and stimulates further explorations using a Nanopore-informatic workflow.

Transcript Isoform-Specific Estimation of Poly(A) Tail Length by Nanopore Sequencing of Native RNA

The poly(A) tail is a homopolymeric stretch of adenosine at the 3'-end of mature RNA transcripts and its length plays an important role in nuclear export, stability, and translational regulation of mRNA. Existing techniques for genome-wide estimation of poly(A) tail length are based on short-read sequencing. These methods are limited because they sequence a synthetic DNA copy of mRNA instead of the native transcripts. Furthermore, they can identify only a short segment of the transcript proximal to the poly(A) tail which makes it difficult to assign the measured poly(A) length uniquely to a single transcript isoform. With the introduction of native RNA sequencing by Oxford Nanopore Technologies, it is now possible to sequence full-length native RNA. A single long read contains both the transcript and the associated poly(A) tail, thereby making transcriptome-wide isoform-specific poly(A) tail length assessment feasible. We developed tailfindr-an R-based package for estimating poly(A) tail length from Oxford Nanopore sequencing data. In this chapter, we describe in detail the pipeline for transcript isoform-specific poly(A) tail profiling based on native RNA Nanopore sequencing-from library preparation to downstream data analysis with tailfindr.

The genomes of Mourilyan virus and Wēnzhōu shrimp virus 1 of prawns comprise 4 RNA segments

Reported here is the complete genome sequence of Mourilyan virus (MoV) that infects giant tiger (Penaeus monodon) and kuruma prawns (P. japonicas) in Australia. Its genome was determined using various PCR strategies based on the sequences of 3 randomly-amplified cDNA clones to its L and M RNA segments discovered in a library generated to determine the genome sequence of gill-associated ronivirus. The sequences of PCR products and clones obtained showed the MoV genome to comprise 4 ssRNA segments (L, M, S1 and S2), as confirmed by Northern blotting using RNA from naïve and MoV-infected prawns, and by Illumina sequence analysis of semi-purified MoV. BLASTn searches identified the MoV L, M and S1 RNA segments to be homologous to Wēnzhōu shrimp virus 1 (WzSV1) segments discovered recently in a P. monodon RNA-Seq library (SRR1745808). Mapping this read library to the MoV S2 RNA segment identified WzSV1 to also possess an equivalent segment. BLASTp searches identified the putative non-structural protein (NSs2; 393-394 aa) encoded in their S2 RNA segments to have no homologs in GenBank. Possibly due to NSs2 being encoded in a discrete RNA segment rather than in ambisense relative to the N protein as in the S RNA segments of other phenuiviruses, each of 6 MoV S1 RNA segment clones sequenced possessed a variable-length (≤ 645 nt) imperfect GA-repeat extending from the N protein stop codon to the more variable ∼90 nt segment terminal sequence. Read mapping of RNA-Seq library SRR1745808 showed the WzSV1 S1 RNA segment to possess a similar GA-repeat. However, paired-read variations hindered definitive assembly of a consensus sequence. All 4 MoV and WzSV1 RNA segments terminated with a 10 nt inverted repeat sequence (5'-ACACAAAGAC.) identical to the RNA segment termini of uukuviruses. Phylogenetic analyses of MoV/WzSV1 RNA-dependant RNA polymerase (L RNA), G1G2 precursor glycoprotein (M RNA) and nucleocapsid (N) protein (S1 RNA) sequences generally clustered them with as yet unassigned crustacean/diptera bunya-like viruses on branches positioned closely to others containing tick-transmitted phenuiviruses. As genome sequences of most phenuiviruses discovered recently have originated from meta-transcriptomics studies, the data presented here showing the MoV and WzSV1 genomes to comprise more than 3 RNA segments, like the plant tenuiviruses, suggests a need to investigate the genomes of these unassigned viruses more closely.

Unexpected variations in posttranscriptional gene silencing induced by differentially produced dsRNAs in tobacco cells

In plants, posttranscriptional gene silencing (PTGS) is induced by small RNAs (sRNAs) generated from various dsRNA precursors. To assess the impact of dsRNA origin, we compared downregulation of GFP expression triggered by inverted repeat (IR), antisense (AS) and unterminated sense (UT) transcripts transiently expressed from the estradiol-inducible promoter. The use of homogeneously responding tobacco BY-2 cell lines allowed monitoring the onset of silencing and its reversibility. In this system, IR induced the strongest and fastest silencing accompanied by dense DNA methylation. At low induction, silencing in individual cells was binary (either strong or missing), suggesting that a certain threshold sRNA level had to be exceeded. The AS variant specifically showed a deviated sRNA-strand ratio shifted in favor of antisense orientation. In AS lines and weakly induced IR lines, only the silencer DNA was methylated, but the same target GFP sequence was not, showing that DNA methylation accompanying PTGS was influenced both by the level and origin of sRNAs, and possibly also by the epigenetic state of the locus. UT silencing appeared to be the least effective and resembled classical sense PTGS. The best responding UT lines behaved relatively heterogeneously possibly due to complexly arranged T-DNA insertions. Unlike IR and AS variants that fully restored GFP expression upon removal of the inducer, only partial reactivation was observed in some UT lines. Our results pointed out several not yet described phenomena and differences between the long-known silencer variants that may direct further research and affect selection of proper silencer variants for specific applications.

Multicopy Targeted Integration for Accelerated Development of High-Producing Chinese Hamster Ovary Cells

The ever-growing biopharmaceutical industry relies on the production of recombinant therapeutic proteins in Chinese hamster ovary (CHO) cells. The traditional timelines of CHO cell line development can be significantly shortened by the use of targeted gene integration (TI). However, broad use of TI has been limited due to the low specific productivity (q_P) of TI-generated clones. Here, we show a 10-fold increase in the q_P of therapeutic glycoproteins in CHO cells through the development and optimization of a multicopy TI method. We used a recombinase-mediated cassette exchange (RMCE) platform to investigate the effect of gene copy number, 5' and 3' gene regulatory elements, and landing pad features on q_P. We evaluated the limitations of multicopy expression from a single genomic site as well as multiple genomic sites and found that a transcriptional bottleneck can appear with an increase in gene dosage. We created a dual-RMCE system for simultaneous multicopy TI in two genomic sites and generated isogenic high-producing clones with q_P of 12-14 pg/cell/day and product titer close to 1 g/L in fed-batch. Our study provides an extensive characterization of the multicopy TI method and elucidates the relationship between gene copy number and protein expression in mammalian cells. Moreover, it demonstrates that TI-generated CHO cells are capable of producing therapeutic proteins at levels that can support their industrial manufacture.

Unusual mtDNA Control Region Length Heteroplasmy in the COS-7 Cell Line

The COS-7 cell line is a workhorse of virology research. To expand this cell line’s utility and to enable studies on mitochondrial DNA (mtDNA) transcription and replication, we determined the complete nucleotide sequence of its mitochondrial genome by Sanger sequencing. In contrast to other available mtDNA sequences from Chlorocebus aethiops, the mtDNA of the COS-7 cell line was found to contain a variable number of perfect copies of a 108 bp unit tandemly repeated in the control region. We established that COS-7 cells are heteroplasmic with at least two variants being present: with four and five repeat units. The analysis of the mitochondrial genome sequences from other primates revealed that tandem repeats are absent from examined mtDNA control regions of humans and great apes, but appear in lower primates, where they are present in a homoplasmic state. To our knowledge, this is the first report of mtDNA length heteroplasmy in primates.

Analysis of the reiteration regions (R1 to R5) of varicella-zoster virus

The varicella-zoster virus (VZV) genome, comprises both unique and repeated regions. The genome also includes reiteration regions, designated R1 to R5, which are tandemly repeating sequences termed elements. These regions represent an understudied feature of the VZV genome. The R4 region is duplicated, with one copy in the internal repeat short (IRs) which we designated R4A and a second copy in the terminal repeat short (TRs) termed R4B. We developed primers to amplify and Sanger sequence these regions, including independent amplification of both R4 regions. Reiteration regions from >80 cases of PCR-confirmed shingles were sequenced and analyzed. Complete genome sequences for the remaining portions of these viruses were determined using Illumina MiSeq. We identified 28 elements not previously reported, including at least one element for each R region. Length heterogeneity was substantial in R3, R4A and R4B. Length heterogeneity between the two copies of R4 was common.

Nucleic acid detection aboard the International Space Station by colorimetric loop-mediated isothermal amplification (LAMP)

Human spaceflight endeavors present an opportunity to expand our presence beyond Earth. To this end, it is crucial to understand and diagnose effects of long‐term space travel on the human body. Developing tools for targeted, on‐site detection of specific DNA sequences will allow us to establish research and diagnostics platforms that will benefit space programs. We describe a simple DNA diagnostic method that utilizes colorimetric loop‐mediated isothermal amplification (LAMP) to enable detection of a repetitive telomeric DNA sequence in as little as 30 minutes. A proof of concept assay for this method was carried out using existing hardware on the International Space Station and the results were read instantly by an astronaut through a simple color change of the reaction mixture. LAMP offers a novel platform for on‐orbit DNA‐based diagnostics that can be deployed on the International Space Station and to the broader benefit of space programs.

Mitochondrial genome characterization of the family Trigonidiidae (Orthoptera) reveals novel structural features and nad1 transcript ends

The Trigonidiidae, a family of crickets, comprises 981 valid species with only one mitochondrial genome (mitogenome) sequenced to date. To explore mitogenome features of Trigonidiidae, six mitogenomes from its two subfamilies (Nemobiinae and Trigonidiinae) were determined. Two types of gene rearrangements involving a trnN-trnS1-trnE inversion and a trnV shuffling were shared by Trigonidiidae. A long intergenic spacer was observed between trnQ and trnM in Trigonidiinae (210-369 bp) and Nemobiinae (80-216 bp), which was capable of forming extensive stem-loop secondary structures in Trigonidiinae but not in Nemobiinae. The anticodon of trnS1 was TCT in Trigonidiinae, rather than GCT in Nemobiinae and other related subfamilies. There was no overlap between nad4 and nad4l in Dianemobius, as opposed to a conserved 7-bp overlap commonly found in insects. Furthermore, combined comparative analysis and transcript verification revealed that nad1 transcripts ended with a U, corresponding to the T immediately preceding a conserved motif GAGAC in the superfamily Grylloidea, plus poly-A tails. The resultant UAA served as a stop codon for species lacking full stop codons upstream of the motif. Our findings gain novel understanding of mitogenome structural diversity and provide insight into accurate mitogenome annotation.

Tandem repeats lead to sequence assembly errors and impose multi-level challenges for genome and protein databases

The widespread occurrence of repetitive stretches of DNA in genomes of organisms across the tree of life imposes fundamental challenges for sequencing, genome assembly, and automated annotation of genes and proteins. This multi-level problem can lead to errors in genome and protein databases that are often not recognized or acknowledged. As a consequence, end users working with sequences with repetitive regions are faced with 'ready-to-use' deposited data whose trustworthiness is difficult to determine, let alone to quantify. Here, we provide a review of the problems associated with tandem repeat sequences that originate from different stages during the sequencing-assembly-annotation-deposition workflow, and that may proliferate in public database repositories affecting all downstream analyses. As a case study, we provide examples of the Atlantic cod genome, whose sequencing and assembly were hindered by a particularly high prevalence of tandem repeats. We complement this case study with examples from other species, where mis-annotations and sequencing errors have propagated into protein databases. With this review, we aim to raise the awareness level within the community of database users, and alert scientists working in the underlying workflow of database creation that the data they omit or improperly assemble may well contain important biological information valuable to others.

tailfindr: alignment-free poly(A) length measurement for Oxford Nanopore RNA and DNA sequencing

Polyadenylation at the 3'-end is a major regulator of messenger RNA and its length is known to affect nuclear export, stability, and translation, among others. Only recently have strategies emerged that allow for genome-wide poly(A) length assessment. These methods identify genes connected to poly(A) tail measurements indirectly by short-read alignment to genetic 3'-ends. Concurrently, Oxford Nanopore Technologies (ONT) established full-length isoform-specific RNA sequencing containing the entire poly(A) tail. However, assessing poly(A) length through base-calling has so far not been possible due to the inability to resolve long homopolymeric stretches in ONT sequencing. Here we present tailfindr, an R package to estimate poly(A) tail length on ONT long-read sequencing data. tailfindr operates on unaligned, base-called data. It measures poly(A) tail length from both native RNA and DNA sequencing, which makes poly(A) tail studies by full-length cDNA approaches possible for the first time. We assess tailfindr's performance across different poly(A) lengths, demonstrating that tailfindr is a versatile tool providing poly(A) tail estimates across a wide range of sequencing conditions.

Production of protein-based polymers in Pichia pastoris

Materials science and genetic engineering have joined forces over the last three decades in the development of so-called protein-based polymers. These are proteins, typically with repetitive amino acid sequences, that have such physical properties that they can be used as functional materials. Well-known natural examples are collagen, silk, and elastin, but also artificial sequences have been devised. These proteins can be produced in a suitable host via recombinant DNA technology, and it is this inherent control over monomer sequence and molecular size that renders this class of polymers of particular interest to the fields of nanomaterials and biomedical research. Traditionally, Escherichia coli has been the main workhorse for the production of these polymers, but the methylotrophic yeast Pichia pastoris is finding increased use in view of the often high yields and potential bioprocessing benefits. We here provide an overview of protein-based polymers produced in P. pastoris. We summarize their physicochemical properties, briefly note possible applications, and detail their biosynthesis. Some challenges that may be faced when using P. pastoris for polymer production are identified: (i) low yields and poor process control in shake flask cultures; i.e., the need for bioreactors, (ii) proteolytic degradation, and (iii) self-assembly in vivo. Strategies to overcome these challenges are discussed, which we anticipate will be of interest also to readers involved in protein expression in P. pastoris in general.

CRISPR/Cas9-mediated knock-in of an optimized TetO repeat for live cell imaging of endogenous loci

Nuclear organization has an important role in determining genome function; however, it is not clear how spatiotemporal organization of the genome relates to functionality. To elucidate this relationship, a method for tracking any locus of interest is desirable. Recently clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) or transcription activator-like effectors were adapted for imaging endogenous loci; however, they are mostly limited to visualization of repetitive regions. Here, we report an efficient and scalable method named SHACKTeR (Short Homology and CRISPR/Cas9-mediated Knock-in of a TetO Repeat) for live cell imaging of specific chromosomal regions without the need for a pre-existing repetitive sequence. SHACKTeR requires only two modifications to the genome: CRISPR/Cas9-mediated knock-in of an optimized TetO repeat and its visualization by TetR-EGFP expression. Our simplified knock-in protocol, utilizing short homology arms integrated by polymerase chain reaction, was successful at labeling 10 different loci in HCT116 cells. We also showed the feasibility of knock-in into lamina-associated, heterochromatin regions, demonstrating that these regions prefer non-homologous end joining for knock-in. Using SHACKTeR, we were able to observe DNA replication at a specific locus by long-term live cell imaging. We anticipate the general applicability and scalability of our method will enhance causative analyses between gene function and compartmentalization in a high-throughput manner.

Rapid and Sensitive Detection of Repetitive Nucleic Acid Sequences Using Magnetically Modulated Biosensors

Repetitive DNA sequences are abundant in the genome of most biological species. These sequences are naturally "preamplified", which makes them a preferential target for a variety of biological assays. Current methods to detect specific DNA sequences are based on the quantitative polymerase chain reaction (PCR), which relies on target amplification by Taq polymerase and uses a fluorescent resonance energy transfer (FRET)-based probe. Here, to rapidly detect a repetitive DNA sequence, we combine a highly sensitive magnetic modulation biosensing (MMB) system and a modified double-quenched FRET-based probe. The high numbers of copies of the female-specific XhoI sequence of the domestic chicken (Gallus gallus), combined with the low background fluorescence levels of the modified double-quenched probe and the high sensitivity of the MMB system, allow us to determine the chick sex in ovo within 13 min, with 100% sensitivity and specificity. Compared to quantitative PCR, the presented assay is 4-9 times faster. More broadly, by specifically tailoring the primers and probe, the proposed assay can detect any target DNA sequence, either repetitive or nonrepetitive.

A seamless and iterative DNA assembly method named PS-Brick and its assisted metabolic engineering for threonine and 1-propanol production

BACKGROUND

DNA assembly is an essential technique enabling metabolic engineering and synthetic biology. Combining novel DNA assembly technologies with rational metabolic engineering can facilitate the construction of microbial cell factories. Amino acids and derived biochemicals are important products in industrial biotechnology with wide application and huge markets. DNA assembly scenarios encountered in metabolic engineering for the construction of amino acid and related compound producers, such as design-build-test-learn cycles, construction of precise genetic circuits and repetitive DNA molecules, usually require for iterative, scarless and repetitive sequence assembly methods, respectively.

RESULTS

Restriction endonuclease (RE)-assisted strategies constitute one of the major categories of DNA assembly. Here, we developed a Type IIP and IIS RE-assisted method named PS-Brick that comprehensively takes advantage of the properties of PCR fragments and REs for iterative, seamless and repetitive sequence assembly. One round of PS-Brick reaction using purified plasmids and PCR fragments was accomplished within several hours, and transformation of the resultant reaction product from this PS-Brick assembly reaction exhibited high efficiency (104-105 CFUs/µg DNA) and high accuracy (~ 90%). An application of metabolic engineering to threonine production, including the release of feedback regulation, elimination of metabolic bottlenecks, intensification of threonine export and inactivation of threonine catabolism, was stepwise resolved in E. coli by rounds of "design-build-test-learn" cycles through the iterative PS-Brick paradigm, and 45.71 g/L threonine was obtained through fed-batch fermentation. In addition to the value of the iterative character of PS-Brick for sequential strain engineering, seamless cloning enabled precise in-frame fusion for codon saturation mutagenesis and bicistronic design, and the repetitive sequence cloning ability of PS-Brick enabled construction of tandem CRISPR sgRNA arrays for genome editing. Moreover, the heterologous pathway deriving 1-propanol pathway from threonine, composed of Lactococcus lactis kivD and Saccharomyces cerevisiae ADH2, was assembled by one cycle of PS-Brick, resulting in 1.35 g/L 1-propanol in fed-batch fermentation.

CONCLUSIONS

To the best of our knowledge, the PS-Brick framework is the first RE-assisted DNA assembly method using the strengths of both Type IIP and IIS REs. In this study, PS-Brick was demonstrated to be an efficient DNA assembly method for pathway construction and genome editing and was successfully applied in design-build-test-learn (DBTL) cycles of metabolic engineering for the production of threonine and threonine-derived 1-propanol. The PS-Brick presents a valuable addition to the current toolbox of synthetic biology and metabolic engineering.

Long-read direct RNA sequencing by 5'-Cap capturing reveals the impact of Piwi on the widespread exonization of transposable elements in locusts

The large genome of the migratory locust (Locusta migratoria) genome accumulates massive amount of accumulated transposable elements (TEs), which show intrinsic transcriptional activities. Hampering the ability to precisely determine full-length RNA transcript sequences are exonized TEs, which produce numerous highly similar fragments that are difficult to resolve using short-read sequencing technology. Here, we applied a 5'-Cap capturing method using Nanopore long-read direct RNA sequencing to characterize full-length transcripts in their native RNA form and to analyze the TE exonization pattern in the locust transcriptome. Our results revealed the widespread establishment of TE exonization and a substantial contribution of TEs to RNA splicing in the locust transcriptome. The results of the transcriptomic spectrum influenced by Piwi expression indicated that TE-derived sequences were the main targets of Piwi-mediated repression. Furthermore, our study showed that Piwi expression regulates the length of RNA transcripts containing TE-derived sequences, creating an alternative UTR usage. Overall, our results reveal the transcriptomic characteristics of TE exonization in the species characterized by large and repetitive genomes.

The Nopp140 gene in Drosophila melanogaster displays length polymorphisms in its large repetitive second exon

Nopp140, often called the nucleolar and Cajal body phosphoprotein (NOLC1), is an evolutionarily conserved chaperone for the transcription and processing of rRNA during ribosome subunit assembly. Metazoan Nopp140 contains an amino terminal LisH dimerization domain and a highly conserved carboxyl domain. A large central domain consists of alternating basic and acidic motifs of low sequence complexity. Orthologous versions of Nopp140 contain variable numbers of repeating basic-acidic units. While vertebrate Nopp140 genes use multiple exons to encode the central domain, the Nopp140 gene in Drosophila uses exclusively exon 2 to encode the central domain. Here, we define three overlapping repeat sequence patterns (P, P', and P″) within the central domain of D. melanogaster Nopp140. These repeat patterns are poorly conserved in other Drosophila species. We also describe a length polymorphism in exon 2 that pertains specifically to the P' pattern in D. melanogaster. The pattern displays either two or three 96 base pair repeats, respectively, referred to as Nopp140-Short and Nopp140-Long. Fly lines homozygous for one or the other allele, or heterozygous for both alleles, show no discernible phenotypes. PCR characterization of the long and short alleles shows a poorly defined, artifactual bias toward amplifying the long allele over the short allele. The significance of this polymorphism will be in discerning the largely unknown properties of Nopp140's large central domain in rDNA transcription and ribosome biogenesis.

Biallelic expansion of an intronic repeat in RFC1 is a common cause of late-onset ataxia

Late-onset ataxia is common, often idiopathic, and can result from cerebellar, proprioceptive, or vestibular impairment; when in combination, it is also termed cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We used non-parametric linkage analysis and genome sequencing to identify a biallelic intronic AAGGG repeat expansion in the replication factor C subunit 1 (RFC1) gene as the cause of familial CANVAS and a frequent cause of late-onset ataxia, particularly if sensory neuronopathy and bilateral vestibular areflexia coexist. The expansion, which occurs in the poly(A) tail of an AluSx3 element and differs in both size and nucleotide sequence from the reference (AAAAG)₁₁ allele, does not affect RFC1 expression in patient peripheral and brain tissue, suggesting no overt loss of function. These data, along with an expansion carrier frequency of 0.7% in Europeans, implies that biallelic AAGGG expansion in RFC1 is a frequent cause of late-onset ataxia.