Tutorial: Investigating SARS-CoV-2 evolution and phylogeny using MNHN-Tree-Tools

The Covid-19 pandemic has caused at more than 3 million deaths by Mai this year. It had a significant impact on the daily life and the global economy. The virus has since its first recorded outbreak in China mutated into new strains. The Nextstrain project has so far been monitoring the evolution of the virus. At the same time we were developing in our lab the MNHN-Tree-Tools toolkit, primarily for the investigation of DNA repeat sequences. We have further extended MNHN-Tree-Tools to guide phylogenetics. As such the toolkit has evolved into a high performance code, allowing for a fast investigation of millions of sequences. Given the context of the pandemic it became evident that we will use our versatile tool to investigate the evolution of SARS-CoV-2 sequences. Our efforts have cumulated in this tutorial that we share with the scientific community.

The Comparative Analysis of the DNA Repeat Composition among Cannabis Sativa L., Humulus Lupulus L. And Humulus Japonicus Siebold & Zucc. With Heteromorphic Sex Chromosomes

Heteromorphic sex chromosomes are rarely found in plants. They were observed only in 47 species from phylogenetically distant families, suggesting that the evolution of sex chromosomes was independent in these species. It was shown that DNA repeat sequences are one of the major factors driving sex chromosomes evolution, and an accumulation or elimination of the repetitive DNA elements are closely linked with the formation of differences in the sex chromosomes. The goal of this study was to characterize the transposon composition in male and female plants of Cannabis sativa L., Humulus lupulus L. and Humulus japonicus Siebold & Zucc. For the first time, the male and female genomes of H. japonicus as well as male genomes of H. lupulus and C. sativa have been sequenced (there were no open data about them). The analysis of genome-wide sequencing data with using Repeatexplorer2 and author’s scripts was carried out. It was shown that accumulation of Ty3-gypsy may be associated with speciation in Cannabaceae family which is the opposite of the theory of speciation throw whole-genome duplication. Moreover, the sex-specific DNA repeat clusters in C. sativa and H. japonicus were found. The analysis also revealed that the concentration of Tekay, Retand and Ikeros repeats in the Y chromosome of C. sativa is lower than in the X chromosome and the Angela concentration is higher in the Y chromosome.

Functional Diversification of Chromatin on Rapid Evolutionary Timescales

Repeat-enriched genomic regions evolve rapidly and yet support strictly conserved functions like faithful chromosome transmission and the preservation of genome integrity. The leading resolution to this paradox is that DNA repeat–packaging proteins evolve adaptively to mitigate deleterious changes in DNA repeat copy number, sequence, and organization. Exciting new research has tested this model of coevolution by engineering evolutionary mismatches between adaptively evolving chromatin proteins of one species and the DNA repeats of a close relative. Here, we review these innovative evolution-guided functional analyses. The studies demonstrate that vital, chromatin-mediated cellular processes, including transposon suppression, faithful chromosome transmission, and chromosome retention depend on species-specific versions of chromatin proteins that package species-specific DNA repeats. In many cases, the ever-evolving repeats are selfish genetic elements, raising the possibility that chromatin is a battleground of intragenomic conflict.

Prospects of telomere-to-telomere assembly in barley: analysis of sequence gaps in the MorexV3 reference genome

The first gapless, telomere-to-telomere (T2T) sequence assemblies of plant chromosomes were reported recently. However, sequence assemblies of most plant genomes remain fragmented. Only recent breakthroughs in accurate long-read sequencing have made it possible to achieve highly contiguous sequence assemblies with a few tens of contigs per chromosome, i.e. a number small enough to allow for a systematic inquiry into the causes of the remaining sequence gaps and the approaches and resources needed to close them. Here, we analyze sequence gaps in the current reference genome sequence of barley cv. Morex (MorexV3). Optical map and sequence raw data, complemented by ChIP-seq data for centromeric histone variant CENH3, were used to estimate the abundance of centromeric, ribosomal DNA and subtelomeric repeats in the barley genome. These estimates were compared with copy numbers in the MorexV3 pseudomolecule sequence. We found that almost all centromeric sequences and 45S ribosomal DNA repeat arrays were absent from the MorexV3 pseudomolecules and that the majority of sequence gaps can be attributed to assembly breakdown in long stretches of satellite repeats. However, missing sequences cannot fully account for the difference between assembly size and flow cytometric genome size estimates. We discuss the prospects of gap closure with ultra-long sequence reads.

Benchmarking tools for DNA repeat identification in diverse genomes

Continuous progression in genomics shows that repeats are important elements of genomes that perform many regulatory and other functions. Eventually, to date, many computational tools have been developed and frequently used for the identification and analysis of genomic repeats. A single tool cannot detect all different types of repeats in diverse species rather pipeline of tools is more effective. But, the choice of such rigorous and robust tools is highly challenging. A method has been implemented to select a set of optimal tools for finding all available classes of perfect and imperfect tandem repeats including microsatellites, minisatellites, and interspersed CRISPRs in genomes. A total of 11 tools have been shortlisted using rule-based selection and then ranked by analyzing rigorousness in searching in diverse species and execution time. Tool comparison shows consistency in perfect microsatellite detection performance but significantly differ for long and imperfect repeats. A web-server has been built which provides a generic platform for various classes of repeat identification from the diverse genome using multiple tools and comparison.

Parent-of-origin effects on nuclear chromatin organization and behavior in a Drosophila model for Williams–Beuren Syndrome

Prognosis of neuropsychiatric disorders in progeny requires consideration of individual (1) parent-of-origin effects (POEs) relying on (2) the nerve cell nuclear 3D chromatin architecture and (3) impact of parent-specific miRNAs. Additionally, the shaping of cognitive phenotypes in parents depends on both learning acquisition and forgetting, or memory erasure. These processes are independent and controlled by different signal cascades: the first is cAMPdependent, the second relies on actin remodeling by small GTPase Rac1 – LIMK1 (LIM-kinase 1). Simple experimental model systems such as Drosophila help probe the causes and consequences leading to human neurocognitive pathologies. Recently, we have developed a Drosophila model for Williams–Beuren Syndrome (WBS): a mutant agnts3 of the agnostic locus (X:11AB) harboring the dlimk1 gene. The agnts3 mutation drastically increases the frequency of ectopic contacts (FEC) in specific regions of intercalary heterochromatin, suppresses learning/memory and affects locomotion. As is shown in this study, the polytene X chromosome bands in reciprocal hybrids between agnts3 and the wild type strain Berlin are heterogeneous in modes of FEC regulation depending either on maternal or paternal gene origin. Bioinformatic analysis reveals that FEC between X:11AB and the other X chromosome bands correlates with the occurrence of short (~30 bp) identical DNA fragments partly homologous to Drosophila 372-bp satellite DNA repeat. Although learning acquisition in a conditioned courtship suppression paradigm is similar in hybrids, the middle-term memory formation shows patroclinic inheritance. Seemingly, this depends on changes in miR-974 expression. Several parameters of locomotion demonstrate heterosis. Our data indicate that the agnts3 locus is capable of trans-regulating gene activity via POEs on the chromatin nuclear organization, thereby affecting behavior.

Echinacea purpurea (L.) Moench treatment of monocytes promotes tonic interferon signaling, increased innate immunity gene expression and DNA repeat hypermethylated silencing of endogenous retroviral sequences

Background Herbal remedies of Echinacea purpurea tinctures are widely used today to reduce common cold respiratory tract infections. Methods Transcriptome, epigenome and kinome profiling allowed a systems biology level characterisation of genomewide immunomodulatory effects of a standardized Echinacea purpurea (L.) Moench extract in THP1 monocytes. Results Gene expression and DNA methylation analysis revealed that Echinaforce® treatment triggers antiviral innate immunity pathways, involving tonic IFN signaling, activation of pattern recognition receptors, chemotaxis and immunometabolism. Furthermore, phosphopeptide based kinome activity profiling and pharmacological inhibitor experiments with filgotinib confirm a key role for Janus Kinase (JAK)-1 dependent gene expression changes in innate immune signaling. Finally, Echinaforce® treatment induces DNA hypermethylation at intergenic CpG, long/short interspersed nuclear DNA repeat elements (LINE, SINE) or long termininal DNA repeats (LTR). This changes transcription of flanking endogenous retroviral sequences (HERVs), involved in an evolutionary conserved (epi) genomic protective response against viral infections. Conclusions Altogether, our results suggest that Echinaforce® phytochemicals strengthen antiviral innate immunity through tonic IFN regulation of pattern recognition and chemokine gene expression and DNA repeat hypermethylated silencing of HERVs in monocytes. These results suggest that immunomodulation by Echinaforce® treatment holds promise to reduce symptoms and duration of infection episodes of common cold corona viruses (CoV), Severe Acute Respiratory Syndrome (SARS)-CoV, and new occurring strains such as SARS-CoV-2, with strongly impaired interferon (IFN) response and weak innate antiviral defense.

Sequence, Chromatin and Evolution of Satellite DNA

Satellite DNA consists of abundant tandem repeats that play important roles in cellular processes, including chromosome segregation, genome organization and chromosome end protection. Most satellite DNA repeat units are either of nucleosomal length or 5–10 bp long and occupy centromeric, pericentromeric or telomeric regions. Due to high repetitiveness, satellite DNA sequences have largely been absent from genome assemblies. Although few conserved satellite-specific sequence motifs have been identified, DNA curvature, dyad symmetries and inverted repeats are features of various satellite DNAs in several organisms. Satellite DNA sequences are either embedded in highly compact gene-poor heterochromatin or specialized chromatin that is distinct from euchromatin. Nevertheless, some satellite DNAs are transcribed into non-coding RNAs that may play important roles in satellite DNA function. Intriguingly, satellite DNAs are among the most rapidly evolving genomic elements, such that a large fraction is species-specific in most organisms. Here we describe the different classes of satellite DNA sequences, their satellite-specific chromatin features, and how these features may contribute to satellite DNA biology and evolution. We also discuss how the evolution of functional satellite DNA classes may contribute to speciation in plants and animals.

MICROSATELLITE INSTABILITY TESTING'S BENEFITS IN A VARIETY OF CANCERS

The accumulation of mutations across the genome, notably in microsatellite (MS) DNA repeat sequences, is a hallmark of MSI/dMMR tumors. Microsatellite instability (MSI) is a genetic change in which microsatellites, which typically have one to six nucleotide repetitions, acquire mutations corresponding to small nucleotide deletions or insertions. Immunohistochemistry or a PCR-based test directed against a set of five MS areas were used to create an MSI detection method. MSI is a significant biomarker for cancer diagnosis, prognosis, and treatment options.