Codon Bias as a Means to Fine-Tune Gene Expression

Evidence for selection on SARS-CoV-2 RNA translation revealed by the evolutionary dynamics of mutations in UTRs and CDSs

RNA translation is the rate-limiting step when cells synthesize proteins. Elevating translation efficiency (TE) is intuitively beneficial. Particularly, when viruses invade host cells, how to compete with endogenous RNAs for efficient translation is a major issue to be resolved. We collected millions of worldwide SARS-CoV-2 sequences during the past year and traced the dynamics of allele frequency of every mutation. We defined adaptive and deleterious mutations according to the rise and fall of their frequencies along time. For 5ʹUTR and synonymous mutations in SARS-CoV-2, the selection on TE is evident near start codons. Adaptive mutations generally decrease GC content while deleterious mutations increase GC content. This trend fades away with increasing distance to start codons. Mutations decreasing GC content near start codons would unravel the complex RNA structure and facilitate translation initiation, which are beneficial to SARS-CoV-2, and vice versa. During this evolutionary arms race between human and virus, SARS-CoV-2 tries to improve its cis elements to compete with host RNAs for rapid translation.

A critical period of translational control during brain development at codon resolution

Translation modulates the timing and amplification of gene expression after transcription. Brain development requires uniquely complex gene expression patterns, but large-scale measurements of translation directly in the prenatal brain are lacking. We measure the reactants, synthesis and products of mRNA translation spanning mouse neocortex neurogenesis, and discover a transient window of dynamic regulation at mid-gestation. Timed translation upregulation of chromatin-binding proteins like Satb2, which is essential for neuronal subtype differentiation, restricts protein expression in neuronal lineages despite broad transcriptional priming in progenitors. In contrast, translation downregulation of ribosomal proteins sharply decreases ribosome biogenesis, coinciding with a major shift in protein synthesis dynamics at mid-gestation. Changing activity of eIF4EBP1, a direct inhibitor of ribosome biogenesis, is concurrent with ribosome downregulation and affects neurogenesis of the Satb2 lineage. Thus, the molecular logic of brain development includes the refinement of transcriptional programs by translation. Modeling of the developmental neocortex translatome is provided as an open-source searchable resource at https://shiny.mdc-berlin.de/cortexomics .

Cell type-specific analysis by single-cell profiling identifies a stable mammalian tRNA-mRNA interface and increased translation efficiency in neurons

The correlation between codon and anticodon pools influences the efficiency of translation, but whether differences exist in these pools across individual cells is unknown. We determined that codon usage and amino acid demand are highly stable across different cell types using available mouse and human single-cell RNA-sequencing atlases. After showing the robustness of ATAC-sequencing measurements for the analysis of tRNA gene usage, we quantified anticodon usage and amino acid supply in both mouse and human single-cell ATAC-seq atlases. We found that tRNA gene usage is overall coordinated across cell types, except in neurons, which clustered separately from other cell types. Integration of these data sets revealed a strong and statistically significant correlation between amino acid supply and demand across almost all cell types. Neurons have an enhanced translation efficiency over other cell types, driven by an increased supply of tRNA^Ala (AGC) anticodons. This results in faster decoding of the Ala-GCC codon, as determined by cell type–specific ribosome profiling, suggesting that the reduction of tRNA^Ala (AGC) anticodon pools may be implicated in neurological pathologies. This study, the first such examination of codon usage, anticodon usage, and translation efficiency resolved at the cell-type level with single-cell information, identifies a conserved landscape of translation elongation across mammalian cellular diversity and evolution.

Chloroplast genome characteristics and phylogenetic analysis of the medicinal plant Blumea balsamifera (L.) DC

Blumea balsamifera (L.) DC., a medicinal plant with high economic value in the Asteraceae family, is widely distributed in China and Southeast Asia. However, studies on the population structure or phylogenetic relationships with other related species are rare owing to the lack of genome information. In this study, through high-throughput sequencing, we found that the chloroplast genome of B. balsamifera was 151,170 bp in length, with a pair of inverted repeat regions (IRa and IRb) comprising 24,982 bp, a large single-copy (LSC) region comprising 82,740 bp, and a small single-copy (SSC) region comprising 18,466 bp. A total of 130 genes were identified in the chloroplast genome of B. balsamifera, including 85 protein-coding, 37 transfer RNA, and 8 ribosomal RNA genes; furthermore, sequence analysis identified 53 simple sequence repeats. Whole chloroplast genome comparison indicated that the inverted regions (IR) were more conserved than large single-copy and SSC regions. Phylogenetic analysis showed that B. balsamifera is closely related to Pluchea indica. Conclusively, the chloroplast genome of B. balsamifera was helpful for species identification and analysis of the genetic diversity and evolution in the genus Blumea and family Asteraceae.

Codon usage bias

Codon usage bias is the preferential or non-random use of synonymous codons, a ubiquitous phenomenon observed in bacteria, plants and animals. Different species have consistent and characteristic codon biases. Codon bias varies not only with species, family or group within kingdom, but also between the genes within an organism. Codon usage bias has evolved through mutation, natural selection, and genetic drift in various organisms. Genome composition, GC content, expression level and length of genes, position and context of codons in the genes, recombination rates, mRNA folding, and tRNA abundance and interactions are some factors influencing codon bias. The factors shaping codon bias may also be involved in evolution of the universal genetic code. Codon-usage bias is critical factor determining gene expression and cellular function by influencing diverse processes such as RNA processing, protein translation and protein folding. Codon usage bias reflects the origin, mutation patterns and evolution of the species or genes. Investigations of codon bias patterns in genomes can reveal phylogenetic relationships between organisms, horizontal gene transfers, molecular evolution of genes and identify selective forces that drive their evolution. Most important application of codon bias analysis is in the design of transgenes, to increase gene expression levels through codon optimization, for development of transgenic crops. The review gives an overview of deviations of genetic code, factors influencing codon usage or bias, codon usage bias of nuclear and organellar genes, computational methods to determine codon usage and the significance as well as applications of codon usage analysis in biological research, with emphasis on plants.

Protein Abundance Prediction Through Machine Learning Methods

Proteins are responsible for most physiological processes, and their abundance provides crucial information for systems biology research. However, absolute protein quantification, as determined by mass spectrometry, still has limitations in capturing the protein pool. Protein abundance is impacted by translation kinetics, which rely on features of codons. In this study, we evaluated the effect of codon usage bias of genes on protein abundance. Notably, we observed differences regarding codon usage patterns between genes coding for highly abundant proteins and genes coding for less abundant proteins. Analysis of synonymous codon usage and evolutionary selection showed a clear split between the two groups. Our machine learning models predicted protein abundances from codon usage metrics with remarkable accuracy, achieving strong correlation with experimental data. Upon integration of the predicted protein abundance in enzyme-constrained genome-scale metabolic models, the simulated phenotypes closely matched experimental data, which demonstrates that our predictive models are valuable tools for systems metabolic engineering approaches.

Complete chloroplast genome sequencing support Angelica decursiva is an independent species from Peucedanum praeruptorum

Peucedani Radix is the dry root of Peucedanum praeruptorum of the umbelliferous family, but the dry root of Angelica decursiva was also the source of Peucedani Radix in the past. As one of the most popular traditional Chinese medicinal herbs, the certified source of Peucedani Radix is still disputed. To better understand the relationship between A. decursiva and P. praeruptorum, we sequenced their chloroplast (cp) genomes. The gene structure, codon usage bias, repeat, simple sequence repeat (SSR), as well as their borders of inverted repeat (IR) regions of the two cp genomes are analyzed to identify potential genetic markers. Great variation is exhibited in the repeat sequences of IR, large single copy regions and the SSRs of the two cp genomes, which can be used as molecular markers to distinguish them. The phylogenetic analysis also indicates that they belong to two different genera in Apiaceae family: A. decursiva is an Angelica plant and P. praeruptorum is a Peucedanum plant. Our observations suggest that the two species are somewhere different in gene features, which contributes to support A. decursiva as an independent species from P. praeruptorum. The results also provide new evidence that A. decursiva should not be regarded as the certified source of Peucedani Radix in taxonomy.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01097-w.

Comparative analysis of transcriptomic data shows the effects of multiple evolutionary selection processes on codon usage in Marsupenaeus japonicus and Marsupenaeus pulchricaudatus

BACKGROUND

Kuruma shrimp, a major commercial shrimp species in the world, has two cryptic or sibling species, Marsupenaeus japonicus and Marsupenaeus pulchricaudatus. Codon usage analysis would contribute to our understanding of the genetic and evolutionary characteristics of the two Marsupenaeus species. In this study, we analyzed codon usage and related indices using coding sequences (CDSs) from RNA-seq data.

RESULTS

Using CodonW 1.4.2 software, we performed the codon bias analysis of transcriptomes obtained from hepatopancreas tissues, which indicated weak codon bias. Almost all parameters had similar correlations for both species. The gene expression level (FPKM) was negatively correlated with A/T3s. We determined 12 and 14 optimal codons for M. japonicus and M. pulchricaudatus, respectively, and all optimal codons have a C/G-ending. The two Marsupenaeus species had different usage frequencies of codon pairs, which contributed to further analysis of transcriptional differences between them. Orthologous genes that underwent positive selection (ω > 1) had a higher correlation coefficient than that of experienced purifying selection (ω < 1). Parity Rule 2 (PR2) and effective number of codons (ENc) plot analysis showed that the codon usage patterns of both species were influenced by both mutations and selection. Moreover, the average observed ENc value was lower than the expected value for both species, suggesting that factors other than GC may play roles in these phenomena. The results of multispecies clustering based on codon preference were consistent with traditional classification.

CONCLUSIONS

This study provides a relatively comprehensive understanding of the correlations among codon usage bias, gene expression, and selection pressures of CDSs for M. japonicus and M. pulchricaudatus. The genetic evolution was driven by mutations and selection pressure. Moreover, the results point out new insights into the specificities and evolutionary characteristics of the two Marsupenaeus species.

mRNA codon optimization with quantum computers

Reverse translation of polypeptide sequences to expressible mRNA constructs is a NP-hard combinatorial optimization problem. Each amino acid in the protein sequence can be represented by as many as six codons, and the process of selecting the combination that maximizes probability of expression is termed codon optimization. This work investigates the potential impact of leveraging quantum computing technology for codon optimization. A Quantum Annealer (QA) is compared to a standard genetic algorithm (GA) programmed with the same objective function. The QA is found to be competitive in identifying optimal solutions. The utility of gate-based systems is also evaluated using a simulator resulting in the finding that while current generations of devices lack the hardware requirements, in terms of both qubit count and connectivity, to solve realistic problems, future generation devices may be highly efficient.

The Dynamic Codon Biaser: calculating prokaryotic codon usage biases

Bacterial genomes often reflect a bias in the usage of codons. These biases are often most notable within highly expressed genes. While deviations in codon usage can be attributed to selection or mutational biases, they can also be functional, for example controlling gene expression or guiding protein structure. Several different metrics have been developed to identify biases in codon usage. Previously we released a database, CBDB: The Codon Bias Database, in which users could retrieve precalculated codon bias data for bacterial RefSeq genomes. With the increase of bacterial genome sequence data since its release a new tool was needed. Here we present the Dynamic Codon Biaser (DCB) tool, a web application that dynamically calculates the codon usage bias statistics of prokaryotic genomes. DCB bases these calculations on 40 different highly expressed genes (HEGs) that are highly conserved across different prokaryotic species. A user can either specify an NCBI accession number or upload their own sequence. DCB returns both the bias statistics and the genome’s HEG sequences. These calculations have several downstream applications, such as evolutionary studies and phage–host predictions. The source code is freely available, and the website is hosted at www.cbdb.info.

Comparative analysis of codon usage patterns in chloroplast genomes of five Miscanthus species and related species

Miscanthus is not only a perennial fiber biomass crop, but also valuable breeding resource for its low-nutrient requirements, photosynthetic efficiency and strong adaptability to environment. In the present study, the codon usage patterns of five different Miscanthus plants and other two related species were systematically analyzed. The results indicated that the cp genomes of the seven representative species were preference to A/T bases and A/T-ending codons. In addition, 21 common high-frequency codons and 4–11 optimal codons were detected in the seven chloroplast genomes. The results of ENc-plot, PR2-plot and neutrality analysis revealed the codon usage patterns of the seven chloroplast genomes are influenced by multiple factors, in which nature selection is the main influencing factor. Comparative analysis of the codon usage frequencies between the seven representative species and four model organisms suggested that Arabidopsis thaliana, Populus trichocarpa and Saccharomyces cerevisiae could be considered as preferential appropriate exogenous expression receptors. These results might not only provide important reference information for evolutionary analysis, but also shed light on the way to improve the expression efficiency of exogenous gene in transgenic research based on codon optimization.

Characterizing RNA Pseudouridylation by Convolutional Neural Networks

Pseudouridine (Ψ) is the most prevalent post-transcriptional RNA modification and is widespread in small cellular RNAs and mRNAs. However, the functions, mechanisms, and precise distribution of Ψs (especially in mRNAs) still remain largely unclear. The landscape of Ψs across the transcriptome has not yet been fully delineated. Here, we present a highly effective model based on a convolutional neural network (CNN), called PseudoUridyLation Site Estimator (PULSE), to analyze large-scale profiling data of Ψ sites and characterize the contextual sequence features of pseudouridylation. PULSE, consisting of two alternatively-stacked convolution and pooling layers followed by a fully-connected neural network, can automatically learn the hidden patterns of pseudouridylation from the local sequence information. Extensive validation tests demonstrated that PULSE can outperform other state-of-the-art prediction methods and achieve high prediction accuracy, thus enabling us to further characterize the transcriptome-wide landscape of Ψ sites. We further showed that the prediction results derived from PULSE can provide novel insights into understanding the functional roles of pseudouridylation, such as the regulations of RNA secondary structure, codon usage, translation, and RNA stability, and the connection to single nucleotide variants. The source code and final model for PULSE are available at https://github.com/mlcb-thu/PULSE.

Direct in vivo observation of the effect of codon usage bias on gene expression in Arabidopsis hybrids

Hybrids are the perfect materials to study cis regulatory elements because the two parental alleles are subjected to identical trans environments. There has been a debate on whether synonymous codon usage could affect gene expression. In vitro experiments found that luciferase genes with enhanced codon optimality showed elevated mRNA expression. However, the underlying mechanism is still unclear, and no direct evidence is observed to support this notion. By mapping the RNA-seq data of hybrids of Arabidopsis thaliana and Arabidopsis lyrata, we quantified the allele-specific reads and estimated the relative expression of orthologous genes. We focused on orthologous genes with dN = 0 and dS > 0, which means that they only differ in synonymous codon usage. We found that orthologous genes with higher codon optimality in A. thaliana tend to have higher expression levels of the A. thaliana allele. Codon usage bias could influence gene expression. This phenomenon is not only found in in vitro experiments but also supported by in vivo observations. Therefore, synonymous mutations could have a broad impact from multiple aspects and should not be automatically ignored in genomic studies. KEY MESSAGE: In Arabidopsis hybrids, alleles with higher codon optimality tend to have higher expression levels.

Regulation of gene expression via translational buffering

Translation of an mRNA represents a critical step during the expression of protein-coding genes. As mechanisms governing post-transcriptional regulation of gene expression are progressively unveiled, it is becoming apparent that transcriptional programs are not fully reflected in the proteome. Herein, we highlight a previously underappreciated post-transcriptional mode of regulation of gene expression termed translational buffering. In principle, translational buffering opposes the impact of alterations in mRNA levels on the proteome. We further describe three types of translational buffering: compensation, which maintains protein levels e.g. across species or individuals; equilibration, which retains pathway stoichiometry; and offsetting, which acts as a reversible mechanism that maintains the levels of selected subsets of proteins constant despite genetic alteration and/or stress-induced changes in corresponding mRNA levels. While mechanisms underlying compensation and equilibration have been reviewed elsewhere, the principal focus of this review is on the less-well understood mechanism of translational offsetting. Finally, we discuss potential roles of translational buffering in homeostasis and disease.

Analysis of Codon Usage Patterns of Six Sequenced Brachypodium distachyon Lines Reveals a Declining CG Skew of the CDSs from the 5'-ends to the 3'-ends

Brachypodium distachyon, a new monocotyledonous model plant, has received wide attention in biological research due to its small genome and numerous genetic resources. Codon usage bias is an important feature of genes and genomes, and it can be used in transgenic and evolutionary studies. In this study, the nucleotide compositions and patterns of codon usage bias were calculated using Codon W. Additionally, an ENC plot, Parity rule 2 and correspondence analyses were used to explore the major factors influencing codon usage bias patterns. The numbers of hydrogen bonds and skews were used to analyze the GC trend in the 5'-ends of the coding sequences. The results showed that minor differences in the codon usage bias patterns were revealed by the ENC plot, Parity rule 2 and correspondence analyses. The analyses of the CG-skew and the number of hydrogen bonds showed a declining trend in the number of cytosines at the 5'-ends of the CDSs (from the 5'-ends to the 3'-ends), indicating that GC may play a major role in codon usage bias. In addition, our results laid a foundation for the study of codon usage bias patterns in Brachypodium genus and suggested that the GC plays a major role in determining these patterns.

Anaerobic Fungal Mevalonate Pathway Genomic Biases Lead to Heterologous Toxicity Underpredicted by Codon Adaptation Indices

Anaerobic fungi are emerging biotechnology platforms with genomes rich in biosynthetic potential. Yet, the heterologous expression of their biosynthetic pathways has had limited success in model hosts like E. coli. We find one reason for this is that the genome composition of anaerobic fungi like P. indianae are extremely AT-biased with a particular preference for rare and semi-rare AT-rich tRNAs in E coli, which are not explicitly predicted by standard codon adaptation indices (CAI). Native P. indianae genes with these extreme biases create drastic growth defects in E. coli (up to 69% reduction in growth), which is not seen in genes from other organisms with similar CAIs. However, codon optimization rescues growth, allowing for gene evaluation. In this manner, we demonstrate that anaerobic fungal homologs such as PI.atoB are more active than S. cerevisiae homologs in a hybrid pathway, increasing the production of mevalonate up to 2.5 g/L (more than two-fold) and reducing waste carbon to acetate by ~90% under the conditions tested. This work demonstrates the bioproduction potential of anaerobic fungal enzyme homologs and how the analysis of codon utilization enables the study of otherwise difficult to express genes that have applications in biocatalysis and natural product discovery.

Cholesterol Is a Dose-Dependent Positive Allosteric Modulator of CCR3 Ligand Affinity and G Protein Coupling

Cholesterol as an allosteric modulator of G protein-coupled receptor (GPCR) function is well documented. This quintessential mammalian lipid facilitates receptor–ligand interactions and multimerization states. Functionally, this introduces a complicated mechanism for the homeostatic modulation of GPCR signaling. Chemokine receptors are Class A GPCRs responsible for immune cell trafficking through the binding of endogenous peptide ligands. CCR3 is a CC motif chemokine receptor expressed by eosinophils and basophils. It traffics these cells by transducing the signal stimulated by the CC motif chemokine primary messengers 11, 24, and 26. These behaviors are close to the human immunoresponse. Thus, CCR3 is implicated in cancer metastasis and inflammatory conditions. However, there is a paucity of experimental evidence linking the functional states of CCR3 to the molecular mechanisms of cholesterol–receptor cooperativity. In this vein, we present a means to combine codon harmonization and a maltose-binding protein fusion tag to produce CCR3 from E. coli. This technique yields ∼2.6 mg of functional GPCR per liter of minimal media. We leveraged this protein production capability to investigate the effects of cholesterol on CCR3 function in vitro. We found that affinity for the endogenous ligand CCL11 increases in a dose-dependent manner with cholesterol concentration in both styrene:maleic acid lipid particles (SMALPs) and proteoliposomes. This heightened receptor activation directly translates to increased signal transduction as measured by the GTPase activity of the bound G-protein α inhibitory subunit 3 (Gα_i3). This work represents a critical step forward in understanding the role of cholesterol-GPCR allostery in regulation of signal transduction.

Codon usage bias analysis of genes linked with esophagus cancer

Esophageal cancer involves multiple genetic alternations. A systematic codon usage bias analysis was completed to investigate the bias among the esophageal cancer responsive genes. GC-rich genes were low (average effective number of codon value was 49.28). CAG and GTA are over-represented and under-represented codons, respectively. Correspondence analysis, neutrality plot, and parity rule 2 plot analysis confirmed the dominance over mutation pressure in modulating the codon usage pattern of genes linked with esophageal cancer.

Human Codon Usage: The Genetic Basis of Pathogen Latency

Infectious diseases pose two main compelling issues. First, the identification of the molecular factors that allow chronic infections, that is, the often completely asymptomatic coexistence of infectious agents with the human host. Second, the definition of the mechanisms that allow the switch from pathogen dormancy to pathologic (re)activation. Furthering previous studies, the present study (1) analyzed the frequency of occurrence of synonymous codons in coding DNA, that is, codon usage, as a genetic tool that rules protein expression; (2) described how human codon usage can inhibit protein expression of infectious agents during latency, so that pathogen genes the codon usage of which does not conform to the human codon usage cannot be translated; and (3) framed human codon usage among the front-line instruments of the innate immunity against infections. In parallel, it was shown that, while genetics can account for the molecular basis of pathogen latency, the changes of the quantitative relationship between codon frequencies and isoaccepting tRNAs during cell proliferation offer a biochemical mechanism that explains the pathogen switching to (re)activation. Immunologically, this study warns that using codon optimization methodologies can (re)activate, potentiate, and immortalize otherwise quiescent, asymptomatic pathogens, thus leading to uncontrollable pandemics.

Inhibition of protein synthesis through RNA-based tandem G-quadruplex formation

We demonstrate that an RNA template containing eight GGG repeat sequences exhibits a unique tandem G-quadruplex structure in which two individual G-quadruplexes are aligned in close proximity. Because of their unexpected stability, tandem G-quadruplexes formed in the coding region of mRNA strands effectively inhibited in vitro protein synthesis.

Codon usage bias and dinucleotide preference in 29 Drosophila species

Codon usage bias, where certain codons are used more frequently than their synonymous counterparts, is an interesting phenomenon influenced by three evolutionary forces: mutation, selection, and genetic drift. To better understand how these evolutionary forces affect codon usage bias, an extensive study to detect how codon usage patterns change across species is required. This study investigated 668 single-copy orthologous genes independently in 29 Drosophila species to determine how the codon usage patterns change with phylogenetic distance. We found a strong correlation between phylogenetic distance and codon usage bias and observed striking differences in codon preferences between the two subgenera Drosophila and Sophophora. As compared to the subgenus Sophophora, species of the subgenus Drosophila showed reduced codon usage bias and a reduced preference specifically for codons ending with C, except for codons with G in the second position. We found that codon usage patterns in all species were influenced by the nucleotides in the codon’s 2nd and 3rd positions rather than the biochemical properties of the amino acids encoded. We detected a concordance between preferred codons and preferred dinucleotides (at positions 2 and 3 of codons). Furthermore, we observed an association between speciation, codon preferences, and dinucleotide preferences. Our study provides the foundation to understand how selection acts on dinucleotides to influence codon usage bias.

Comparative analysis of plastomes in Oxalidaceae: Phylogenetic relationships and potential molecular markers

The wood sorrel family, Oxalidaceae, is mainly composed of annual or perennial herbs, a few shrubs, and trees distributed from temperate to tropical zones. Members of Oxalidaceae are of high medicinal, ornamental, and economic value. Despite the rich diversity and value of Oxalidaceae, few molecular markers or plastomes are available for phylogenetic analysis of the family. Here, we reported four new whole plastomes of Oxalidaceae and compared them with plastomes of three species in the family, as well as the plastome of Rourea microphylla in the closely related family Connaraceae. The eight plastomes ranged in length from 150,673 bp (Biophytum sensitivum) to 156,609 bp (R. microphylla). Genome annotations revealed a total of 129-131 genes, including 83-84 protein-coding genes, eight rRNA genes, 37 tRNA genes, and two to three pseudogenes. Comparative analyses showed that the plastomes of these species have minor variations at the gene level. The smaller plastomes of herbs B. sensitivum and three Oxalis species are associated with variations in IR region sizes, intergenic region variation, and gene or intron loss. We identified sequences with high variation that may serve as molecular markers in taxonomic studies of Oxalidaceae. The phylogenetic trees of selected superrosid representatives based on 76 protein-coding genes corroborated the Oxalidaceae position in Oxalidales and supported it as a sister to Connaraceae. Our research also supported the monophyly of the COM (Celastrales, Oxalidales, and Malpighiales) clade.

Tailoring in fungi for next generation cellulase production with special reference to CRISPR/CAS system

Cellulose is the utmost plenteous source of biopolymer in our earth, and fungi are the most efficient and ubiquitous organism in degrading the cellulosic biomass by synthesizing cellulases. Tailoring through genetic manipulation has played a substantial role in constructing novel fungal strains towards improved cellulase production of desired traits. However, the traditional methods of genetic manipulation of fungi are time-consuming and tedious. With the availability of the full-genome sequences of several industrially relevant filamentous fungi, CRISPR-CAS (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein) technology has come into the focus for the proficient development of manipulated strains of filamentous fungi. This review summarizes the mode of action of cellulases, transcription level regulation for cellulase expression, various traditional strategies of genetic manipulation with CRISPR-CAS technology to develop modified fungal strains for a preferred level of cellulase production, and the futuristic trend in this arena of research.

Analysis of Codon Usage Patterns in Giardia duodenalis Based on Transcriptome Data from GiardiaDB

Giardia duodenalis, a flagellated parasitic protozoan, the most common cause of parasite-induced diarrheal diseases worldwide. Codon usage bias (CUB) is an important evolutionary character in most species. However, G. duodenalis CUB remains unclear. Thus, this study analyzes codon usage patterns to assess the restriction factors and obtain useful information in shaping G. duodenalis CUB. The neutrality analysis result indicates that G. duodenalis has a wide GC3 distribution, which significantly correlates with GC12. ENC-plot result—suggesting that most genes were close to the expected curve with only a few strayed away points. This indicates that mutational pressure and natural selection played an important role in the development of CUB. The Parity Rule 2 plot (PR2) result demonstrates that the usage of GC and AT was out of proportion. Interestingly, we identified 26 optimal codons in the G. duodenalis genome, ending with G or C. In addition, GC content, gene expression, and protein size also influence G. duodenalis CUB formation. This study systematically analyzes G. duodenalis codon usage pattern and clarifies the mechanisms of G. duodenalis CUB. These results will be very useful to identify new genes, molecular genetic manipulation, and study of G. duodenalis evolution.

RNA Modifications in Pathogenic Bacteria: Impact on Host Adaptation and Virulence

RNA modifications are involved in numerous biological processes and are present in all RNA classes. These modifications can be constitutive or modulated in response to adaptive processes. RNA modifications play multiple functions since they can impact RNA base-pairings, recognition by proteins, decoding, as well as RNA structure and stability. However, their roles in stress, environmental adaptation and during infections caused by pathogenic bacteria have just started to be appreciated. With the development of modern technologies in mass spectrometry and deep sequencing, recent examples of modifications regulating host-pathogen interactions have been demonstrated. They show how RNA modifications can regulate immune responses, antibiotic resistance, expression of virulence genes, and bacterial persistence. Here, we illustrate some of these findings, and highlight the strategies used to characterize RNA modifications, and their potential for new therapeutic applications.

Codon Deoptimization of UL54 in meq-Deleted Marek's Disease Vaccine Candidate Eliminates Lymphoid Atrophy but Reduces Vaccinal Protection

Marek's disease (MD) is an oncogenic, lymphoproliferative, and highly contagious disease of chickens. Its etiologic agent is the alphaherpesvirus Marek's disease virus (MDV, Gallid alphaherpesvirus 2), and it is a chronic and ubiquitous problem for the poultry industry with significant economic impact in the United States and worldwide. We have previously demonstrated that MDV attenuated by dicodon deoptimization of the UL54 gene results in reduced gene product accumulation in vitro, with reduced viral genome copy number upon infection and reduced atrophy of bursa and thymus in vivo as well. In this report we detail our attempts to use the same attenuation strategy on a meq-deleted MDV mutant, rMd5B40ΔMeq. Unlike the wild-type rMd5B40 virus the rMd5B40ΔMeq is no longer oncogenic, but infected birds experience an unacceptable amount of bursa and thymus atrophy (BTA). We produced two meq-deleted MDV recombinants with a dicodon-deoptimized UL54 (rMd5B40ΔMeq/UL54deop1 and -deop2) and tested their tendency to cause BTA and to serve as a protective vaccine. We found that, although dicodon deoptimization of the UL54 gene results in a virus that spares the infected animal from atrophy of the bursa and thymus, the meq-deleted UL54-deoptimized recombinant is also less protective than the meq-deleted virus without UL54 deoptimization, the HVT + SB1 combination vaccine, or the Rispens (CVI988) vaccine.

Signal metrics analysis of oscillatory patterns in bacterial multi-omic networks

MOTIVATION

One of the branches of Systems Biology is focused on a deep understanding of underlying regulatory networks through the analysis of the biomolecules oscillations and their interplay. Synthetic Biology exploits gene or/and protein regulatory networks towards the design of oscillatory networks for producing useful compounds. Therefore, at different levels of application and for different purposes, the study of biomolecular oscillations can lead to different clues about the mechanisms underlying living cells. It is known that network-level interactions involve more than one type of biomolecule as well as biological processes operating at multiple omic levels. Combining network/pathway-level information with genetic information it is possible to describe well-understood or unknown bacterial mechanisms and organism-specific dynamics.

RESULTS

Following the methodologies used in signal processing and communication engineering, a methodology is introduced to identify and quantify the extent of multi-omic oscillations. These are due to the process of multi-omic integration and depend on the gene positions on the chromosome. Ad hoc signal metrics are designed to allow further biotechnological explanations and provide important clues about the oscillatory nature of the pathways and their regulatory circuits. Our algorithms designed for the analysis of multi-omic signals are tested and validated on 11 different bacteria for thousands of multi-omic signals perturbed at the network level by different experimental conditions. Information on the order of genes, codon usage, gene expression and protein molecular weight is integrated at three different functional levels. Oscillations show interesting evidence that network-level multi-omic signals present a synchronized response to perturbations and evolutionary relations along taxa.

AVAILABILITY AND IMPLEMENTATION

The algorithms, the code (in language R), the tool, the pipeline and the whole dataset of multi-omic signal metrics are available at: https://github.com/lodeguns/Multi-omicSignals.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

The mitochondrial genome of the semi-slug Omalonyx unguis (Gastropoda: Succineidae) and the phylogenetic relationships within Stylommatophora

Here we report the first complete mitochondrial genome of the semi-slug Omalonyx unguis (d’Orbigny, 1836) (Gastropoda: Succineidae). Sequencing was performed on a specimen from Argentina. Assembly was performed using Sanger data and Illumina next generation sequencing (NGS). The mitogenome was 13,984 bp in length and encoded the 37 typical Metazoan genes. A potential origin for mitochondrial DNA replication was found in a non-coding intergenic spacer (49 bp) located between cox3 and tRNA-Ile genes, and its secondary structure was characterized. Secondary structure models of the tRNA genes of O. unguis largely agreed with those proposed for other mollusks. Secondary structure models for the two rRNA genes were also obtained. To our knowledge, the 12S-rRNA model derived here is the first complete one available for mollusks. Phylogenetic analyses based on the mitogenomes of O. unguis and 37 other species of Stylommatophora were performed using amino acid sequences from the 13 protein-coding genes. Our results located Succineoidea as a sister group of Helicoidea + Urocoptoidea, similar to previous studies based on mitochondrial genomes. The gene arrangement of O. unguis was identical to that reported for another species of Succineoidea. The unique rearrangements observed for this group within Stylommatophora, may constitute synapomorphies for the superfamily.

Genome-wide role of codon usage on transcription and identification of potential regulators

Codon usage bias is a fundamental feature of all genomes and plays an important role in determining gene expression levels. The codon usage was thought to influence gene expression mainly due to its impact on translation. Recently, however, codon usage was shown to affect transcription of fungal and mammalian genes, indicating the existence of a gene regulatory phenomenon with unknown mechanism. In Neurospora, codon usage biases strongly correlate with mRNA levels genome-wide, and here we show that the correlation between codon usage and RNA levels is maintained in the nucleus. In addition, codon optimality is tightly correlated with both total and nuclear RNA levels, suggesting that codon usage broadly influences mRNA levels through transcription in a translation-independent manner. A large-scale RNA sequencing-based genetic screen in Neurospora identified 18 candidate factors that when deleted decreased the genome-wide correlation between codon usage and RNA levels and reduced the codon usage effect on gene expression. Most of these factors, such as the H3K36 methyltransferase, are chromatin regulators or transcription factors. Together, our results suggest that the transcriptional effect of codon usage is mediated by multiple transcriptional regulatory mechanisms.

Exploring Codon Adjustment Strategies towards Escherichia coli-Based Production of Viral Proteins Encoded by HTH1, a Novel Prophage of the Marine Bacterium Hypnocyclicus thermotrophus

Marine viral sequence space is immense and presents a promising resource for the discovery of new enzymes interesting for research and biotechnology. However, bottlenecks in the functional annotation of viral genes and soluble heterologous production of proteins hinder access to downstream characterization, subsequently impeding the discovery process. While commonly utilized for the heterologous expression of prokaryotic genes, codon adjustment approaches have not been fully explored for viral genes. Herein, the sequence-based identification of a putative prophage is reported from within the genome of Hypnocyclicus thermotrophus, a Gram-negative, moderately thermophilic bacterium isolated from the Seven Sisters hydrothermal vent field. A prophage-associated gene cluster, consisting of 46 protein coding genes, was identified and given the proposed name Hypnocyclicus thermotrophus phage H1 (HTH1). HTH1 was taxonomically assigned to the viral family Siphoviridae, by lowest common ancestor analysis of its genome and phylogeny analyses based on proteins predicted as holin and DNA polymerase. The gene neighbourhood around the HTH1 lytic cassette was found most similar to viruses infecting Gram-positive bacteria. In the HTH1 lytic cassette, an N-acetylmuramoyl-L-alanine amidase (Amidase_2) with a peptidoglycan binding motif (LysM) was identified. A total of nine genes coding for enzymes putatively related to lysis, nucleic acid modification and of unknown function were subjected to heterologous expression in Escherichia coli. Codon optimization and codon harmonization approaches were applied in parallel to compare their effects on produced proteins. Comparison of protein yields and thermostability demonstrated that codon optimization yielded higher levels of soluble protein, but codon harmonization led to proteins with higher thermostability, implying a higher folding quality. Altogether, our study suggests that both codon optimization and codon harmonization are valuable approaches for successful heterologous expression of viral genes in E. coli, but codon harmonization may be preferable in obtaining recombinant viral proteins of higher folding quality.

Association between a genetic variant in scavenger receptor class B type 1 and its role on codon usage bias with increased risk of developing coronary artery disease

OBJECTIVE

Coronary artery disease (CAD) as an important cause of morbidity and mortality globally. The scavenger receptor class B type 1 (SCARB1) plays an essential role in the reverse cholesterol transport. We have explored the association between a genetic variant, rs5888, in the SCARB1 gene with CAD and serum HDL-C levels.

METHODS

Patients were categorized into two groups' angiogram positive (>50% coronary stenosis) and angiogram negative (<50% coronary stenosis). Genotyping was carried out using polymerase chain reaction-amplification refractory mutation system. The association between the SNP rs5888 and serum HDL-C was analyzed using a logistic regression model.

RESULTS

The results showed that the subjects carrying a T allele was associated with a decreased serum HDL-C levels compared to the C allele in total population (p < 0.001). The risk of angiogram positivity in subjects carrying a T allele was 3.1-fold higher than for the control group (p < 0.001).

CONCLUSION

CVD patients carrying the T allele of rs5888 variant in the SCARB1 gene was associated with decreased serum level of HDL.

Next-Generation Sequencing of CYP2C19 in Stent Thrombosis: Implications for Clopidogrel Pharmacogenomics

PURPOSE

Describe CYP2C19 sequencing results in the largest series of clopidogrel-treated cases with stent thrombosis (ST), the closest clinical phenotype to clopidogrel resistance. Evaluate the impact of CYP2C19 genetic variation detected by next-generation sequencing (NGS) with comprehensive annotation and functional studies.

METHODS

Seventy ST cases on clopidogrel identified from the PLATO trial (n = 58) and Mayo Clinic biorepository (n = 12) were matched 1:1 with controls for age, race, sex, diabetes mellitus, presentation, and stent type. NGS was performed to cover the entire CYP2C19 gene. Assessment of exonic variants involved measuring in vitro protein expression levels. Intronic variants were evaluated for potential splicing motif variations.

RESULTS

Poor metabolizers (n = 4) and rare CYP2C19*8, CYP2C19*15, and CYP2C19*11 alleles were identified only in ST cases. CYP2C19*17 heterozygote carriers were observed more frequently in cases (n = 29) than controls (n = 18). Functional studies of CYP2C19 exonic variants (n = 11) revealed 3 cases and only 1 control carrying a deleterious variant as determined by in vitro protein expression studies. Greater intronic variation unique to ST cases (n = 169) compared with controls (n = 84) was observed with predictions revealing 13 allele candidates that may lead to a potential disruption of splicing and a loss-of-function effect of CYP2C19 in ST cases.

CONCLUSION

NGS detected CYP2C19 poor metabolizers and paradoxically greater number of so-called rapid metabolizers in ST cases. Rare deleterious exonic variation occurs in 4%, and potentially disruptive intronic alleles occur in 16% of ST cases. Additional studies are required to evaluate the role of these variants in platelet aggregation and clopidogrel metabolism.

Comparative analysis of the relationship between translation efficiency and sequence features of endogenous proteins in multiple organisms

The translation efficiency of protein genes is known to be affected by sequence features. Previous studies have found that various sequence features based on codon usage and mRNA secondary structure contribute to translation efficiency. However, most studies have focused on a specific organism, usually a model organism such as Escherichia coli or Saccharomyces cerevisiae. Here, we investigate whether the relationship between translation efficiency and sequence features is conserved among multiple organisms using publicly available ribosome profiling data and RNA-Seq data. We analyze nine organisms from various taxa: Staphylococcus aureus, five species of Streptomyces, two strains of E. coli, and S. cerevisiae. We reveal that the relationship between translation efficiency and sequence features differs across organisms, partly reflecting their taxonomy. The codon adaptation index shows high correlation in all analyzed organisms. Our study provides an insight into the diversity and commonality of sequence determinants of protein expression in these organisms.

Signaling levels mold the RAS mutation tropism of urethane

RAS genes are commonly mutated in human cancer. Despite many possible mutations, individual cancer types often have a 'tropism' towards a specific subset of RAS mutations. As driver mutations, these patterns ostensibly originate from normal cells. High oncogenic RAS activity causes oncogenic stress and different oncogenic mutations can impart different levels of activity, suggesting a relationship between oncoprotein activity and RAS mutation tropism. Here, we show that changing rare codons to common in the murine Kras gene to increase protein expression shifts tumors induced by the carcinogen urethane from arising from canonical Q₆₁ to biochemically less active G₁₂ Kras driver mutations, despite the carcinogen still being biased towards generating Q₆₁ mutations. Conversely, inactivating the tumor suppressor p53 to blunt oncogenic stress partially reversed this effect, restoring Q₆₁ mutations. One interpretation of these findings is that the RAS mutation tropism of urethane arises from selection in normal cells for specific mutations that impart a narrow window of signaling that promotes proliferation without causing oncogenic stress.

Development of Clostridium saccharoperbutylacetonicum as a Whole Cell Biocatalyst for Production of Chirally Pure (R)-1,3-Butanediol

Chirally pure (R)-1,3-butanediol ((R)-1,3-BDO) is a valuable intermediate for the production of fragrances, pheromones, insecticides and antibiotics. Biotechnological production results in superior enantiomeric excess over chemical production and is therefore the preferred production route. In this study (R)-1,3-BDO was produced in the industrially important whole cell biocatalyst Clostridium saccharoperbutylacetonicum through expression of the enantio-specific phaB gene from Cupriavidus necator. The heterologous pathway was optimised in three ways: at the transcriptional level choosing strongly expressed promoters and comparing plasmid borne with chromosomal gene expression, at the translational level by optimising the codon usage of the gene to fit the inherent codon adaptation index of C. saccharoperbutylacetonicum, and at the enzyme level by introducing point mutations which led to increased enzymatic activity. The resulting whole cell catalyst produced up to 20 mM (1.8 g/l) (R)-1,3-BDO in non-optimised batch fermentation which is a promising starting position for economical production of this chiral chemical.

Porcine Reproductive and Respiratory Syndrome Virus: Immune Escape and Application of Reverse Genetics in Attenuated Live Vaccine Development

Porcine reproductive and respiratory syndrome virus (PRRSV), an RNA virus widely prevalent in pigs, results in significant economic losses worldwide. PRRSV can escape from the host immune response in several processes. Vaccines, including modified live vaccines and inactivated vaccines, are the best available countermeasures against PRRSV infection. However, challenges still exist as the vaccines are not able to induce broad protection. The reason lies in several facts, mainly the variability of PRRSV and the complexity of the interaction between PRRSV and host immune responses, and overcoming these obstacles will require more exploration. Many novel strategies have been proposed to construct more effective vaccines against this evolving and smart virus. In this review, we will describe the mechanisms of how PRRSV induces weak and delayed immune responses, the current vaccines of PRRSV, and the strategies to develop modified live vaccines using reverse genetics systems.

Bacterial Growth Inhibition Screen (BGIS): harnessing recombinant protein toxicity for rapid and unbiased interrogation of protein function

In two proof-of-concept studies, we established and validated the Bacterial Growth Inhibition Screen (BGIS), which explores recombinant protein toxicity in Escherichia coli as a largely overlooked and alternative means for basic characterization of functional eukaryotic protein domains. By applying BGIS, we identified an unrecognized RNA-interacting domain in the DEK oncoprotein (this study) and successfully combined BGIS with random mutagenesis as a screening tool for loss-of-function mutants of the DNA modulating domain of DEK [1]. Collectively, our findings shed new light on the phenomenon of recombinant protein toxicity in E. coli. Given the easy and rapid implementation and wide applicability, BGIS will extend the repertoire of basic methods for the identification, analysis and unbiased manipulation of proteins.

A role for circular code properties in translation

Circular codes represent a form of coding allowing detection/correction of frame-shift errors. Building on recent theoretical advances on circular codes, we provide evidence that protein coding sequences exhibit in-frame circular code marks, that are absent in introns and are intimately linked to the keto-amino transformation of codon bases. These properties strongly correlate with translation speed, codon influence and protein synthesis levels. Strikingly, circular code marks are absent at the beginning of coding sequences, but stably occur 40 codons after the initiator codon, hinting at the translation elongation process. Finally, we use the lens of circular codes to show that codon influence on translation correlates with the strong-weak dichotomy of the first two bases of the codon. The results can lead to defining new universal tools for sequence indicators and sequence optimization for bioinformatics and biotechnological applications, and can shed light on the molecular mechanisms behind the decoding process.

Context-dependent and -independent selection on synonymous mutations revealed by 1,135 genomes of Arabidopsis thaliana

BACKGROUND

Synonymous mutations do not alter the amino acids and therefore are regarded as neutral for a long time. However, they do change the tRNA adaptation index (tAI) of a particular codon (independent of its context), affecting the tRNA availability during translation. They could also change the isoaccepting relationship with its neighboring synonymous codons in particular context, which again affects the local translation process. Evidence of selection pressure on synonymous mutations has emerged.

RESULTS

The proposed selection patterns on synonymous mutations are never formally and systematically tested in plant species. We fully take advantage of the SNP data from 1,135 A. thaliana lines, and found that the synonymous mutations that increase tAI or the isoaccepting mutations in isoaccepting codon context tend to have higher derived allele frequencies (DAF) compared to other synonymous mutations of the opposite effects.

CONCLUSIONS

Synonymous mutations are not strictly neutral. The synonymous mutations that increase tAI or the isoaccepting mutations in isoaccepting codon context are likely to be positively selected. We propose the concept of context-dependent and -independent selection on synonymous mutations. These concepts broaden our knowledge of the functional consequences of synonymous mutations, and should be appealing to phytologists and evolutionary biologists.

Elevated expression of the adhesion GPCR ADGRL4/ELTD1 promotes endothelial sprouting angiogenesis without activating canonical GPCR signalling

ADGRL4/ELTD1 is an orphan adhesion GPCR (aGPCR) expressed in endothelial cells that regulates tumour angiogenesis. The majority of aGPCRs are orphan receptors. The Stachel Hypothesis proposes a mechanism for aGPCR activation, in which aGPCRs contain a tethered agonist (termed Stachel) C-terminal to the GPCR-proteolytic site (GPS) cleavage point which, when exposed, initiates canonical GPCR signalling. This has been shown in a growing number of aGPCRs. We tested this hypothesis on ADGRL4/ELTD1 by designing full length (FL) and C-terminal fragment (CTF) ADGRL4/ELTD1 constructs, and a range of potential Stachel peptides. Constructs were transfected into HEK293T cells and HTRF FRET, luciferase-reporter and Alphascreen GPCR signalling assays were performed. A stable ADGRL4/ELTD1 overexpressing HUVEC line was additionally generated and angiogenesis assays, signalling assays and transcriptional profiling were performed. ADGRL4/ELTD1 has the lowest GC content in the aGPCR family and codon optimisation significantly increased its expression. FL and CTF ADGRL4/ELTD1 constructs, as well as Stachel peptides, did not activate canonical GPCR signalling. Furthermore, stable overexpression of ADGRL4/ELTD1 in HUVECs induced sprouting angiogenesis, lowered in vitro anastomoses, and decreased proliferation, without activating canonical GPCR signalling or MAPK/ERK, PI3K/AKT, JNK, JAK/HIF-1α, beta catenin or STAT3 pathways. Overexpression upregulated ANTXR1, SLC39A6, HBB, CHRNA, ELMOD1, JAG1 and downregulated DLL4, KIT, CCL15, CYP26B1. ADGRL4/ELTD1 specifically regulates the endothelial tip-cell phenotype through yet undefined signalling pathways.

Codon-based indices for modeling gene expression and transcript evolution

Codon usage bias (CUB) refers to the phenomena that synonymous codons are used in different frequencies in most genes and organisms. The general assumption is that codon biases reflect a balance between mutational biases and natural selection. Today we understand that the codon content is related and can affect all gene expression steps. Starting from the 1980s, codon-based indices have been used for answering different questions in all biomedical fields, including systems biology, agriculture, medicine, and biotechnology. In general, codon usage bias indices weigh each codon or a small set of codons to estimate the fitting of a certain coding sequence to a certain phenomenon (e.g., bias in codons, adaptation to the tRNA pool, frequencies of certain codons, transcription elongation speed, etc.) and are usually easy to implement. Today there are dozens of such indices; thus, this paper aims to review and compare the different codon usage bias indices, their applications, and advantages. In addition, we perform analysis that demonstrates that most indices tend to correlate even though they aim to capture different aspects. Due to the centrality of codon usage bias on different gene expression steps, it is important to keep developing new indices that can capture additional aspects that are not modeled with the current indices.

CDH1 gene rs1801552 C/T polymorphism increases susceptibility to esophageal squamous cell carcinoma but not to gastric cardiac adenocarcinoma

PURPOSE

The present study aimed to investigate whether the single nucleotide polymorphism (SNP) rs1801552 C/T in CDH1 gene is correlated with the risk of esophageal squamous cell carcinoma (ESCC) and gastric cardiac adenocarcinoma (GCA), as a preliminary study.

METHODS

The rs1801552 C/T polymorphism was genotyped by the method of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 1316 cancer patients (810 ESCC and 506 GCA) and 1966 controls in north China. We performed two case-control studies, each of which included a population-based set and a hospital-based set.

RESULTS

The data showed that the rs1801552 C/T polymorphism was associated with the risk of ESCC. Allelotype and genotype distributions of the rs1801552 C/T polymorphism in ESCC patients of high-incidence region and hospital were significantly different from that in their respective controls (P < 0.05). Compared with C/C genotype, T/T genotype increased the risk of ESCC in high-incidence region and hospital (age, sex, smoking status and family history of UGIC adjusted odds ratio (OR) = 1.79 and 2.10, 95% confidence interval (CI) = 1.23 - 2.60 and 1.10 - 4.04, respectively). Allelotype and genotype distributions of the rs1801552 C/T polymorphism in GCA patients were not significantly different from that in their controls, respectively (P > 0.05).

CONCLUSIONS

The findings in the present pilot study suggest that the rs1801552 C/T polymorphism was associated with the risk of ESCC, but was not associated with the risk of GCA in high-incidence region and hospital.

Inferring Adaptive Codon Preference to Understand Sources of Selection Shaping Codon Usage Bias

Alternative synonymous codons are often used at unequal frequencies. Classically, studies of such codon usage bias (CUB) attempted to separate the impact of neutral from selective forces by assuming that deviations from a predicted neutral equilibrium capture selection. However, GC-biased gene conversion (gBGC) can also cause deviation from a neutral null. Alternatively, selection has been inferred from CUB in highly expressed genes, but the accuracy of this approach has not been extensively tested, and gBGC can interfere with such extrapolations (e.g., if expression and gene conversion rates covary). It is therefore critical to examine deviations from a mutational null in a species with no gBGC. To achieve this goal, we implement such an analysis in the highly AT rich genome of Dictyostelium discoideum, where we find no evidence of gBGC. We infer neutral CUB under mutational equilibrium to quantify "adaptive codon preference," a nontautologous genome wide quantitative measure of the relative selection strength driving CUB. We observe signatures of purifying selection consistent with selection favoring adaptive codon preference. Preferred codons are not GC rich, underscoring the independence from gBGC. Expression-associated "preference" largely matches adaptive codon preference but does not wholly capture the influence of selection shaping patterns across all genes, suggesting selective constraints associated specifically with high expression. We observe patterns consistent with effects on mRNA translation and stability shaping adaptive codon preference. Thus, our approach to quantifying adaptive codon preference provides a framework for inferring the sources of selection that shape CUB across different contexts within the genome.

mRNA vaccines for COVID-19: what, why and how

The Coronavirus disease-19 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus -2 (SARS-CoV-2), has impacted human lives in the most profound ways with millions of infections and deaths. Scientists and pharmaceutical companies have been in race to produce vaccines against SARS-CoV-2. Vaccine generation usually demands years of developing and testing for efficacy and safety. However, it only took less than one year to generate two mRNA vaccines from their development to deployment. The rapid production time, cost-effectiveness, versatility in vaccine design, and clinically proven ability to induce cellular and humoral immune response have crowned mRNA vaccines with spotlights as most promising vaccine candidates in the fight against the pandemic. In this review, we discuss the general principles of mRNA vaccine design and working mechanisms of the vaccines, and provide an up-to-date summary of pre-clinical and clinical trials on seven anti-COVID-19 mRNA candidate vaccines, with the focus on the two mRNA vaccines already licensed for vaccination. In addition, we highlight the key strategies in designing mRNA vaccines to maximize the expression of immunogens and avoid intrinsic innate immune response. We also provide some perspective for future vaccine development against COVID-19 and other pathogens.

Adaptation of codon and amino acid use for translational functions in highly expressed cricket genes

BACKGROUND

For multicellular organisms, much remains unknown about the dynamics of synonymous codon and amino acid use in highly expressed genes, including whether their use varies with expression in different tissue types and sexes. Moreover, specific codons and amino acids may have translational functions in highly transcribed genes, that largely depend on their relationships to tRNA gene copies in the genome. However, these relationships and putative functions are poorly understood, particularly in multicellular systems.

RESULTS

Here, we studied codon and amino acid use in highly expressed genes from reproductive and nervous system tissues (male and female gonad, somatic reproductive system, brain and ventral nerve cord, and male accessory glands) in the cricket Gryllus bimaculatus. We report an optimal codon, defined as the codon preferentially used in highly expressed genes, for each of the 18 amino acids with synonymous codons in this organism. The optimal codons were mostly shared among tissue types and both sexes. However, the frequency of optimal codons was highest in gonadal genes. Concordant with translational selection, a majority of the optimal codons had abundant matching tRNA gene copies in the genome, but sometimes obligately required wobble tRNAs. We suggest the latter may comprise a mechanism for slowing translation of abundant transcripts, particularly for cell-cycle genes. Non-optimal codons, defined as those least commonly used in highly transcribed genes, intriguingly often had abundant tRNAs, and had elevated use in a subset of genes with specialized functions (gametic and apoptosis genes), suggesting their use promotes the translational upregulation of particular mRNAs. In terms of amino acids, we found evidence suggesting that amino acid frequency, tRNA gene copy number, and amino acid biosynthetic costs (size/complexity) had all interdependently evolved in this insect model, potentially for translational optimization.

CONCLUSIONS

Collectively, the results suggest a model whereby codon use in highly expressed genes, including optimal, wobble, and non-optimal codons, and their tRNA abundances, as well as amino acid use, have been influenced by adaptation for various functional roles in translation within this cricket. The effects of expression in different tissue types and the two sexes are discussed.

Synonymous variants that disrupt messenger RNA structure are significantly constrained in the human population

BACKGROUND

The role of synonymous single-nucleotide variants in human health and disease is poorly understood, yet evidence suggests that this class of "silent" genetic variation plays multiple regulatory roles in both transcription and translation. One mechanism by which synonymous codons direct and modulate the translational process is through alteration of the elaborate structure formed by single-stranded mRNA molecules. While tools to computationally predict the effect of non-synonymous variants on protein structure are plentiful, analogous tools to systematically assess how synonymous variants might disrupt mRNA structure are lacking.

RESULTS

We developed novel software using a parallel processing framework for large-scale generation of secondary RNA structures and folding statistics for the transcriptome of any species. Focusing our analysis on the human transcriptome, we calculated 5 billion RNA-folding statistics for 469 million single-nucleotide variants in 45,800 transcripts. By considering the impact of all possible synonymous variants globally, we discover that synonymous variants predicted to disrupt mRNA structure have significantly lower rates of incidence in the human population.

CONCLUSIONS

These findings support the hypothesis that synonymous variants may play a role in genetic disorders due to their effects on mRNA structure. To evaluate the potential pathogenic impact of synonymous variants, we provide RNA stability, edge distance, and diversity metrics for every nucleotide in the human transcriptome and introduce a "Structural Predictivity Index" (SPI) to quantify structural constraint operating on any synonymous variant. Because no single RNA-folding metric can capture the diversity of mechanisms by which a variant could alter secondary mRNA structure, we generated a SUmmarized RNA Folding (SURF) metric to provide a single measurement to predict the impact of secondary structure altering variants in human genetic studies.