Effects of codon usage on gene expression: empirical studies on Drosophila

Analysis of Codon Usage Bias of 30 Chloroplast Genomes in Ulva (Ulvophyceae, Chlorophyta)

BACKGROUND

Ulva is a globally distributed genus with ecological and economic significance, yet the codon usage bias of the Ulva chloroplast genome remains poorly understood.

METHODS

We assessed the Ulva chloroplast genome codon usage patterns and their drivers by analyzing 30 genomes across 16 Ulva species.

RESULTS

The nucleotide composition analysis demonstrated that Ulva chloroplast genomes are rich in A/T, and prefer to use codons that ended with A/T. The relative synonymous codon usage analysis suggested that related species have similar codon usage patterns. A total of 25 high-frequency codons and 7-14 optimal codons were identified in these chloroplast genomes. The ENC values ranged from 31.40 to 32.76, all of which are less than 35, illustrating a strong codon bias of the Ulva genus. Our comparative analyses suggested that natural selection played the main role in the formation of the codon usage bias. Furthermore, the correlation analysis indicated that an influence of the base composition and gene expression levels on the codon usage bias.

CONCLUSIONS

This study provides the first comprehensive analysis of the codon usage patterns in Ulva chloroplast genomes, improving our understanding of the genetics and evolution of these economically and ecologically important macroalgae.

Factors affecting rAAV titers during triple-plasmid transient transfection in HEK-293 cells

The efficiency of triple-plasmid transfection in recombinant Adeno-Associated Virus (rAAV) production was analyzed by examining two distinct HEK-293 cells lines. These were categorized as high producer (HP) and low producer (LP) based on their differing levels of productivity under identical conditions. Analysis of RNA expression levels of viral genes revealed disparities in plasmid derived gene expression between the cell lines. Further assessment of transfection efficiency utilizing labeled plasmids revealed lower plasmid uptake and less efficient nuclear transport in LP cell line. Additionally, we observed inferior translation activity in LP, contributing to its shortcomings in overall productivity. In our attempt to optimize plasmid ratios to enhance fully packaged rAAV particle yield, we discovered cell-line-specific optimization potential. The findings highlight the transfection's complexity, urging tailored strategies for improved rAAV production based on each cell line's characteristics, enhancing understanding and guiding further efficiency optimization in rAAV production.

Comparative analysis of codon usage bias in chloroplast genomes of ten medicinal species of Rutaceae

Rutaceae family comprises economically important plants due to their extensive applications in spices, food, oil, medicine, etc. The Rutaceae plants is able to better utilization through biotechnology. Modern biotechnological approaches primarily rely on the heterologous expression of functional proteins in different vectors. However, several proteins are difficult to express outside their native environment. The expression potential of functional genes in heterologous systems can be maximized by replacing the rare synonymous codons in the vector with preferred optimal codons of functional genes. Codon usage bias plays a critical role in biogenetic engineering-based research and development. In the current study, 727 coding sequences (CDSs) obtained from the chloroplast genomes of ten Rutaceae plant family members were analyzed for codon usage bias. The nucleotide composition analysis of codons showed that these codons were rich in A/T(U) bases and preferred A/T(U) endings. Analyses of neutrality plots, effective number of codons (ENC) plots, and correlations between ENC and codon adaptation index (CAI) were conducted, which revealed that natural selection is a major driving force for the Rutaceae plant family's codon usage bias, followed by base mutation. In the ENC vs. CAI plot, codon usage bias in the Rutaceae family had a negligible relationship with gene expression level. For each sample, we screened 12 codons as preferred and high-frequency codons simultaneously, of which GCU encoding Ala, UUA encoding Leu, and AGA encoding Arg were the most preferred codons. Taken together, our study unraveled the synonymous codon usage pattern in the Rutaceae family, providing valuable information for the genetic engineering of Rutaceae plant species in the future.

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.

Analysis of synonymous codon usage of transcriptome database in Rheum palmatum

Background

Rheum palmatum is an endangered and important medicinal plant in Asian countries, especially in China. However, there is little knowledge about the codon usage bias for R. palmatum CDSs. In this project, codon usage bias was determined based on the R. palmatum 2,626 predicted CDSs from R. palmatum transcriptome.

Methods

In this study, all codon usage bias parameters and nucleotide compositions were calculated by Python script, Codon W, DNA Star, CUSP of EMBOSS.

Results

The average GC and GC3 content are 46.57% and 46.6%, respectively, the results suggested that there exists a little more AT than GC in the R. palmatum genes, and the codon bias of R. palmatum genes preferred to end with A/T. We concluded that the codon bias in R. palmatum was affect by nucleotide composition, mutation pressure, natural selection, gene expression levels, and the mutation pressure is the prominent factor. In addition, we figured out 28 optimal codons and most of them ended with A or U. The project here can offer important information for further studies on enhancing the gene expression using codon optimization in heterogeneous expression system, predicting the genetic and evolutionary mechanisms in R. palmatum.

Codon usage similarity between viral and some host genes suggests a codon-specific translational regulation

The codon usage pattern is a specific characteristic of each species; however, the codon usage of all of the genes in a genome is not uniform. Intriguingly, most viruses have codon usage patterns that are vastly different from the optimal codon usage of their hosts. How viral genes with different codon usage patterns are efficiently expressed during a viral infection is unclear. An analysis of the similarity between viral codon usage and the codon usage of the individual genes of a host genome has never been performed. In this study, we demonstrated that the codon usage of human RNA viruses is similar to that of some human genes, especially those involved in the cell cycle. This finding was substantiated by its concordance with previous reports of an upregulation at the protein level of some of these biological processes. It therefore suggests that some suboptimal viral codon usage patterns may actually be compatible with cellular translational machineries in infected conditions.

Comparative in silico analysis of ftsZ gene from different bacteria reveals the preference for core set of codons in coding sequence structuring and secondary structural elements determination

The deluge of sequence information in the recent times provide us with an excellent opportunity to compare organisms on a large genomic scale. In this study we have tried to decipher the variation in the gene organization and structuring of a vital bacterial gene called ftsZ which codes for an integral component of the bacterial cell division, the FtsZ protein. FtsZ is homologous to tubulin protein and has been found to be ubiquitous in eubacteria. FtsZ is showing increasing promise as a target for antibacterial drug discovery. Our study of ftsZ protein from 143 different bacterial species spanning a wider range of morphological and physiological type demonstrates that the ftsZ gene of about ninety three percent of the organisms show relatively biased codon usage profile and significant GC deviation from their genomic GC content. Comparative codon usage analysis of ftsZ and a core housekeeping gene rpoB demonstrated that codon usage pattern of ftsZ CDS is shaped by natural selection to a large extent and mimics that of a housekeeping gene. We have also detected a tendency among the different organisms to utilize a core set of codons in structuring the ftsZ coding sequence. We observed that the compositional frequency of the amino acid serine in the FtsZ protein appears to be a indicator of the bacterial lifestyle. Our meticulous analysis of the ftsZ gene linked with the corresponding FtsZ protein show that there is a bias towards the use of specific synonymous codons particularly in the helix and strand regions of the multi-domain FtsZ protein. Overall our findings suggest that in an indispensable and vital protein such as FtsZ, there is an inherent tendency to maintain form for optimized performance in spite of the extrinsic variability in coding features.

Codon Usage Differences among Genes Expressed in Different Tissues of Drosophila melanogaster

Codon usage patterns are affected by both mutational biases and translational selection. The frequency at which each codon is used in the genome is directly linked to the cellular concentrations of their corresponding tRNAs. Transfer RNA abundances—as well as the abundances of other potentially relevant factors, such as RNA-binding proteins—may vary across different tissues, making it possible that genes expressed in different tissues are subject to different translational selection regimes, and thus differ in their patterns of codon usage. These differences, however, are poorly understood, having been studied only in Arabidopsis, rice and human, with controversial results in human. Drosophila melanogaster is a suitable model organism to study tissue-specific codon adaptation given its large effective population size. Here, we compare 2,046 genes, each expressed specifically in one tissue of D. melanogaster. We show that genes expressed in different tissues exhibit significant differences in their patterns of codon usage, and that these differences are only partially due to differences in GC content, expression levels, or protein lengths. Remarkably, these differences are stronger when analyses are restricted to highly expressed genes. Our results strongly suggest that genes expressed in different tissues are subject to different regimes of translational selection.

A novel framework for evaluating the performance of codon usage bias metrics

The unequal utilization of synonymous codons affects numerous cellular processes including translation rates, protein folding and mRNA degradation. In order to understand the biological impact of variable codon usage bias (CUB) between genes and genomes, it is crucial to be able to accurately measure CUB for a given sequence. A large number of metrics have been developed for this purpose, but there is currently no way of systematically testing the accuracy of individual metrics or knowing whether metrics provide consistent results. This lack of standardization can result in false-positive and false-negative findings if underpowered or inaccurate metrics are applied as tools for discovery. Here, we show that the choice of CUB metric impacts both the significance and measured effect sizes in numerous empirical datasets, raising questions about the generality of findings in published research. To bring about standardization, we developed a novel method to create synthetic protein-coding DNA sequences according to different models of codon usage. We use these benchmark sequences to identify the most accurate and robust metrics with regard to sequence length, GC content and amino acid heterogeneity. Finally, we show how our benchmark can aid the development of new metrics by providing feedback on its performance compared to the state of the art.

Analysis of synonymous codon usage pattern of genes in unique non-blood-sucking leech Whitmania pigra

Whitmania pigra is a unique, fluid-sucking ectoparasite and an anticoagulant medical leech. The codon usage bias (CUB) is the nonuniform usage of synonymous codons in which some codons are more preferred than others. Here, we performed a comprehensive analysis of CUB of genes in W. pigra, analyzing 140 780 transcripts, 59 553 unigenes, and 20 304 qualified coding sequences (CDSs) from the transcriptomic data of W. pigra. The effective number of codons values suggested that the CUB was low in these genes. We recognized profoundly favored codons in W. pigra that have a G/C-ending. Parity rule two-bias plots suggested that both mutation pressure and natural selection might have influenced the CUB. However, neutrality plots revealed that natural selection might have played a major role while mutation pressure might have played a minor role in shaping the CUB. We applied principal component analysis to relative synonymous codon usage values for divided CDSs based on GC content and codon-ending bases. Codon usage in W. pigra had a general inclination toward C-ending codons and natural selection rather than mutation pressure is the dominant force in the genetic evolution of W. pigra. To our knowledge, this is the first study to describe a complete codon usage analysis of W. pigra; this will increase the understanding of CUB and evolution in W. pigra. The analysis of codon usage patterns in W. pigra aids in understanding its evolution and genetic architecture.

Incompatible Translation Drives a Convergent Evolution and Viral Attenuation During the Development of Live Attenuated Vaccine

Live attenuated vaccines are widely used to protect humans or animals from pathogen infections. We have previously developed a chicken embryo-attenuated Duck Hepatitis A Virus genotype 1 (DHAV-1) vaccine (CH60 strain). This study aims to understand the mechanisms that drive a virulent strain to an attenuated virus. Here, we systematically compared five DHAV-1 chicken embryo attenuated strains and 68 virulent strains. Phylogenetic analysis indicated that duck virulent strains isolated from different geographic regions of China undergo a convergent evolution in the chicken embryos. Comparative analysis indicated that the codon usage bias of the attenuated strains were shaped by chicken codons usage bias, which essentially contributed to viral adaption in the unsuitable host driven by incompatible translation. Of note, the missense mutations in coding region and mutations in untranslated regions may also contribute to viral attenuation of DHAV-1 to some extent. Importantly, we have experimentally confirmed that the expression levels of four viral proteins (2A3pro, 2A3pro, 3C^pro, and 3D^pro) in the liver and kidney of ducks infected with an attenuated strain are significantly lower than that infected with a virulent strain, despite with similar virus load. Thus, the key mechanisms of viral attenuation revealed by this study may lead to innovative and easy approaches in designing live attenuated vaccines.

Analysis of codon usage patterns in Hirudinaria manillensis reveals a preference for GC-ending codons caused by dominant selection constraints

Background

Hirudinaria manillensis is an ephemeral, blood-sucking ectoparasite, possessing anticoagulant capacities with potential medical applications. Analysis of codon usage patterns would contribute to our understanding of the evolutionary mechanisms and genetic architecture of H. manillensis, which in turn would provide insight into the characteristics of other leeches. We analysed codon usage and related indices using 18,000 coding sequences (CDSs) retrieved from H. manillensis RNA-Seq data.

Results

We identified four highly preferred codons in H. manillensis that have G/C-endings. Points generated in an effective number of codons (ENC) plot distributed below the standard curve and the slope of a neutrality plot was less than 1. Highly expressed CDSs had lower ENC content and higher GC content than weakly expressed CDSs. Principal component analysis conducted on relative synonymous codon usage (RSCU) values divided CDSs according to GC content and divided codons according to ending bases. Moreover, by determining codon usage, we found that the majority of blood-diet related genes have undergone less adaptive evolution in H. manillensis, except for those with homologous sequences in the host species.

Conclusions

Codon usage in H. manillensis had an overall preference toward C-endings and indicated that codon usage patterns are mediated by differential expression, GC content, and biological function. Although mutation pressure effects were also notable, the majority of genetic evolution in H. manillensis was driven by natural selection.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4937-x) contains supplementary material, which is available to authorized users.

An AlgU-Regulated Antisense Transcript Encoded within the Pseudomonas syringae fleQ Gene Has a Positive Effect on Motility

Production of bacterial flagella is controlled by a multitiered regulatory system that coordinates the expression of 40 to 50 subunits and ordered assembly of these elaborate structures. Flagellar expression is environmentally controlled, presumably to optimize the benefits and liabilities of having these organelles on cell growth and survival. We recently reported a global survey of AlgU-dependent regulation and binding in Pseudomonas syringae pv. tomato DC3000 that included evidence for strong downregulation of many flagellar and chemotaxis motility genes. Here, we returned to those data to look for other AlgU-dependent influences on the flagellar regulatory network. We identified an AlgU-dependent antisense transcript expressed from within the fleQ gene, the master regulator of flagellar biosynthesis in Pseudomonas We tested whether expression of this antisense RNA influenced bacterial behavior and found that it reduces AlgU-dependent downregulation of motility. Importantly, this antisense expression influenced motility only under conditions in which AlgU was expressed. Comparative sequence analysis of the locus containing the antisense transcript's AlgU-dependent promoter in over 300 Pseudomonas genomes revealed sequence conservation in most strains that encode AlgU. This suggests that the antisense transcript plays an important role that is conserved across most of the genus Pseudomonas IMPORTANCE Pseudomonas syringae is a globally distributed host-specific bacterial pathogen that causes disease in a wide-range of plants. An elaborate gene expression regulation network controls flagellum production, which is important for proper flagellum assembly and a key aspect of certain lifestyle transitions. P. syringae pv. tomato DC3000 uses flagellum-powered motility in the early stages of host colonization and adopts a sessile lifestyle after entering plant tissues, but the regulation of this transition is not understood. Our work demonstrates a link between regulation of motility and global transcriptional control that facilitates bacterial growth and disease in plants. Additionally, sequence comparisons suggest that this regulation mechanism is conserved in most members of the genus Pseudomonas.

The Code of Silence: Widespread Associations Between Synonymous Codon Biases and Gene Function

Some mutations in gene coding regions exchange one synonymous codon for another, and thus do not alter the amino acid sequence of the encoded protein. Even though they are often called 'silent,' these mutations may exhibit a plethora of effects on the living cell. Therefore, they are often selected during evolution, causing synonymous codon usage biases in genomes. Comparative analyses of bacterial, archaeal, fungal, and human cancer genomes have found many links between a gene's biological role and the accrual of synonymous mutations during evolution. In particular, highly expressed genes in certain functional categories are enriched with optimal codons, which are decoded by the abundant tRNAs, thus enhancing the speed and accuracy of the translating ribosome. The set of genes exhibiting codon adaptation differs between genomes, and these differences show robust associations to organismal phenotypes. In addition to selection for translation efficiency, other distinct codon bias patterns have been found in: amino acid starvation genes, cyclically expressed genes, tissue-specific genes in animals and plants, oxidative stress response genes, cellular differentiation genes, and oncogenes. In addition, genomes of organisms harboring tRNA modifications exhibit particular codon preferences. The evolutionary trace of codon bias patterns across orthologous genes may be examined to learn about a gene's relevance to various phenotypes, or, more generally, its function in the cell.