Introns and gene expression: cellular constraints, transcriptional regulation, and evolutionary consequences

Hippocampal transcriptome-wide association study and pathway analysis of mitochondrial solute carriers in Alzheimer's disease

The etiopathogenesis of late-onset Alzheimer's disease (AD) is increasingly recognized as the result of the combination of the aging process, toxic proteins, brain dysmetabolism, and genetic risks. Although the role of mitochondrial dysfunction in the pathogenesis of AD has been well-appreciated, the interaction between mitochondrial function and genetic variability in promoting dementia is still poorly understood. In this study, by tissue-specific transcriptome-wide association study (TWAS) and further meta-analysis, we examined the genetic association between mitochondrial solute carrier family (SLC25) genes and AD in three independent cohorts and identified three AD-susceptibility genes, including SLC25A10, SLC25A17, and SLC25A22. Integrative analysis using neuroimaging data and hippocampal TWAS-predicted gene expression of the three susceptibility genes showed an inverse correlation of SLC25A22 with hippocampal atrophy rate in AD patients, which outweighed the impacts of sex, age, and apolipoprotein E4 (ApoE4). Furthermore, SLC25A22 downregulation demonstrated an association with AD onset, as compared with the other two transcriptome-wide significant genes. Pathway and network analysis related hippocampal SLC25A22 downregulation to defects in neuronal function and development, echoing the enrichment of SLC25A22 expression in human glutamatergic neurons. The most parsimonious interpretation of the results is that we have identified AD-susceptibility genes in the SLC25 family through the prediction of hippocampal gene expression. Moreover, our findings mechanistically yield insight into the mitochondrial cascade hypothesis of AD and pave the way for the future development of diagnostic tools for the early prevention of AD from a perspective of precision medicine by targeting the mitochondria-related genes.

DNA Damage, Genome Stability, and Adaptation: A Question of Chance or Necessity?

DNA damage causes the mutations that are the principal source of genetic variation. DNA damage detection and repair mechanisms therefore play a determining role in generating the genetic diversity on which natural selection acts. Speciation, it is commonly assumed, occurs at a rate set by the level of standing allelic diversity in a population. The process of speciation is driven by a combination of two evolutionary forces: genetic drift and ecological selection. Genetic drift takes place under the conditions of relaxed selection, and results in a balance between the rates of mutation and the rates of genetic substitution. These two processes, drift and selection, are necessarily mediated by a variety of mechanisms guaranteeing genome stability in any given species. One of the outstanding questions in evolutionary biology concerns the origin of the widely varying phylogenetic distribution of biodiversity across the Tree of Life and how the forces of drift and selection contribute to shaping that distribution. The following examines some of the molecular mechanisms underlying genome stability and the adaptive radiations that are associated with biodiversity and the widely varying species richness and evenness in the different eukaryotic lineages.

Genome-wide characterization of SmZHD gene family and the role of SmZHD12 in regulating anthocyanin biosynthesis in eggplant (Solanum melongena L.)

KEY MESSAGE

SmZHDs was highly expressed in anthocyanin-rich parts of eggplant. SmZHD12 can activate the expression of SmCHS, SmANS, SmDFR and SmF3H. Overexpression of SmZHD12 promotes anthocyanin biosynthesis in Arabidopsis. The Zinc finger-homeodomain (ZHD) proteins family genes are known to play a significant role in plant development and physiological processes. However, the evolutionary history and function of the ZHD gene family in eggplant remain largely unexplored. This study categorizes a total of 15 SmZHD genes into SmMIF and SmZHD subfamilies based on conserved domains. The phylogeny, gene structure, conserved motifs, promoter elements, and chromosomal locations of the SmZHD genes were comprehensively analyzed. Tissue expression profiles indicate that the majority of SmZHD genes are expressed in anthocyanin-rich areas. qRT-PCR assays revealed distinct expression patterns of SmZHD genes in response to various treatments, indicating their potential involvement in multiple signaling pathways. Analysis of transcriptomic data from light-treated eggplant peel identified SmZHD12 as the most light-responsive gene among the 15 SmZHD genes. Consequently, this study provides further evidence that SmZHD12 facilitates anthocyanin accumulation in Arabidopsis leaves by upregulating the expression of anthocyanin biosynthesis structural genes, as confirmed by dual-luciferase assays and Arabidopsis genetic transformation. Our study will lay a solid foundation for the in-depth study of the involvement of SmZHD genes in the regulation of anthocyanin biosynthesis.

Rapid adaptation of cellular metabolic rate to the MicroRNA complements of mammals and its relevance to the evolution of endothermy

The metabolic efficiency of mammalian cells depends on the attenuation of intrinsic translation noise by microRNAs. We devised a metric of cellular metabolic rate (cMR), rMR/Mexp optimally fit to the number of microRNA families (mirFam), that is robust to variation in mass and sensitive to body temperature (Tb), consistent with the heat dissipation limit theory of Speakman and Król (2010). Using mirFam as predictor, an Ornstein-Uhlenbeck process of stabilizing selection, with an adaptive shift at the divergence of Boreoeutheria, accounted for 95% of the variation in cMR across mammals. Branchwise rates of evolution of cMR, mirFam and Tb concurrently increased 6- to 7-fold at the divergence of Boreoeutheria, independent of mass. Cellular MR variation across placental mammals was also predicted by the sum of model conserved microRNA-target interactions, revealing an unexpected degree of integration of the microRNA-target apparatus into the energy economy of the mammalian cell.

Transcript accumulation rates in the early Caenorhabditis elegans embryo

Dynamic transcriptional changes are widespread in rapidly dividing developing embryos when cell fate decisions are made quickly. The Caenorhabditis elegans embryo overcomes these constraints partly through the rapid production of high levels of transcription factor mRNAs. Transcript accumulation rates for some developmental genes are known at single-cell resolution, but genome-scale measurements are lacking. We estimate zygotic mRNA accumulation rates from single-cell RNA sequencing data calibrated with single-molecule transcript imaging. Rapid transcription is common in the early C. elegans embryo with rates highest soon after zygotic transcription begins. High-rate genes are enriched for recently duplicated cell-fate regulators and share common genomic features. We identify core promoter elements associated with high rate and measure their contributions for two early endomesodermal genes, ceh-51 and sdz-31. Individual motifs modestly affect accumulation rates, suggesting multifactorial control. These results are a step toward estimating absolute transcription kinetics and understanding how transcript dosage drives developmental decisions.

Spurious intragenic transcription is a feature of mammalian cellular senescence and tissue aging

Mammalian aging is characterized by the progressive loss of tissue function and increased risk for disease. Accumulation of senescent cells in aging tissues partly contributes to this decline, and targeted depletion of senescent cells in vivo ameliorates many age-related phenotypes. The fundamental molecular mechanisms responsible for the decline of cellular health and fitness during senescence and aging are largely unknown. In this study, we investigated whether chromatin-mediated loss of transcriptional fidelity, known to contribute to fitness and survival in yeast and worms, also occurs during human cellular senescence and mouse aging. Our findings reveal aberrant transcription initiation inside genes during senescence and aging that co-occurs with changes in the chromatin landscape. Interventions that alter these spurious transcripts have profound consequences on cellular health, primarily affecting intracellular signal transduction pathways. We propose that age-related spurious transcription promotes a noisy transcriptome and degradation of coherent transcriptional networks.

Plastomes of Garcinia mangostana L. and Comparative Analysis with Other Garcinia Species

The two varieties of mangosteen (Garcinia mangostana L.) cultivated in Malaysia are known as Manggis and Mesta. The latter is preferred for its flavor, texture, and seedlessness. Here, we report a complete plastome (156,580 bp) of the Mesta variety that was obtained through a hybrid assembly approach using PacBio and Illumina sequencing reads. It encompasses a large single-copy (LSC) region (85,383 bp) and a small single-copy (SSC) region (17,137 bp) that are separated by 27,230 bp of inverted repeat (IR) regions at both ends. The plastome comprises 128 genes, namely, 83 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The plastome of the Manggis variety (156,582 bp) obtained from reference-guided assembly of Illumina reads was found to be nearly identical to Mesta except for two indels and the presence of a single-nucleotide polymorphism (SNP). Comparative analyses with other publicly available Garcinia plastomes, including G. anomala, G. gummi-gutta, G. mangostana var. Thailand, G. oblongifolia, G. paucinervis, and G. pedunculata, found that the gene content, gene order, and gene orientation were highly conserved among the Garcinia species. Phylogenomic analysis divided the six Garcinia plastomes into three groups, with the Mesta and Manggis varieties clustered closer to G. anomala, G. gummi-gutta, and G. oblongifolia, while the Thailand variety clustered with G. pedunculata in another group. These findings serve as future references for the identification of species or varieties and facilitate phylogenomic analysis of lineages from the Garcinia genus to better understand their evolutionary history.

CRISPR/Cas9-Targeted Disruption of Two Highly Homologous Arabidopsis thaliana DSS1 Genes with Roles in Development and the Oxidative Stress Response

Global climate change has a detrimental effect on plant growth and health, causing serious losses in agriculture. Investigation of the molecular mechanisms of plant responses to various environmental pressures and the generation of plants tolerant to abiotic stress are imperative to modern plant science. In this paper, we focus on the application of the well-established technology CRISPR/Cas9 genome editing to better understand the functioning of the intrinsically disordered protein DSS1 in plant response to oxidative stress. The Arabidopsis genome contains two highly homologous DSS1 genes, AtDSS1(I) and AtDSS1(V). This study was designed to identify the functional differences between AtDSS1s, focusing on their potential roles in oxidative stress. We generated single dss1(I) and dss1(V) mutant lines of both Arabidopsis DSS1 genes using CRISPR/Cas9 technology. The homozygous mutant lines with large indels (dss1(I)del25 and dss1(V)ins18) were phenotypically characterized during plant development and their sensitivity to oxidative stress was analyzed. The characterization of mutant lines revealed differences in root and stem lengths, and rosette area size. Plants with a disrupted AtDSS1(V) gene exhibited lower survival rates and increased levels of oxidized proteins in comparison to WT plants exposed to oxidative stress induced by hydrogen peroxide. In this work, the dss1 double mutant was not obtained due to embryonic lethality. These results suggest that the DSS1(V) protein could be an important molecular component in plant abiotic stress response.

The position of the longest intron is related to biological functions in some human genes

The evidence that introns can influence different levels of transfer of genetic information between DNA and the final product is increasing. Longer first introns were found to be a general property of eukaryotic gene structure and shown to contain a higher fraction of conserved sequence and different functional elements. Our work brings more precise information about the position of the longest introns in human protein-coding genes and possible connection with biological function and gene expression. According to our results, the position of the longest intron can be localized to the first third of introns in 64%, the second third in 19%, and the third in 17%, with notable peaks at the middle and last introns of approximately 5% and 6%, respectively. The median lengths of the longest introns decrease with increasing distance from the start of the gene from approximately 15,000 to 5,000 bp. We have shown that the position of the longest intron is in some cases linked to the biological function of the given gene. For example, DNA repair genes have the longest intron more often in the second or third. In the distribution of gene expression according to the position of the longest intron, tissue-specific profiles can be traced with the highest expression usually at the absolute positions of intron 1 and 2. In this work, we present arguments supporting the hypothesis that the position of the longest intron in a gene is another biological factor modulating the transmission of genetic information. The position of the longest intron is related to biological functions in some human genes.

Adaptive Bird-like Genome Miniaturization During the Evolution of Scallop Swimming Lifestyle

Genome miniaturization drives key evolutionary innovations of adaptive traits in vertebrates, such as the flight evolution of birds. However, whether similar evolutionary processes exist in invertebrates remains poorly understood. Derived from the second-largest animal phylum, scallops are a special group of bivalve molluscs and acquire the evolutionary novelty of the swimming lifestyle, providing excellent models for investigating the coordinated genome and lifestyle evolution. Here, we show for the first time that genome sizes of scallops exhibit a generally negative correlation with locomotion activity. To elucidate the co-evolution of genome size and swimming lifestyle, we focus on the Asian moon scallop (Amusium pleuronectes) that possesses the smallest known scallop genome while being among scallops with the highest swimming activity. Whole-genome sequencing of A. pleuronectes reveals highly conserved chromosomal macrosynteny and microsynteny, suggestive of a highly contracted but not degenerated genome. Genome reduction of A. pleuronectes is facilitated by significant inactivation of transposable elements, leading to reduced gene length, elevated expression of genes involved in energy-producing pathways, and decreased copy numbers and expression levels of biomineralization-related genes. Similar evolutionary changes of relevant pathways are also observed for bird genome reduction with flight evolution. The striking mimicry of genome miniaturization underlying the evolution of bird flight and scallop swimming unveils the potentially common, pivotal role of genome size fluctuation in the evolution of novel lifestyles in the animal kingdom.

Co-transcriptional splicing efficiency is a gene-specific feature that can be regulated by TGFβ

Differential splicing efficiency of specific introns is a mechanism that dramatically increases protein diversity, based on selection of alternative exons for the final mature mRNA. However, it is unclear whether splicing efficiency of introns within the same gene is coordinated and eventually regulated as a mechanism to control mature mRNA levels. Based on nascent chromatin-associated RNA-sequencing data, we now find that co-transcriptional splicing (CTS) efficiency tends to be similar between the different introns of a gene. We establish that two well-differentiated strategies for CTS efficiency exist, at the extremes of a gradient: short genes that produce high levels of pre-mRNA undergo inefficient splicing, while long genes with relatively low levels of pre-mRNA have an efficient splicing. Notably, we observe that genes with efficient CTS display a higher level of mature mRNA relative to their pre-mRNA levels. Further, we show that the TGFβ signal transduction pathway regulates the general CTS efficiency, causing changes in mature mRNA levels. Taken together, our data indicate that CTS efficiency is a gene-specific characteristic that can be regulated to control gene expression.

Co-transcriptional splicing efficiency is a gene-specific characteristic that can be regulated by TGFβ to modulate gene expression.

Genome-wide characterization and expression analysis of Erf gene family in cotton

BACKGROUND

AP2/ERF transcription factors are important in a variety of biological activities, including plant growth, development, and responses to biotic and abiotic stressors. However, little study has been done on cotton's AP2/ERF genes, although cotton is an essential fibre crop. We were able to examine the tissue and expression patterns of AP2/ERF genes in cotton on a genome-wide basis because of the recently published whole genome sequence of cotton. Genome-wide analysis of ERF gene family within two diploid species (G. arboreum & G. raimondii) and two tetraploid species (G. barbadense, G. hirsutum) was performed.

RESULTS

A total of 118, 120, 213, 220 genes containing the sequence of single AP2 domain were identified in G. arboreum, G. raimondii, G. barbadense and G. hirsutum respectively. The identified genes were unevenly distributed across 13/26 chromosomes of A and D genomes of cotton. Synteny and collinearity analysis revealed that segmental duplications may have played crucial roles in the expansion of the cotton ERF gene family, as well as tandem duplications played a minor role. Cis-acting elements of the promoter sites of Ghi-ERFs genes predict the involvement in multiple hormone responses and abiotic stresses. Transcriptome and qRT-PCR analysis revealed that Ghi-ERF-2D.6, Ghi-ERF-12D.13, Ghi-ERF-6D.1, Ghi-ERF-7A.6 and Ghi-ERF-11D.5 are candidate genes against salinity tolerance in upland cotton.

CONCLUSION

Overwhelmingly, the present study paves the way to better understand the evolution of cotton ERF genes and lays a foundation for future investigation of ERF genes in improving salinity stress tolerance in cotton.

Rosiglitazone Ameliorates Spinal Cord Injury via Inhibiting Mitophagy and Inflammation of Neural Stem Cells

BACKGROUND

Neurodegenerative diseases, such as Alzheimer's disease, and traumatic brain and spinal cord injury (SCI) are prevalent in clinical practice. Inhibition of hyperactive inflammation and proliferation of endogenous neural stem cells (NSCs) is a promising treatment strategy for SCI. Our previous studies demonstrated the beneficial effects of rosiglitazone (Rosi) on SCI, but its roles in inflammation inhibition and proliferation of NSCs are unknown.

METHODS

SCI in a rat model was established, and the effects of Rosi on motor functions were assessed. The effects of Rosi on NSC proliferation and the underlying mechanisms were explored in details.

RESULTS

We showed that Rosi ameliorated impairment of moto functions in SCI rats, inhibited inflammation, and promoted proliferation of NSCs in vivo. Rosi increased ATP production through enhancing glycolysis but not oxidative phosphorylation. Rosi reduced mitophagy by downregulating PTEN-induced putative kinase 1 (PINK1) transcription to promote NSC proliferation, which was effectively reversed by an overexpression of PINK1 in vitro. Through KEGG analysis and experimental validations, we discovered that Rosi reduced the expression of forkhead box protein O1 (FOXO1) which was a critical transcription factor of PINK1. Three FOXO1 consensus sequences (FCSs) were found in the first intron of the PINK1 gene, which could be potentially binding to FOXO1. The proximal FCS (chr 5: 156680169-156680185) from the translation start site exerted a more significant influence on PINK1 transcription than the other two FCSs. The overexpression of FOXO1 entirely relieved the inhibition of PINK1 transcription in the presence of Rosi.

CONCLUSIONS

Besides inflammation inhibition, Rosi suppressed mitophagy by reducing FOXO1 to decrease the transcription of PINK1, which played a pivotal role in accelerating the NSC proliferation.

Assembled and annotated 26.5 Gbp coast redwood genome: a resource for estimating evolutionary adaptive potential and investigating hexaploid origin

Sequencing, assembly, and annotation of the 26.5 Gbp hexaploid genome of coast redwood (Sequoia sempervirens) was completed leading toward discovery of genes related to climate adaptation and investigation of the origin of the hexaploid genome. Deep-coverage short-read Illumina sequencing data from haploid tissue from a single seed were combined with long-read Oxford Nanopore Technologies sequencing data from diploid needle tissue to create an initial assembly, which was then scaffolded using proximity ligation data to produce a highly contiguous final assembly, SESE 2.1, with a scaffold N50 size of 44.9 Mbp. The assembly included several scaffolds that span entire chromosome arms, confirmed by the presence of telomere and centromere sequences on the ends of the scaffolds. The structural annotation produced 118,906 genes with 113 containing introns that exceed 500 Kbp in length and one reaching 2 Mb. Nearly 19 Gbp of the genome represented repetitive content with the vast majority characterized as long terminal repeats, with a 2.9:1 ratio of Copia to Gypsy elements that may aid in gene expression control. Comparison of coast redwood to other conifers revealed species-specific expansions for a plethora of abiotic and biotic stress response genes, including those involved in fungal disease resistance, detoxification, and physical injury/structural remodeling and others supporting flavonoid biosynthesis. Analysis of multiple genes that exist in triplicate in coast redwood but only once in its diploid relative, giant sequoia, supports a previous hypothesis that the hexaploidy is the result of autopolyploidy rather than any hybridizations with separate but closely related conifer species.

Comprehensive Analyses of NAC Transcription Factor Family in Almond (Prunus dulcis) and Their Differential Gene Expression during Fruit Development

As plant specific transcription factors, NAC (NAM, ATAF1/2, CUC2) domain is involved in the plant development and stress responses. Due to the vitality of NAC gene family, BLASTp was performed to identify NAC genes in almond (Prunus dulcis). Further, phylogenetic and syntenic analyses were performed to determine the homology and evolutionary relationship. Gene duplication, gene structure, motif, subcellular localization, and cis-regulatory analyses were performed to assess the function of PdNAC. Whereas RNA-seq analysis was performed to determine the differential expression of PdNAC in fruits at various developmental stages. We identified 106 NAC genes in P. dulcis genome and were renamed according to their chromosomal distribution. Phylogenetic analysis in both P. dulcis and Arabidopsis thaliana revealed the presence of 14 subfamilies. Motif and gene structure followed a pattern according to the PdNAC position in phylogenetic subfamilies. Majority of NAC are localized in the nucleus and have ABA-responsive elements in the upstream region of PdNAC. Differential gene expression analyses revealed one and six PdNAC that were up and down-regulated, respectively, at all development stages. This study provides insights into the structure and function of PdNAC along with their role in the fruit development to enhance an understanding of NAC in P. dulcis.

Genome-wide identification of ZF-HD gene family in Triticum aestivum: Molecular evolution mechanism and function analysis

ZF-HD family genes play important roles in plant growth and development. Studies about the whole genome analysis of ZF-HD gene family have been reported in some plant species. In this study, the whole genome identification and expression profile of the ZF-HD gene family were analyzed for the first time in wheat. A total of 37 TaZF-HD genes were identified and divided into TaMIF and TaZHD subfamilies according to the conserved domain. The phylogeny tree of the TaZF-HD proteins was further divided into six groups based on the phylogenetic relationship. The 37 TaZF-HDs were distributed on 18 of 21 chromosomes, and almost all the genes had no introns. Gene duplication and Ka/Ks analysis showed that the gene family may have experienced powerful purification selection pressure during wheat evolution. The qRT-PCR analysis showed that TaZF-HD genes had significant expression patterns in different biotic stress and abiotic stress. Through subcellular localization experiments, we found that TaZHD6-3B was located in the nucleus, while TaMIF4-5D was located in the cell membrane and nucleus. Our research contributes to a comprehensive understanding of the TaZF-HD family, provides a new perspective for further research on the biological functions of TaZF-HD genes in wheat.

Transcript Profiling of MIKCc MADS-Box Genes Reveals Conserved and Novel Roles in Barley Inflorescence Development

MADS-box genes have a wide range of functions in plant reproductive development and grain production. The ABCDE model of floral organ development shows that MADS-box genes are central players in these events in dicotyledonous plants but the applicability of this model remains largely unknown in many grass crops. Here, we show that transcript analysis of all MIKCc MADS-box genes through barley (Hordeum vulgare L.) inflorescence development reveals co-expression groups that can be linked to developmental events. Thirty-four MIKCc MADS-box genes were identified in the barley genome and single-nucleotide polymorphism (SNP) scanning of 22,626 barley varieties revealed that the natural variation in the coding regions of these genes is low and the sequences have been extremely conserved during barley domestication. More detailed transcript analysis showed that MADS-box genes are generally expressed at key inflorescence developmental phases and across various floral organs in barley, as predicted by the ABCDE model. However, expression patterns of some MADS genes, for example HvMADS58 (AGAMOUS subfamily) and HvMADS34 (SEPALLATA subfamily), clearly deviate from predicted patterns. This places them outside the scope of the classical ABCDE model of floral development and demonstrates that the central tenet of antagonism between A- and C-class gene expression in the ABC model of other plants does not occur in barley. Co-expression across three correlation sets showed that specifically grouped members of the barley MIKCc MADS-box genes are likely to be involved in developmental events driving inflorescence meristem initiation, floral meristem identity and floral organ determination. Based on these observations, we propose a potential floral ABCDE working model in barley, where the classic model is generally upheld, but that also provides new insights into the role of MIKCc MADS-box genes in the developing barley inflorescence.

Shark and ray genomics for disentangling their morphological diversity and vertebrate evolution

Developmental studies of sharks and rays (elasmobranchs) have provided much insight into the process of morphological evolution of vertebrates. Although those studies are supposedly fueled by large-scale molecular sequencing information, whole-genome sequences of sharks and rays were made available only recently. One compelling difficulty of elasmobranch developmental biology is the low accessibility to embryonic study materials and their slow development. Another limiting factor is the relatively large size of their genomes. Moreover, their large body sizes restrict sustainable captive breeding, while their high body fluid osmolarity prevents reproducible cell culturing for in vitro experimentation, which has also limited our knowledge of their chromosomal organization for validation of genome sequencing products. This article focuses on egg-laying elasmobranch species used in developmental biology and provides an overview of the characteristics of the shark and ray genomes revealed to date. Developmental studies performed on a gene-by-gene basis are also reviewed from a whole-genome perspective. Among the popular regulatory genes studied in developmental biology, I scrutinize shark homologs of Wnt genes that highlight vanishing repertoires in many other vertebrate lineages, as well as Hox genes that underwent an unexpected modification unique to the elasmobranch lineage. These topics are discussed together with insights into the reconstruction of developmental programs in the common ancestor of vertebrates and its subsequent evolutionary trajectories that mark the features that are unique to, and those characterizing the diversity among, cartilaginous fishes.

Late embryogenesis abundant (LEA) gene family in Salvia miltiorrhiza: identification, expression analysis, and response to drought stress

Late embryogenesis abundant (LEA) proteins play important roles in plant defense response to drought stress. However, genome-wide identification of the LEA gene family was not revealed in Salvia miltiorrhiza. In this study, 61 SmLEA genes were identified from S. miltiorrhiza and divided into 7 subfamilies according to their conserved domains and phylogenetic relationships. SmLEA genes contained the LEA conserved motifs and few introns. SmLEA genes of the same subfamilies had similar gene structures and predicted subcellular locations. Our results indicated that the promoters of SmLEA genes contained various cis-acting elements associated with abiotic stress response. In addition, RNA-seq and real-time PCR results suggested that SmLEA genes are specifically expressed in different tissue, and most SmLEA genes can be induced by drought stress. These results provide a valuable foundation for future functional investigations of SmLEA genes and drought stress-resistant breeding of S. miltiorrhiza.

Nanopore long-read RNA-seq and absolute quantification delineate transcription dynamics in early embryo development of an insect pest

The olive fruit fly, Bactrocera oleae, is the most important pest for the olive fruit but lacks adequate transcriptomic characterization that could aid in molecular control approaches. We apply nanopore long-read RNA-seq with internal RNA standards allowing absolute transcript quantification to analyze transcription dynamics during early embryo development for the first time in this organism. Sequencing on the MinION platform generated over 31 million reads. Over 50% of the expressed genes had at least one read covering its entire length validating our full-length approach. We generated a de novo transcriptome assembly and identified 1768 new genes and a total of 79,810 isoforms; a fourfold increase in transcriptome diversity compared to the current NCBI predicted transcriptome. Absolute transcript quantification per embryo allowed an insight into the dramatic re-organization of maternal transcripts. We further identified Zelda as a possible regulator of early zygotic genome activation in B. oleae and provide further insights into the maternal-to-zygotic transition. These data show the utility of long-read RNA in improving characterization of non-model organisms that lack a fully annotated genome, provide potential targets for sterile insect technic approaches, and provide the first insight into the transcriptome landscape of the developing olive fruit fly embryo.

The transcriptional trajectories of pluripotency and differentiation comprise genes with antithetical architecture and repetitive-element content

Background

Extensive molecular differences exist between proliferative and differentiated cells. Here, we conduct a meta-analysis of publicly available transcriptomic datasets from preimplantation and differentiation stages examining the architectural properties and content of genes whose abundance changes significantly across developmental time points.

Results

Analysis of preimplantation embryos from human and mouse showed that short genes whose introns are enriched in Alu (human) and B (mouse) elements, respectively, have higher abundance in the blastocyst compared to the zygote. These highly expressed genes encode ribosomal proteins or metabolic enzymes. On the other hand, long genes whose introns are depleted in repetitive elements have lower abundance in the blastocyst and include genes from signaling pathways. Additionally, the sequences of the genes that are differentially expressed between the blastocyst and the zygote contain distinct collections of pyknon motifs that differ between up- and down-regulated genes. Further examination of the genes that participate in the stem cell-specific protein interaction network shows that their introns are short and enriched in Alu (human) and B (mouse) elements. As organogenesis progresses, in both human and mouse, we find that the primarily short and repeat-rich expressed genes make way for primarily longer, repeat-poor genes. With that in mind, we used a machine learning-based approach to identify gene signatures able to classify human adult tissues: we find that the most discriminatory genes comprising these signatures have long introns that are repeat-poor and include transcription factors and signaling-cascade genes. The introns of widely expressed genes across human tissues, on the other hand, are short and repeat-rich, and coincide with those with the highest expression at the blastocyst stage.

Conclusions

Protein-coding genes that are characteristic of each trajectory, i.e., proliferation/pluripotency or differentiation, exhibit antithetical biases in their intronic and exonic lengths and in their repetitive-element content. While the respective human and mouse gene signatures are functionally and evolutionarily conserved, their introns and exons are enriched or depleted in organism-specific repetitive elements. We posit that these organism-specific repetitive sequences found in exons and introns are used to effect the corresponding genes’ regulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-020-00928-8.

Genome-wide identification and expression analysis of the ERF transcription factor family in pineapple (Ananas comosus (L.) Merr.)

Pineapple (Ananas comosus (L.) Merr.) is an important tropical fruit with high economic value. The quality and yield of pineapple will be affected by various environmental conditions. Under adverse conditions, plants can produce a complex reaction mechanism to enhance their resistance. It has been reported that the member of ethylene responsive transcription factors (ERFs) plays a crucial role in plant developmental process and stress response. However, the function of these proteins in pineapple remains limited. In this study, a total of 74 ERF genes (AcoERFs) were identified in pineapple genome, named from AcoERF1 to AcoERF74, and divided into 13 groups based on phylogenetic analysis. We also analyzed gene structure, conserved motif and chromosomal location of AcoERFs, and the AcoERFs within the same group possess similar gene structures and motif compositions. Three genes (AcoERF71, AcoERF73 and AcoERF74) were present on unanchored scaffolds, so they could not be conclusively mapped on chromosome. Synteny and cis-elements analysis of ERF genes provided deep insight into the evolution and function of pineapple ERF genes. Furthermore, we analyzed the expression profiling of AcoERF in different tissues and developmental stages, and 22 AcoERF genes were expressed in all examined tissues, in which five genes (AcoERF13, AcoERF16, AcoERF31, AcoERF42, and AcoERF65) had high expression levels. Additionally, nine AcoERF genes were selected for functional verification by qRT-PCR. These results provide useful information for further investigating the evolution and functions of ERF family in pineapple.

Molecular Identification, Characterization, and Expression Analysis of a Metallothionein Gene from Septifer virgatus

This study provides a preliminary characterization of a metallothionein (MT) gene in Septifer virgatus and highlights its potential use in biomonitoring. The full-length SvMT cDNA and the complete sequence of the SvMT gene were identified using reverse transcriptase PCR coupled with the rapid amplification of cDNA ends and the primer walking method. The SvMT cDNA encodes a protein of 72 amino acids having nine classical Cys-X-Cys motifs. Moreover, the deduced amino acids contained the conserved motif (Cys-x-Cys-x(3)-Cys-Thr-Gly-x(3)-Cys-x-Cys-x(3)-Cys-x-Cys-Lys) of MT family 2. Its molecular mass and isoelectric point were estimated to be 7.01 kDa and 7.00, respectively. BLAST-based searching indicated that SvMT shared 81.0% amino acid sequence identity with Mytilus edulis MT-20-II. The SvMT gene has three coding exons and two introns. After exposure to 1 mg/L cadmium chloride, the expression of SvMT increased 15-fold by 3 days (d), with a maximum expression of 27-fold by 5 d compared with the pre-exposure level. After exposure to 2 mg/L zinc chloride, the expression of SvMT increased 2.5-fold by 3 d and 4.7-fold by 5 d compared with the pre-exposure level. A significant increase in the expression level of SvMT mRNA was observed after the exposure of S. virgatus to the combination of 0.003 mg/L cadmium chloride and 0.2 mg/L zinc chloride compared with the pre-exposure level. Our work indicates that the SvMT gene is associated with stress responses and could be a potential biomarker for marine pollution.

A 51 bp indel polymorphism within the PTH1R gene is significantly associated with chicken growth and carcass traits

Parathyroid hormone (PTH) is a crucial regulator of calcium homeostasis and bone remodeling, and the parathyroid hormone 1 receptor (PTH1R) belongs to a class II G-protein-coupled receptor. PTH activates PTH1R, which mediates catabolic and anabolic processes in the skeleton. However, the functional mechanism of PTH1R has not been thoroughly elucidated in organisms. This study identified a 51 bp indel mutation in the first intron of the PTH1R gene and elucidated the effect of this gene mutation on the growth and carcass traits in chickens. The results indicated that the 51 bp indel was significantly associated with subcutaneous fat thickness, abdominal fat weight, body weight and daily gain over 4-8 weeks. Furthermore, we found that PTH1R gene expression was highest in the kidney and liver tissues, and it showed a trend of decreasing in leg and breast muscle tissues at different embryonic stages. In addition, we examined the expression of the three genotypes of the PTH1R gene in the liver, breast muscle and abdominal fat and found that the II genotype was significantly higher than the DD and ID genotypes. In summary, these findings suggest that the PTH1R gene can serve as a potential molecular marker for chicken breeding.

Maternal control of early patterning in sea urchin embryos

Sea urchin development has been studied extensively for more than a century and considered regulative since the first experimental evidence. Further investigations have repeatedly supported this standpoint by revealing the presence of inductive mechanisms that alter cell fate decisions at early cleavage stages and flexibility of development in response to environmental conditions. Some features indicate that sea urchin development is not completely regulative, but actually includes determinative events. In 16-cell embryos, mesomeres and macromeres represent multipotency, while the cell fate of most vegetal micromeres is restricted. It is known that the mature sea urchin eggs are polarized by the asymmetrical distribution of some maternal mRNAs and proteins. Spatially-distributed maternal factors are necessary for the orientation of the primary animal-vegetal axis, which is established by both maternal and zygotic mechanisms later in development. The secondary dorsal-ventral axis is conditionally specified later in development. Dorsal-ventral polarity is very liable during the early cleavages, though more recent data argue that its direction may be oriented by maternal asymmetry. In this review, we focus on the role of maternal factors in initial embryonic patterning during the first cleavages of sea urchin embryos before activation of the embryonic genome.

Genomic Indexing by Somatic Gene Recombination of mRNA/ncRNA - Does It Play a Role in Genomic Mosaicism, Memory Formation, and Alzheimer's Disease?

Recent evidence indicates that genomic individuality of neurons, characterized by DNA-content variation, is a common if not universal phenomenon in the human brain that occurs naturally but can also show aberrancies that have been linked to the pathomechanism of Alzheimer’s disease and related neurodegenerative disorders. Etiologically, this genomic mosaic has been suggested to arise from defects of cell cycle regulation that may occur either during brain development or in the mature brain after terminal differentiation of neurons. Here, we aim to draw attention towards another mechanism that can give rise to genomic individuality of neurons, with far-reaching consequences. This mechanism has its origin in the transcriptome rather than in replication defects of the genome, i.e., somatic gene recombination of RNA. We continue to develop the concept that somatic gene recombination of RNA provides a physiological process that, through integration of intronless mRNA/ncRNA into the genome, allows a particular functional state at the level of the individual neuron to be indexed. By insertion of defined RNAs in a somatic recombination process, the presence of specific mRNA transcripts within a definite temporal context can be “frozen” and can serve as an index that can be recalled at any later point in time. This allows information related to a specific neuronal state of differentiation and/or activity relevant to a memory trace to be fixed. We suggest that this process is used throughout the lifetime of each neuron and might have both advantageous and deleterious consequences.

Differential Gene Expression between Fungal Mating Types Is Associated with Sequence Degeneration

Degenerative mutations in non-recombining regions, such as in sex chromosomes, may lead to differential expression between alleles if mutations occur stochastically in one or the other allele. Reduced allelic expression due to degeneration has indeed been suggested to occur in various sex-chromosome systems. However, whether an association occurs between specific signatures of degeneration and differential expression between alleles has not been extensively tested, and sexual antagonism can also cause differential expression on sex chromosomes. The anther-smut fungus Microbotryum lychnidis-dioicae is ideal for testing associations between specific degenerative signatures and differential expression because 1) there are multiple evolutionary strata on the mating-type chromosomes, reflecting successive recombination suppression linked to mating-type loci; 2) separate haploid cultures of opposite mating types help identify differential expression between alleles; and 3) there is no sexual antagonism as a confounding factor accounting for differential expression. We found that differentially expressed genes were enriched in the four oldest evolutionary strata compared with other genomic compartments, and that, within compartments, several signatures of sequence degeneration were greater for differentially expressed than non-differentially expressed genes. Two particular degenerative signatures were significantly associated with lower expression levels within differentially expressed allele pairs: upstream insertion of transposable elements and mutations truncating the protein length. Other degenerative mutations associated with differential expression included nonsynonymous substitutions and altered intron or GC content. The association between differential expression and allele degeneration is relevant for a broad range of taxa where mating compatibility or sex is determined by genes located in large regions where recombination is suppressed.

Comprehensive phylogenomic analysis of ERF genes in sorghum provides clues to the evolution of gene functions and redundancy among gene family members

APETALA2/Ethylene-Responsive transcription factors (AP2/ERF), with their multifunctional roles in plant development, hormone signaling and stress tolerance, are important candidates for engineering crop plants. Here, we report identification and analysis of gene structure, phylogenetic distribution, expression, chromosomal localization and cis-acting promoter analysis of AP2/ERF genes in the C4 crop plant sorghum. We identified 158 ERF genes in sorghum with 52 of them encoding dehydration-responsive binding elements (DREB) while 106 code for ERF subfamily proteins. Phylogenetic analysis organized sorghum ERF proteins into 11 distinct groups exhibiting clade-specific expansion. About 68% ERF genes have paralogs indicating gene duplications as major cause of expansion of ERF family in sorghum. Analysis of spatiotemporal expression patterns using publicly available data revealed their tissue/genotype-preferential accumulation. In addition, 40 ERF genes exhibited differential accumulation in response to heat and/or drought stress. About 25% of the segmental gene pairs and eleven tandem duplicated genes exhibited high correlation (> 0.7) in their expression patterns indicating genetic redundancy. Comparative phylogenomic analysis of sorghum ERFs with 74 genetically characterized ERF genes from other plant species provided significant clues to sorghum ERF functions. Overall data generated here provides an overview of evolutionary relationship among ERF gene family members in sorghum and with respect to previously characterized ERF genes from other plant species. This information will be instrumental in initiating functional genomic studies of ERF candidates in sorghum.

Efficient generation of zebrafish maternal-zygotic mutants through transplantation of ectopically induced and Cas9/gRNA targeted primordial germ cells

The clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology has been widely utilized for knocking out genes involved in various biological processes in zebrafish. Despite this technology is efficient for generating different mutations, one of the main drawbacks is low survival rate during embryogenesis when knocking out some embryonic lethal genes. To overcome this problem, we developed a novel strategy using a combination of CRISPR/Cas9 mediated gene knockout with primordial germ cell (PGC) transplantation (PGCT) to facilitate and speed up the process of zebrafish mutant generation, particularly for embryonic lethal genes. Firstly, we optimized the procedure for CRISPR/Cas9 targeted PGCT by increasing the efficiencies of genome mutation in PGCs and induction of PGC fates in donor embryos for PGCT. Secondly, the optimized CRISPR/Cas9 targeted PGCT was utilized for generation of maternal-zygotic (MZ) mutants of tcf7l1a (gene essential for head development), pou5f3 (gene essential for zygotic genome activation) and chd (gene essential for dorsal development) at F1 generation with relatively high efficiency. Finally, we revealed some novel phenotypes in MZ mutants of tcf7l1a and chd, as MZtcf7l1a showed elevated neural crest development while MZchd had much severer ventralization than its zygotic counterparts. Therefore, this study presents an efficient and powerful method for generating MZ mutants of embryonic lethal genes in zebrafish. It is also feasible to speed up the genome editing in commercial fishes by utilizing a similar approach by surrogate production of CRISPR/Cas9 targeted germ cells.

Intronic RNA: Ad'junk' mediator of post-transcriptional gene regulation

RNA splicing, the process through which intervening segments of noncoding RNA (introns) are excised from pre-mRNAs to allow for the formation of a mature mRNA product, has long been appreciated for its capacity to add complexity to eukaryotic proteomes. However, evidence suggests that the utility of this process extends beyond protein output and provides cells with a dynamic tool for gene regulation. In this review, we aim to highlight the role that intronic RNA plays in mediating specific splicing outcomes in pre-mRNA processing, as well as explore an emerging class of stable intronic sequences that have been observed to act in gene expression control. Building from underlying flexibility in both sequence and structure, intronic RNA provides mechanisms for post-transcriptional gene regulation that are amenable to the tissue and condition specific needs of eukaryotic cells. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.

SERPINE2 rs16865421 polymorphism is associated with a lower risk of chronic obstructive pulmonary disease in the Uygur population: A case-control study

BACKGROUND

The present study aimed to investigate the relationship between seven polymorphisms of the serine protease inhibitor-2 (SERPINE2) gene and the risk of chronic obstructive pulmonary disease (COPD) in the Uygur population via a case-control study.

METHODS

In total, 440 Uygur patients with COPD were included in the patient group and 384 healthy individuals were recruited in the matched control group. Data on demographic variables, smoking status, occupational dust exposure history and living conditions were collected. Polymorphism analysis was performed for seven loci of the SERPINE2 gene by mass spectrometry.

RESULTS

The genotype distribution of rs16865421 showed a significant difference between the patient and control groups (p < 0.05). Participants carrying the rs16865421-AG heterozygous mutant genotype had a lower risk of COPD compared to those with the rs16865421-A allele (odds ratio = 0.68, 95% confidence interval = 0.47-0.98, p = 0.041). However, no such association was found for rs1438831, rs6734100, rs6748795, rs7583463, rs840088 and rs975278. No significant interaction was observed between the genotypes and risk factors.

CONCLUSIONS

Polymorphisms of rs16865421-AG carried by the Uygur population may be protective against COPD.

In vivo measurements reveal a single 5'-intron is sufficient to increase protein expression level in Caenorhabditis elegans

Introns can increase gene expression levels using a variety of mechanisms collectively referred to as Intron Mediated Enhancement (IME). IME has been measured in cell culture and plant models by quantifying expression of intronless and intron-bearing reporter genes in vitro. We developed hardware and software to implement microfluidic chip-based gene expression quantification in vivo. We altered position, number and sequence of introns in reporter genes controlled by the hsp-90 promoter. Consistent with plant and mammalian studies, we determined a single, natural or synthetic, 5'-intron is sufficient for the full IME effect conferred by three synthetic introns, while a 3'-intron is not. We found coding sequence can affect IME; the same three synthetic introns that increase mcherry protein concentration by approximately 50%, increase mEGFP by 80%. We determined IME effect size is not greatly affected by the stronger vit-2 promoter. Our microfluidic imaging approach should facilitate screens for factors affecting IME and other intron-dependent processes.

tRNA Fragments Show Intertwining with mRNAs of Specific Repeat Content and Have Links to Disparities

tRNA-derived fragments (tRF) are a class of potent regulatory RNAs. We mined the datasets from The Cancer Genome Atlas (TCGA) representing 32 cancer types with a deterministic and exhaustive pipeline for tRNA fragments. We found that mitochondrial tRNAs contribute disproportionally more tRFs than nuclear tRNAs. Through integrative analyses, we uncovered a multitude of statistically significant and context-dependent associations between the identified tRFs and mRNAs. In many of the 32 cancer types, these associations involve mRNAs from developmental processes, receptor tyrosine kinase signaling, the proteasome, and metabolic pathways that include glycolysis, oxidative phosphorylation, and ATP synthesis. Even though the pathways are common to multiple cancers, the association of specific mRNAs with tRFs depends on and differs from cancer to cancer. The associations between tRFs and mRNAs extend to genomic properties as well; specifically, tRFs are positively correlated with shorter genes that have a higher density in repeats, such as ALUs, MIRs, and ERVLs. Conversely, tRFs are negatively correlated with longer genes that have a lower repeat density, suggesting a possible dichotomy between cell proliferation and differentiation. Analyses of bladder, lung, and kidney cancer data indicate that the tRF-mRNA wiring can also depend on a patient's sex. Sex-dependent associations involve cyclin-dependent kinases in bladder cancer, the MAPK signaling pathway in lung cancer, and purine metabolism in kidney cancer. Taken together, these findings suggest diverse and wide-ranging roles for tRFs and highlight the extensive interconnections of tRFs with key cellular processes and human genomic architecture. SIGNIFICANCE: Across 32 TCGA cancer contexts, nuclear and mitochondrial tRNA fragments exhibit associations with mRNAs that belong to concrete pathways, encode proteins with particular destinations, have a biased repeat content, and are sex dependent.

CDK12 loss in cancer cells affects DNA damage response genes through premature cleavage and polyadenylation

Cyclin-dependent kinase 12 (CDK12) modulates transcription elongation by phosphorylating the carboxy-terminal domain of RNA polymerase II and selectively affects the expression of genes involved in the DNA damage response (DDR) and mRNA processing. Yet, the mechanisms underlying such selectivity remain unclear. Here we show that CDK12 inhibition in cancer cells lacking CDK12 mutations results in gene length-dependent elongation defects, inducing premature cleavage and polyadenylation (PCPA) and loss of expression of long (>45 kb) genes, a substantial proportion of which participate in the DDR. This early termination phenotype correlates with an increased number of intronic polyadenylation sites, a feature especially prominent among DDR genes. Phosphoproteomic analysis indicated that CDK12 directly phosphorylates pre-mRNA processing factors, including those regulating PCPA. These results support a model in which DDR genes are uniquely susceptible to CDK12 inhibition primarily due to their relatively longer lengths and lower ratios of U1 snRNP binding to intronic polyadenylation sites.

Cdk12 is primarily involved in the regulation of DNA damage response (DDR) gene transcription as well as mRNA processing. Here, the authors demonstrate that CDK12 suppresses intronic polyadenylation, and that inhibition of this kinase primarily affects the expression of long genes with higher numbers of polyA sites, features common to many DDR genes.

Efficient Generation of Endogenous Fluorescent Reporters by Nested CRISPR in Caenorhabditis elegans

CRISPR-based genome-editing methods in model organisms are evolving at an extraordinary speed. Whereas the generation of deletion or missense mutants is quite straightforward, the production of endogenous fluorescent reporters is more challenging. We have developed Nested CRISPR, a cloning-free ribonucleoprotein-driven method that robustly produces endogenous fluorescent reporters with EGFP, mCherry or wrmScarlet in Caenorhabditis elegans This method is based on the division of the fluorescent protein (FP) sequence in three fragments. In the first step, single-stranded DNA (ssDNA) donors (≤200 bp) are used to insert the 5' and 3' fragments of the FP in the locus of interest. In the second step, these sequences act as homology regions for homology-directed repair using a double-stranded DNA (dsDNA) donor (PCR product) containing the middle fragment, thus completing the FP sequence. In Nested CRISPR, the first step involving ssDNA donors is a well-established method that yields high editing efficiencies, and the second step is reliable because it uses universal CRISPR RNAs (crRNAs) and PCR products. We have also used Nested CRISPR in a nonessential gene to produce a deletion mutant in the first step and a transcriptional reporter in the second step. In the search for modifications to optimize the method, we tested synthetic single guide RNAs (sgRNAs), but did not observe a significant increase in efficiency. To streamline the approach, we combined all step 1 and step 2 reagents in a single injection and were successful in three of five loci tested with editing efficiencies of up to 20%. Finally, we discuss the prospects of this method in the future.

The single nucleotide polymorphism g.133A>C in the stearoyl CoA desaturase gene (SCD) promoter affects gene expression and quali-quantitative properties of river buffalo milk

The stearoyl-CoA desaturase (SCD) gene has been investigated in depth in ruminants because of its effect on milk fat composition. In river buffalo, the single nucleotide polymorphism (SNP) g.133A>C in the gene promoter has been associated with milk quality and yield. However, the biological reason for such effects remains unexplored. In this study, we combined mRNA profile analysis, an electromobility shift assay, and quantitative PCR to elucidate the role of this SNP on gene transcription and its effects on milk fat traits. A preliminary genotyping of g.133A>C was carried out on a group of 303 river buffaloes to choose individuals for the downstream applications. Analysis of allele frequencies showed an increase in the minor allele C (0.25) compared with previous findings (0.16). Six animals (2 for each genotype) were chosen for cloning and 216 positive cDNA recombinant clones for SCD (72 per genotype) were analyzed by PCR. All clones showed the same length on agarose gel; therefore, random clones were chosen for sequencing. No qualitative differences were found and all gene transcripts assembled correctly. An electrophoretic mobility shift assay was performed to evaluate the binding of the transcription factor Sp1 to DNA sequences including g.133A>C. Genotype CC showed a higher binding (mean ± standard error of the mean) than genotype AA in 2 different conditions [Enzo buffer (EB), Enzo Life Science Inc., Farmingdale, NY: 201.77 ± 4.06 vs. 141.65 ± 3.77 band intensity values and Poletto buffer (PB): 95.90 ± 1.15 vs. 67.30 ± 2.14 band intensity values]. The subsequent quantitative PCR confirmed the upregulation of the CC genotype compared with the AA and AC genotypes. The association study with milk fat traits revealed a favorable effect of allele C. The heterozygous genotype had the highest values for monounsaturated fatty acids, oleic acid (C18:1 cis-9), polyunsaturated fatty acids, and odd- and branched-chain fatty acids, and the lowest values for saturated fatty acids and atherogenic and thrombogenic indices; the heterozygous genotype differed significantly from the AA genotype. The AC genotype has previously been associated with higher milk yield. Therefore, the g.133A>C SNP is a marker with dual effects and is an interesting candidate for assisted selection programs in river buffalo. These data clarified the biological role of the SNP g.133A>C in the SCD promoter and how it affects gene function, providing important knowledge on the genetic background of lipid metabolism, including the future possibility of selecting alleles with quantitatively or qualitatively favorable effects.

Enter the Matrix: Factorization Uncovers Knowledge from Omics

Omics data contain signals from the molecular, physical, and kinetic inter- and intracellular interactions that control biological systems. Matrix factorization (MF) techniques can reveal low-dimensional structure from high-dimensional data that reflect these interactions. These techniques can uncover new biological knowledge from diverse high-throughput omics data in applications ranging from pathway discovery to timecourse analysis. We review exemplary applications of MF for systems-level analyses. We discuss appropriate applications of these methods, their limitations, and focus on the analysis of results to facilitate optimal biological interpretation. The inference of biologically relevant features with MF enables discovery from high-throughput data beyond the limits of current biological knowledge - answering questions from high-dimensional data that we have not yet thought to ask.

Origin and Spread of Spliceosomal Introns: Insights from the Fungal Clade Zymoseptoria

Spliceosomal introns are a key feature of eukaryote genome architecture and have been proposed to originate from selfish group II introns from an endosymbiotic bacterium, that is, the ancestor of mitochondria. However, the mechanisms underlying the wide spread of spliceosomal introns across eukaryotic genomes have been obscure. In this study, we characterize the dynamic evolution of spliceosomal introns in the fungal genus Zymoseptoria at different evolutionary scales, that is, within a genome, among conspecific strains within species, and between different species. Within the genome, spliceosomal introns can proliferate in unrelated genes and intergenic regions. Among conspecific strains, spliceosomal introns undergo rapid turnover (gains and losses) and frequent sequence exchange between geographically distinct strains. Furthermore, spliceosomal introns could undergo introgression between distinct species, which can further promote intron invasion and proliferation. The dynamic invasion and proliferation processes of spliceosomal introns resemble the life cycles of mobile selfish (group I/II) introns, and these intron movements, at least in part, account for the dramatic processes of intron gain and intron loss during eukaryotic evolution.

Intron retention and nuclear loss of SFPQ are molecular hallmarks of ALS

Mutations causing amyotrophic lateral sclerosis (ALS) strongly implicate ubiquitously expressed regulators of RNA processing. To understand the molecular impact of ALS-causing mutations on neuronal development and disease, we analysed transcriptomes during in vitro differentiation of motor neurons (MNs) from human control and patient-specific VCP mutant induced-pluripotent stem cells (iPSCs). We identify increased intron retention (IR) as a dominant feature of the splicing programme during early neural differentiation. Importantly, IR occurs prematurely in VCP mutant cultures compared with control counterparts. These aberrant IR events are also seen in independent RNAseq data sets from SOD1- and FUS-mutant MNs. The most significant IR is seen in the SFPQ transcript. The SFPQ protein binds extensively to its retained intron, exhibits lower nuclear abundance in VCP mutant cultures and is lost from nuclei of MNs in mouse models and human sporadic ALS. Collectively, we demonstrate SFPQ IR and nuclear loss as molecular hallmarks of familial and sporadic ALS.

AOX1-Subfamily Gene Members in Olea europaea cv. "Galega Vulgar"-Gene Characterization and Expression of Transcripts during IBA-Induced in Vitro Adventitious Rooting

Propagation of some Olea europaea L. cultivars is strongly limited due to recalcitrant behavior in adventitious root formation by semi-hardwood cuttings. One example is the cultivar ”Galega vulgar”. The formation of adventitious roots is considered a morphological response to stress. Alternative oxidase (AOX) is the terminal oxidase of the alternative pathway of the plant mitochondrial electron transport chain. This enzyme is well known to be induced in response to several biotic and abiotic stress situations. This work aimed to characterize the alternative oxidase 1 (AOX1)-subfamily in olive and to analyze the expression of transcripts during the indole-3-butyric acid (IBA)-induced in vitro adventitious rooting (AR) process. OeAOX1a (acc. no. MF410318) and OeAOX1d (acc. no. MF410319) were identified, as well as different transcript variants for both genes which resulted from alternative polyadenylation events. A correlation between transcript accumulation of both OeAOX1a and OeAOX1d transcripts and the three distinct phases (induction, initiation, and expression) of the AR process in olive was observed. Olive AOX1 genes seem to be associated with the induction and development of adventitious roots in IBA-treated explants. A better understanding of the molecular mechanisms underlying the stimulus needed for the induction of adventitious roots may help to develop more targeted and effective rooting induction protocols in order to improve the rooting ability of difficult-to-root cultivars.

Transcript analysis at DGAT1 reveals different mRNA profiles in river buffaloes with extreme phenotypes for milk fat

Buffalo DGAT1 (diacylglycerol O-acyltransferase 1) was mainly investigated for the characterization of the gene itself and for the identification of the K232A polymorphism, similar to what has been accomplished in cattle, although no information has been reported so far at the mRNA level. The importance of DGAT1 for lipid metabolism led us to investigate the transcript profiles of lactating buffaloes characterized as high (9.13 ± 0.23) and low (7.94 ± 0.29) for milk fat percentage, and to explore the genetic diversity at the RNA and DNA level. A total of 336 positive clones for the DGAT1 cDNA were analyzed by PCR and chosen for sequencing according to the differences in length. The clone assembling revealed a very complex mRNA pattern with a total of 21 transcripts differently represented in the 2 groups of animals. Apart from the correct transcript (17 exons long), the skipping of exon 12 is the most significant in terms of distribution of clones with 11.6% difference between the 2 groups, whereas a totally different mRNA profile was found in approximately 12% of clones. The sequencing of genomic DNA allowed the identification of 10 polymorphic sites at the intron level, which clarify, at least partially, the genetic events behind the production of complex mRNA. Genetic diversity was found also at the exon level. The single nucleotide polymorphism c.1053C>T represents the first example of polymorphism in a coding region for the DGAT1 in the Italian Mediterranean breed. To establish whether this polymorphism is present in other buffalo breeds, a quick method based on PCR-RFLP was set up for allelic discrimination in the Italian Mediterranean and the Romanian Murrah (200 animals in total). The alleles were equally represented in the overall population, whereas the analysis of the 2 breeds showed different frequencies, likely indicating diverse genetic structure of the 2 breeds. The T allele might be considered as the ancestral condition of the DGAT1 gene, being present in the great part of the sequenced species. These data add knowledge at the transcript and genetic levels for the buffalo DGAT1 and open the opportunity for further investigation of other genes involved in milk fat metabolism for the river buffalo, including the future possibility of selecting alleles with quantitative or qualitative favorable effects (or both).

Introns Protect Eukaryotic Genomes from Transcription-Associated Genetic Instability

Transcription is a source of genetic instability that can notably result from the formation of genotoxic DNA:RNA hybrids, or R-loops, between the nascent mRNA and its template. Here we report an unexpected function for introns in counteracting R-loop accumulation in eukaryotic genomes. Deletion of endogenous introns increases R-loop formation, while insertion of an intron into an intronless gene suppresses R-loop accumulation and its deleterious impact on transcription and recombination in yeast. Recruitment of the spliceosome onto the mRNA, but not splicing per se, is shown to be critical to attenuate R-loop formation and transcription-associated genetic instability. Genome-wide analyses in a number of distant species differing in their intron content, including human, further revealed that intron-containing genes and the intron-richest genomes are best protected against R-loop accumulation and subsequent genetic instability. Our results thereby provide a possible rationale for the conservation of introns throughout the eukaryotic lineage.

RNA splicing in human disease and in the clinic

Defects at the level of the pre-mRNA splicing process represent a major cause of human disease. Approximately 15-50% of all human disease mutations have been shown to alter functioning of basic and auxiliary splicing elements. These elements are required to ensure proper processing of pre-mRNA splicing molecules, with their disruption leading to misprocessing of the pre-mRNA molecule and disease. The splicing process is a complex process, with much still to be uncovered before we are able to accurately predict whether a reported genomic sequence variant (GV) represents a splicing-associated disease mutation or a harmless polymorphism. Furthermore, even when a mutation is correctly identified as affecting the splicing process, there still remains the difficulty of providing an exact evaluation of the potential impact on disease onset, severity and duration. In this review, we provide a brief overview of splicing diagnostic methodologies, from in silico bioinformatics approaches to wet lab in vitro and in vivo systems to evaluate splicing efficiencies. In particular, we provide an overview of how the latest developments in high-throughput sequencing can be applied to the clinic, and are already changing clinical approaches.

Exon-intron structure and sequence variation of the calreticulin gene among Rhipicephalus sanguineus group ticks

Background

Calreticulin proteins (CRTs) are important components of tick saliva, which is involved in the blood meal success, pathogen transmission and host allergic responses. The characterization of the genes encoding for salivary proteins, such as CRTs, is pivotal to understand the mechanisms of tick-host interaction during blood meal and to develop tick control strategies based on their inhibition. In hard ticks, crt genes were shown to have only one intron with conserved position among species. In this study we investigated the exon-intron structure and variation of the crt gene in Rhipicephalus spp. ticks in order to assess the crt exon-intron structure and the potential utility of crt gene as a molecular marker.

Methods

We sequenced the exon-intron region of crt gene in ticks belonging to so-called tropical and temperate lineages of Rhipicephalus sanguineus (sensu lato), Rhipicephalus sp. I, Rhipicephalus sp. III, Rhipicephalus sp. IV, R. guilhoni, R. muhsamae and R. turanicus. Genetic divergence and phylogenetic relationships between the sequences obtained were estimated.

Results

All individuals belonging to the tropical lineage of R. sanguineus (s.l.), R. guilhoni, R. muhsamae, R. turanicus, Rhipicephalus sp. III and Rhipicephalus sp. IV analysed showed crt intron-present alleles. However, both crt intron-present and intron-absent alleles were found in Rhipicephalus sp. I and the temperate lineage of R. sanguineus (s.l.), showing the occurrence of an intraspecific intron presence-absence polymorphism. Phylogenetic relationships among the crt intron-present sequences showed distinct lineages for all taxa, with the tropical and temperate lineages of R. sanguineus (s.l.) being more closely related to each other.

Conclusions

We expanded previous studies about the characterization of crt gene in hard ticks. Our results highlighted a previously overlooked variation in the crt structure among Rhipicephalus spp., and among hard ticks in general. Notably, the intron presence/absence polymorphism observed herein can be a candidate study-system to investigate the early stages of intron gain/loss before fixation at species level and some debated questions about intron evolution. Finally, the sequence variation observed supports the suitability of the crt gene for molecular recognition of Rhipicephalus spp. and for phylogenetic studies in association with other markers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1909-3) contains supplementary material, which is available to authorized users.