PLoS Genetics最新文献

Meiotic recombination is an evolutionary force that acts by breaking up genomic linkage, increasing the efficacy of selection. Recombination is initiated with a double-strand break which is resolved via a crossover, which involves the reciprocal exchange of genetic material between homologous chromosomes, or a non-crossover, which results in small tracts of non-reciprocal exchange of genetic material. Crossover and non-crossover rates vary between species, populations, individuals, and across the genome. In recent years, recombination rate has been associated with the distribution of ancestry derived from past interspecific hybridization (introgression) in a variety of species. We explore this interaction of recombination and introgression by sequencing spores and detecting crossovers and non-crossovers from two crosses of the yeast Saccharomyces uvarum. One cross is between strains which each contain introgression from their sister species, S. eubayanus, while the other cross has no introgression present. We find that the recombination landscape is significantly different between S. uvarum crosses, and that some of these differences can be explained by the presence of introgression in one cross. Crossovers are significantly reduced in heterozygous introgression compared to syntenic regions in the cross without introgression. This translates to reduced allele shuffling within introgressed regions, and an overall reduction of shuffling on most chromosomes with introgression compared to the syntenic regions and chromosomes without introgression. Our results suggest that hybridization can significantly influence the recombination landscape, and that the reduction in allele shuffling contributes to the initial purging of introgression in the generations following a hybridization event.

Tibetan adaptation to high-altitude hypoxia remains a classic example of Darwinian selection in humans. Amongst Tibetan populations, alleles in the EPAS1 gene - whose protein product, HIF-2α, is a central regulator of the hypoxia response - have repeatedly been shown to carry some of the strongest signals of positive selection in humans. However, selective sweep signals alone may only account for some of the phenotypes that differentiate high-altitude adapted populations from closely related lowlanders. Therefore, there is a pressing need to functionally probe adaptive alleles and their impact at both the locus-specific and genome-wide levels and across cell types to uncover the full range of beneficial traits. To this end, we established a library of induced pluripotent stem cells (iPSCs) derived from Tibetan and Han Chinese individuals, a robust model system allowing precise exploration of allelic effects on transcriptional responses, and we differentiated them into vascular endothelium. Using this system, we focus first on a hypoxia-dependent enhancer (ENH5) that contributes to the regulation of EPAS1 to investigate its locus-specific effects in endothelium. Then, to cast a wider net, we harness the same experimental system to compare the transcriptome of Tibetan and Han Chinese cells in hypoxia and find evidence that angiogenesis, energy metabolism and immune pathways differ between these two populations with different histories of long-term residence at high altitude. Coupled with evidence of polygenic adaptations targeting the same pathways, these results suggests that the observed transcriptional differences between the two populations were shaped by natural selection.

Chronic obstructive pulmonary disease (COPD) is a leading cause of death globally. Gastroesophageal reflux disease (GERD) is a common comorbidity in COPD associated with worse pulmonary symptoms, reduced quality of life, and increased exacerbations and hospitalizations. GERD treatment in COPD is associated with a lower risk of exacerbations and mortality; however, it is not clear whether these findings can be attributed to aging populations where both diseases are likely to co-occur or reflect shared etiology. To test for the influence of common etiology in both diseases, we aimed to identify shared genetic etiology between GERD and COPD. We performed the first whole-genome sequence association analysis of comorbid GERD and COPD in 12,438 multi-ancestry participants. The co-heritability of GERD and COPD was 39.7% (h2 = 0.397, SE = 0.074) and we identified several ancestry-independent loci associated with co-morbid GERD and COPD (within LINC02493 and FRYL) known to be involved in oxidative stress and G protein-coupled receptor (GPCR) signaling mechanisms. We found several loci associated with co-morbid GERD and COPD previously associated with GERD or COPD individually, including HCG17, which plays a role in oxidative stress mechanisms. Gene set enrichment identified GPCR signaling pathways in co-morbid GERD and COPD loci. Rare variants in ZFP42, encoding key regulators of the IL6/STAT3 pathway, have been previously implicated with GI disorders and were associated with co-morbid GERD and COPD. We identified common genetic etiology for GERD in COPD which begins to provide a mechanistic foundation for the potential therapeutic utility of STAT3, oxidation, and GPCR signaling pathway modulators in both GERD and COPD.

Plasmid conjugation is a major route for the dissemination of antibiotic resistances and adaptive genes among bacterial populations. Obtaining precise conjugation rates is thus key to understanding how antibiotic resistances spread. Plasmid conjugation is typically modeled as a density-dependent process, where the formation of new transconjugants depends on the rate of encounters between donor and receptor cells. By analyzing conjugation dynamics at different cell concentrations, here we show that this assumption only holds at very low bacterial densities. At higher cell concentrations, conjugation becomes limited by the engagement time, the interval required between two successful matings. Plasmid conjugation therefore follows a Holling´s Type II functional response, characterized by the encounter rate and the engagement time, which represent, respectively, the density and frequency-dependent limits of plasmid transmission. Our results demonstrate that these parameters are characteristic of the transfer machinery, rather than the entire plasmid genome, and that they are robust to environmental and transcriptional perturbation. Precise parameterization of plasmid conjugation will contribute to better understanding the propagation dynamics of antimicrobial resistances.

Ethylene is a plant hormone involved in many aspects of plant growth and development as well as responses to stress. The role of ethylene in plant-microbe interactions has been explored from the perspective of plants. However, only a small number of studies have examined the role of ethylene in microbes. We demonstrated that Azospirillum brasilense contains a functional ethylene receptor that we call Azospirillum Ethylene Response1 (AzoEtr1) after the nomenclature used in plants. AzoEtr1 directly binds ethylene with high affinity. Treating cells with ethylene or disrupting the receptor reduces biofilm formation and colonization of plant root surfaces. Additionally, RNA sequencing and untargeted metabolomics showed that ethylene causes wide-spread metabolic changes that affect carbon and nitrogen metabolism. One result is the accumulation of poly-hydroxybutyrate. Our data suggests a model in which ethylene from host plants alters the density of colonization by A. brasilense and re-wires its metabolism, suggesting that the bacterium implements an adaptation program upon sensing ethylene. These data provide potential new targets to regulate beneficial plant-microbe interactions.

Precise regulation of gene expression is essential to understand a wide range of biological processes. Control over gene expression can be achieved using site-directed recombinases and endonucleases. However, their efficiency is variable and dependent on the genomic context. Here, we develop a self-cleaving ribozyme-based tool to control mRNA levels of endogenous targets in zebrafish. Using an in vivo reporter strategy, we first show that inserting the T3H48 self-cleaving ribozyme in an intron enables rapid pre-mRNA cleavage, with up to 20-fold reduction in expression, and that this ribozyme displays superior activity compared with other ribozymes. We then inserted the T3H48 ribozyme in the second intron of the albino gene using a CRISPR/Cas9 strategy and observed a pigmentation phenotype similar to that in the mutant. Using a base-editing strategy to inactivate the ribozyme, we also show that this phenotype is reversible, illustrating the specificity of the approach. In addition, we generated a Flippase- and Cre-activatable version of the T3H48 ribozyme, called RiboFlip, to control the mRNA levels of the albino gene. RiboFlip activation induced mRNA knockdown and also recapitulated the albino mutant phenotype. Furthermore, we show that a Cre- and Dre-controllable Gal4/UAS reporter in the RiboFlip cassette can label knocked-down cells independently of the expression of the target gene. Altogether, we introduce the RiboFlip cassette as a flexible tool to control endogenous gene expression in a vertebrate model and as an alternative to existing conditional knockdown strategies.

The Shaker/Kv1 subfamily of voltage-gated potassium (K+) channels is essential for modulating membrane excitability. Their loss results in prolonged depolarization and excessive calcium influx. These channels have also been implicated in a variety of other cellular processes, but the underlying mechanisms remain poorly understood. Through comprehensive screening of K+ channel mutants in C. elegans, we discovered that shk-1 mutants are highly susceptible to bacterial pathogen infection and oxidative stress. This vulnerability is associated with reduced glycogen levels and substantial mitochondrial dysfunction, including decreased ATP production and dysregulated mitochondrial membrane potential under stress conditions. SHK-1 is predominantly expressed and functions in body wall muscle to maintain glycogen storage and mitochondrial homeostasis. RNA-sequencing data reveal that shk-1 mutants have decreased expression of a set of cation-transporting ATPases (CATP), which are crucial for maintaining electrochemical gradients. Intriguingly, overexpressing catp-3, but not other catp genes, restores the depolarization of mitochondrial membrane potential under stress and enhances stress tolerance in shk-1 mutants. This finding suggests that increased catp-3 levels may help restore electrochemical gradients disrupted by shk-1 deficiency, thereby rescuing the phenotypes observed in shk-1 mutants. Overall, our findings highlight a critical role for SHK-1 in maintaining stress tolerance by regulating glycogen storage, mitochondrial homeostasis, and gene expression. They also provide insights into how Shaker/Kv1 channels participate in a broad range of cellular processes.

Tissue maintenance is underpinned by resident stem cells whose activity is modulated by microenvironmental cues. Using Drosophila as a simple model to identify regulators of stem cell behaviour and survival in vivo, we have identified novel connections between the conserved transmembrane proteoglycan Syndecan, nuclear properties and stem cell function. In the Drosophila midgut, Syndecan depletion in intestinal stem cells results in their loss from the tissue, impairing tissue renewal. At the cellular level, Syndecan depletion alters cell and nuclear shape, and causes nuclear lamina invaginations and DNA damage. In a second tissue, the developing Drosophila brain, live imaging revealed that Syndecan depletion in neural stem cells results in nuclear envelope remodelling defects which arise upon cell division. Our findings reveal a new role for Syndecan in the maintenance of nuclear properties in diverse stem cell types.

To elucidate the molecular function of SHORT AND SWOLLEN ROOT1 (SSR1), we screened for suppressors of the ssr1-2 (sus) was performed and identified over a dozen candidates with varying degrees of root growth restoration. Among these, the two most effective suppressors, sus1 and sus2, resulted from G87D and T55M single amino acid substitutions in HSCA2 (At5g09590) and ISU1 (At4g22220), both crucial components of the mitochondrial iron-sulfur (Fe-S) cluster assembly machinery. SSR1 displayed a robust cochaperone-like activity and interacted with HSCA2 and ISU1, facilitating the binding of HSCA2 to ISU1. In comparison to the wild-type plants, ssr1-2 mutants displayed increased iron accumulation in root tips and altered expression of genes responsive to iron deficiency. Additionally, the enzymatic activities of several iron-sulfur proteins and the mitochondrial membrane potential were reduced in ssr1-2 mutants. Interestingly, SSR1 appears to be exclusive to plant lineages and is induced by environmental stresses. Although HSCA2G87D and ISU1T55M can effectively compensate for the phenotypes associated with SSR1 deficiency under favorable conditions, their compensatory effects are significantly diminished under stress. Collectively, SSR1 represents a new and significant component of the mitochondrial Fe-S cluster assembly (ISC) machinery. It may also confer adaptive advantages on plant ISC machinery in response to environmental stress.

Classifying viruses systematically has remained a key challenge of virology due to the absence of universal genes and vast genetic diversity of viruses. In particular, the most dominant and diverse group of viruses, the tailed double-stranded DNA viruses of prokaryotes belonging to the class Caudoviricetes, lack sufficient homology in the genetic machinery that unifies them to reconstruct inclusive, stable phylogenies of these genes. While previous approaches to organize tailed phage diversity have managed to distinguish various taxonomic levels, these methods are limited in scalability and reproducibility, and they do not include modes of evolution, like gene gains and losses. Here, we present a novel, comprehensive, and reproducible framework for examining evolutionary relationships of tailed phages. In this framework, we compare phage genomes based on presences and absences of a fixed set of gene families which is used as binary trait data that is input into maximum likelihood models and include heterogeneous rates of trait losses and gains. Our resulting phylogeny stably recovers known taxonomic families of tailed phages, with and without the inclusion of metagenomic phages. We also quantify the mosaicism of replication and structural genes among known families. Our results suggest that these exchanges likely underpin the emergence of new families. Additionally, we apply this framework to large phages (>100 kilobases) to map emergences of traits associated with genome expansion. Taken together, this evolutionary framework for charting and organizing tailed phage diversity improves the systemization of phage taxonomy, which can unify phage studies and advance our understanding of their evolution.