PLoS Genetics最新文献

All cells possess mechanisms to maintain and replicate their genomes, whose integrity and transmission are constantly challenged by DNA damage and replication impediments. In eukaryotes, the protein kinase Ataxia-Telangiectasia and Rad3-related (ATR), a member of the phosphatidylinositol 3-kinase-like family, acts as a master regulator of the eukaryotic response to DNA injuries, ensuring DNA replication completion and genome stability. Here we aimed to investigate the functional relevance of the ATR homolog in the DNA metabolism of Leishmania major, a protozoan parasite with a remarkably plastic genome. CRISPR/cas9 genome editing was used to generate a Myc-tagged ATR cell line (mycATR), and a Myc-tagged C-terminal knockout of ATR (mycATRΔC-/-). We show that the nuclear localisation of ATR depends upon its C-terminus. Moreover, its deletion results in single-stranded DNA accumulation, impaired cell cycle control, increased levels of DNA damage, and delayed DNA replication re-start after replication stress. In addition, we show that ATR plays a key role in maintaining L. major's unusual DNA replication program, where larger chromosomes duplicate later than smaller chromosomes. Our data reveals loss of the ATR C-terminus promotes the accumulation of DNA replication signal around replicative stress fragile sites, which are enriched in larger chromosomes. Finally, we show that these alterations to the DNA replication program promote chromosome instability. In summary, our work shows that ATR acts to modulate DNA replication timing, limiting the plasticity of the Leishmania genome.

Cells can match gene expression to a range of a particular signal. For example, budding yeast expresses at least seven hexose-transporter ([Formula: see text]) genes in different concentration ranges of extracellular glucose. Using time-lapse microscopy, microfluidics, dynamic glucose inputs, and mathematical modelling, we determine how this glucose matching of [Formula: see text] expression occurs mechanistically. The glucose-sensing network generates a push-pull regulation using two pairs of regulators: rising glucose weakens, or "pulls", repression via regulators Mth1 and Std1 while simultaneously strengthening, or "pushing", repression via regulators Mig1 and Mig2; falling glucose reverses this push-pull. The regulators' combined activity reports extracellular glucose. Cells match [Formula: see text] expression to glucose because [Formula: see text] promoters couple to the regulators in ways specific to low, medium, or high-affinity transporters. By rewiring transcription and using model-predicted perturbations, we demonstrate how an [Formula: see text] encoding a medium-affinity transporter can respond as one encoding either a low- or a high-affinity transporter. Matching gene expression to a pattern of input is fundamental; we believe push-pull regulation to be widespread.

Tendons are dynamic structures that efficiently transmit force and enable movement. From birth, tendons undergo dramatic changes from a principally cellular tissue to a hypocellular one characterized by a dense and highly ordered extracellular matrix. During this time, tendon cells change morphology from rounded to stellate in appearance and their proliferative rates decline. Significant expansion and maturation of the extracellular matrix (ECM) grow the tendons in length and diameter and alter their biomechanical properties to sustain increased physical activities. Surprisingly, for such an important stage of tendon maturation, we understand very little about the transcriptional and epigenetic regulators that direct these processes. Here, we present a roadmap of genes that are differentially regulated during the early neonatal and postnatal time period. We find differentially expressed genes fall into specific transcriptional modules, representing expression increases, decreases, or gene sets undergoing dynamic changes over postnatal time. By pairing our transcriptomic data with epigenetic data, we performed an integrative analysis of the datasets and further defined modules with highly correlated changes in gene expression and chromatin accessibility. From this analysis, several new pathways emerge. Among them, we focus on Yap1, a transcriptional co-activator of the Hippo signaling pathway. We observe accessible regions near to differentially expressed genes, containing motifs for TEAD, the transcription factor that binds Yap to regulate transcription. Conditional loss of Yap1 at postnatal stages alters early expression of Col1a1 and matrix organization and density but does not affect gross ultrastructural and mechanical properties at later stages. Together, our analyses identify a regulator of early matrix formation and provides a rich dataset with which to interrogate transcriptional networks and pathways during this poorly understood time in tendon growth.

Many metazoans switch between asexual and sexual reproduction based on environmental changes, life cycle phases, or both. This reproductive strategy enables them to benefit from the features of both reproductive modes. In general, asexual reproduction is broadly divided into parthenogenesis and vegetative reproduction. As in parthenogenesis, individuals develop ovaries and lay eggs, the most significant event in switching from parthenogenesis to sexual reproduction is the production of testes. Meanwhile, in vegetative reproduction, individuals do not need germ cells themselves. Thus, they must post-embryonically develop and maintain germ cells derived from pluripotent cells as they switch from vegetative to sexual reproduction. The complicated mechanisms for controlling the postembryonic reproductive development remain unknown. The planarian Dugesia ryukyuensis can switch from vegetative to sexual reproduction by stimulating bioactive compounds called sex-inducing substances, which are widely conserved in Platyhelminthes, including parasitic flatworms. The two reproductive modes are facilitated by the presence of adult pluripotent stem cells, which generate any type of somatic tissue in the asexual state and produce and maintain hermaphroditic reproductive organs in the sexual state. In this study, using RNA sequencing analysis in experimental sexualization by sex-inducing substances, we identified four essential genes for sexualization. A common feature following the knockdown of the four essential genes was a blockage of testicular differentiation. One of the four essential genes was a gap junction gene, Dr-siri (Dugesia ryukyuensis-sexual induction-related innexin). We suggest that the establishment of a testicular stem cell niche supported by Dr-siri protein is responsible for the breakthrough of dormancy in postembryonic reproductive development in planarian reproductive switching. Our findings suggest that the production of testes might be crucial for even switching from vegetative to sexual reproduction.

Non-crossover gene conversion is a type of meiotic recombination characterized by the non-reciprocal transfer of genetic material between homologous chromosomes. Gene conversions are thought to occur within relatively short tracts of DNA. In this study, we propose a statistical method to model the length distribution of gene conversion tracts in humans, using nearly one million gene conversion tracts detected from the UK Biobank whole autosome data. To handle the large number of tracts, we designed a computationally efficient inferential framework. Our method further accounts for regional variation in the density of variant sites and heterozygosity across the genome, which can influence the observed length of gene conversion tracts. We allow for multiple candidate tract length distributions and select the best fitting distribution using the Bayesian Information Criterion (BIC). Using a mixture of two geometric components for the tract length distribution, we estimate that the smaller component has a mean of 16.9 bp (95% CI: [16.4, 17.0]), and the larger component has a mean of 724.7 bp (95% CI: [720.1, 728.7]). We further estimate the proportion of tracts from the second component to be 0.00525 (95% CI: [0.005, 0.00525]). After stratifying by crossover-hotspot overlap, we infer that tracts whose midpoints lie within crossover hotspots are, on average, longer than the remaining tracts.

During meiosis, the programmed formation of DNA double-strand breaks (DSBs) by Spo11, a conserved topoisomerase VI family protein, initiates homologous recombination that leads to crossovers between homologous chromosomes, essential for accurate chromosome segregation and genome evolution. The DSB number, distribution and timing of formation are regulated during meiosis to ensure crossing over on all chromosomes and prevent genome instability. In S. cerevisiae, DSB interference suppresses the coincident formation of DSBs in neighboring hotspots through a Tel1/ATM dependent mechanism that remains unexplored. Here, we demonstrate that Tel1 is recruited to meiotic DSB hotspots and chromosomal axis sites in a DSB-dependent manner. This supports the tethered loop-axis complex (TLAC) model that postulates meiotic DSBs are formed within the chromosome axis environment. Tel1 recruitment to meiotic DSBs, DSB interference and the meiotic DNA damage checkpoint are all dependent on the C-terminal moiety of Xrs2, known to mediate Tel1-Xrs2 interaction in vegetative cells. However, mutation of the Xrs2 FxF/Y motif, known to stabilize Tel1 interaction with Xrs2, does not affect DSBs interference but abolishes the Tel1-dependent DNA damage checkpoint. Altogether, this work uncovers the dynamic association of Tel1 with meiotic chromosomes and highlights the critical role of its interaction with Xrs2 in fine-tuning both the meiotic DNA damage checkpoint and DSB interference.

The CRISPR/Cas9 gene-editing system is a powerful tool in plant genetic engineering; however, screening for Cas9-free edited plants remains complex and time-consuming. To address this limitation, we developed an RNA aptamer-assisted CRISPR/Cas9 system, termed 3WJ-4 × Bro/Cas9. In this system, the engineered RNA aptamer 3WJ-4 × Bro functions as a transcriptional reporter, serving as an alternative to traditional fluorescent proteins and thus avoiding their potential interference with Cas9 activity. Compared to the conventional GFP/Cas9 system, 3WJ-4 × Bro/Cas9 showed more efficient transformation and higher accuracy in fluorescence-based selection of positive T1 transformants, without significantly affecting plant growth. Furthermore, 3WJ-4 × Bro/Cas9 achieved a 78.6% increase in the T1 mutation rate compared to GFP/Cas9, with the homozygous mutation rate reaching 1.78%. In addition, 3WJ-4 × Bro/Cas9 enabled fluorescence-based visual screening in the T2 generation for rapid identification of Cas9-free mutants, improving sorting efficiency by 30.2% over the GFP-based method. Moreover, 3WJ-4 × Bro/Cas9 enabled more efficient generation of homozygous double-target mutants compared to GFP/Cas9. These results demonstrate that the 3WJ-4 × Bro/Cas9 system provides a non-transgenic, efficient, and broadly applicable strategy for plant genome editing and selection.

Obligate host-associated bacteria with reduced genomes, such as phytoplasmas, face strong evolutionary constraints, including metabolic dependence on hosts, limited opportunities for horizontal gene transfer (HGT), and frequent population bottlenecks. Despite these limitations, phytoplasmas, which are parasitic, insect-transmitted plant pathogens, maintain a diverse arsenal of secreted effectors that manipulate both plant and insect hosts to promote infection and transmission. These effectors can suppress immunity and reprogram plant development, inducing alterations such as witch's broom and leaf-like flowers, through ubiquitin-independent degradation of key transcription factors. However, how phytoplasmas diversify and maintain these effectors in the absence of frequent genetic exchange remains unclear. To address this, we analysed the effectoromes of 239 phytoplasma genomes and identified a diverse set of secreted proteins, which we designated as putative Phytoplasma Effectors (PhAMEs). We found that PhAMEs targeting evolutionarily conserved and structurally constrained surfaces of host proteins are widespread across phytoplasmas. These effectors adopt compact, efficient folds. They often function as molecular scaffolds with dual interaction surfaces capable of linking host proteins or integrating signalling pathways. Such scaffolding PhAMEs have evolved multiple times independently, providing clear evidence of convergent evolution. Despite severe genomic constrains imposed by genome reduction and limited HGT, gene duplications, interface variations, domain fusions, and repeat expansions have helped the shaping effector fold and diversity. While the overall effector repertoire of phytoplasmas appeared largely unique, some PhAME domains share similarities with proteins from other mollicutes and pathogens. Collectively, our findings shed light on how genome-reduced bacteria innovate molecular functions and offer insights into phytoplasma biology, effector evolution, and host-pathogen dynamics. They also lay the groundwork for protein engineering approaches aimed at discovering or designing novel biomolecules with biotechnological potential.

The fungal genus Cryptococcus includes several life-threatening human pathogens as well as diverse saprobic species whose genome architecture, ecology, and evolutionary history remain less well characterized. Understanding how some lineages evolved into major pathogens remains a central challenge and may be advanced by comparisons with their nonpathogenic counterparts. Integrative approaches have become essential for delimiting species and reconstructing evolutionary relationships, particularly in lineages with cryptic diversity or extensive chromosomal rearrangements. Here, we formally characterize six Cryptococcus species representing distinct evolutionary lineages, comprising both newly discovered and previously recognized but unnamed taxa, through a combination of phylogenomic analyses, divergence metrics, chromosomal comparisons, mating assays, and phenotypic profiling. Among pathogenic taxa, we formally name Cryptococcus hyracis sp. nov., corresponding to the previously characterized VGV lineage within the C. gattii complex. In parallel, we describe five saprobic, nonpathogenic species isolated from fruit, soil, and bark beetle galleries, spanning four phylogenetic clades. We identify a strong ecological association with bark beetles for Cryptococcus porticicola sp. nov., the only newly described nonpathogenic species with multiple sequenced strains from diverse sites. In this species, we detect strain-level chromosomal variation and evidence of sexual reproduction, along with population-level signatures of recombination. Across the genus, chromosome-level comparisons reveal extensive structural variation, including species- and strain-specific rearrangements that may restrict gene flow. We also identify multiple instances of chromosome number reduction, often accompanied by genomic signatures consistent with centromere inactivation or loss of centromeric identity. Comparative metabolic profiling with Biolog phenotype microarrays reveals clade-level differentiation and distinct substrate preferences, which may reflect metabolic divergence and habitat-specific diversification. Notably, we confirm that thermotolerance is restricted to clinically relevant taxa. These findings refine the species-level taxonomy of Cryptococcus, broaden its known genomic and ecological diversity, and strengthen the framework for investigating speciation, adaptation, and the emergence of pathogenicity within the genus.

Dysregulation of the cellular mechanisms that coordinate the interpretation and transduction of microenvironmental biophysical signals are a unifying feature of tissue remodeling pathologies such as fibrosis and cancer. While genomic regulation downstream of normal mechanotransduction (i.e., cases where cells sense soft and stiff appropriately) is well studied, significantly less is known about the consequences of abnormal mechanoperception and subsequent misinterpretation of the mechanical environment. Leveraging Thy-1 (CD90) loss as a model of impaired mechanoperception, we employed ATAC- and RNA-sequencing in parallel to characterize the changes in lung fibroblast genomic activity in response to a combination of substrate stiffness and culture time. Notably, we find perturbed mechanoperception elicits a near-complete shutdown of HOXA5, a transcription factor responsible for pattern specification and development in the nascent lung. In vitro investigation of HOXA5 expression reveals a potential mechanism connecting increased αv integrin signaling, cytoskeletal tension, and SRC kinase activity to HOXA5 silencing. These results establish novel links between integrin signaling and the expression dynamics of genes necessary for tissue formation and regeneration in the injured and/or developing lung, particularly HOXA5.