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Borges, A.

Publications and source records attributed to Borges, A..

14 recordsLinked to original sources

StressNET: an adaptable deep-learning model for mechanical stress inference in tissues

Mechanical interactions between cells are fundamental to tissue morphogenesis during development and regeneration. Computational methods that infer intercellular stresses from microscopy images of cell shapes offer a non-invasive alternative to experimental perturbation techniques, yet all existing approaches rely on explicit physical models. Here we present StressNET, a Graph Neural Network (GNN) that infers intercellular mechanical stresses directly from tissue geometry, without assuming any underlying physical model. We generated synthetic datasets to train and benchmark StressNET, and demonstrate that its predictions achieve state-of-the-art correlation with experimental stress proxies in zebrafish neuromasts and Xenopus embryos. Analysis of the network's latent space reveals that StressNET learns global organizational principles of mechanical stress distribution, beyond local cell-cell interactions. StressNET is open-source and provides pre-trained models that can be fine-tuned on in vivo data, making it a broadly adaptable tool for studying tissue mechanics across biological systems.

bioinformatics↗

Apomixis frequency in polyploid wild populations of Psidium cattleyanum f. lucidum (Myrteae, Myrtaceae)

Background and AimsApomictic reproduction and polyploidy are closely related in plants, and their causes and consequences have given rise to numerous hypotheses that continue to evolve as more representative taxa are studied. Psidium cattleyanum is a valuable model for investigating this relationship, as it is a polyploid species with multiple ploidy levels and exhibits pseudogamous gametophytic apomixis. In addition, it is a fruit tree of commercial, agricultural, and medicinal interest in its native range, but it is also an aggressive invasive species in regions where it has been introduced. In this study, we aim to determine the predominant reproductive mode in natural populations of the polyploid Psidium cattleyanum f. lucidum and to investigate whether this mode is associated with specific ploidy levels. Furthermore, we investigate whether these reproductive traits are linked to patterns of genetic diversity and population genetic structure. MethodsWe assessed the reproductive mode in wild populations representing the four ploidy levels (2C = 5x, 6x, 7x, 8x) present in Uruguay. Reproductive pathways were inferred by combining flow cytometric seed screen (FCSS) analysis with microsatellite (SSR) genotyping of progeny arrays. Population-level differences were evaluated across both data sets. Key ResultsPseudogamous apomixis is the predominant reproductive mode in Uruguayan P. cattleyanum f. lucidum populations. The proportions of apomictic versus sexual reproduction, and the types of progenies produced, differed significantly among populations and ploidy levels. Genotyping revealed predominantly clonal progeny, yet with high genetic variability, and populations exhibit strong genetic structure. The ploidy level of the gametes and their combinations were characteristic of each population, leading to different reproductive strategies. ConclusionsFacultative pseudogamous apomixis is the primary reproductive mode in natural populations of Psidium cattleyanum f. lucidum. Ploidy level influences reproductive strategy, as reflected in the apomixis/sexuality ratios and the type of progeny produced. Population genetic structure is shaped by the reproductive strategy adopted by each population.

plant biology↗

Shedding light on the embryo:endosperm balance diversity that pseudogamy can achieve in the polyploid apomictic Psidium cattleyanum (Myrtaceae, Myrteae)

Apomixis is defined as the asexual mode of reproduction through seeds. Nearly all gametophytic apomictic species are polyploid. Psidium cattleyanum, a polyploid species with various described ploidy levels, exhibits apomixis and requires effective pollination for fruiting (pseudogamy). The aim of this study was to determine the frequency of apomixis and sexuality in P. cattleyanum among heptaploid and octoploid accessions, and to analyze the maternal and paternal contribution to endosperm formation. Flow cytometry was employed on mature seeds obtained from hand-pollinated crosses between two octoploid and two heptaploid accessions to determine the ploidy levels of embryo and endosperm. Within the 492 analyzed seeds the ploidy balance of embryo:endosperm ranged from the expected 2:5 (64.2%, pseudogamous apomixis) and 2:3 (4.7%, sexuality involving reduced gametophytes), to unexpected values, including 1:3 (0.4%),), 2:6 (2.4%), 2:7 (0.2%), 3:5 (8.8%), 2:3:5 (18.5%) and 2:4:6 (0.8%), associated with polyhaploid parthenogenesis, pseudogamous apomixis involving reduced and unreduced gametophytes, and female gametophytes with two or three polar nuclei in the central cell. The interpretations and implications of these results for apomictic polyploid species and their consequences for wild populations are discussed.

genetics↗

Combination of Cas9 and adeno-associated vectors (AAVs) enables efficient in vivo knockdown of precise miRNAs in the rodent brain

Although the advent of Cas9 technology has expanded our ability to precisely edit the genome, manipulating microRNAs in vivo has been shown to be particularly challenging, especially in the brain. Here, we sought to generate novel tools aiming at targeting and efficiently downregulating defined microRNAs species in a cell-specific manner so that their function in discrete neuronal networks could be investigated. Focusing on miR-124, a microRNA highly expressed in the mammalian brain and transcribed from three independent chromosomal loci, we designed and validated different guide RNAs directed against this miRNA. In vitro, our Cas9 designs show not only a significant reduction in miR-124 levels but also a functional effect on miR-124 silencing. Similarly, when packed into AAV vectors and injected into the mouse cortex, miR-124-Cas9 vectors strongly downregulate miR-124 levels without affecting the expression of other miRNAs. In parallel, levels of endogenous miR-124 targets exhibit a significant increase supporting the release of its silencing activity. To functionally validate our tools, we provide evidences that deletion of miR-124 in the subventricular zone altered migration of newly generated neurons into the olfactory bulb. Finally, we also showed that our vectors modified the Ca2+ permeability of AMPA receptors, a robust functional output downstream of miR-124. These tools are expected to help elucidating miRNA function in complex experimental settings such as brain networks in vivo.

neuroscience↗

Ethylene modulates cell wall mechanics for root responses to compaction

Soil stresses impact crop yields, presenting global agricultural challenges. Soil compaction triggers root length reduction and radial expansion driven by the plant hormone ethylene. We report how ethylene controls cell wall properties to promote root radial expansion. We demonstrate how soil compaction stress, via ethylene, upregulates Auxin Response Factor1 in the root cortex, which represses Cellulose Synthase (CESA) genes. CESA repression drives radial expansion of root cortical cells by modifying the thickness and mechanics of their cell walls, which result in a "stiff epidermis-soft cortex" contrast. Our research thus connects ethylene signaling with root mechanics via cell wall strength, and reveals how dynamic regulation of cellulose synthesis crucially controls root growth in compacted soil.

plant biology↗

Local control of cellular proliferation underlies neuromast regeneration in zebrafish

Biological systems are never in equilibrium but maintain stability despite continuous external disturbances. A prime example of this is organ regeneration, where, despite intrinsically stochastic damage, organs are rebuilt through controlled cellular proliferation. In this study, we employ a cell- based computational modelling approach to investigate the proliferative response to injury. We developed a minimal two-dimensional Cellular Potts Model (CPM) using empirical data from regenerating neuromasts in larval zebrafish. Remarkably, the CPM both qualitatively and quantitatively recapitulates the regenerative response of neuromasts following laser-mediated cell ablation. Assuming that cell proliferation is locally regulated by a delayed switch, mitotic activity ceases once the type-dependent number of neighbouring cells exceeds a deterministic critical threshold. An intriguing corollary of our findings is that a local negative feedback loop among identical cells may represent a general mechanism underlying organ-level proportional homeostasis.

developmental biology↗

ForSys: non-invasive stress inference from time-lapse microscopy

During tissue development and regeneration, cells interpret and exert mechanical forces that are challenging to measure in vivo. Therefore, stress inference algorithms have emerged as powerful tools to estimate tissue stresses. However, how to incorporate tissue dynamics effectively into the inference remains elusive. Here, we present ForSys, a Python-based software that estimates intercellular stresses and intracellular pressures using time-lapse microscopy. We validated ForSys in silico and in vivo using the well-characterized mucociliary epithelium of the Xenopus embryo. We applied ForSys to study the migrating zebrafish lateral line primordium. We found that stress increases during cell rounding just before cell division and predicted the onset of epithelial rosettogenesis with high accuracy. Finally, we analyzed the development of the zebrafish neuromast and inferred mechanical asymmetries in a cell type-specific adhesion pattern. The versatility and simplicity of ForSys enhance the toolkit for studying spatiotemporal patterns of mechanical forces during tissue morphogenesis in vivo.

systems biology↗

Comprehensive Analysis of Nascent Transcriptome Reveals Diverse Transcriptional Profiles Across the Trypanosoma cruzi Genome Underlining the Regulatory Role of Genome Organization, Chromatin Status, and Cis-Acting Elements

Trypanosomatids are eukaryotic parasites exhibiting polycistronic transcription and trans-splicing. Post-transcriptional mechanisms are acknowledged as pivotal in gene expression regulation of their protein-coding genes. To comprehensively investigate the impact of transcription on gene expression in Trypanosoma cruzi and the association with the epigenetic landscape, we conducted a genome-wide nascent transcriptomic analysis. Our findings reveal significant asymmetrical transcriptional abundance across the genome, notably between polycistronic transcription units (PTUs) enriched in conserved genes (core PTUs) and those containing virulence genes (disruptive PTUs). We found that trypanosomes exploit linear genome organization to regulate transcription abundance by embedding virulence genes into highly transcribed core-enriched PTUs, by positioning PTUs near non-coding regions of small non-coding RNAs (e.g., tRNAs, snoRNAs), and by placing core CDSs in PTUs of various sizes. Additionally, we found correlations between open chromatin status and nascent transcript levels, both globally and particularly at transcription starting regions (divergent strand switch regions - dSSRs), indicating a crucial role for chromatin architecture in transcriptional regulation. While both core and disruptive dSSRs exhibit similar levels of some epigenetic marks (H2B.V deposition and 5mC), disruptive dSSRs display significantly higher 5hmC content and nucleosome occupancy compared to core dSSRs. Furthermore, we identified distinct conserved motifs within dSSRs of core and disruptive PTUs. These findings challenge the notion of constitutive and uniform transcription in T. cruzi, underscoring the paramount importance of linear genome organization, cis-acting motifs, and chromatin landscape in transcriptional regulation.

molecular biology↗

The actomyosin system is essential for the integrity of the endosomal system in bloodstream form Trypanosoma brucei

The actin cytoskeleton is a ubiquitous feature of eukaryotic cells, yet its complexity varies across different taxa. In the parasitic protist Trypanosoma brucei, a rudimentary actomyosin system consisting of one actin gene and two myosin genes has been retained despite significant investment in the microtubule cytoskeleton. The functions of this highly simplified actomyosin system remain unclear, but appear to centre on the endomembrane system. Here, advanced light and electron microscopy imaging techniques together with biochemical and biophysical assays were used to explore the relationship between the actomyosin and endomembrane systems. The class I myosin (TbMyo1) had a large cytosolic pool and its ability to translocate actin filaments in vitro was shown here for the first time. TbMyo1 exhibited strong association with the endosomal system and was additionally found on glycosomes. At the endosomal membranes, TbMyo1 colocalised with markers for early and late endosomes (TbRab5A and TbRab7, respectively), but not with the marker associated with recycling endosomes (TbRab11). Actin and myosin were simultaneously visualised for the first time in trypanosomes using an anti-actin chromobody. Disruption of the actomyosin system using the actin-depolymerising drug latrunculin A resulted in a delocalisation of both the actin chromobody signal and an endosomal marker, and was accompanied by a specific loss of endosomal structure. This suggests that the actomyosin system is required for maintaining endosomal integrity in T. brucei.

cell biology↗

Continuous endosomes form functional subdomains and orchestrate rapid membrane trafficking in trypanosomes

Endocytosis is a common process observed in most eukaryotic cells, although its complexity varies among different organisms. In Trypanosoma brucei, the endocytic machinery is under special selective pressure because rapid membrane recycling is essential for immune evasion. This unicellular parasite effectively removes host antibodies from its cell surface through hydrodynamic drag and fast endocytic internalization. The entire process of membrane recycling occurs exclusively through the flagellar pocket, an extracellular organelle situated at the posterior pole of the spindle-shaped cell. The high-speed dynamics of membrane flux in trypanosomes do not seem compatible with the conventional concept of distinct compartments for early, late and recycling endosomes. To investigate the underlying structural basis for the remarkably fast membrane traffic in trypanosomes, we employed advanced techniques in light and electron microscopy to examine the three-dimensional architecture of the endosomal system. Our findings reveal that the endosomal system in trypanosomes exhibits a remarkably intricate structure. Instead of being compartmentalized, it constitutes a continuous membrane system, with specific functions of the endosome segregated into membrane subdomains enriched with classical markers for early, late, and recycling endosomes. These membrane subdomains can partly overlap or are interspersed with areas that are negative for endosomal markers. This continuous endosome allows fast membrane flux by facilitated diffusion that is not slowed by multiple fission and fusion events.

cell biology↗

Endocytosis is required for access of surface-bound cargo to the flagellar pocket of trypanosomes

All endo- and exocytosis in the African trypanosome Trypanosoma brucei occurs at a single subdomain of the plasma membrane. This subdomain, the flagellar pocket, is a small vase-shaped invagination containing the root of the cells single flagellum. Several cytoskeleton-associated multiprotein complexes are coiled around the neck of the flagellar pocket on its cytoplasmic face. One of these, the hook complex, was proposed to affect macromolecule entry into the flagellar pocket lumen. In previous work, knockdown of the hook complex component TbMORN1 resulted in larger cargo being unable to enter the flagellar pocket. In this study, the hook complex component TbSmee1 was characterised in bloodstream form Trypanosoma brucei and was found to be essential for cell viability. TbSmee1 knockdown resulted in flagellar pocket enlargement and impaired access to the flagellar pocket membrane by surface-bound cargo, similar to depletion of TbMORN1. Unexpectedly, inhibition of endocytosis by knockdown of clathrin phenocopied TbSmee1 knockdown, suggesting that endocytic activity itself is a prerequisite for the entry of surface-bound cargo into the flagellar pocket. SummaryCharacterisation of the essential trypanosome protein TbSmee1 suggests that endocytosis is required for flagellar pocket access of surface-bound cargo.

cell biology↗

Size matters: an analytical study on the role of tissue size in spatiotemporal distribution of morphogens unveils a transition between different reaction-diffusion regimes

The reaction-diffusion model constitutes one of the most influential mathematical models to study distribution of morphogens in tissues. Despite its widespread use, the effect of finite tissue size on model-predicted spatiotemporal morphogen distributions has not been completely elucidated. In this study, we analytically investigated the spatiotemporal distributions of morphogens predicted by a reaction-diffusion model in a finite 1D domain, as a proxy for a biological tissue, and compared it with the solution of the infinite-domain model. We explored the reduced parameter, the tissue length in units of a characteristic reaction-diffusion length, and identified two reaction-diffusion regimes separated by a crossover tissue size estimated in [~]3.3 characteristic reaction-diffusion lengths. While above this crossover the infinite-domain model constitutes a good approximation, it breaks below this crossover, whereas the finite-domain model faithfully describes the entire parameter space. We evaluated whether the infinite-domain model renders accurate estimations of diffusion coefficients when fitted to finite spatial profiles, a procedure typically followed in Fluorescence Recovery After Photobleaching (FRAP) experiments. We found that the infinite-domain model overestimates diffusion coefficients when the domain is smaller than the crossover tissue size. Thus, the crossover tissue size may be instrumental in selecting the suitable reaction-diffusion model to study tissue morphogenesis.

systems biology↗

Eya1-dependent homeostasis of morphogenetic territories during collective cell migration

Mutations in the transcriptional co-activator Eya1 cause branchio-oto-renal syndrome (BOR) in humans, and the equivalent conditions in vertebrates. BOR has an incidence of 1/40,000 and is characterized by congenital branchial fistulas, malformations of the inner ear and kidney hypoplasia. Therapeutic interventions for BOR are currently limited to reparative surgery, hearing aids and dialysis. Here we use the mechanosensory lateral line in zebrafish to better understand the role of Eya1 in organogenesis. The lateral line develops from a primordium formed by approximately 150 cells that move together from head to tail of the embryo at a constant velocity. This invariant migration occurs over a trail of Sdf1a chemokine and is controlled by the simultaneous action of two receptors. The CXCR4b is expressed in the front half of the primordium where it acts as a chemokine sensor, whereas the CXCR7b is present in the rear half, serving as a chemokine sink to ensure persistent directionality. We show that the loss of Eya1 strongly reduces the expression of CXCR7b, disrupting the coherent motion of the primordium and leading to lateral-line truncations. We also find evidence of reduced epithelial maturation in primordia lacking Eya1. These findings argue for abnormal collective cell chemotaxis as the origin of organ dysmorphia in BOR.

developmental biology↗

Direct observation of genome surveillance by CRISPR-Cas in bacteria

CRISPR-Cas systems are prokaryotic adaptive immune systems that have been well characterized biochemically, but in vivo spatiotemporal regulation and cell biology remains largely unaddressed. Here, we used fluorescent fusion proteins to study the localization of the Type I-F CRISPR-Cas system native to Pseudomonas aeruginosa. When targeted to an integrated prophage, the crRNA-guided (Csy) complex and a majority of Cas3 molecules in the cell are recruited to a single focus. When lacking a target in the cell, however, the Csy complex is broadly nucleoid bound, while Cas3 is diffuse in the cytoplasm. Nucleoid association for the Csy proteins is crRNA-dependent, and inhibited by expression of anti-CRISPR AcrIF2, which blocks PAM binding. The Cas9 nuclease is also nucleoid localized, only when gRNA-bound, which is abolished by PAM mimic, AcrIIA4. Our findings reveal PAM-dependent nucleoid surveillance and spatiotemporal regulation in Type I CRISPR-Cas that separates the nuclease-helicase Cas3 from the crRNA-guided surveillance complex.

microbiology↗