Biology subjects

Abbasi, M.

Publications and source records attributed to Abbasi, M..

11 recordsLinked to original sources

bioRxiv2026

Representation Methods of Transcriptomics with Applications in Neuroimmune Biology

Interpretable representations of gene expression are used to define cellular identities and the molecular programs active within cells, two related, but distinct phenomena. In the case of microglia, a cell type with high transcriptomic, functional, and morphological heterogeneity, the predominant representation of transcriptomic data presumes the adoption of distinct molecular identities, despite a lack of easily separable transcriptional states. Here, we explore alternative transcriptomic representations by comparing two single-cell analysis methods: differential expression analysis for identities and co-expression network analysis for molecular programs. For microglia, co-expression network analysis identifies highly significant functional ontologies not resolved by differential expression analysis. The identified co-expression modules are preserved across transcriptomic datasets and suggest reducible functional programs that activate and modulate depending on context. We conclude that co-expression analysis constitutes a best practice for single cell analysis of an individual cell type and describing microglia function as concurrent molecular programs offers a more parsimonious model of microglia function.

bioinformatics↗

bioRxiv2025

Wheat and barley stripe rust pan-genome facilitates discovery of the predominant North American lineage's origin in somatic hybridization

Wheat and barley stripe rust, caused by Puccinia striiformis formae speciales tritici (Pst) and hordei (Psh) respectively is a perennial and endemic threat to those crops worldwide. Outside the Himalayan region the fungus has not been observed reproducing sexually, despite being characterised extensively over the past 100 years by researchers in many countries. Scientific literature divides P. striiformis into lineages termed PstS0, PstS1, up to PstS18. Here we describe the first North American P. striiformis pan-genome, comprising 24 Pst and 3 Psh genomes from North America including five phased assemblies using chromosome conformation capture to separate two haploid genomes. We identify the origin of the predominant North American Pst lineage; PstS18, as a somatic hybridization event between PstS1 and another unknown lineage. As well as identifying gene families which distinguish haplotypes on a trans-lineage and trans-species level, we also show ongoing gene family loss and expansion in clonal lineages after their emergence.

microbiology↗

bioRxiv2025

GPU-accelerated, self-optimizing processing for 3D multiplexed iterative RNA-FISH experiments

Imaging-based spatial transcriptomic approaches rely on iterative labeling and imaging of carefully prepared samples, followed by solving a computational inverse problem to determine the location and identity of the targeted RNA. Because these approaches require high-resolution optics, the Nyquist-Shannon determined voxel size is small relative to typical tissue sample footprints. A common solution to speed up both experiments and computation is to increase the distance in between focal planes, trading off local information content to sample a larger imaging area in a reasonable time. In this work we introduce a GPU-accelerated computational framework, merfish3d-analysis, designed to speed up the computational processing of barcoded, in situ imaging-based spatial transcriptomics. Using this framework, we quantify the information lost due to axial sampling changes in simulated imaging-based spatial transcriptomic experiments, robustly reprocess publicly available multiplexed error-robust fluorescence in situ hybridization (MERFISH) datasets, and analyze new MERFISH experiments performed on a post-mortem human olfactory bulb sample. To improve the quality of experimental data in the post-mortem human sample, we designed a multi-step autofluorescence quenching protocol specific for in situ imaging-based spatial transcriptomic strategies. Taken together, we hope that the sample preparation protocols and single workstation, GPU-accelerated processing will further democratize imaging-based spatial transcriptomic experiments.

bioinformatics↗

bioRxiv2025

Perturbation of epithelial and limbal stem cell identity in a mouse model of pathologic corneal neovascularization

The epithelial layer of the cornea is a critical physical and ocular immune barrier for maintaining tissue integrity, homeostasis, and transparency for proper vision. Corneal injury can trigger inflammation, impair wound healing and compromise immune privilege and avascularity, leading to vision loss. Moreover, injury to the cornea can disrupt the engine of epithelial repair and restoration, the limbal stem cell (LSC) niche. Here we used a corneal suture model to induce epithelial damage, sustained inflammation and neovascularization, to examine the impact on LSCs. Using single-cell transcriptomics, we analyzed corneal cell state changes and additionally evaluated the potential of duloxetine, an FDA-approved medicine, to promote wound healing and corneal homeostasis. Single-cell RNA-seq analysis revealed loss of homeostatic limbal stem cells, basal and differentiated epithelial cells and an increase in distinct limbal-like, conjunctival, inflammatory, and vascular cell states, suggesting a coordinated wound healing response in different tissue layers. Importantly, duloxetine treatment promoted epithelial homeostasis, enhanced stem cell-like and stromal repair processes, and suppressed immune and vascular responses. Examination of corneal cell perturbation and transformations at the single-cell level thorough marker profile annotations can improve the understanding of LSC plasticity and function while yielding potential biomarkers of corneal repair processes.

molecular biology↗

bioRxiv2024

Fusobacterium necrophorum and Fusobacterium varium are commensal members of the bovine reproductive microbiota and may colonize calf prenatally

Fusobacterium necrophorum is an important pathogen associated with several infectious diseases in cattle. However, recent sequencing-based studies have indicated that F. necrophorum is positively associated with pregnancy in beef cows and that Fusobacterium is the most abundant genus in the bull seminal microbiota, suggesting the potential role of Fusobacterium in reproductive health and fertility. Here, we performed a comprehensive screening to 1) determine whether Fusobacterium necrophorum (subspecies necrophorum [FNN] and funduliforme [FNF]), and Fusobacterium varium (FV) are part of the commensal members of the reproductive microbiota in cattle; 2) to explore whether these Fusobacterium spp. are colonized in calf prenatally. For this, we screened 11 different sample types including bovine and ram semen, bovine vaginal and uterine swabs, and bull fecal samples, as well as samples from 180- and 260-days old calf fetuses and their respective dams using both quantitative PCR (514 samples) and targeted culturing (499 samples). By qPCR, all the targeted Fusobacterium spp. were detected across all sample types, with FNF being the highly prevalent in the bull semen (66.7%) and maternal ruminal fluids (87.1%), which was confirmed by culturing. All the targeted Fusobacterium were identified in vaginal and uterine (3.1%-9.4%) as well as placental caruncles, and fetal fluids, ruminal and meconium samples (2.7% - 26.3%) by qPCR and were not isolated by culture method. Overall, our results suggest that F. necrophorum is a commensal member of healthy male reproductive microbiota, and that FNF, FNN and FV are present in bovine vagino-uterine microbiota, and calf intestine prenatally.

microbiology↗

bioRxiv2023

Looking for a needle in a haystack: de novo phenotypic target identification reveals Hippo pathway-mediated miR-202 regulation of egg production

Understanding microRNA (miRNA) functions has been hampered by major difficulties in identifying their biological target(s). Currently, the main limitation is the lack of a suitable strategy to identify biologically relevant targets among a high number of putative targets. Here we provide a proof of concept of successful de novo (i.e., without prior knowledge of its identity) miRNA phenotypic target (i.e., target whose de-repression contributes to the phenotypic outcomes) identification from RNA-seq data. Using the medaka mir-202 knock-out (KO) model in which inactivation leads to a major organism-level reproductive phenotype, including reduced egg production, we introduced novel criteria including limited fold-change in KO and low interindividual variability in gene expression to reduce the list of 2,853 putative targets to a short list of 5. We selected tead3b, a member of the evolutionarily-conserved Hippo pathway, known to regulate ovarian functions, due to its remarkably strong and evolutionarily conserved binding affinity for miR-202-5p. Deleting the miR-202-5p binding site in the 3 UTR of tead3b, but not of other Hippo pathway members sav1 and vgll4b, triggered a reduced egg production phenotype. This is one of the few successful examples of de novo functional assignment of a miRNA phenotypic target in vivo in vertebrates.

genomics↗

bioRxiv2023

Uncovering the history of recombination and population structure in western Canadian stripe rust populations through mating-type alleles

The population structure of crop pathogens such as Puccinia striiformis f. sp. tritici (Pst); the cause of wheat stripe rust, is of interest to researchers looking to understand these pathogens on a molecular level, as well as those with an applied focus such as disease epidemiology. Cereal rusts can reproduce sexually or asexually, and the introduction of novel genetic lineages has the potential to cause serious epidemics such as the one caused by Warrior lineage in Europe. In a global context, Pst lineages in Canada were not well-characterized and origin of foreign incursions was not known. We used a whole-genome/transcriptome sequencing approach for the Canadian Pst population to identify lineages in a global context, origin, and evidence for foreign incursion. More importantly, for the first time ever, we identified nine alleles of the homeodomain mating-type locus in the worldwide Pst population and show that previously identified lineages generally exhibit a single pair of these alleles. In addition, we find only two pheromone receptor alleles. We show that the recent population shift from the PstS1 lineage to the PstS1-related lineage is also associated with the introduction of a novel mating-type allele (b-3) to the Canadian population. We also show evidence for high levels of mating-type diversity in samples associated with the Himalayan center of diversity for Pst, including a single Canadian race previously identified as PstPr (probable recombinant) which we identify as a foreign incursion from China circa. 2010. These data provide comprehensive details on the population biology of Canadian Pst diversity and mating-type alleles in the global Pst population which can be utilized in testing several research questions and hypotheses around sexuality and parasexuality in rust fungi.

genomics↗

bioRxiv2021

Improved Unsupervised Representation Learning of Spatial Transcriptomic Data with Sparse Filtering

Unsupervised learning methods are commonly used to detect features within transcriptomic data and ultimately derive meaningful representations of biology. Contributions of individual genes to any feature however becomes convolved with each learning step, requiring followup analysis and validation to understand what biology might be represented by a cluster on a low dimensional plot. We sought learning methods that could preserve the gene information of detected features, using the spatial transcriptomic data and anatomical labels of the Allen Mouse Brain Atlas as a test dataset with verifiable ground truth. We established metrics for accurate representation of molecular anatomy to find sparse learning approaches were uniquely capable of generating anatomical representations and gene weights in a single learning step. Fit to labeled anatomy was highly correlated with intrinsic properties of the data, offering a means to optimize parameters without established ground truth. Once representations were derived, complementary gene lists could be further compressed to generate a low complexity dataset, or to probe for individual features with >95% accuracy. We demonstrate the utility of sparse learning as a means to derive biologically meaningful representations from transcriptomic data and reduce the complexity of large datasets while preserving intelligible gene information throughout the analysis.

bioinformatics↗

bioRxiv2021

The microtubule plus-end tracking protein Bik1 is required for chromosome congression

During mitosis, sister chromatids congress on both sides of the spindle equator to facilitate the correct partitioning of the genomic material. Chromosome congression requires a finely tuned control of microtubule dynamics by the kinesin motor proteins. In Saccharomyces cerevisiae, the kinesin proteins Cin8, Kip1, and Kip3 have a pivotal role in chromosome congression. It has been hypothesized that additional proteins that modulate microtubule dynamics are also involved. Here, we show that the microtubule plus-end tracking protein Bik1 - the budding yeast ortholog of CLIP-170 - is essential for chromosome congression. We find that nuclear Bik1 localizes to the kinetochores in a cell-cycle-dependent manner. Disrupting the nuclear pool of Bik1 with a nuclear export signal (Bik1-NES) leads to a slower cell cycle progression characterized by a delayed metaphase-anaphase transition. Bik1-NES cells have mispositioned kinetochores along the spindle in metaphase. Furthermore, using proximity-dependent methods, we identify Cin8 as an interaction partner of Bik1. Deleting CIN8 reduces the amount of Bik1 at the spindle. In contrast, Cin8 retains its typical bilobed distribution in the Bik1-NES mutant and does not localize to the unclustered kinetochores. Thus, we propose that Bik1 functions with Cin8 to regulate kinetochore-microtubule dynamics for correct kinetochore positioning and chromosome congression.

cell biology↗

bioRxiv2020

Functional partnership between carbonic anhydrase and malic enzyme in promoting gluconeogenesis in Leishmania major

Leishmania has a remarkable ability to proliferate under widely fluctuating levels of essential nutrients, such as glucose. For this the parasite is heavily dependent on its gluconeogenic machinery. One perplexing aspect of gluconeogenesis in Leishmania is the lack of the crucial pyruvate carboxylase (PC) gene. PC-catalyzed conversion of pyruvate to oxaloacetate is a key entry point through which gluconeogenic amino acids are funnelled into this pathway. Absence of PC in Leishmania thus raises question about the mechanism of pyruvate entry into the gluconeogenic route. We report here that this task is accomplished in Leishmania major through a novel functional partnership between its mitochondrial malic enzyme (LmME) and cytosolic carbonic anhydrase (LmCA1). Using a combination of pharmacological inhibition studies with genetic manipulation, we showed that both these enzymes are necessary in promoting gluconeogenesis and supporting parasite growth under glucose limiting condition. Functional crosstalk between LmME and LmCA1 was evident when it was observed that the growth retardation caused by inhibition of any one of these enzymes could be protected to a significant extent by overexpressing the other enzyme. We also found that while LmCA1 exhibited constitutive expression, LmME protein level was strongly upregulated in low glucose condition. Notably, both LmME and LmCA1 were found to be important for survival of Leishmania amastigotes within host macrophages. Taken together, our results indicate that LmCA1 by virtue of its CO2 concentrating ability stimulates LmME-catalyzed pyruvate carboxylation, thereby driving gluconeogenesis through pyruvate-malate-oxaloacetate bypass pathway. Additionally, our study establishes LmCA1 and LmME as promising therapeutic targets.

biochemistry↗

bioRxiv2020

Experimental glaucoma retinal proteomics identifies mutually exclusive and overlapping molecular characteristics with human glaucoma

Current evidence suggests that exposure to chronically induced intraocular pressure (IOP) leads to neurodegenerative changes in the inner retina. This study aimed to determine retinal proteomic alterations in a rat model of glaucoma and compared findings with human retinal proteomics changes in glaucoma reported previously. We developed an experimental glaucoma rat model by subjecting the rats to increased IOP (9.3{+/-}0.1 vs 20.8{+/-}1.6 mm Hg) by weekly microbead injections into the eye (8 weeks). The retinal tissues were harvested from control and glaucomatous eyes and protein expression changes analysed using multiplexed quantitative proteomics approach. Immunofluorescence was performed for selected protein markers for data validation. Our study identified 4304 proteins in the rat retinas. Out of these, 139 proteins were downregulated ([≤]0.83) while expression of 109 proteins was upregulated ([≥]1.2-fold change) under glaucoma conditions (p[≤]0.05). Computational analysis revealed reduced expression of proteins associated with glutathione metabolism, mitochondrial dysfunction/oxidative phosphorylation, cytoskeleton and actin filament organisation, along with increased expression coagulation cascade, apoptosis, oxidative stress and RNA processing markers. Further functional network analysis highlighted the differential modulation of nuclear receptor signalling, cellular survival, protein synthesis, transport and cellular assembly pathways. Alterations in crystallin family, glutathione metabolism and mitochondrial dysfunction associated proteins shared similarities between the animal model of glaucoma and the human disease condition. In contrast, the activation of the classical complement pathway and upregulation of cholesterol transport proteins, were exclusive to the human glaucoma. These findings provide insights into the neurodegenerative mechanisms that are specifically affected in the retina in response to chronically elevated IOP.

neuroscience↗