Biology subjects

Khatri, D.

Publications and source records attributed to Khatri, D..

8 recordsLinked to original sources

bioRxiv2026

u4atac regulates cilium biogenesis through splicing of the minor intron of tmem107l and rfx7b in zebrafish developing brain

Bi-allelic variants of RNU4ATAC, transcribed into the minor spliceosome component U4atac snRNA, are associated to variable severity of microcephaly, growth retardation, skeletal dysplasia and immunodeficiency as main features. Previous studies highlighted the dramatic effect of U4atac deficiency on splicing of U12-type introns, which represent less than 1% of all introns in the human genome. More recently, our team evidenced a link between U4atac and the primary cilium/centrosome complex through the identification of patients carrying RNU4ATAC bi-allelic variants and exhibiting an atypical Joubert syndrome, a well-known ciliopathy. Yet, the underlying mechanisms remain elusive. Here, we further explored the link of RNU4ATAC to primary cilium and aimed at identifying ciliary U12-type intron containing genes that contribute to the brain abnormalities seen in patients. For that, we performed a transcriptomic analysis of heads of our morpholino oligonucleotide (MO)-mediated u4atac zebrafish model. Through the combined analysis of the generated dataset with those obtained from RNU4ATAC patient cells, we identified two candidate genes: TMEM107, coding for a structural protein of the cilium transition zone, and RFX7, encoding a transcription factor involved in primary cilium formation. By conducting complementary genetic approaches in zebrafish model, we showed that both gene orthologues, tmem107l and rfx7b, functionally interact with u4atac and are required for correct brain development. Altogether, our findings establish TMEM107 and RFX7 as key components of the molecular pathway linking U4atac dysfunction to ciliary defects and impaired brain development, providing new physiopathological insights and therapeutic perspectives for RNU4ATAC-related disorders.

genetics↗

bioRxiv2026

J-AST: a web-based analysis platform for antimicrobial susceptibility testing

Antimicrobial resistance and tolerance pose escalating global health threats, necessitating reproducible and accessible tools for antimicrobial susceptibility testing (AST). While disk diffusion assays (DDAs) and Epsilometer tests (Etests) are widely used, there are limited open-source tools to analyze them. We present J-AST, a free, open-source, web-based platform for analyzing both DDAs and Etests. It provides automated and interactive annotation of regions of interest and metadata management, and quantifies microbial resistance and tolerance. J-AST outputs correlate strongly with those of existing tools, and equivalent DDA and Etest results correlate strongly with each other. The automated MIC detection achieved >90% agreement with manual readouts. J-AST is deployable both as desktop software and cloud service, unifies automated analysis with interactive review, and advances both fundamental research and clinical AST workflows.

bioinformatics↗

bioRxiv2024

Deep learning-based reconstruction of embryonic cell-division cycle from label-free microscopy time-series of evolutionarily diverse nematodes

Microscopy of cellular dynamics during embryogenesis of non-model organisms can be tech- nically challenging due to limitations of molecular labelling methods. Label-free differential interference contrast (DIC) microscopy of the first embryonic cell division of nematodes related to Caenorhabditis elegans has been successfully employed to examine the constraints and divergence of intra-cellular mechanisms during this asymmetric cell division. However, identifying stages of the cell division cycle were performed interactively, pointing to a need to automate of cell stage identification from DIC microscopy. To this end, we have trained deep convolutional neural networks (CNNs), both pre-existing such as ResNet, VGGNet and EfficientNet, and a customized shallow network, EvoCellNet, to automatically classify first-embryonic division into the stages: (i) pro-nuclear migration and (ii) centration and rotation, (iii) spindle elongation and (iv) cytokinesis, with all networks performing with 91% or greater accuracy. The activations of the networks superimposed on the images result in segmentation-free detection of intracellular features such as pro-nuclei, spindle and spindle- poles in case of the shallow EvoCellNet, while ResNet, VGGNet and and EfficientNet detect large-scale, features that are less biologically meaningful. The UMAP space representation combined with support vector machines (SVM) allows for stage boundary identification and recovers a cyclical map connecting the states (i) to (iv) of the division. This approach could be used to automate quantification of cell division stages and sub-cellular dynamics without explicit labelling in label-free microscopy. SummaryWe have trained multiple convolutional neural networks (CNNs) to classify the stages of cell division from the first embryonic division of diverse nematodes, evolutionarily related to Caenorhabditis elegans. We find two classifiers, VggNet and a customized EvoCellNet, can detect intracellular features and a UMAP representation can reconstruct the cyclical progression of first embryonic division from related species.

developmental biology↗

bioRxiv2023

Multi-protein chimeric antigens, a novel combined approach for efficiently targeting and blocking the blood stage of Plasmodium falciparum

Plasmodium falciparum-induced malaria remains a fatal disease affecting millions of people worldwide. Mainly, the blood stage of malaria is highly pathogenic and symptomatic, rapidly damaging the host organs and occasionally leading to death. Currently, no vaccines are approved for use against the blood stage of malaria. Canonical vaccines in the past have selected the most immunodominant or essential protein to block the growth of the parasite. This strategy works efficiently for low-complexity organisms such as viruses and a few bacteria but has not shown promising results for a malaria vaccine. Plasmodium has a complex life cycle and vaccine candidates especially during blood stage are ineffective due to multiple gene families showing redundancy, immune evasion, and insufficient antibody titer. Herein, we demonstrate a novel strategy of combining multiple antigens from the blood stage of Plasmodium falciparum using only the most immunodominant peptide sequences as a way of tackling polymorphism and redundancy. We created three chimeric antigens targeting eight PfEMP1 proteins (chimeric varB) and eight merozoite surface proteins (chimeric MSP and InvP) by selecting and stitching B-cell epitopes. Our chimeric constructs show naturally circulating antibodies against individual peptides using epitope-mapping microarray as well as entire proteins in malaria-infected patients. We demonstrate that anti-varB antibodies are neutralizing in nature and significantly reduce the cytoadhesion on an organ-on-chip system with a microfluidic device mimicking physiological conditions. We have applied a Deep Learning based method to quantify the number of adhered RBCs under fluidic conditions that is used to study cytoadhesion. Furthermore, the anti-MSP and InvP antibodies show complete growth inhibition in a single cycle at a combined concentration of 0.13 mg/ml. Overall, our results show that a combination of antigenic peptides from multiple antigens can function as a next-generation vaccine and effectively block the blood stage by reducing cytoadhesion and inhibiting the parasite growth.

molecular biology↗

bioRxiv2023

Unveiling a Novel Memory Center in Humans: Neurochemical Identification of the Nucleus Incertus, a Key Pontine Locus Implicated in Stress and Neuropathology

BackgroundThe nucleus incertus (NI) was originally described by Streeter in 1903, as a midline region in the floor of the fourth ventricle (4V) of the human brain with an unknown function. More than a century later, the neuroanatomy of the NI including its forebrain target regions has been described in lower vertebrates, but not in humans. Therefore, we examined the neurochemical anatomy of the human NI using several markers, including the neuropeptide, relaxin-3 (RLN3), and began to explore the distribution of the NI-related RLN3 innervation of the hippocampus. MethodsHistochemical staining of serial, coronal sections (30 {micro}m) of control human postmortem pons was conducted to reveal the presence of the NI by detection of immunoreactivity (IR) for the neuronal marker, microtubule-associated protein-2 (MAP2), two markers present in rat NI, glutamic acid dehydrogenase (GAD)-65/67 and corticotrophin releasing hormone receptor 1 (CRHR1), and RLN3, which is highly expressed in a major population of NI neurons in diverse species. RLN3 and vesicular GABA transporter 1 (vGAT1) mRNA was detected by multiplex, fluorescence in situ hybridization. Postmortem pons sections containing the NI from an Alzheimers disease (AD) case were immunostained for phosphorylated-tau (AT8 antibody), to explore potential relevance to neurodegenerative diseases. Lastly, sections of human hippocampus were stained to detect RLN3-IR and somatostatin (SST)-IR, as SST is expressed in interneurons targeted by RLN3 projections in rodents. ResultsIn the dorsal, anterior-medial region of the human pons, neurons containing RLN3- and MAP2-IR, and RLN3/vGAT1 mRNA-positive neurons were observed in an anatomical pattern consistent with that of the NI in other species. GAD65/67- and CRHR1-immunopositive neurons were also detected within this area. Furthermore, RLN3- and AT8-IR were co-localized within NI neurons of an AD subject. Lastly, RLN3-IR was detected in neurons within the CA1, CA2, CA3, and DG areas of the hippocampus, in the absence of RLN3 mRNA. In the DG, RLN3- and SST-IR were co-localized in a small population of neurons. ConclusionsAspects of the anatomy of the human NI are shared across species, including a population of RLN3-expressing neurons and a RLN3 innervation of the hippocampus. Accumulation of phosphorylated-tau in the NI suggests its possible involvement in AD pathology. Further characterization of the neurochemistry of the human NI will increase our understanding of its functional role in health and disease. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=75 SRC="FIGDIR/small/556922v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@f4c439org.highwire.dtl.DTLVardef@17e85f5org.highwire.dtl.DTLVardef@18ca7faorg.highwire.dtl.DTLVardef@168246c_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract Created with BioRender.com C_FIG

neuroscience↗

bioRxiv2022

Effect of Size Variability, Filamentation and Division Dynamics on Escherichia coli Allometry

The cell surface area (SA) increase with volume (V) for cells is determined by growth and regulation of size and shape. Most studies of the rod-shaped model bacterium Escherichia coli have focussed on the phenomenology or molecular mechanisms governing such scaling. Here, we proceed to examine the role of population statistics and cell division dynamics in such scaling by a combination of microscopy, image analysis and statistical simulations. We find that while cells sampled from mid-log cultures follow a 2/3 exponent, similar to geometric (Platonic) solids, drug induced filamentous cells have higher exponent values. Modulating the growth rate to change the proportion of filamentous cells, we find SA-V scales with an exponent > 2/3, exceeding that predicted by the geometric scaling law. However, since increasing growth rates alter the mean and spread of population cell size distributions, we use statistical modeling to disambiguate between the effect of the mean size and variability. Simulating (i) increasing mean cell length with a constant standard deviation (s.d.) and (ii) a constant mean length with increasing s.d. results in scaling exponents that exceed the 2/3 geometric law, when population variability is included. In order to overcome possible effects of statistical sampling of unsynchronized cell populations, we virtually synchronized the estimation of SA-V scaling from single cell growth experiments. We find the exponent depends on the stage with the maximal cell length heterogeneity and scaling exponent observed during the intermediate period between birth (B) and division (D) stages. These results point to a need to consider population statistics and a role for cell growth and division when estimating SA-V scaling of bacterial cells.

biophysics↗

bioRxiv2022

Emergence of flagella-like oscillations in single microtubules driven by collective dynein transport

Flagellar and ciliary oscillations result from a combination of stereotypical axonemal geometry, collective mechanics of motors, microtubules (MTs), elastic linkers and biochemical regulation. However, the minimal essential components and constraints resulting in flagellar oscillations remain unclear. Here, we demonstrate that periodic, low-frequency waves of flagella-like oscillations in vitro emerge from a ATP-driven collective molecular motor transport of MTs clamped at one end. The spontaneous oscillations arise without any external forcing and can be explained by an in silico model of molecular motor binding driven MT bending and buckling followed by motor detachment driven recovery stroke. We demonstrate that transitions in single MT patterns between flapping, flagellar-beating and looping are determined solely by the self-organization of collective motor transport and filament elasticity.

biophysics↗

bioRxiv2021

Evolutionary divergence of anaphase spindle mechanics in nematode embryos constrained by antagnonistic pulling and viscous forces

Cells are the basic unit of biological organization, and their division is remarkably conserved across phyla. However from an evolutionary perspective, it remains unclear how much cellular parameters can diverge, without altering the basic function they sustain. We address the mechanics of asymmetric mitotic spindle positioning during the first embryonic division of six nematode species. We propose a viscoelastic model of spindle positioning and mobility that can provide a physical explanation of why in C. elegans it undergoes oscillations during elongation, whereas most others lack oscillations. To test this model, we measured the pulling forces and opposing cytoplasmic drag by a combination of laser ablation of the anaphase spindle and tracking of intracellular granules. While centrosomes of all species recoil on spindle cutting, quantitative differences correlate with the cytoplasmic viscosity. In fact, increased viscosity correlates with decreased oscillation speeds of intact spindles across species. However, the absence of oscillations despite low viscosity in some species, can only be explained by smaller pulling forces. Consequently, we find that spindle mobility across the species analyzed here is characterized by a tradeoff between cytoplasmic viscosity and pulling forces. Our work provides a framework for understanding mechanical constraints on evolutionary diversification of spindle mobility.

biophysics↗