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Biology subjects

Nandy, A.

Publications and source records attributed to Nandy, A..

14 recordsLinked to original sources

Mapping the diverse topologies of protein-protein interaction fitness landscapes

De novo binder discovery is unpredictable and inefficient due to a lack of quantitative understanding of protein-protein interaction (PPI) sequence-function landscapes. Here, we use our PANCS-Binder technology to perform >1,300 independent selections of various library sizes and compositions of a randomized small protein to identify binders to a panel of 96 distinct target proteins. For successful selections, we discovered reproducible fitness landscapes that group into a few, target-specific, clusters. Each cluster defines a minimal binding motif whose frequency is inversely proportional to the number of specified amino acids ([~]2-8) and determines selection success, which is quantifiable by the density of binders to the target within a theoretical sequence space. We leverage these data to develop a supervised contrastive learning approach that discriminates binders from non-binders and demonstrates generalization beyond a threshold amount of data. Together, this framework renders PPI landscapes measurable and predictive, accelerating de novo binder discovery and optimization.

synthetic biology↗

Causal Dynamics of Social Gaze in Primate Prefrontal-Amygdala Networks Revealed by Dynamic Bayesian Modeling

Social gaze is a fundamental channel of primate communication, shaping dynamic interactions and fostering mutual understanding. While prior studies have mapped the behavioral correlates of social gaze across the prefrontal-amygdala circuits, the causal architecture of these interactions remains poorly understood. Here, we introduce a novel algorithm to integrate independently recorded sessions into "super-sessions", validated using ground-truth synthetic data, enabling the reconstruction of simultaneous multi-area recordings aligned to matched gaze sequences. Applying Dynamic Bayesian Network analysis to these super-sessions, we uncover temporally structured, behavior-dependent causal interactions among the amygdala, orbitofrontal cortex, dorsomedial prefrontal cortex (dmPFC), and anterior cingulate cortex. When macaques were the targets of social gaze, the brain-behavior network exhibited positive temporal modulations, with the dmPFC emerging as the dominant source and the amygdala as a primary recipient of influence. When macaques directed their gaze toward their partners, the dmPFC and amygdala retained their respective roles. Prefrontal regions positively modulated one another, while the amygdala acted solely as a downstream target receiving exclusively negatively modulated prefrontal inputs. These findings reveal previously unknown directional interactions in the primate social brain and highlight distinct causal architectures underlying the bidirectional dynamics of social attention.

neuroscience↗

A high-throughput platform for biophysical antibody developability assessment to enable AI/ML model training

Antibodies must bind their targets with high affinity and specificity to achieve useful therapeutic activity. They must also possess suitable developability properties (e.g., thermostability, solubility, viscosity, polyreactivity) to ensure favorable manufacturing, formulation, and in vivo performance. Both binding and developability properties are inherent to a given antibody amino acid sequence. Identification or selection of antibodies possessing suitable binding characteristics is now routine, and de novo computational design models, trained on extensive complementarity-determining region sequence and structural data, are rapidly improving. Developability properties, however, remain difficult to predict largely due to insufficient training data, with empirical testing being heavily used to avoid challenges in late-stage antibody development. To fill this gap, we built a high-throughput antibody developability assay platform designed to generate the large datasets needed to train improved machine learning (ML) models. We optimized and automated known developability assays [Jain et al., 2017], and developed a robust integrated data analytics pipeline. Here we report data on 246 antibodies--representing 106 approved, 135 clinical-stage, and 5 preregistration/withdrawn molecules--across a panel of 10 developability assays, in a "tidy data" format suitable for AI/ML modeling. We used these data to develop an XGBoost [Chen et al., 2016] ML model that better predicts similarity to approved antibodies compared to conventional use of developability warning thresholds. Additionally, we confirm that preliminary predictive models do improve with more training data. Our high-throughput PROPHET-Ab platform enables data generation at the scale needed to develop improved ML models to predict antibody developability. SignificanceSuccessful antibody drugs exhibit important "developability" properties, beyond tight and specific binding to their target, including high expressibility, high stability and solubility, low aggregation propensity, low viscosity, low polyreactivity, and long in vivo half-life. Collectively, developability properties predict favorable manufacturing, storage, administration, and safety, and deficiencies in these properties increase risk for clinical failure. Despite progress in developing machine learning models to predict structure and binding, antibody developability models lag, largely due to a lack of sufficiently large training datasets. We have built a high-throughput platform, PROPHET-Ab, that enables data generation at the scale needed to train improved AI/ML models to predict antibody developability.

biophysics↗

Spatial context non-uniformly modulates inter-laminar communication in the primary visual cortex

Our visual experience is a result of the concerted activity of neuronal ensembles in the sensory hierarchy. Yet how the spatial organization of objects influences neural activity in this hierarchy remains poorly understood. We investigate how the inter-laminar interactions in the primary visual cortex (V1) are affected by visual stimuli in isolation or with flanking stimuli at various spatial configurations that are known to cause non-uniform degradation of perception. By employing dimensionality reduction approaches to simultaneous layer-specific population recordings, we establish that cortical layers interact through a structurally stable communication subspace. Spatial configuration of contextual stimuli differentially modulates inter-laminar communication efficacy, the balance between feedforward and feedback signaling, and contextual signaling in the superficial layers. Remarkably, these modulations mirror the spatially non-uniform aspects of perceptual degradation. Our results suggest a model of retinotopically non-uniform cortical connectivity in the output layers of V1 that influences communication in the sensory hierarchy.

neuroscience↗

Widespread Receptive Field Remapping in Early Visual Cortex

Our eyes are in constant motion, yet we perceive the visual world as stable. Predictive remapping of receptive fields is thought to be one of the critical mechanisms for enforcing perceptual stability during eye movements. While receptive field remapping has been identified in several cortical areas, the spatiotemporal dynamics of remapping, and its consequences on the tuning properties of neurons, remain poorly understood. Here, we tracked remapping receptive fields in hundreds of neurons from visual Area V2 while subjects performed a cued saccade task. We found that remapping was far more widespread in Area V2 than previously reported and can be found in neurons from all recorded cortical layers and cell types. Surprisingly, neurons undergoing remapping exhibit sensitivity to two punctate locations in visual space. Furthermore, we found that feature selectivity is not only maintained during remapping but transiently increases due to untuned suppression. Taken together, these results shed light on the spatiotemporal dynamics of remapping and its ubiquitous prevalence in the early visual cortex, and force us to revise current models of perceptual stability.

neuroscience↗

Methotrexate inhibition of muropeptide transporter SLC46A2 controls psoriatic skin inflammation

Cytosolic innate immune sensing is critical for protecting barrier tissues. NOD1 and NOD2 are cytosolic sensors of small peptidoglycan fragments (muropeptides) derived from the bacterial cell wall. These muropeptides enter cells, especially epithelial cells, through unclear mechanisms. We previously implicated SLC46 transporters in muropeptide transport in Drosophila immunity. Here we focus on Slc46a2, which is highly expressed in mammalian epidermal keratinocytes, and show that it is critical for delivery of DAP-muropeptides and activation of NOD1 in keratinocytes, while the related transporter Slc46a3 is critical for responding to MDP, the NOD2 ligand. In a mouse model, Slc46a2 and Nod1 deficiency strongly suppressed psoriatic inflammation, while methotrexate, a commonly used psoriasis therapeutic, inhibited Slc46a2-dependent transport of DAP-muropeptides. Collectively these studies define SLC46A2 as a transporter of NOD1 activating muropeptides, with critical roles in the skin barrier, and identify this transporter as an important target for anti-inflammatory intervention.

immunology↗

IL-10 inhibits STAT1-dependent macrophage accumulation during microbiota-induced colitis

Loss of IL-10R function leads to severe early onset colitis and in murine models is associated with the accumulation of immature inflammatory colonic macrophages. We have shown that IL-10R-deficient colonic macrophages exhibit increased STAT1-dependent gene expression, suggesting that IL-10R-mediated inhibition of STAT1 signaling in newly recruited colonic macrophages might interfere with the development of an inflammatory phenotype. Indeed Stat1-/- mice exhibit defects in colonic macrophage accumulation following Helicobacter hepaticus infection and IL-10R blockade, and this was phenocopied in mice lacking IFNGR, an inducer of STAT1 activation. Radiation chimeras demonstrated that reduced accumulation of STAT1-deficient macrophages was based on a cell-intrinsic defect. Unexpectedly, mixed radiation chimeras generated with both WT and IL-10R-deficient bone marrow indicated that rather than directly interfering with STAT1 function, IL-10R prevents the generation of a cell extrinsic signal that promotes the accumulation of immature macrophages. These results define essential mechanisms controlling inflammatory macrophage accumulation in inflammatory bowel diseases. SummaryIntrinsic STAT1-function drives the accumulation of macrophages within the colon following the loss of IL-10R signaling. IL-10R prevents this STAT1-dependent process through a non-cell autonomous mechanism.

immunology↗

Group 3 Innate Lymphoid Cells are regulated by WASP in a microbiota-dependent manner

Wiskott-Aldrich syndrome protein (WASP) is a cytoskeletal regulator that is largely restricted to hematopoietic cells. While WASP expression in both lymphocytes and macrophages play a critical role in maintaining intestinal homeostasis, the function of WASP in innate lymphoid cells is unknown. Here we analyzed the role of WASP in the differentiation and function of group 3 innate lymphoid cells (ILC3s). WASP-deficient mice (Was-/-) have a marked reduction in ILC3s. Moreover, antimicrobial peptide expression in response to ILC3-derived IL-22 was also reduced in the absence of WASP. In Was-/- mice, we observed a reduction in CCR6+ ILC3s, cells known to restrict immune responses to commensal bacteria. WASP-deficient mice were more susceptible to Citrobacter rodentium, an enteric infection controlled by ILC3s. Interestingly, there was no reduction in ILC3s in Was-/- germ-free mice when compared to WT germ-free mice. ILC3s lacking WASP expression also demonstrated microbially-dependent alterations in gene expression associated with cell migration. Finally, ILC3-like (Rorgt+CD3-) cells were reduced in the GI tract of WASP-deficient patients. In conclusion, ILC3-specific expression of WASP is critical for the generation and function of ILC3s in the presence of commensal microflora. Aberrant ILC3 function in the setting of WASP-deficiency may contribute to underlying disease pathogenesis.

immunology↗

Demands of visual processing hierarchy shape laminar compartmentalization of attention modulation of luminance contrast in area V4

Contrast is a key feature of the visual scene that aids object recognition. Attention has been shown to selectively enhance the responses to low contrast stimuli in visual area V4, a critical hub that sends projections both up and down the visual hierarchy. Veridical encoding of contrast information is a key computation in early visual areas, while later stages encode higher level features that benefit from improved sensitivity to low contrast. How area V4 meets these distinct information processing demands in the attentive state is not known. We found that attentional modulation of contrast responses in area V4 is cortical layer and cell-class specific. Putative excitatory neurons in the superficial output layers that project to higher areas show enhanced boosting of low contrast information. On the other hand, putative excitatory neurons of deep output layers that project to early visual areas exhibit contrast-independent scaling. Computational modeling revealed that such layer-wise differences may result from variations in spatial integration extent of inhibitory neurons. These findings reveal that the nature of interactions between attention and contrast in V4 is highly compartmentalized, in alignment with the demands of the visual processing hierarchy.

neuroscience↗

Cortical Mechanisms of Saccadic Suppression

Saccades are a ubiquitous and crucial component of our visual system, allowing for the efficient deployment of the fovea and its accompanying neural resources. Initiation of a saccade is known to cause saccadic suppression, a temporary reduction in visual sensitivity1, 2 and visual cortical firing rates3-6. While saccadic suppression has been well characterized at the level of perception and single neurons, relatively little is known about the visual cortical networks governing this phenomenon. Here we examine the effects of saccadic suppression on distinct neural subpopulations within visual area V4. We find cortical layer- and cell type-specific differences in the magnitude and timing of peri-saccadic modulation. Neurons in the input layer show changes in firing rate and inter-neuronal correlations prior to saccade onset, indicating that this layer receives information about impending saccades. Putative inhibitory interneurons in the input layer elevate their firing rate during saccades, suggesting they play a role in suppressing the activity of other cortical subpopulations. A computational model of this circuit recapitulates our empirical observations and demonstrates that an input layer-targeting pathway can initiate saccadic suppression by enhancing local inhibitory activity. Collectively, our results provide a mechanistic understanding of how eye movement signaling interacts with cortical circuitry to enforce visual stability.

neuroscience↗

High throughput detection and genetic epidemiology of SARS-CoV-2 using COVIDSeq next generation sequencing

The rapid emergence of coronavirus disease 2019 (COVID-19) as a global pandemic affecting millions of individuals globally has necessitated sensitive and high-throughput approaches for the diagnosis, surveillance and for determining the genetic epidemiology of SARS-CoV-2. In the present study, we used the COVIDSeq protocol, which involves multiplex-PCR, barcoding and sequencing of samples for high-throughput detection and deciphering the genetic epidemiology of SARS-CoV-2. We used the approach on 752 clinical samples in duplicates, amounting to a total of 1536 samples which could be sequenced on a single S4 sequencing flow cell on NovaSeq 6000. Our analysis suggests a high concordance between technical duplicates and a high concordance of detection of SARS-CoV-2 between the COVIDSeq as well as RT-PCR approaches. An in-depth analysis revealed a total of six samples in which COVIDSeq detected SARS-CoV-2 in high confidence which were negative in RT-PCR. Additionally, the assay could detect SARS-CoV-2 in 21 samples and 16 samples which were classified inconclusive and pan-sarbeco positive respectively suggesting that COVIDSeq could be used as a confirmatory test. The sequencing approach also enabled insights into the evolution and genetic epidemiology of the SARS-CoV-2 samples. The samples were classified into a total of 3 clades. This study reports two lineages B.1.112 and B.1.99 for the first time in India. This study also revealed 1,143 unique single nucleotide variants and added a total of 73 novel variants identified for the first time. To the best of our knowledge, this is the first report of the COVIDSeq approach for detection and genetic epidemiology of SARS-CoV-2. Our analysis suggests that COVIDSeq could be a potential high sensitivity assay for detection of SARS-CoV-2, with an additional advantage of enabling genetic epidemiology of SARS-CoV-2.

genomics↗

Rational Design of Peptide Vaccines for the Highly Lethal Nipah and Hendra Viruses

The Nipah virus disease is a lethal infection that has led to 40% to 75% fatalities in Malaysia, Bangladesh and India. The reports of human-to-human transmission documented in Bangladesh has raised the specter of pandemic potential and has caused the World Health Organization to list the Nipah virus as one of the pathogens to be considered for development of drugs and vaccines on urgent basis, neither of which exist against the Nipah virus as of now, although many proposals have been made and trials initiated. Given that there are established country-specific differences in the virus effects and fatalities, meeting the sudden need for a vaccine in case of an epidemic will require design, development and preparation for a peptide vaccine. Thus, we propose a protocol for creating peptide vaccines that can be tailor-made for these specific countries, an approach which is being advocated for the first time. Here, we analyze the surface proteins, Fusion protein and Glycoprotein, of the strains currently affecting the three countries on a large scale and determine the specific country-based epitope differences.

bioinformatics↗

Optogenetically induced low-frequency correlations impair perception

Deployment of covert attention to a spatial location can cause large decreases in low-frequency correlated variability among neurons in macaque area V4 whose receptive-fields lie at the attended location. It has been estimated that this reduction accounts for a substantial fraction of the attention-mediated improvement in sensory processing. These estimates depend on assumptions about how population signals are decoded and the conclusion that correlated variability impairs perception, is purely hypothetical. Here we test this proposal directly by optogenetically inducing low-frequency fluctuations, to see if this interferes with performance in an attention-demanding task. We find that low- frequency optical stimulation of neurons in V4 elevates correlations among pairs of neurons and impairs the animals ability to make fine sensory discriminations. Stimulation at higher frequencies does not impair performance, despite comparable modulation of neuronal responses. These results support the hypothesis that attention-dependent reductions in correlated variability contribute to improved perception of attended stimuli.

neuroscience↗

Necrosis triggered by Mycobacterium tuberculosis alters macrophage triglyceride metabolism and inflammatory response in a DGAT1-dependent manner

Tuberculosis granulomas represent a site of controlling bacterial dissemination at the cost of host tissue damage. Within the heterogenous array of TB granulomas, some contain triglyceride (TG) rich foamy macrophages, the etiology and function of which remains largely unexplained. Here we show that necrosis of tuberculosis lesions and M. tuberculosis (Mtb) infected macrophages elicits a bystander response of triglyceride storage. We elucidate a role for the RD1 region of mycobacterial genome to be a key player in this phenomenon. TG storage in necrosis associated foamy macrophages promoted the pro-inflammatory state of macrophages while silencing expression of diacylglycerol O-acyltransferase (DGAT1) suppressed expression of pro-inflammatory genes. Surprisingly, acute infection with Mtb led to lipolysis of host TG, rather than synthesis, suggesting mobilization of triglyceride stored within macrophage lipid droplets to be involved in the inflammatory response to infection. Our data is likely to open new avenues for management of the inflammatory response during infection.

immunology↗