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Xie, M.

Publications and source records attributed to Xie, M..

At least 73 records · Page 4Linked to original sources

MaskGraphene: Advancing joint embedding, clustering, and batch correction for spatial transcriptomics using graph-based self-supervised learning

Recent advancements in spatial transcriptomics (ST) have underscored the importance of integrating data from multiple ST slices for joint analysis. A major challenge remains generating interpretable joint embeddings that preserve geometric information for downstream analyses. Here we introduce MaskGraphene, a graph neural network that combines self-supervised and self-contrastive training to integrate gene expression and spatial location into joint embeddings. By employing clusterwise alignment and a graph attention autoencoder with masked self-supervised and triplet loss optimizations, MaskGraphene effectively preserves geometric structures while achieving batch correction. In benchmarks against seven state-of-the-art methods, MaskGraphene consistently demonstrated superior alignment accuracy and geometric fidelity across diverse ST datasets. Its interpretable embeddings significantly enhanced downstream applications, including domain identification, spatial trajectory reconstruction, biomarker discovery, and the creation of topographical maps of brain slices. Notably, MaskGraphene successfully recovered layer-wise brain structures with near-perfect accuracy. MaskGraphene provides a powerful and versatile framework for advancing ST data integration and analysis, unlocking valuable biological insights.

bioinformatics↗

A neutral process of genome reduction in marine bacterioplankton

Marine bacterioplankton communities are dominated by cells equipped with small genomes. Streamlining selection has been accepted as the main force driving their genome reduction. Here, we report that a neutral evolutionary mechanism governs genome reduction in the Roseobacter group that represents 5-20% of the bacterioplankton cells in coastal waters. Using representative strains that fall into three genome size groups (2-3, 3-4, and 4-5 Mbp), we measured their genomic mutation rates () through long-term mutation accumulation experiments followed by genome sequencing the resulting 437 mutant lines. We further calculated their effective population sizes (Ne) based on and the neutral genetic diversity of the studied species, the latter estimated based on multiple genome sequences of natural isolates collected from global oceans with their population structure considered. A surprising finding is that Ne scales positively with genome size, which is the opposite of the expectation from the streamlining selection theory. As the strength of random genetic drift is the inverse of Ne, this result instead suggests drift as the primary driver of genome reduction. Additionally, we report a negative scaling between and genome size, which is the first experimental evidence for the long-lasting hypothesis that mutation rate increases play a part in marine bacterial genome reduction. As scales inversely with Ne, genetic drift appears to be the ultimate cause of genome reduction in these Roseobacters. Our finding discounts, but is insufficient to reject, the streamlining theory because streamlining process is expected to be more effective in oligotrophic open ocean waters.

microbiology↗

Impaired microglial phagocytosis promotes seizure development

In the central nervous system, triggering receptor expressed on myeloid cells 2 (TREM2) is exclusively expressed by microglia and is critical for microglial proliferation, migration, and phagocytosis. TREM2 plays an important role in neurodegenerative diseases, such as Alzheimers disease and amyotrophic lateral sclerosis. However, little is known about the role TREM2 plays in epileptogenesis. To investigate this, we utilized TREM2 knockout (KO) mice within the murine intra-amygdala kainic acid seizure model. Electroencephalographic analysis, immunocytochemistry, and RNA sequencing revealed that TREM2 deficiency significantly promoted seizure-induced pathology. We found that TREM2 KO increased both acute status epilepticus and spontaneous recurrent seizures characteristic of chronic focal epilepsy. Mechanistically, phagocytic clearance of damaged neurons by microglia was impaired in TREM2 KO mice and the reduced phagocytic capacity correlated with increased spontaneous seizures. Analysis of human tissue from patients who underwent surgical resection for drug resistant temporal lobe epilepsy also showed a negative correlation between microglial phagocytic activity and focal to bilateral tonic-clonic generalized seizure history. These results indicate that microglial TREM2 and phagocytic activity may be important to epileptogenesis and the progression of focal temporal lobe epilepsy. One Sentence SummaryPhagocytic activity of microglia may impact generalized seizure development within both mice and humans.

neuroscience↗

A distinct subpopulation of adipocytes in adult perirenal adipose tissue arises through brown-to-white conversion but reverts to a thermogenic phenotype upon cold exposure

Perirenal adipose tissue (PRAT) is a unique visceral depot that contains a mixture of brown and white adipocytes. The origin and plasticity of such cellular heterogeneity remains unknown. Here, we combine single-nucleus RNA sequencing with genetic lineage tracing to reveal the existence of a distinct subpopulation of Ucp1-/Cidea+ adipocytes that arises from brown-to-white conversion during postnatal life in the peri-ureter region of mouse PRAT. Cold exposure restores Ucp1 expression and a thermogenic phenotype in this subpopulation. These cells have a transcriptome that is distinct from subcutaneous beige adipocytes and may represent a unique type of cold-recruitable adipocytes. These results pave the way for studies of PRAT physiology and mechanisms controlling the plasticity of brown/white adipocyte phenotypes.

developmental biology↗

Microglial P2Y6 calcium signaling promotes phagocytosis and shapes neuroimmune responses in epileptogenesis

Microglial calcium signaling is rare in a baseline state but shows strong engagement during early epilepsy development. The mechanism and purpose behind microglial calcium signaling is not known. By developing an in vivo UDP fluorescent sensor, GRABUDP1.0, we discovered that UDP release is a conserved response to seizures and excitotoxicity across brain regions. UDP signals to the microglial P2Y6 receptor for broad increases in calcium signaling during epileptogenesis. UDP-P2Y6 signaling is necessary for lysosome upregulation across limbic brain regions and enhances production of pro-inflammatory cytokines--TNF and IL-1{beta}. Failures in lysosome upregulation, observed in P2Y6 KO mice, can also be phenocopied by attenuating microglial calcium signaling in Calcium Extruder ("CalEx") mice. In the hippocampus, only microglia with P2Y6 expression can perform full neuronal engulfment, which substantially reduces CA3 neuron survival and impairs cognition. Our results demonstrate that calcium activity, driven by UDP-P2Y6 signaling, is a signature of phagocytic and pro-inflammatory function in microglia during epileptogenesis.

neuroscience↗

TREM2 mediates MHCII-associated CD4+ T cell response against gliomas

Triggering receptor expressed on myeloid cells 2 (TREM2) was recently highlighted as a novel immune suppressive marker in peripheral tumors. The aim of this study was to characterize TREM2 expression in gliomas and investigate its contribution in glioma progression by using Trem2-/-mouse line. Our results showed that higher TREM2 expression was correlated with poor prognosis in glioma patients. Unexpectedly, TREM2 deficiency did not have a beneficial effect in a pre-clinical model of glioma. The increased TREM2 expression in glioma was likely due to increased myeloid cell infiltration, as evidenced by our single-cell analysis showing that almost all microglia and macrophages in gliomas were TREM2+. Furthermore, we found that deficiency of TREM2 impaired tumor-myeloid phagocytosis and MHCII presentation, and significantly reduced CD4+ T cells in tumor hemispheres. Our results revealed a previously unrecognized protective role of tumor-myeloid TREM2 in promoting MHCII-associated CD4+ T cell response against gliomas. SUMMARYAuthors found that although higher TREM2 expression is correlated with poor prognosis in glioma patients, its absence has no beneficial effect in a pre-clinical model of glioma. Deficiency of TREM2 impairs myeloid cell phagocytosis of tumor debris, leading to a reduction in MHCII-dependent CD4+ anti-glioma immunity.

neuroscience↗

Transcription Factor Dynamics in Cross-Regulation of Plant Hormone Signaling Pathways

Cross-regulation between hormone signaling pathways is indispensable for plant growth and development. However, the molecular mechanisms by which multiple hormones interact and co-ordinate activity need to be understood. Here, we generated a cross-regulation network explaining how hormone signals are integrated from multiple pathways in etiolated Arabidopsis (Arabidopsis thaliana) seedlings. To do so we comprehensively characterized transcription factor activity during plant hormone responses and reconstructed dynamic transcriptional regulatory models for six hormones; abscisic acid, brassinosteroid, ethylene, jasmonic acid, salicylic acid and strigolactone/karrikin. These models incorporated target data for hundreds of transcription factors and thousands of protein-protein interactions. Each hormone recruited different combinations of transcription factors, a subset of which were shared between hormones. Hub target genes existed within hormone transcriptional networks, exhibiting transcription factor activity themselves. In addition, a group of MITOGEN-ACTIVATED PROTEIN KINASES (MPKs) were identified as potential key points of cross-regulation between multiple hormones. Accordingly, the loss of function of one of these (MPK6) disrupted the global proteome, phosphoproteome and transcriptome during hormone responses. Lastly, we determined that all hormones drive substantial alternative splicing that has distinct effects on the transcriptome compared with differential gene expression, acting in early hormone responses. These results provide a comprehensive understanding of the common features of plant transcriptional regulatory pathways and how cross-regulation between hormones acts upon gene expression.

plant biology↗

StereoCell enables high accuracy single cell segmentation for spatial transcriptomic dataset

BackgroundOwing to recent advances in resolution and field-of-view, spatially resolved transcriptomics sequencing, such as Stereo-seq, has emerged as a cutting-edge technology for the interpretation of large tissues at the single-cell level. To generate accurate single-cell spatial gene expression profiles from high-resolution spatial omics data, a powerful computational tool is required. FindingsWe present CellBin, an image-facilitated one-stop pipeline for high-resolution and large field-of-view spatial transcriptomic data of Stereo-seq. CellBin provides a comprehensive and systematic platform for generating high-confidence single-cell spatial gene expression profiles, which specifically includes image stitching, image registration, tissue segmentation, nuclei segmentation and molecule labeling. CellBin is user-friendly and does not require a specific level of omics and image analysis expertise. ConclusionsDuring image stitching and molecule labeling, CellBin delivers better-performing algorithms to reduce stitching error and time, in addition to improving the signal-to-noise ratio of single-cell gene expression data, in comparison with existing methods. Additionally, CellBin has been shown to obtain highly accurate single-cell spatial data using mouse brain tissue, which facilitated clustering and annotation.

bioinformatics↗

StereoSiTE: A framework to spatially and quantitatively profile the cellular neighborhood organized iTME

With emerging of Spatial Transcriptomics (ST) technology, a powerful algorithmic framework to quantitatively evaluate the active cell-cell interactions in the bio-function associated iTME unit will pave the ways to understand the mechanism underlying tumor biology. This study provides the StereoSiTE incorporating open source bioinformatics tools with the self-developed algorithm, SCII, to dissect a cellular neighborhood (CN) organized iTME based on cellular compositions, and to accurately infer the functional cell-cell communications with quantitatively defined interaction intensity in ST data. We applied StereoSiTE to deeply decode ST data of the xenograft models receiving immunoagonist. Results demonstrated that the neutrophils dominated CN5 might attribute to iTME remodeling after treatment. To be noted, SCII analyzed the spatially resolved interaction intensity inferring a neutrophil leading communication network which was proved to actively function by analysis of Transcriptional Factor Regulon and Protein-Protein Interaction. Altogether, StereoSiTE is a promising framework for ST data to spatially reveal tumoribiology mechanisms.

cancer biology↗

MSL2 targets histone genes in Drosophila virilis

Histone genes are amongst the most evolutionary conserved in eukaryotic genomes, yet cis-regulatory mechanisms of histone gene regulation differ considerably amongst species. In Drosophila melanogaster, an interaction between GA-rich cis elements in the H3/H4 promoter and the GA-binding transcription factor CLAMP is important for promoting histone gene regulation and factor recruitment to the locus. CLAMP also participates in male dosage compensation by recruiting the Male Specific Lethal Complex (MSLc) to the X-chromosome. We discovered that the male-specific protein of MSLc, MSL2, is recruited to the autosomal major histone locus in D. virilis but not to the minor locus or to the single histone locus in other species. While the histone coding sequences are well conserved between species, the critical GA-rich cis elements in the H3/H4 promoter are poorly conserved between D. melanogaster and D. virilis. We show that CLAMP still targets the two D. virilis histone loci in vivo. Further, CLAMP interacts with the D. virilis H3/H4 promoter in vitro, even when the poorly-conserved GA-rich cis elements are deleted, indicating that the protein interacts differently with the D. virilis promoter than it does with the D. melanogaster promoter. Since CLAMP and MSL2 directly interact in D. melanogaster, we propose that D. virilis CLAMP recruits MSL2 to an ectopic autosomal site through interaction with X-like cis elements. Further, localization of MSL2 to one of the D. virilis histone loci suggests that the loci are regulated differently and that males and females have different requirements for histone gene regulation.

genetics↗

Fortuitous Somatic Mutations during Antibody Evolution Endow Broad Neutralization against SARS-CoV-2 Omicron Variants

Striking antibody evasion by emerging circulating SARS-CoV-2 variants drives the identification of broadly neutralizing antibodies (bNAbs). However, how a bNAb acquires increased neutralization breadth during antibody evolution is still elusive. Here, we identified a clonally-related antibody family from a convalescent individual. One of the members, XG005, exhibited potent and broad neutralizing activities against SARS-CoV-2 variants, while the other members showed significant reductions in neutralization breadth and potency, especially against the Omicron sublineages. Structural analysis visualizing the XG005-Omicron spike binding interface revealed how crucial somatic mutations endowed XG005 with greater neutralization potency and breadth. A single administration of XG005 with extended half-life, reduced antibody-dependent enhancement (ADE) effect, and increased antibody product quality, exhibited a high therapeutic efficacy in BA.2- and BA.5-challenged mice. Our results provided a natural example to show the importance of somatic hypermutation during antibody evolution for SARS-CoV-2 neutralization breadth and potency.

immunology↗

A conserved sequence in Drosophila Argonaute1 mRNA contributes to stress response via inducing miR-999 degradation

MicroRNAs (miRNAs) load onto Argonaute (AGO) proteins and target messenger RNAs (mRNA) to directly suppress gene expression at the post-transcriptional level. However, miRNA degradation can be triggered when there is extended base-pairing between miRNAs and the target RNAs. Such base-pairing can induce confirmational change of AGO and recruitment of ZSWIM8 ubiquitin ligase to mark AGO for proteasomal degradation, while the miRNAs are subsequently degraded. This target RNA-directed miRNA degradation (TDMD) mechanism appears to be an evolutionary conserved mechanism, but recent studies have focused on identifying endogenous TDMD events in the mammalian systems. Here, we performed AGO1-CLASH (crosslinking and sequencing of miRNA-mRNA hybrids) in Drosophila S2 cells, with Dora (ortholog of vertebrate ZSWIM8) knockout (KO) mediated by CRISPR-Cas9 to identify five TDMD triggers (sequences that can induce miRNA degradation). Interestingly, one trigger residing in the 3' UTR of AGO1 mRNA induces miR-999 degradation. CRISPR-Cas9 KO of the AGO1 trigger in S2 cells and in Drosophila elevates miR-999 abundance, with concurrent repression of the miR-999 targets. AGO1 trigger-KO flies respond poorly to hydrogen peroxide-induced stress, demonstrating the physiological importance of a single TDMD event.

molecular biology↗

Identifying Patients with Cognitive Motor Dissociation Using Resting-state Temporal Stability

BackgroundUsing task-dependent neuroimaging techniques, recent studies discovered a fraction of patients with disorders of consciousness (DOC) who had no command-following behaviors but showed a clear sign of awareness, which was defined as cognitive motor dissociation (CMD). Although many efforts were made to identify the CMD, existing task-dependent approaches might fail when patients had multiple cognitive function (e.g., attention, memory) impairments, and thus lead to false-negative findings. However, recent advances in resting-state fMRI (rs-fMRI) analysis allow investigation of the dynamic change of spontaneous brain activity, which might be a powerful tool to test the patients cognitive functions, while its capacity in identifying CMD was unclear. MethodsThe rs-fMRI study included 119 participants from three independent research sites. A sliding-window approach was used to investigate the dynamic functional connectivity of the brain in two aspects: the global and regional temporal stability, which measures how stable the brain functional architecture is across time. The temporal stability was compared in the first dataset (36/16 DOC/controls), and then a Support Vector Machine (SVM) classifier was built to discriminate DOC patients from controls. Furthermore, the generalizability of the SVM classifier was tested in the second independent dataset (35/21 DOC/controls). Finally, the SVM classifier was applied to the third independent dataset where patients underwent an rs-fMRI and brain-computer interface assessment (4/7 CMD/potential non-CMD), to test its performance in identifying CMD. ResultsOur results showed that the global and regional temporal stability were impaired in DOC patients, especially in regions from the cingulo-opercular task control, default mode, fronto-parietal task control, and salience network. Using the temporal stability as features, the SVM model not only showed a good performance in the first dataset (accuracy = 90 %), but a good generalizability in the second dataset (accuracy = 82 %). Most importantly, the SVM model generalized well in identifying CMD in the third dataset (accuracy = 91 %). ConclusionThe current findings suggested that rs-fMRI could be a potential tool to assist in diagnosing CMD. Furthermore, the temporal stability investigated in this study also contributed to a deeper understanding of the neural mechanism of the consciousness.

neuroscience↗

Specific connectivity optimizes learning in thalamocortical loops

1Cortico-thalamo-cortical loops have a central role in cognition and motor control, but precisely how thalamus contributes to these processes is unclear. Recent studies showing evidence of plasticity in thalamocortical synapses indicate a role for thalamus in shaping cortical dynamics - and thus behavior - through learning. Since corticothalamic projections compress cortical activity into a lower-dimensional thalamic activity space, we hypothesized that the computational role of thalamus would depend critically on the structure of corticothalamic connectivity. To test this, we identified the optimal corticothalamic structure that promotes biologically plausible learning in thalamocortical synapses. We found that corticothalamic structures specialized to carry an efference copy of the cortical output benefit motor control, while corticothalamic connections that communicate the directions of highest variance in cortical activity are optimal for working memory tasks. We analyzed neural recordings from mice performing grasping and delayed discrimination, and found corticothalamic interactions consistent with these predictions. These results suggest that thalamus orchestrates cortical dynamics in a functionally precise manner through structured connectivity.

neuroscience↗

Studies on the Escherichia coli ExbD Transmembrane Domain, Residue L132, and an Inhibitory Cyclic Peptide.

The TonB system of Escherichia coli uses the cytoplasmic membrane protonmotive force (PMF) to energize active transport of nutrients across the otherwise unenergized outer membrane. Because it overcomes limitations for nutrient diffusion through outer membrane size-limiting porins, it provides a growth advantage and is widespread among Gram-negative bacteria. It consists of three known cytoplasmic membrane proteins, TonB, ExbB and ExbD that energize a variety of customized TonB-dependent transporters in the outer membrane. The sole ExbD transmembrane domain is proposed to consist of residues 23-43 (Kampfenkel and Braun, 1992, J. Bacteriol. 174:5485-7). Here we showed that the charge and location of residue Asp25 were essential for activity of the TonB system, thus identifying it as the only PMF-responsive element in the TonB system. The proposed boundaries of the transmembrane domain -helix were revised to consist of residues 23-39, with residues 40-43 initiating the subsequent disordered region required for signal transduction (Kopp and Postle, 2020, J. Bacteriol. 202, e00687-19). Trapping of disulfide-linked ExbD homodimers through T42C or V43C prevented TonB system activity that was restored by addition of the reducing agent dithiothreitol, indicating a requirement for motion. In vivo photo-cross-linking experiments suggested that motion was rotation of ExbD transmembrane domains. Inactivity of ExbD L132Q, the first ExbD mutant identified, was likely due to steric hindrance. A conserved and defined site of in vivo ExbD interaction with TonB was identified. Exogenous addition of a cyclic peptide based on that site inhibited ExbD-TonB interaction while concomitantly decreasing iron transport efficiency. This suggested that a novel antimicrobial strategy against ESKAPE and other Gram-negative pathogens could be developed by targeting ExbD protein-protein interactions.

molecular biology↗

Max is likely not at the Drosophila histone locus

The histone locus body (HLB) is a conserved nuclear body that regulates histone mRNA production in metazoans. While some HLB components are known, there are likely uncharacterized factors that target the histone locus. We identified the Drosophila melanogaster protein Max, which interacts with known HLB member Myc, as an HLB candidate. We mapped Max ChIP-seq and ChIP-nexus datasets, which revealed encouraging signal over the histone gene array. However, we discovered that Max does not colocalize with HLB components on polytene chromosomes. Therefore, we conclude that Max is likely not at the D. melanogaster histone locus.

genetics↗

Task-dependent optimal representations for cerebellarlearning

The cerebellar granule cell layer has inspired numerous theoretical models of neural representations that support learned behaviors, beginning with the work of Marr and Albus. In these models, granule cells form a sparse, combinatorial encoding of diverse sensorimotor inputs. Such sparse representations are optimal for learning to discriminate random stimuli. However, recent observations of dense, low-dimensional activity across granule cells have called into question the role of sparse coding in these neurons. Here, we generalize theories of cerebellar learning to determine the optimal granule cell representation for tasks beyond random stimulus discrimination, including continuous input-output transformations as required for smooth motor control. We show that for such tasks, the optimal granule cell representation is substantially denser than predicted by classic theories. Our results provide a general theory of learning in cerebellum-like systems and suggest that optimal cerebellar representations are task-dependent.

neuroscience↗

Decoding Subject's Own Name in the Primary Auditory Cortex

Current studies have shown that perception of subjects own name (SON) involves multiple multimodal brain regions, while activities in unimodal sensory regions (i.e., primary auditory cortex) and their interaction with multimodal regions during the self-processing remain unclear. To answer this, we combined multivariate pattern analysis and dynamic causal modelling analysis to explore the regional activation pattern and inter-region effective connection during the perception of SON. We found that SON and other names could be decoded from the activation pattern in the primary auditory cortex. In addition, we found an excitatory effect of SON on connections from the anterior insula/inferior frontal gyrus to the primary auditory cortex, and to the temporal parietal junction. Our findings extended the current knowledge of self-processing by showing that primary auditory cortex could discriminate SON from other names. Furthermore, our findings highlighted the importance of influence of the insula on the primary auditory cortex during self-processing.

neuroscience↗