Biology subjects

Alvarez, V. E.

Publications and source records attributed to Alvarez, V. E..

7 recordsLinked to original sources

bioRxiv2026

"Dynamic SUMOylation Controls RNA Polymerase I Extranucleolar Organization and Antigenic Variation in Trypanosoma brucei"

Antigenic variation in Trypanosoma brucei relies on strict monoallelic expression of variant surface glycoprotein (VSG) genes from a single telomeric expression site (ES), a process sustained by the extranucleolar RNA polymerase I (Pol I) transcriptional body known as the expression site body (ESB). Although the ESB is essential for VSG expression, the mechanisms governing its assembly and maintenance remain poorly understood. Here, we identify SUMOylation as a central regulator of ESB organization and demonstrate that the balance between SUMO conjugation and deconjugation determines the transcriptional state of VSG expression sites. Ectopic expression of the SUMO protease TbSENP disrupted the highly SUMOylated nuclear focus associated with the active-ES, displaced Pol I from its extranucleolar compartment, and markedly increased VSG in situ switching frequency, indicating that continuous SUMOylation is required to preserve ESB integrity. Conversely, targeted recruitment of the SUMO-conjugating enzyme TbUBC9 to a silent ES locally restored SUMOylation, induced de novo formation of an extranucleolar Pol I compartment, activated transcription of the corresponding telomeric VSG gene, and generated stable antigenic switchers expressing the new surface coat. Local SUMOylation preceded Pol I redistribution, supporting a model in which SUMO-dependent interactions nucleate assembly of a transcriptionally competent ESB. Together, our findings identify SUMOylation as both a structural and regulatory determinant of nuclear organization in T. brucei and suggest that dynamic SUMO homeostasis governs the assembly, maintenance, and remodeling of this specialized transcriptional body. Significance StatementAntigenic variation in Trypanosoma brucei depends on the monoallelic expression of Variant Surface Glycoprotein (VSG) genes from a specialized RNA polymerase I transcriptional compartment known as the Expression Site Body (ESB). However, the molecular signals that govern transitions between active and silent expression sites have remained unknown. We show that SUMOylation acts as a reversible molecular switch: disruption of SUMO homeostasis dismantles ESB organization and promotes VSG switching, whereas localized SUMOylation is sufficient to nucleate a functional transcriptional compartment and activate a silent VSG expression site. Our findings establish SUMOylation as a central regulator of nuclear architecture and antigenic variation.

microbiology↗

bioRxiv2024

Repetitive head impacts induce neuronal loss and neuroinflammation in young athletes

Repetitive head impacts (RHI) sustained from contact sports are the largest risk factor for chronic traumatic encephalopathy (CTE). Currently, CTE can only be diagnosed after death and the multicellular cascade of events that trigger initial hyperphosphorylated tau (p-tau) deposition remain unclear. Further, the symptoms endorsed by young individuals with early disease are not fully explained by the extent of p-tau deposition, severely hampering development of therapeutic interventions. Here, we show that RHI exposure associates with a multicellular response in young individuals (<51 years old) prior to the onset of CTE p-tau pathology that correlates with number of years of RHI exposure. Leveraging single nucleus RNA sequencing of tissue from 8 control, 9 RHI-exposed, and 11 low stage CTE individuals, we identify SPP1+ inflammatory microglia, angiogenic and inflamed endothelial cell profiles, reactive astrocytes, and altered synaptic gene expression in excitatory and inhibitory neurons in all individuals with exposure to RHI. Surprisingly, we also observe a significant loss of cortical sulcus layer 2/3 neurons in contact sport athletes compared to controls independent of p-tau pathology. Finally, we identify TGFB1 as a potential signal mediating microglia-endothelial cell cross talk through ligand-receptor analysis. These results provide robust evidence that multiple years of RHI exposure is sufficient to induce lasting cellular alterations that may underlie p-tau deposition and help explain the early pathogenesis in young former contact sport athletes. Furthermore, these data identify specific cellular responses to repetitive head impacts that may direct future identification of diagnostic and therapeutic strategies for CTE.

neuroscience↗

bioRxiv2023

SUMO chains depolymerization induces slender to stumpy differentiation in T. brucei bloodstream parasites

Trypanosoma brucei are extracellular protozoan parasites transmitted by tsetse flies that cause sleeping sickness in humans and nagana in cattle. Inside the mammalian host, differentiation from a bloodstream replicative slender form into a quiescent stumpy form allows the persistence of the parasite and the spread of the infection. SUMOylation is a reversible and dynamic post-translational modification of proteins that regulates diverse nuclear processes, such as DNA replication, repair and transcription. SUMO can be attached to its target proteins either as a single monomer or forming polymeric chains. We found that transgenic cell lines able to conjugate SUMO just as a monomer are attenuated in vivo. SUMO chain mutant monomorphic parasites display relapsing and remitting waves of parasitemia, at variance with wild-type parasites that cause unremitting parasitemia and mice death. Furthermore, when mice are infected with an analogous SUMO chain mutant generated in a differentiation-competent pleomorphic background, stumpy cells can be observed at unusually low parasitemia values. Our study reveals that SUMO depolymerization could represent a coordinated signal triggered during a quiescence activation program.

molecular biology↗

bioRxiv2022

Antibodies to protozoan variable surface antigens induce antigenic variation

The genomes of most protozoa encode families of variant surface antigens, whose mutually exclusive changes in expression allow parasitic microorganisms to evade the host immune response1,2. It is widely assumed that antigenic variation in protozoan parasites is accomplished by the spontaneous appearance within the population of cells expressing antigenic variants that escape antibody-mediated cytotoxicity1,2. Here we show, both in vitro and in animal infections, that antibodies to Variant-specific Surface Proteins (VSPs) of the intestinal parasite Giardia lamblia are not cytotoxic, inducing instead VSP clustering into liquid-ordered phase membrane microdomains that trigger a massive release of microvesicles carrying the original VSP and switch in expression to different VSPs by a calcium-dependent mechanism. Surface microvesiculization and antigenic switching are also stimulated when Trypanosoma brucei and Tetrahymena thermophila are confronted to antibodies directed to their GPI-anchored variable surface glycoproteins. This novel mechanism of surface antigen clearance throughout its release into microvesicles coupled to the stochastic induction of new phenotypic variants not only changes the current paradigm of spontaneous antigenic switching but also provides a new framework for understanding the course of protozoan infections as a host/parasite adaptive process.

microbiology↗

bioRxiv2021

Machine learning applied to molecular identification of Acinetobacter baumannii Global Clone 1

Since the emergence of high-risk clones worldwide, constant investigations have been undertaken to comprehend the molecular basis that led to their prevalent dissemination in nosocomial settings over time. So far, the complex and multifactorial genetic traits of this type of epidemic clones have only allowed the identification of biomarkers with low specificity. A machine learning algorithm was able to recognize unequivocally a biomarker for the early and accurate detection of Acinetobacter baumannii Global Clone 1 (GC1), one of the most disseminated high-risk clones. Support Vector Machine identified the U1 sequence with 367 nucleotides length that matched a fragment of the moaCB gene, which encodes the molybdenum cofactor biosynthesis C and B proteins. U1 differentiates specifically between A. baumannii GC1 and non-GC1 strains, becoming a suitable biomarker capable of being translated into clinical settings as a molecular typing method for early diagnosis based on PCR as shown here. Since the metabolic pathways of Mo enzymes have been recognized as putative therapeutic targets for ESKAPE pathogens, our findings highlighted that machine learning can be also useful in intricate knowledge gaps of high-risk clones and implies noteworthy support to the literature to identify challenging nosocomial biomarkers for other multidrug-resistant high-risk clones. IMPORTANCEA. baumannii GC1 is an important high-risk clone that rapidly develops extreme drug resistance in the nosocomial niche. Furthermore, several strains were identified worldwide in environmental samples exacerbating the risk of human interactions. Early diagnosis is mandatory to limit its dissemination and to outline appropriate antibiotic stewardship schedules. A region of 367 bp length (U1) within the moaCB gene not subjected to Lateral Genetic Transfer or to antibiotic pressures was successfully found by Support Vector Machine algorithm that predicts A. baumannii GC1 strains. PCR assays have confirmed that U1 specifically identifies A. baumannii GC1 strains. At the same time, research on the group of Mo enzymes proposed this metabolic pathway related to superbu[g]s metabolism as a potential future drug target site for ESKAPE pathogens due to its central role in bacterial fitness during infection. These findings confirmed the importance of machine learning applied to the burden of the rise of antibiotic resistance.

bioinformatics↗

bioRxiv2020

A Complex Containing HNRNPA2B1 and N6-methyladenosine Modified Transcripts Mediates Actions of Toxic Tau Oligomers

The microtubule associated protein tau oligomerizes in response to stress and disease, but the function of oligomeric tau (oTau) and the ultimate mechanisms of toxicity are unknown. To gain insights, we have now used Cry2-based optogenetics to induce tau oligomers (oTau-c) in neuronal cultures. oTau-c can seed tau aggregation and biochemical fractionates in a manner similar to oTau. Optical induction of oTau elicits a translational stress response that includes cytoplasmic translocation of the TIA1, abundant stress granules (SGs) and reduced protein synthesis. Proteomic analysis identifies HNRNPA2B1 as a principle target of oTau. Imaging and immunoprecipitation verify the HNRNPA2B1 association with endogenous oTau in neurons, animal models and human Alzheimer brain tissue. Mechanistic studies demonstrate that HNRNPA2B1 functions as a linker, connecting oTau with N6-methyladenosine modified transcripts (m6A). Knockdown of HNRNPA2B1 prevents oTau from associating with m6A, prevents oTau-induced reductions in protein synthesis and reduces oTau-induced toxicity. Finally, we show striking increases in m6A-oTau and -HNRNPA2B1 complexes in brains of Alzheimer subjects and P301S tau mice. These results reveal a novel complex containing oTau, HNRNPA2B1 and m6A that contributes to the integrated stress response of oTau. HighlightsO_LIDevelopment of a powerful method combining optical induction of tau oligomerization with precision mass spectrometry to obtain time resolved evolution of protein interaction networks. C_LIO_LIDemonstration of a tripartite complex that links tau oligomers with HNRNPA2B1 and N6-methyladenosine modified RNA in cytoplasmic stress granules. C_LIO_LIKnockdown of HNRNPA2B 1 abrogates the interactions of oTau with N6-methyladenosine modified RNA, as well as inhibits oTau-mediated neurodegeneration. C_LIO_LIDiscovery that N6-methyladenosine modified RNA is significantly increased in the brains of P301S tau transgenic mice and in patients with Alzheimers disease. C_LI

neuroscience↗

bioRxiv2020

Altered oligodendroglia and astroglia in chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a progressive tauopathy found in contact sport athletes, military veterans, and others exposed to repetitive head impacts (RHI)1-6. White matter atrophy and axonal loss have been reported in CTE but have not been characterized on a molecular or cellular level2,7,8. Here, we present RNA sequencing profiles of cell nuclei from postmortem dorsolateral frontal white matter from eight individuals with neuropathologically confirmed CTE and eight age- and sex-matched controls. Analyzing these profiles using unbiased clustering approaches, we identified eighteen transcriptomically distinct cell groups (clusters), reflecting cell types and/or cell states, of which a subset showed differences between CTE and control tissue. Independent in situ methods applied on tissue sections adjacent to that used in the single-nucleus RNA-seq work yielded similar findings. Oligodendrocytes were found to be most severely affected in the CTE white matter samples; they were diminished in number and altered in relative proportions across subtype clusters. Further, the CTE-enriched oligodendrocyte population showed greater abundance of transcripts relevant to iron metabolism and cellular stress response. CTE tissue also demonstrated excessive iron accumulation histologically. Astrocyte alterations were more nuanced; total astrocyte number was indistinguishable between CTE and control samples, but transcripts associated with neuroinflammation were elevated in the CTE astrocyte groups as compared to controls. These results demonstrate specific molecular and cellular differences in CTE oligodendrocytes and astrocytes and may provide a starting point for the development of diagnostics and therapeutic interventions.

genomics↗