Biology subjects

Tavares, A.

Publications and source records attributed to Tavares, A..

7 recordsLinked to original sources

bioRxiv2026

Distinct regulation across the transcription cycle drives mitotic transcriptional silencing

In most organisms, as cells enter mitosis, transcription is globally silenced. While individual studies have shown that each stage of the transcription cycle can be modulated during mitosis, how initiation, elongation, and termination are temporally and kinetically regulated to ensure transcriptional silencing remains unclear. Here, we combine real-time quantitative imaging of ongoing transcription in early Drosophila embryos with mathematical modelling to systematically dissect how transcriptional kinetics change as cells progress into mitosis. We found that transcription initiation undergoes a gradual repression starting in prophase, while elongation rates remain unaltered. After nuclear envelope breakdown, an abrupt mechanism causes premature termination of elongating RNA, driven at least in part by the SNF-helicase-like protein Transcription Termination factor 2 / Lodestar (TTF2/Lds). Our study provides a quantitative framework for understanding how transcription is modulated across the cell cycle, demonstrating that mitotic repression arises from multiple processes with different dynamics that collectively ensure the precise shutdown of gene expression.

cell biology↗

bioRxiv2024

Placentas from SARS-CoV-2 infection during pregnancy exhibit foci of oxidative stress and DNA damage

ProblemCOVID-19 during pregnancy is linked to increased maternal morbidity and a higher incidence of preterm births, yet the underlying mechanisms remain unclear. Cellular senescence, characterized by the irreversible cessation of cell division, is a critical process in placental function and its dysregulation has been implicated in pregnancy complications like preterm birth. Senescence can be induced by various stressors, including oxidative stress, DNA damage, and viral infections. Method of StudyIn this study, we determined whether COVID-19 had an impact on placental senescence. We examined placentas from women infected with SARS-CoV-2 (n=10 term, 4 preterm) compared to uninfected controls (n=10 term, 3 preterm). The placentas were analyzed for SARS-CoV-2 infection/replication (Spike and Nucleocapsid viral proteins), markers of DNA damage ({gamma}H2AX) and oxidative stress (ROS), and senescence (telomere length; cell cycle regulators, SASP). ResultsWhile no overall differences in cellular senescence markers were observed between the COVID-19 positive and negative groups, we found increased secreted SASP markers and confocal microscopy revealed localized areas of oxidative stress and DNA damage in the placentas from COVID-19 positive cases. ConclusionsThese findings indicate that SARS-CoV-2 infection induces localized placental damage, warranting further investigation into its impact on maternal and perinatal outcomes.

microbiology↗

bioRxiv2024

SV2A is expressed in synapse subpopulations in mouse and human brain: implications for PET radiotracer studies

Synapse pathology is a feature of most brain diseases and there is a pressing need to monitor the onset and progression of this pathology using brain imaging in living patients. A major step toward this goal has been the development of small-molecule radiotracers that bind to synaptic vesicle glycoprotein 2A (SV2A) for use in positron emission tomography (PET). Changes in SV2A radiotracer binding in PET are widely interpreted to report differences in the density of all synapses throughout brain regions. Here, we analyse the expression of SV2A at single-synapse resolution across regions of adult mouse and human brain. We find that SV2A is expressed in fewer than 50% of excitatory and inhibitory synapses and that the density of SV2A-positive synapses differs between brain regions. Furthermore, individual synapses differ in their amounts of SV2A. These findings have important implications for the interpretation of PET imaging studies in a clinical setting and point to the need for a detailed understanding of SV2A synaptome architecture in both healthy brain and disease cases where PET imaging is being applied.

neuroscience↗

bioRxiv2022

An SNF2 helicase-like protein links mitotic transcription termination to sister chromatid resolution

AO_SCPLOWBSTRACTC_SCPLOWMitotic chromatin is largely assumed incompatible with transcription due to changes in the transcription machinery and chromosome architecture. However, the mechanisms of mitotic transcriptional inactivation and their interplay with chromosome assembly remain largely unknown. By monitoring ongoing transcription in Drosophila early embryos, we reveal that eviction of nascent mRNAs from mitotic chromatin occurs after substantial chromosome compaction and is not promoted by condensin I. Instead, we show that the timely removal of transcripts from mitotic chromatin is driven by the SNF2 helicase-like protein Lodestar (Lds), identified here as a modulator of sister chromatid cohesion defects. In addition to transcriptional termination, we uncovered that Lds cooperates with Topoisomerase 2 to ensure efficient sister chromatid resolution and mitotic fidelity. We conclude that mitotic transcriptional termination is not a passive consequence of cell cycle progression and/or chromosome compaction but occurs via dedicated mechanisms with functional parallelisms to sister chromatid resolution.

cell biology↗

bioRxiv2022

In vivo 18F-DOPA PET imaging identifies a dopaminergic deficit in a rat model with a G51D α-synuclein mutation

Parkinsons disease (PD) is a neurodegenerative condition with several major hallmarks, including loss of substantia nigra neurons, reduction in striatal dopaminergic function, and formation of -synuclein-rich Lewy bodies. Mutations in SNCA, encoding for -synuclein, are a known cause of familial PD, and the G51D mutation causes a particularly aggressive form of the condition. CRISPR/Cas9 technology was used to introduce the G51D mutation into the endogenous rat SNCA gene. SNCAG51D/+ and SNCAG51D/G51D rats were born in Mendelian ratios and did not exhibit any severe behavourial defects. L-3,4-dihydroxy-6-18F-fluorophenylalanine (18F-DOPA) positron emission tomography (PET) imaging was used to investigate this novel rat model. Wild-type (WT), SNCAG51D/+ and SNCAG51D/G51D rats were characterised over the course of ageing (5, 11, and 16 months old) using 18F-DOPA PET imaging and kinetic modelling. We measured the influx rate constant (Ki) and effective distribution volume ratio (EDVR) of 18F-DOPA in the striatum relative to the cerebellum in WT, SNCAG51D/+ and SNCAG51D/G51D rats. A significant reduction in EDVR was observed in SNCAG51D/G51D rats at 16 months of age indicative of increased dopamine turnover. Furthermore, we observed a significant asymmetry in EDVR between the left and right striatum in aged SNCAG51D/G51D rats. The increased and asymmetric dopamine turnover observed in the striatum of aged SNCAG51D/G51D rats is similar to prodromal PD, which suggests the presence of compensatory mechanisms. SNCAG51D rats represent a novel genetic model of PD, and kinetic modelling of 18F-DOPA PET data has identified a highly relevant early disease phenotype.

neuroscience↗

bioRxiv2022

Endoplasmic Reticulum membranes are continuously required to maintain mitotic spindle size and forces

Membrane organelle function, localization, and proper partitioning upon cell division depend on interactions with the cytoskeleton. Whether, reciprocally, membrane organelles also impact on the function of cytoskeletal elements remains less clear. Here, we show that acute disruption of the Endoplasmic Reticulum (ER) around spindle poles affects mitotic spindle size and function in Drosophila syncytial embryos. Acute ER disruption was achieved through the inhibition of ER membrane fusion by the dominant-negative cytoplasmic domain of Atlastin. We reveal that when the ER is disrupted specifically at metaphase, mitotic spindles become smaller, despite no significant changes in microtubule dynamics. These smaller spindles are still able to mediate sister chromatid separation, yet with decreased velocity. Furthermore, by inducing mitotic exit, we found that nuclear separation and distribution are affected upon ER disruption. Our results suggest that ER integrity around spindle poles is crucial for the maintenance of mitotic spindle shape and pulling forces. Additionally, ER integrity also ensures nuclear spacing during syncytial divisions.

cell biology↗

bioRxiv2022

Condensin II is required for efficient Spindle Assembly Checkpoint activation in Drosophila male meiosis

Reductional nuclear division in meiosis is essential for diploid life. A fundamental event in meiosis is chromatin condensation, through mechanisms not yet fully understood. Current data suggest that Condensins are key players in building and sustaining mitotic and meiotic chromosome structure. In Drosophila, Condensin II appears to be dispensable for faithful mitosis in somatic tissues yet essential in the germline. Previous work has demonstrated that in Drosophila male meiosis, Condensin II is required for the segregation of homologous chromosomes into distinct territories during prophase I, possibly through the resolution of chromosomal intertwines. Here we show that in addition to this well-established function in meiotic chromatin assembly, Condensin II is required for robust Spindle Assembly Checkpoint (SAC) signaling in male meiosis. In the absence of Condensin II, spermatocytes undergo faster meiotic divisions and display reduced ability to prolong meiosis in the presence of spindle poisons. This is attributed to the inability to recruit a key SAC component (Mad1) to the kinetochore. Importantly, we demonstrate that the absence of a robust SAC response in Condensin II mutants, and consequent accelerated meiosis, is a strong contributor to the meiotic defects associated with these mutants. We show that artificial prolongation of meiotic divisions, using conditions that delay anaphase onset in a SAC-independent manner, is sufficient to rescue segregation defects and aneuploidy associated with Condensin II mutations. We therefore conclude that Condensin II can be dispensable for the resolution of topological problems and chromosome condensation if cells are able to prolong meiosis. Yet, the newly found role of this complex in the robustness of the SAC reduces meiotic timing leading to severe chromosome segregation defects.

cell biology↗