Biology subjects

Kubik, S.

Publications and source records attributed to Kubik, S..

13 recordsLinked to original sources

bioRxiv2026

Partial lesions of hypocretin neurons of the rat lateral hypothalamus affect wake and sleep regulation under increased sleep pressure

Hypocretin(orexin)-producing neurons in the lateral hypothalamic area are important for sleep and wake regulation in mammals and their damage in humans manifests clinically as narcolepsy. While in previous studies experimentally induced massive loss of these neurons revealed their physiological importance, small lesions and their manifestations can uncover more subtle features of sleep regulation and help understand the delicate processes in early stages of pathogenesis of narcolepsy. We studied the effects of partial lesions (approximately 30%) of hypocretin producing neurons in the lateral hypothalamus on sleep patterns and EEG in rats. The lesions did not change the normal sleep and wake pattern in undisturbed rats. The effects of lesions manifested under increased sleep pressure after six hours of sleep deprivation, when they led to accelerated dynamics of compensatory slow wave sleep. The lesions also led to a slight decrease in theta frequency in wakefulness and in REM sleep, which we observed during undisturbed sleep and wake behavior as well as after sleep deprivation.

neuroscience↗

bioRxiv2024

Critical assay parameters facilitating confident detection of expression changes, fusions and short variants in RNA isolated from tissue

Molecular assays based on next-generation sequencing of RNA can provide clinically relevant information by measuring gene expression levels, identifying gene fusions, aberrant transcript isoforms and detecting small variants. Nevertheless, achieving good performance and reliable result interpretation present a significant challenge. In this work, we dissect the impact of various technical factors on the concurrent detection of several biomarker types using a hybridization enrichment-based targeted RNA sequencing applied to a cohort of more than one hundred samples derived from diverse solid tumors. We demonstrate that several critical parameters inferred from the sequencing data should be controlled to interpret the results accurately. These include molecular coverage of reference genes as a proxy of RNA conversion, DNA content measure, and the extent of target molecular coverage. We summarize our findings with recommendations allowing maximum reliable information recovery from targeted RNA sequencing data.

cancer biology↗

bioRxiv2024

CA1 ensemble plasticity is coupled to context change and modulated by task familiarity

When should plasticity mechanisms get recruited (stability-plasticity dilemma)? Environments change over time, re/entering a given context increases uncertainty and predicts the need for updating. Hippocampus (HPC) is key to tracking context change but also navigation in relation to moving targets. CA1 ensembles expressing immediate-early genes (IEGs) are contextually specific, while the amount of IEG expression correlates with HPC-dependent task demands. However, task effects on the IEG-expressing ensembles per se remain unclear. In three experiments, we tested the effect of context change and HPC task demands on CA1 IEG+ ensembles in rats. Experiment 1 showed that the IEG+ (Arc, Homer1a RNA) ensemble size drops to baseline level during uninterrupted 30 min exploration, reflecting familiarization and decreasing uncertainty, unless context change is present; the ensemble sizes reflect both context identity and context change. Experiment 2 showed no evidence of task-specificity of IEG+ ensembles during highly HPC-dependent mobile robot avoidance nor HPC-independent stationary robot avoidance. Experiment 3 replicated the findings of Experiment 2 for c-Fos protein. Nonetheless, the data suggest that ensembles shrink with task mastery/familiarity and grow with novelty presented by acquisition of behavioral extinction. Overall, our results shed light on the temporal dynamics, and the context and task control of CA1 IEG+ ensembles. The present results and the relevant literature suggest that context change resets the ensemble of IEG-expressing CA1 neurons and novelty delays the time-dependent ensemble shrinking. HIGHLIGHTSO_LIPlasticity and learning rate should reflect novelty and familiarity, i.e. uncertainty C_LIO_LIChange of context and task requirements increase uncertainty C_LIO_LIFamiliarization with context and task reduces uncertainty C_LIO_LIFor context, this pattern is matched by dynamics of IEG+ ensembles in CA1 C_LIO_LITask demands have modulating influence on CA1 IEG+ ensembles C_LI GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/608588v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@12808c0org.highwire.dtl.DTLVardef@156ad3corg.highwire.dtl.DTLVardef@1876f0aorg.highwire.dtl.DTLVardef@8b13f4_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Spatio-temporal mechanisms of consolidation, recall and reconsolidation in reward-related memory trace

The formation of memories is a complex, multi-scale phenomenon, especially when it involves integration of information from various brain systems. We have investigated the differences between a novel and consolidated association of spatial cues and amphetamine administration, using an in-situ hybridisation method to track the short-term dynamics during the recall testing. We have found that remote recall group involves smaller, but more consolidated groups of neurons, which is consistent with their specialisation. By employing machine learning analysis, we have shown this pattern is especially pronounced in the VTA; furthermore, we also uncovered significant activity patterns in retrosplenial and prefrontal cortices, as well as in the DG and CA3 subfields of the hippocampus. The behavioural propensity towards the associated localisation appears to be driven by the nucleus accumbens, however, further modulated by a trio of the amygdala, VTA and hippocampus, as the trained association is confronted with test experience. These results show that memory mechanisms must be modelled considering individual differences in motivation, as well as covering dynamics of the process.

neuroscience↗

bioRxiv2022

Microphysiological vascular malformation model reveals a role of dysregulated Rac1 and mTORC1/2 in lesion formation.

Somatic activating mutations of PIK3CA are associated with the development of vascular malformations (VMs). Here, we describe a microfluidic model of PIK3CA-driven VMs consisting of human umbilical vein endothelial cells (HUVECs) expressing PIK3CA activating mutations embedded in 3D hydrogels. We observed enlarged and irregular vessel phenotypes, consistent with clinical signatures and concomitant with PI3K-driven upregulation of Rac1/PAK, MEK/ERK, and mTORC1/2 signaling. We observed differential effects between Alpelisib, a PIK3CA inhibitor, and Rapamycin, an mTORC1 inhibitor, in mitigating matrix degradation and vascular network topology. While both drugs are effective in preventing vessel enlargement, Alpelisib suppressed mTORC2-dependent AKT1 phosphorylation and MEK/ERK signaling. Rapamycin failed to reduce MEK/ERK and mTORC2 activity and resulted in vascular hyperbranching, while inhibiting PAK, MEK1/2, and mTORC1/2 signaling mitigates abnormal growth and vascular dilation. Collectively, these findings establish an in vitro platform for modeling VMs and confirm a role of dysregulated Rac1/PAK and mTORC1/2 signaling in PIK3CA-driven VMs.

bioengineering↗

bioRxiv2021

Mutational hotspot in the SARS-CoV-2 Spike protein N-terminal domain conferring immune escape potential

Global efforts are being taken to monitor the evolution of SARS-CoV-2, aiming at early identification of mutations with the potential of increasing viral infectivity or virulence. We report a striking increase in the frequency of recruitment of diverse substitutions at a critical residue (W152), positioned in the N-terminal domain (NTD) of the Spike protein, observed repeatedly across independent phylogenetic and geographical contexts. We investigate the impact these mutations might have on the evasion of neutralizing antibodies. Finally, we uncover that NTD is a region exhibiting particularly high frequency of mutation recruitments, suggesting an evolutionary path on which the virus maintains optimal efficiency of ACE2 binding combined with the flexibility facilitating the immune escape.

genomics↗

bioRxiv2021

ChEC-seq: a robust method to identify protein-DNA interactions genome-wide

Mittal et al. (2021; first brought to our attention in May 2019) have raised concerns regarding the Chromatin Endogenous Cleavage-sequencing (ChEC-seq) technique (Zentner et al., 2015) that may create a false impression that this method has fundamental flaws which prevent one from distinguishing between signal and noise. Although Mittal et al. focus on studies of the global co-activators SAGA, TFIID and Mediator that we were not involved in, we feel obliged to highlight here several of our own publications (Albert et al., 2019; Bruzzone et al., 2018; Hafner et al., 2018; Kubik et al., 2019; Kubik et al., 2018), as well as recent unpublished data, that employed ChEC-seq and directly addressed the observation raised by Mittal et al. that cleavage maps for various MNase fusion proteins often qualitatively resemble each other and those generated by "free" (unfused) MNase. Our studies lay out a clear path for determining sites of preferential factor localization by normalization of ChEC-seq experimental data to matched free-MNase controls. They also demonstrate the use of in vivo functional assays to assess ChEC-seq reliability and reveal examples where ChEC-seq identifies functional binding sites missed by conventional ChIP-seq analysis.

molecular biology↗

bioRxiv2020

Guidelines for accurate genotyping of SARS-CoV-2 using amplicon-based sequencing of clinical samples

BackgroundSARS-CoV-2 genotyping has been instrumental to monitor virus evolution and transmission during the pandemic. The reliability of the information extracted from the genotyping efforts depends on a number of aspects, including the quality of the input material, applied technology and potential laboratory-specific biases. These variables must be monitored to ensure genotype reliability. The current lack of guidelines for SARS-CoV-2 genotyping leads to inclusion of error-containing genome sequences in studies of viral spread and evolution. ResultsWe used clinical samples and synthetic viral genomes to evaluate the impact of experimental factors, including viral load and sequencing depth, on correct sequence determination using an amplicon-based approach. We found that at least 1000 viral genomes are necessary to confidently detect variants in the genome at frequencies of 10% or higher. The broad applicability of our recommendations was validated in >200 clinical samples from six independent laboratories. The genotypes of clinical isolates with viral load above the recommended threshold cluster by sampling location and period. Our analysis also supports the rise in frequency of 20A.EU1 and 20A.EU2, two recently reported European strains whose dissemination was favoured by travelling during the summer 2020. ConclusionsWe present much-needed recommendations for reliable determination of SARS-CoV-2 genome sequence and demonstrate their broad applicability in a large cohort of clinical samples.

genomics↗

bioRxiv2019

Opposing chromatin remodelers control transcription initiation frequency and start site selection

Precise nucleosome organization at eukaryotic promoters is thought to be generated by multiple chromatin remodeler (CR) enzymes and to affect transcription initiation. Using an integrated analysis of chromatin remodeler binding and nucleosome displacement activity following rapid remodeler depletion, we investigate the interplay between these enzymes and their impact on transcription in budding yeast. We show that many promoters are acted upon by multiple CRs that operate either cooperatively or in opposition to position the key transcription start site-associated +1 nucleosome. Functional assays suggest that +1 nucleosome positioning often reflects a trade-off between maximizing RNA Polymerase II recruitment and minimizing transcription initiation at incorrect sites. Finally, we show that nucleosome movement following CR inactivation usually results from the activity of another CR and that in the absence of any remodeling activity +1 nucleosomes maintain their positions. Our results provide a detailed picture of fundamental mechanisms linking promoter nucleosome architecture to transcription initiation.

molecular biology↗

bioRxiv2019

The mechanistic basis for chromatin invasion and remodeling by the yeast pioneer transcription factor Rap1

Pioneer transcription factors (pTFs) bind to target sites within compact chromatin initiating chromatin remodeling and controlling the recruitment of downstream factors. The mechanisms by which pTFs overcome the chromatin barrier are not well understood. Here we reveal, using single-molecule fluorescence approaches, how the yeast transcription factor Rap1 invades and remodels chromatin. Using a reconstituted chromatin system replicating yeast promoter architecture we demonstrate that Rap1 can bind nucleosomal DNA within a chromatin fiber, but with shortened dwell times compared to naked DNA. Moreover, we show that Rap1 binding opens chromatin fiber structure by inhibiting nucleosome-nucleosome contacts. Finally, we reveal that Rap1 collaborates with the chromatin remodeler RSC to destabilize promoter nucleosomes, paving the way to form long-lived bound states on now exposed DNA. Together, our results provide a mechanistic view of how Rap1 gains access and opens chromatin, thereby establishing an active promoter architecture and controlling gene expression.

biophysics↗

bioRxiv2018

Sfp1 regulates transcriptional networks driving cell growth and division through multiple promoter binding modes

Understanding how transcriptional programs help to coordinate cell growth and division is an important unresolved problem. Here we report that the nutrient- and stress-regulated transcription factor Sfp1 is rate-limiting for expression of several large classes of genes involved in yeast cell growth, including ribosomal protein, ribosome biogenesis, and snoRNA genes. Remarkably, the spectrum of Sfp1 transcription effects is concordant with a combination of chromatin immunoprecipitation and chromatin endogenous cleavage binding analyses, which together provide evidence for two distinct modes of Sfp1 promoter binding, one requiring a co-factor and the other a specific DNA-recognition motif. In addition to growth-related genes, Sfp1 binds to and regulates the promoters of cell cycle \"START\" regulon genes, including the key G1/S cyclins CLN1 and CLN2. Our findings suggest that Sfp1 acts as a master regulator of cell growth and cell size by coordinating the expression of genes implicated in mass accumulation and cell division.

molecular biology↗

bioRxiv2018

General Regulatory Factors control the fidelity of transcription by restricting non-coding and ectopic initiation

The fidelity of transcription initiation is essential for accurate gene expression, but the determinants of start site selection are not fully understood. Rap1 and other General Regulatory Factors (GRFs) control the expression of many genes in yeast. We show that depletion of these factors induces widespread ectopic transcription initiation within promoters. This generates many novel non-coding RNAs and transcript isoforms with diverse stability, profoundly altering the coding potential of the transcriptome. Ectopic transcription initiation strongly correlates with altered nucleosome positioning. We show that Rap1 sterically constrains nucleosomes as its mere binding to the DNA can be sufficient for restoration normal nucleosome positioning, transcription initiation and gene expression. These results demonstrate an essential role for GRFs in the fidelity of transcription initiation and in the suppression of pervasive transcription, redefining current models of their function. They have general implications for the mechanism of transcription initiation and the control of gene expression.\n\nHIGHLIGHTSO_LIRap1, Abf1 and Reb1 control the fidelity of transcription initiation and suppress pervasive transcription\nC_LIO_LIWidespread ectopic transcription initiation in Rap1-deficient cells induces variegated alterations in gene expression\nC_LIO_LIAltered nucleosome positioning in GRFs-defective cells correlate with ectopic transcription initiation.\nC_LIO_LIRap1 controls nucleosomes positioning and transcription initiation at least partially by a steric hindrance mechanism\nC_LI

genomics↗

bioRxiv2018

Sequence-directed action of RSC remodeler and pioneer factors positions +1 nucleosome to facilitate transcription

Accessible chromatin is important for RNA polymerase II recruitment and transcription initiation at eukaryotic promoters. We investigated the mechanistic links between promoter DNA sequence, nucleosome positioning and transcription. Our results indicate that precise positioning of the transcription start site-associated +1 nucleosome in yeast is critical for efficient TBP binding, and is driven by two key factors, the essential chromatin remodeler RSC and a small set of ubiquitous pioneer transcription factors. We find no evidence for recruitment of RSC by pioneer factors, but show instead that the strength and directionality of RSC action on nucleosomes depends upon the arrangement of two specific DNA motifs that promote its binding and nucleosome displacement activity at promoters. Thus, despite their widespread co-localization, RSC and pioneer factors predominantly act independently to generate accessible chromatin. Our results provide insight into how promoter DNA sequence instructs trans-acting factors to control nucleosome architecture and stimulate transcription initiation.

molecular biology↗