Biology subjects

Katz, N.

Publications and source records attributed to Katz, N..

12 recordsLinked to original sources

bioRxiv2025

Towards Clinical Phage Microbiology for Biofilm Infections: A Comparative Study and a Suggested Protocol

Non-resolving bacterial infections involve biofilm formation and are often complicating treatments. Utilizing lytic bacteriophages with antibiotics holds promise in biofilm eradication. Accurately matching phage-antibiotic combinations against target bacteria, termed Clinical Phage Microbiology (CPM), is crucial in effective phage therapy treatments. However, compared to planktonic cultures, performing CPM on biofilm infections poses a significant challenge due to the lack of effective methods and a standard protocol. This study compared various CPM approaches in biofilms. To this end, the activity of five phages was assessed against Pseudomonas aeruginosa biofilms using nine methods and multiple approaches. Here, we discuss various aspects of each technique, including sensitivity, duration, ease of implementation in diagnostic labs, and labor. Finally, we offer a preliminary protocol for testing phage-sensitivity in biofilm, which was tested on various bacteria species, and may serve as a basis for comprehensive CPM in biofilm.

microbiology↗

bioRxiv2024

Tunable, self-contained gene dosage control via proteolytic cleavage of CRISPR-Cas systems

The ability to modulate gene expression through modular and universal genetic tools like CRISPR-Cas has greatly advanced gene therapy for therapeutics and basic science. Yet, the inherent stochasticity of delivery methods cause variation in target gene expression at the single-cell level, limiting their applicability in systems that require more precise expression. Thus, we implement a modular incoherent feedforward loop based on proteolytic cleavage of Cas to reduce gene expression variability against the variability of vector delivery. We target a genome-integrated marker and demonstrate dosage control of gene activation and repression, post-delivery tuning, and RNA-based compatibility of the system. To illustrate therapeutic relevance, we target the gene RAI1, the haploinsufficiency and triplosensitivity of which cause two autism-related syndromes. We demonstrate dosage-controlled gene activation for both human and mouse Rai1 via viral delivery to patient-derived cell lines and mouse cortical neurons. Overall, we established a robust dosage control circuit for uniform gene expression, beneficial for basic and translational research.

synthetic biology↗

bioRxiv2024

Dorsal CA1 silencing degrades tactile short-term memory

Previous studies in rodents showed that the hippocampus is involved in spatial short-term memory (STM), but hippocampal necessity for maintaining short-term sensory memories is unknown. Here, we develop tactile discrimination and STM tasks for freely-moving mice. Subjects learn to discriminate between textures after four shaping sessions and a single post-shaping session, and learn the STM task within a dozen sessions. Transient closed-loop silencing of dorsal hippocampal region CA1 during memory maintenance degrades task performance, compared to interleaved control blocks. Thus, uninterrupted hippocampal activity is required for acting upon tactile information maintained in STM. The findings suggest that the role of the hippocampus extends beyond spatial navigation, encoding memories, and long-term consolidation of experiences.

neuroscience↗

bioRxiv2024

PCNA unloading is crucial for the bypass of DNA lesions by homologous recombination

The DNA Damage Tolerance (DDT) mechanisms allow cells to bypass lesions in the DNA during replication. This allows the cells progress normally through the cell cycle in face of abnormalities in their DNA. PCNA, a homotrimeric sliding clamp complex plays a central role in the coordination of various processes during DNA replication, including the choice of mechanism used during DNA damage bypass. Mono-or poly-ubiquitination of PCNA facilitate an error-prone or an error-free bypass mechanism, respectively. In contrast, SUMOylation recruits the Srs2 helicase, which prevents local homologous recombination. The Elg1 RFC-like complex plays an important role in unloading PCNA from the chromatin. We analyse the interaction of mutations that destabilize PCNA with mutations in the Elg1 clamp unloader and the Srs2 helicase. Our results suggest that in addition to its role as a coordinator of bypass mechanisms, the very presence of PCNA on the chromatin prevents homologous recombination, even in the absence of the Srs2 helicase. Thus, PCNA unloading seems to be a pre-requisite for recombinational repair.

genetics↗

bioRxiv2022

Modular and programmable RNA sensing using ADAR editing in living cells

With the increasing availability of single-cell transcriptomes, RNA signatures offer a promising basis for targeting living cells. Molecular RNA sensors would enable the study of and therapeutic interventions for specific cell types/stats in diverse contexts, particularly in human patients and non-model organisms. Here we describe a modular and programmable design for live RNA sensing using adenosine deaminases acting on RNA (RADAR). We validated and then expanded our basic design, characterized its performance, and thoroughly analyzed its compatibility with the human/mouse transcriptomes. We also identified strategies to further boost output levels and improve the dynamic range. We show that RADAR is programmable and modular, and uniquely enables compact AND logic. In addition to being quantitative, RADAR can distinguish disease-relevant point mutations. Finally, we demonstrate that RADAR is a self-contained system with the potential to function in diverse organisms.

bioengineering↗

bioRxiv2021

A cell-free assay for rapid screening of inhibitors of hACE2-receptor - SARS-CoV-2-Spike binding

We present a cell-free assay for rapid screening of candidate inhibitors of protein binding, focusing on inhibition of the interaction between the SARS-CoV-2 Spike receptor binding domain (RBD) and human angiotensin-converting enzyme 2 (hACE2). The assay has two components: fluorescent polystyrene particles covalently coated with RBD, termed virion-particles (v-particles), and fluorescently-labeled hACE2 (hACE2F) that binds the v-particles. When incubated with an inhibitor, v-particle - hACE2F binding is diminished, resulting in a reduction in the fluorescent signal of bound hACE2F relative to the non-inhibitor control, which can be measured via flow cytometry or fluorescence microscopy. We determine the amount of RBD needed for v-particle preparation, v-particle incubation time with hACE2F, hACE2F detection limit, and specificity of v-particle binding to hACE2F. We measure the dose response of the v-particles to a known inhibitor. Finally, we demonstrate that RNA-hACE2F granules trap v-particles effectively, providing a basis for potential RNA-hACE2F therapeutics.

synthetic biology↗

bioRxiv2019

Overcoming the design, build, test (DBT) bottleneck for synthesis of nonrepetitive protein-RNA binding cassettes for RNA applications

The design-build-test (DBT) cycle in synthetic biology is considered to be a major bottleneck for progress in the field. The emergence of high-throughput experimental techniques, such as oligo libraries (OLs), combined with machine learning (ML) algorithms, provide the ingredients for a potential "big-data" solution that can generate a sufficient predictive capability to overcome the DBT bottleneck. In this work, we apply the OL-ML approach to the design of RNA cassettes used in gene editing and RNA tracking systems. RNA cassettes are typically made of repetitive hairpins, therefore hindering their retention, synthesis, and functionality. Here, we carried out a high-throughput OL-based experiment to generate thousands of new binding sites for the phage coat proteins of bacteriophages MS2 (MCP), PP7 (PCP), and Q{beta} (QCP). We then applied a neural network to vastly expand this space of binding sites to millions of additional predicted sites, which allowed us to identify the structural and sequence features that are critical for the binding of each RBP. To verify our approach, we designed new non-repetitive binding site cassettes and tested their functionality in U2OS mammalian cells. We found that all our cassettes exhibited multiple trackable puncta. Additionally, we designed and verified two additional cassettes, the first containing sites that can bind both PCP and QCP, and the second with sites that can bind either MCP or QCP, allowing for an additional orthogonal channel. Consequently, we provide the scientific community with a novel resource for rapidly creating functional non-repetitive binding site cassettes using one or more of three phage coat proteins with a variety of binding affinities for any application spanning bacteria to mammalian cells.

synthetic biology↗

bioRxiv2019

Exome-by-phenome-wide rare variant gene burden association with electronic health record phenotypes

BackgroundBy coupling large-scale DNA sequencing with electronic health records (EHR), \"genome-first\" approaches can enhance our understanding of the contribution of rare genetic variants to disease. Aggregating rare, loss-of-function variants in a candidate gene into a \"gene burden\" to test for association with EHR phenotypes can identify both known and novel clinical implications for the gene in human disease. However, this methodology has not yet been applied on both an exome-wide and phenome-wide scale, and the clinical ontologies of rare loss-of-function variants in many genes have yet to be described.\n\nMethodsWe leveraged whole exome sequencing (WES) data in participants (N=11,451) in the Penn Medicine Biobank (PMBB) to address on an exome-wide scale the association of a burden of rare loss-of-function variants in each gene with diverse EHR phenotypes using a phenome-wide association study (PheWAS) approach. For discovery, we collapsed rare (minor allele frequency (MAF) [≤] 0.1%) predicted loss-of-function (pLOF) variants (i.e. frameshift insertions/deletions, gain/loss of stop codon, or splice site disruption) per gene to perform a gene burden PheWAS. Subsequent evaluation of the significant gene burden associations was done by collapsing rare (MAF [≤] 0.1%) missense variants with Rare Exonic Variant Ensemble Learner (REVEL) scores [≥] 0.5 into corresponding yet distinct gene burdens, as well as interrogation of individual low-frequency to common (MAF > 0.1%) pLOF variants and missense variants with REVEL[≥] 0.5. We replicated our findings using the UK Biobanks (UKBB) whole exome sequence dataset (N=49,960).\n\nResultsFrom the pLOF-based discovery phase, we identified 106 gene burdens with phenotype associations at p<10-6 from our exome-by-phenome-wide association studies. Positive-control associations included TTN (cardiomyopathy, p=7.83E-13), MYBPC3 (hypertrophic cardiomyopathy, p=3.48E-15), CFTR (cystic fibrosis, p=1.05E-15), CYP2D6 (adverse effects due to opiates/narcotics, p=1.50E-09), and BRCA2 (breast cancer, p=1.36E-07). Of the 106 genes, 12 gene-phenotype relationships were also detected by REVEL-informed missense-based gene burdens and 19 by single-variant analyses, demonstrating the robustness of these gene-phenotype relationships. Three genes showed evidence of association using both additional methods (BRCA1, CFTR, TGM6), leading to a total of 28 robust gene-phenotype associations within PMBB. Furthermore, replication studies in UKBB validated 30 of 106 gene burden associations, of which 12 demonstrated robustness in PMBB.\n\nConclusionOur study presents 12 exome-by-phenome-wide robust gene-phenotype associations, which include three proof-of-concept associations and nine novel findings. We show the value of aggregating rare pLOF variants into gene burdens on an exome-wide scale for unbiased association with EHR phenotypes to identify novel clinical ontologies of human genes. Furthermore, we show the significance of evaluating gene burden associations through complementary, yet non-overlapping genetic association studies from the same dataset. Our results suggest that this approach applied to even larger cohorts of individuals with WES or whole-genome sequencing data linked to EHR phenotype data will yield many new insights into the relationship of genetic variation and disease phenotypes.

genomics↗

bioRxiv2019

Live dynamical tracking of slncRNA speckles in single E. coli cells reveals bursts of fluorescence degradation

Liquid-solid transition, also known as gelation, is a specific form of phase separation in which molecules cross-link to form a highly interconnected compartment with solid - like dynamical properties. Here, we utilize RNA hairpin coat-protein binding sites to form synthetic RNA based gel-like granules via liquid-solid phase transition. We show both in-vitro and in-vivo that hairpin containing synthetic long non-coding RNA (slncRNA) molecules granulate into bright localized puncta. We further demonstrate that upon introduction of the coat-proteins, less-condensed gel-like granules form with the RNA creating an outer shell with the proteins mostly present inside the granule. Moreover, by tracking puncta fluorescence signals over time, we detected addition or shedding events of slncRNA-CP nucleoprotein complexes. Consequently, our granules constitute a genetically encoded storage compartment for protein and RNA with a programmable controlled release profile that is determined by the number of hairpins encoded into the RNA. Our findings have important implications for the potential regulatory role of naturally occurring granules and for the broader biotechnology field.

biophysics↗

bioRxiv2017

Synthetic protein-sensing riboswitches

We study translational regulation by a 5 UTR sequence encoding the binding site of an RNA-binding protein (RBP) in bacteria, using a reporter assay and Selective 2-hydroxyl acylation analysed by primer extension sequencing (SHAPE-Seq). We tested constructs containing a single hairpin, based on the binding sites of the coat RBPs of bacteriophages GA, MS2, PP7, and Q{beta}, positioned in the 5 UTR of a reporter gene. With specifically-bound RBP present, either weak repression or up-regulation is observed, depending on the binding site and its flanking sequence. SHAPE-Seq data for a representative construct exhibiting up-regulation, indicates a partially-folded hairpin and non-reactive upstream and downstream flanking region, which we attribute to intermediate structures that apparently blocks translation. RBP binding stabilizes the fully-folded hairpin state and thus facilitates translation, suggesting that the up-regulating constructs are RBP-sensing riboswitches. This finding is further supported by lengthening the binding-site stem, which in turn destabilizes the translationally-inactive state, and abolishes the up-regulating behavior. Finally, we found that the combination of two binding sites, positioned in the 5 UTR and gene-header of the same transcript, can yield a cooperative regulatory response. Together, we show that the interaction of an RBP with its RNA target facilitates structural changes in the RNA, which is reflected by a controllable range of binding affinities and dose response behaviors. Thus, demonstrating that RNA-RBP interactions can provide a platform for constructing gene regulatory networks that are based on translational, rather than transcriptional, regulation.

synthetic biology↗

bioRxiv2017

An in vivo binding assay for RNA-binding proteins based on repression of a reporter gene

We employ a reporter assay and Selective 2'-hydroxyl acylation analysed by primer extension sequencing (SHAPE-seq) to study translational regulation by RNA-binding proteins, in bacteria. We designed 82 constructs, each with a single hairpin based on the binding sites of the RNA-binding coat proteins of phages MS2, PP7, GA, and Q{beta}, at various positions within the N-terminus of a reporter gene. In the absence of RNA-binding proteins, the translation level depends on hairpin location, and exhibits a three-nucleotide periodicity. For hairpin positions within the initiation region, we observe strong translational repression in the presence of its cognate RNA-binding protein. In vivo SHAPE-seq results for a representative construct indicate that the repression phenomenon correlates with a wide-swath of protection, including the hairpin and extending past the ribosome binding site. Consequently, our data suggest that the protection provided by the RBP-hairpin complex inhibits ribosomal initiation. Finally, utilizing the repression phenomenon for quantifying protein-RNA binding affinity in vivo, we both observe partially contrasting results to previous in vitro and in situ studies, and additionally, show that this method can be used in a high-throughput assay for a quantitative study of protein-RNA binding in vivo.

synthetic biology↗

bioRxiv2017

Demonstration of de novo chemotaxis in E. coli using a real-time, quantitative, and digital-like approach

Chemotaxis is the movement of an organism in response to an external chemical stimulus. This system enables bacteria to sense their immediate environment and adapt to changes in its chemical composition. Bacterial chemotaxis is mediated by chemoreceptors, membrane proteins that bind an effector and transduce the signal to the downstream proteins. From a synthetic biology perspective, the natural chemotactic repertoire is of little use since bacterial chemoreceptors have evolved to sense specific ligands that either benefit or harm the cell. Here we demonstrate that using a combined computational design approach together with a quantitative, real-time, and digital detection approach, we can rapidly design, manufacture, and characterize a synthetic chemoreceptor in E. coli for histamine (a ligand for which there are no known chemoreceptors). First, we employed a computational protocol that uses the Rosetta bioinformatics software together with high threshold filters to design mutational variants to the native Tar ligand binding domain that target histamine. Second, we tested different ligand-chemoreceptors pairs with a novel chemotaxis assay, based on optical reflectance interferometry of porous silicon (PSi) optical transducers, enabling label-free quantification of chemotaxis by monitoring real-time changes in the optical readout (expressed as the effective optical thickness, EOT). We found that different ligands can be characterized by an individual set of fingerprints in our assay. Namely, a binary, digital-like response in EOT change (i.e. positive or negative) that differentiates between attractants and repellants, the amplitude of change of EOT response, and the rate by which steady state in EOT change is reached. Using this assay, we were able to positively identify and characterize a single mutational chemoreceptor variant for histamine that mediated chemotaxis comparably to the natural Tar-aspartate system. Our results demonstrate the possibility of not only expanding the natural chemotaxis repertoire, but also provide a new quantitative assay by which to characterize the efficacy of the chemotactic response.

synthetic biology↗