Biology subjects

Hill, H. J.

Publications and source records attributed to Hill, H. J..

7 recordsLinked to original sources

bioRxiv2026

Determinants of dicentric chromosome breakage in Drosophila

Eukaryotic genomes often have fragile sites where chromosomes are particularly prone to break. In Drosophila, when dicentric ring chromosomes try to segregate, they break at nonrandom hotspots. Here, we precisely map breakage hotspots produced by dicentric ring chromosomes in Drosophila. Our study provides three key results about the nature of dicentric chromosome breakage. First, duplications produced by dicentric ring chromosome breakage are surprisingly complex and involve many structural rearrangements, indicating that healing of these breaks is not a simple process. Second, characterization of one particular hotspot showed that new termini all occurred within a single intron of a large testis-expressed gene, suggesting that replication-transcription conflict may be a key determinant of chromosome fragile sites. Third, the new ends are often located near preexisting transposons, suggesting that transposon insertions may contribute to fragility or participate in stabilization of broken ends.

genetics↗

bioRxiv2026

Wolbachia-induced cytoplasmic incompatibility produces heritable chromatin modifications that suppress position-effect variegation

Maternally transmitted Wolbachia often cause cytoplasmic incompatibility (CI), a sperm modification that kills host embryos lacking the endosymbiont. CI produces defects in paternal chromosome replication, condensation, and segregation during the first zygotic cell cycle, but a significant fraction of embryos progress normally through this and subsequent cycles and only exhibit defects at later developmental stages. These results, together with documented CI-induced epigenetic chromatin modifications, suggest heritable chromatin modifications are responsible for the developmentally delayed defects. Here, we conducted a Position-Effect Variegation (PEV) screen in Drosophila melanogaster using In(1)wm4to test for persistent effects on heterochromatin-mediated silencing in adults that survived CI. We show that Wolbachia acts as a variegation suppressor, or Su(var), increasing eye pigment when present in CI-inducing fathers, a reproducible effect observed across several maternal genotypes that differed in CI strength. That is, passage of the In(1)wm4through Wolbachia-infected males limits the spread of heterochromatin into the neighboring euchromatin in the progeny. This effect is consistent with disruption of heterochromatin establishment at the mid-blastula transition, when stochastic spreading of heterochromatin determines whether the displaced white gene is silenced. Surprisingly, maternal Wolbachia did not revert the PEV modification, and in one genotype, Wolbachia increased suppression. Together, our results demonstrate that Wolbachia-mediated chromatin effects persist to adulthood, are not corrected by CifA-dependent rescue, and can be compounded by maternal Wolbachia. These findings establish that rescue is incomplete at the level of heterochromatin-mediated silencing and suggest that CI-specific and constitutive Wolbachia chromatin effects may operate through at least partially independent pathways.

genetics↗

bioRxiv2024

Drosophila ring chromosomes interact with sisters and homologs to produceanaphase bridges in mitosis.

Ring chromosomes are known in many eukaryotic organisms, including humans. They are typically associated with a variety of maladies, including abnormal development and lethality. Underlying these phenotypes are anaphase chromatin bridges that can lead to chromosome loss, nondisjunction and breakage. By cytological examination of ring chromosomes in Drosophila melanogaster we identified five causes for anaphase bridges produced by ring chromosomes. Catenation of sister chromatids is the most common cause and these bridges frequently resolve during anaphase, presumably by the action of topoisomerase II. Sister chromatid exchange and chromosome breakage followed by sister chromatid union also produce anaphase bridges. Mitotic recombination with the homolog was rare, but was another route to generation of anaphase bridges. Most surprising, was the discovery of homolog capture, where the ring chromosome was connected to its linear homolog in anaphase. We hypothesize that this is a remnant of mitotic pairing and that the linear chromosome is connected to the ring by multiple wraps produced through the action of topoisomerase II during establishment of homolog pairing. In support, we showed that in a ring/ring homozygote the two rings are frequently catenated in mitotic metaphase, a configuration that requires breaking and rejoining of at least one chromosome.

genetics↗

bioRxiv2022

Multi-omic spatial profiling reveals the unique virus-driven immune landscape of COVID-19 placentitis

COVID-19 placentitis, a rare complication of maternal SARS-CoV-2 infection, only shows detectable virus in the placenta of a subset of cases. We provide a deep multi-omic spatial characterisation of placentitis from obstetrically complicated maternal COVID-19 infection. We found that SARS-CoV-2 infected placentas have a distinct transcriptional and immunopathological signature. This signature overlaps with virus-negative cases supporting a common viral aetiology. An inverse correlation between viral load and disease duration suggests viral clearance over time. Quantitative spatial analyses revealed a unique microenvironment surrounding virus-infected trophoblasts characterised by PDL1-expressing macrophages, T-cell exclusion, and interferon blunting. In contrast to uninfected mothers, ACE2 was localised to the maternal side of the placental trophoblast layer of almost all mothers with placental SARS-CoV-2 infection, which may explain variable susceptibility to placental infection. Our results demonstrate a pivotal role for direct placental SARS-CoV-2 infection in driving the unique immunopathology of COVID-19 placentitis. Graphical Abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

immunology↗

bioRxiv2022

Dicentric chromosome breakage in Drosophila melanogaster is influenced by pericentric heterochromatin and reveals a novel class of fragile site.

Chromosome breakage plays an important role in the evolution of karyotypes, and can produce deleterious effects within a single individual, such as aneuploidy or cancer. Forces that influence how and where chromosomes break are not well understood. In humans, breakage tends to occur in conserved hotspots called common fragile sites (CFS), especially during replication stress. By following the fate of dicentric chromosomes in Drosophila melanogaster we find that breakage under tension also tends to occur in specific hotspots. Our experimental approach was to induce sister chromatid exchange in a ring chromosome to generate a dicentric chromosome with a double chromatid bridge. In the following cell division, the dicentric bridges may break. We analyzed the breakage patterns of three different ring-X chromosomes. These chromosomes differ by the amount and quality of heterochromatin they carry as well as their genealogical history. For all three chromosomes, breakage occurs preferentially in several hotspots. Surprisingly, we found that the hotspot locations are not conserved between the three chromosomes: each displays a unique array of breakage hotspots. The lack of hotspot conservation, along with a lack of response to aphidicolin, suggests that these breakage sites are not entirely analogous to CFS and may reveal new mechanisms of chromosome fragility.. Additionally, the frequency of dicentric breakage and the durability of their spindle attachment varies significantly between the three chromosomes and is correlated with the origin of the centromere and the amount of pericentric heterochromatin they carry. We suggest that different centromere strengths could account for this.

genetics↗

bioRxiv2021

Supramolecular cylinders target bulge structures in the 5-prime UTR of the RNA genome of SARS-CoV-2 and inhibit viral replication

The untranslated regions (UTRs) of viral genomes contain a variety of conserved yet dynamic structures crucial for viral replication, providing drug targets for the development of broad spectrum anti-virals. We combine in vitro RNA analysis with Molecular Dynamics simulations to build the first 3D models of the structure and dynamics of key regions of the 5 UTR of the SARS-CoV-2 genome. Furthermore, we determine the binding of metallo-supramolecular helicates (cylinders) to this RNA structure. These nano-size agents are uniquely able to thread through RNA junctions and we identify their binding to a 3-base bulge and the central cross 4-way junction located in the stem loop 5. Finally, we show these RNA-binding cylinders suppress SARS-CoV-2 replication, highlighting their potential as novel antiviral agents.

biochemistry↗

bioRxiv2021

The hyperlipidaemic drug fenofibrate significantly reduces infection by SARS-CoV-2 in cell culture models

The SARS-CoV-2 pandemic has caused a significant number of fatalities and worldwide disruption. To identify drugs to repurpose to treat SARS-CoV-2 infections, we established a screen to measure dimerization of ACE2, the primary receptor for the virus. This screen identified fenofibric acid, the active metabolite of fenofibrate. Fenofibric acid also destabilized the receptor binding domain (RBD) of the viral spike protein and inhibited RBD binding to ACE2 in ELISA and whole cell binding assays. Fenofibrate and fenofibric acid were tested by two independent laboratories measuring infection of cultured Vero cells using two different SARS-CoV-2 isolates. In both settings at drug concentrations which are clinically achievable, fenofibrate and fenofibric acid reduced viral infection by up to 70%. Together with its extensive history of clinical use and its relatively good safety profile, these studies identify fenofibrate as a potential therapeutic agent requiring urgent clinical evaluation to treat SARS-CoV-2 infection. TeaserThe approved drug fenofibrate inhibits infection by SARS-COV-2

pharmacology and toxicology↗