Biology subjects

Crisp, A.

Publications and source records attributed to Crisp, A..

7 recordsLinked to original sources

bioRxiv2026

DNA supercoiling links transcription and chromatin architecture during human stem cell differentiation

Transcription imposes torsional stress on chromatin, leading to over- or under-winding of the DNA helix. Yet, how supercoiling evolves during dynamic changes in gene expression, and how it influences three-dimensional chromatin contacts in the densely packed human genome, remains unclear. Here, we map genome-wide negative supercoiling and chromatin interactions at high resolution in human embryonic stem cells, using the transcriptional changes that drive differentiation to explore their interplay at multiple scales. We demonstrate that gene activation increases negative supercoiling despite enhanced topoisomerase recruitment. Moreover, elevated negative supercoiling correlates with increased DNA contacts within domains at multiple scales, from genes to topologically associating domains, consistent with transcription-generated torsional stress enhancing contact frequency. Thus, negative supercoiling likely contributes to the genome architectural remodelling that accompanies the execution of developmental programs.

genomics↗

bioRxiv2026

A genome language model for mapping DNA replication origins

Origin firing is a central process during DNA replication, but specific sequences defining replication origin usage have not been defined in human cells. Here, we show that a genome language model can accurately predict which sequences can act as an origin of replication, thereby enabling the fast and cost-effective creation of genome-wide replication origin maps. We fine-tuned a genome language model on the primary sequence of mapped human origins to establish ORILINX (ORIgin of replication Language-model Inference via Nucleotide conteXt) and found that it learns a rich representation of sequence features linked to replication initiation, extending beyond known predictive features such as GC-content and G-quadruplex motifs. When applied genome-wide, the models sequence-derived origin calling closely mirrors origin efficiency inferred from replication timing, suggesting that intrinsic sequence context encodes information relevant to initiation frequency. Furthermore, we performed Short Nascent Strand sequencing (SNS-seq) and Repli-seq to demonstrate that ORILINX can generalise to other mammalian genomes, such as those of mice and sheep, as well as other vertebrates such as chickens. Finally, we packaged ORILINX into a simple, easy-to-use tool which is available at https://github.com/Pfuderer/ORILINX.git.

genomics↗

bioRxiv2025

Stalling of elongating Pol II triggers Ser7 phosphorylation in trans to drive transcription recovery

DNA is scattered with obstacles that stall RNA polymerase II (Pol II) and block the production of full-length transcripts. Two mechanisms are known to resolve stalled Pol II: transcription-coupled nucleotide excision repair (TC-NER) and the "last resort" Pol II ubiquitylation-degradation pathway. Here, we uncover a third, distinct mechanism that alerts incoming Pol II molecules to roadblocks ahead and primes them for efficient elongation. We show that transcription stalling triggers GSK3-mediated phosphorylation of Ser7 residues (Ser7P) on the Pol II C-terminal domain. Unexpectedly, this phosphorylation occurs in trans: obstacles in gene bodies induce Ser7P on Pol II complexes at gene beginnings. This modification enables processive transcription while restraining excessive Pol II degradation by the "last resort" pathway. Our findings reveal an adaptive system that preserves transcriptional homeostasis by coordinating polymerase behavior across the gene in response to elongation stress.

molecular biology↗

bioRxiv2019

MALT1 mediates IL-17 Neural Signaling to regulate C. elegans behavior, immunity and longevity

Besides well-known immune roles, the evolutionarily ancient cytokine interleukin-17 (IL-17) modulates neural circuit function. We investigate how IL-17 signals in neurons, and the extent to which this signaling can alter organismal phenotypes. We combine immunoprecipitation and mass spectrometry to biochemically characterize endogenous signaling complexes that function downstream of IL-17 receptors in C. elegans (Ce) neurons. We identify the Ce ortholog of MALT1 as a critical output of the pathway. MALT1 was not previously implicated in IL-17 signaling or in nervous system function. MALT1 forms a complex with homologs of Act1 and IRAK and functions both as a scaffold for I{kappa}B recruitment, and as a protease. MALT1 is expressed broadly in the Ce nervous system, and neuronal IL-17-MALT1 signaling regulates many phenotypes, including escape behavior, associative learning, immunity and longevity. Our data suggest MALT1 has an ancient role modulating neural function downstream of IL-17 to remodel physiological and behavioral state.

neuroscience↗

bioRxiv2019

Transcriptomics supports that pleuropodia of insect embryos function in degradation of the serosal cuticle to enable hatching

Pleuropodia are limb-derived vesicular organs that transiently appear on the first abdominal segment of embryos from the majority of insect \"orders\". They are missing in the model Drosophila and little is known about them. Experiments carried out on orthopteran insects eighty years ago indicated that the pleuropodia secrete a \"hatching enzyme\" that at the end of embryogenesis digests the serosal cuticle to enable the larva to hatch. This hypothesis contradicts the view that insect cuticle is digested by enzymes produced by the tissue that deposited it. We studied the development of the pleuropodia in embryos of the locust Schistocerca gregaria (Orthoptera) using transmission electron microscopy. RNA-seq was applied to generate a comprehensive embryonic reference transcriptome that was used to study genome-wide gene expression of ten stages of pleuropodia development. We show that the mature and secretion releasing pleuropodia are primarily enriched in transcripts associated with transport functions. They express genes encoding enzymes capable of digesting cuticular protein and chitin. These include the potent cuticulo-lytic Chitinase 5, whose transcript rises just before hatching. The pleuropodia are also enriched in transcripts for immunity-related enzymes, including the Toll signaling pathway, melanization cascade and lysozymes. These data provide transcriptomic evidence that the pleuropodia of orthopterans produce the \"hatching enzyme\", whose important component is the Chitinase 5. They also indicate that the organs facilitate epithelial immunity and may function in embryonic immune defense. Based on their gene expression the pleuropodia appear to be an essential part of insect physiology.

developmental biology↗

bioRxiv2018

S phase R-loop formation is restricted by PrimPol-mediated repriming

During DNA replication, conflicts with ongoing transcription are frequent and require careful management to avoid genetic instability. R-loops, three stranded nucleic acid structures comprising a DNA:RNA hybrid and displaced single stranded DNA, are important drivers of damage arising from such conflicts. How R-loops stall replication and the mechanisms that restrain their formation during S phase are incompletely understood. Here we show in vivo how R-loop formation drives a short purine-rich repeat, (GAA)10, to become a replication impediment that requires the repriming activity of the primase-polymerase PrimPol for its processive replication. Further, we show that loss of PrimPol results in a significant increase in R-loop formation around the repeat during S phase. We extend this observation by showing that PrimPol suppresses R-loop formation in genes harbouring secondary structure-forming sequences, exemplified by G quadruplex and H-DNA motifs, across the genome in both avian and human cells. Thus, R-loops promote the creation of replication blocks at susceptible sequences, while PrimPol-dependent repriming limits the extent of unscheduled R-loop formation at these sequences, mitigating their impact on replication.

molecular biology↗

bioRxiv2017

Comparative genomics of bdelloid rotifers: evaluating the effects of asexuality and desiccation tolerance on genome evolution

Bdelloid rotifers are microscopic invertebrates that have existed for millions of years apparently without sex or meiosis. They inhabit a variety of temporary and permanent freshwater habitats globally, and many species are remarkably tolerant of desiccation. Bdelloids offer an opportunity to better understand the evolution of sex and recombination, but previous work has emphasized desiccation as the cause of several unusual genomic features in this group. Here, we evaluate the relative effects of asexuality and desiccation tolerance on genome evolution by comparing whole genome sequences for three bdelloid species: Adineta ricciae (desiccation tolerant), Rotaria macrura and Rotaria magnacalcarata (both desiccation intolerant) to the only published bdelloid genome to date, that of Adineta vaga (also desiccation tolerant). We find that tetraploidy is conserved among all four bdelloid species, but homologous divergence in obligately aquatic Rotaria genomes is low, well within the range observed between alleles in obligately sexual, diploid animals. In addition, we find that homologous regions in A. ricciae are largely collinear and do not form palindromic repeats as observed in the published A. vaga assembly. These findings are contrary to current understanding of the role of desiccation in shaping the bdelloid genome, and indicate that various features interpreted as genomic evidence for long-term ameiotic evolution are not general to all bdelloid species, even within the same genus. Finally, we substantiate previous findings of high levels of horizontally transferred non-metazoan genes encoded in both desiccating and non-desiccating bdelloid species, and show that this is a unique feature of bdelloids among related animal phyla. Comparisons within bdelloids and to other desiccation-tolerant animals, however, again call into question the purported role of desiccation in horizontal transfer.

evolutionary biology↗