Biology subjects

Buczacki, S. J. A.

Publications and source records attributed to Buczacki, S. J. A..

4 recordsLinked to original sources

bioRxiv2026

Postnatal Reprogramming Shapes Human Intestinal Epithelial Immune Competency

At birth, the intestine must rapidly adapt to enable nutritional function and immune microbial tolerance. Here, integrating single-cell multi-omics and spatial transcriptomics we define the circuits underpinning this process. We identify asynchronous developmental trajectories with postnatal epithelial reprogramming characterised by coordinated changes in metabolism, junctional structure and innate defence. At birth epithelial stem cells demonstrate dynamic enhancer remodelling, with accessibility often preceding transcription. Fetal stemness elements remain accessible despite reduced transcription across epithelial lineages, retaining plasticity potential. Post-natal epithelia experience sequential homing of myeloid cells followed by innate T cells with peri-epithelial B cells localising later in infancy. Using developmentally staged organoids, we show that epithelial responses to inflammatory stimuli are age-dependent and constrained in early life. We identify BHLHE40 as an early-life regulator that attenuates the impact of interferon- and NF-{kappa}B-driven signalling. Altogether we define the events driving epithelial licensing and barrier adaptation at birth and through infancy.

cell biology↗

bioRxiv2023

Mutational order and epistasis determine the consequences of FBXW7 mutations during colorectal cancer evolution

Somatic driver mutations, in genes such as FBXW7, have been discovered in phenotypically normal colonic tissue, however their role in cancer initiation remains elusive. Using normal and gene-edited patient-derived human colon organoids as models of early tumour evolution we observed that FBXW7-/- mutations exerted an epistatic effect on subsequent transcription depending on the mutational background of the cell. Specifically, the timing of acquiring an FBXW7-/- mutation respective to an APC mutation, led to profound phenotypic and transcriptomic differences. When FBXW7 was mutated before APC, a near-normal cell state was maintained alongside repression of the APC transcriptional response. However, when APC was mutated before FBXW7, cells acquired classical cancer-stem cell features. Single-cell RNA sequencing revealed that mutation of FBXW7 in normal tissue subtly switched cells from adult to a foetal/regenerative stem cell state. Further analysis using transposase-accessible chromatin sequencing identified this cellular plasticity was driven by changes in chromatin accessibility of transcriptional start site regions associated with TEAD, SNAI1 and AP-1 motifs, which in turn activate the foetal-like state. Taken together, we demonstrate a critical role of FBXW7 mutations in preventing colorectal cancer initiation and provide exemplar evidence for the importance of epistasis and mutational order in cancer biology.

cancer biology↗

bioRxiv2021

Inherited MUTYH mutations cause elevated somatic mutation rates and distinctive mutational signatures in normal human cells

Cellular DNA damage caused by reactive oxygen species is repaired by the base excision repair (BER) pathway which includes the DNA glycosylase MUTYH. Inherited biallelic MUTYH mutations cause predisposition to colorectal adenomas and carcinoma. However, the mechanistic progression from germline MUTYH mutations to MUTYH-Associated Polyposis (MAP) is incompletely understood. Here, we sequenced normal tissue DNAs from 10 individuals with MAP. Somatic base substitution mutation rates in intestinal epithelial cells were elevated 2 to 5-fold in all individuals, except for one showing a 33-fold increase, and were also increased in other tissues. The increased mutation burdens were of multiple mutational signatures characterised by C>A changes. Different mutation rates and signatures between individuals were likely due to different MUTYH mutations or additional inherited mutations in other BER pathway genes. The elevated base substitution rate in normal cells likely accounts for the predisposition to neoplasia in MAP. Despite ubiquitously elevated mutation rates, individuals with MAP do not display overt evidence of premature ageing. Thus, accumulation of somatic mutations may not be sufficient to cause the global organismal functional decline of ageing. Summary

genomics↗

bioRxiv2021

FXR inhibition reduces ACE2 expression, SARS-CoV-2 infection and may improve COVID-19 outcome

Prevention of SARS-CoV-2 entry in cells through the modulation of viral host receptors, such as ACE2, could represent a new therapeutic approach complementing vaccination. However, the mechanisms controlling ACE2 expression remain elusive. Here, we identify the farnesoid X receptor (FXR) as a direct regulator of ACE2 transcription in multiple COVID19-affected tissues, including the gastrointestinal and respiratory systems. We demonstrate that FXR antagonists, including the over-the-counter compound z-guggulsterone (ZGG) and the off-patent drug ursodeoxycholic acid (UDCA), downregulate ACE2 levels, and reduce susceptibility to SARS-CoV-2 infection in lung, cholangiocyte and gut organoids. We then show that therapeutic levels of UDCA downregulate ACE2 in human organs perfused ex situ and reduce SARS-CoV-2 infection ex vivo. Finally, we perform a retrospective study using registry data and identify a correlation between UDCA treatment and positive clinical outcomes following SARS-CoV-2 infection, including hospitalisation, ICU admission and death. In conclusion, we identify a novel function of FXR in controlling ACE2 expression and provide evidence that this approach could be beneficial for reducing SARS-CoV-2 infection, thereby paving the road for future clinical trials.

microbiology↗