Biology subjects

Ponting, C.

Publications and source records attributed to Ponting, C..

8 recordsLinked to original sources

bioRxiv2025

Alternate Splicing Directs PMCA2 to Lysosomes and is Linked to Neurodegeneration

Plasma membrane calcium ATPases (PMCAs) are believed to function exclusively at the plasma membrane where they expel calcium from the cytosol. We have unexpectedly identified a splice variant-dependent localisation of the PMCA isoform PMCA2 to the lysosome, where it forms an evolutionarily conserved complex with NPC1, the lysosomal membrane protein defective in the rare lysosomal storage disease Niemann-Pick disease type C (NPC). This interaction is required for lysosomal Ca2+ homeostasis and implicates PMCA2 as a mediator of Ca2+ uptake into lysosomes. Disruption of the NPC1-PMCA2 complex contributes to the pathophysiology of both Niemann-Pick disease type C and Parkinsons disease, revealing an unrecognised intracellular function for PMCA2 and a shared mechanism linking lysosomal Ca2+ and lipid regulation in neurodegeneration.

cell biology↗

bioRxiv2020

Protein citrullination was introduced into animals by horizontal gene transfer from cyanobacteria

Protein post-translational modifications (PTMs) add an enormous amount of sophistication to biological systems but their origins are largely unexplored. Citrullination, a key regulatory mechanism in human physiology and pathophysiology, is particularly enigmatic in an evolutionary context. The citrullinating enzymes peptidylarginine deiminases (PADIs) are ubiquitous across vertebrates but absent from yeast, worms and flies. Here, we map the surprising evolutionary trajectory of PADIs into the animal lineage. We present strong phylogenetic support for a clade encompassing animal and cyanobacterial PADIs that excludes fungal and other bacterial homologues. The animal and cyanobacterial PADIs share unique, functionally relevant synapomorphies that are absent from all other homologues. Molecular clock calculations and sequence divergence analyses using the fossil record estimate the last common ancestor of the cyanobacterial and animal PADIs to be approximately 1 billion years old, far younger than the 3.35-4.52 billion years known to separate bacterial and eukaryotic lineages. Under an assumption of vertical descent, PADI sequence change is anachronistically slow during this evolutionary time frame, even when compared to mitochondrial proteins, products of likely endosymbiont gene transfer and some of the most highly conserved proteins in life. The consilience of evidence indicates that PADIs were introduced from cyanobacteria into animals by horizontal gene transfer (HGT). The ancestral cyanobacterial protein is enzymatically active and can citrullinate eukaryotic proteins, suggesting that the PADI HGT event introduced a new catalytic capability into the regulatory repertoire of animals. This study reveals the unusual evolution of a pleiotropic protein modification with clear relevance in human physiology and disease.

evolutionary biology↗

bioRxiv2020

Altered Thalamocortical Connectivity in Six-Week Old Infants at High Familial Risk for Autism Spectrum Disorder

Converging evidence from neuroimaging studies has revealed altered connectivity in cortical-subcortical networks in youth and adults with autism spectrum disorder (ASD). Comparatively little is known about the development of cortical-subcortical connectivity in infancy, before the emergence of overt ASD symptomatology. Here we examined early functional and structural connectivity of thalamocortical networks in infants at high familial risk for ASD (HR) and lowrisk controls (LR). Resting-state functional connectivity (rs-fcMRI) and diffusion tensor imaging (DTI) data were acquired 52 six-week-old infants. Functional connectivity was examined between six cortical seeds -prefrontal, motor, somatosensory, temporal, parietal, and occipital regions- and bilateral thalamus. We found significant thalamic-prefrontal underconnectivity, as well as thalamic-occipital and thalamic-motor overconnectivity in HR infants, relative to LR infants. Subsequent structural connectivity analyses also revealed atypical white matter integrity in thalamic-occipital tracts in HR infants, compared to LR infants. Notably, aberrant rs-fcMRI and DTI connectivity indices at 6 weeks predicted atypical social development between 6 and 36 months of age, as assessed with eye-tracking and diagnostic measures. These findings indicate that thalamocortical connectivity is disrupted at both the functional and structural level in HR infants as early as six weeks of age, providing a possible early marker of risk for ASD.

neuroscience↗

bioRxiv2020

FAM111A regulates replication origin activation and cell fitness

FAM111A is a replisome associated protein and dominant mutations within its trypsin-like peptidase domain are linked to severe human developmental syndromes. However, FAM111A functions and its putative substrates remain largely unknown. Here, we showed that FAM111A promotes origin activation and interacts with the putative peptidase FAM111B, and we identified the first potential FAM111A substrate, the suicide enzyme HMCES. Moreover, unrestrained expression of FAM111A wild-type and patient mutants impaired DNA replication and caused cell death only when the peptidase domain remained intact. Altogether our data reveal how FAM111A promotes DNA replication in normal conditions and becomes harmful in a disease context.

molecular biology↗

bioRxiv2019

Biologically indeterminate yet ordered promiscuous gene expression in single medullary thymic epithelial cells

During thymic negative selection, medullary thymic epithelial cells (mTEC) collectively express most protein coding genes, a process termed promiscuous gene expression (PGE). Although PGE is crucial for inducing central T-cell tolerance, this process has not been established definitively as being either stochastic or coordinated. To resolve this question, we sequenced the transcriptomes of 6,894 single mTEC, including 1,795 rare cells expressing either of two tissue-restricted antigens, TSPAN8 or GP2. Transcriptional heterogeneity allowed partitioning of mTEC into 15 robustly-defined subpopulations representing distinct maturational stages and subtypes. Although 50 gene co-expression groups were robustly identified, few could be explained by chromosomal location, biological pathway, or tissue specificity. Further, GP2+ mTEC were randomly dispersed spatially within medullary islands. Thus although PGE exhibits ordered co-expression, biologically it is indeterminate. This likely enhances the presentation of diverse antigens to passing thymocytes during their medullary residency, while simultaneously maintaining mTEC identity throughout PGE.

immunology↗

bioRxiv2018

Cerox1 and microRNA-488-3p noncoding RNAs jointly regulate mitochondrial complex I catalytic activity

To generate energy efficiently, the cell is uniquely challenged to co-ordinate the abundance of electron transport chain protein subunits expressed from both nuclear and mitochondrial genomes. How an effective stoichiometry of this many constituent subunits is co-ordinated post-transcriptionally remains poorly understood. Here we show that Cerox1, an unusually abundant cytoplasmic long noncoding RNA (lncRNA), modulates the levels of mitochondrial complex I subunit transcripts in a manner that requires binding to microRNA-488-3p. Increased abundance of Cerox1 cooperatively elevates complex I subunit protein abundance and enzymatic activity, decreases reactive oxygen species production, and protects against the complex I inhibitor rotenone. Cerox1 function is conserved across placental mammals: human and mouse orthologues effectively modulate complex I enzymatic activity in mouse and human cells, respectively. Cerox1 is the first lncRNA demonstrated, to our knowledge, to regulate mitochondrial oxidative phosphorylation (OXPHOS) and, with miR-488-3p, represent novel targets for the modulation of complex I activity.

biochemistry↗

bioRxiv2018

Molecularly distinct astrocyte subpopulations spatially pattern the adult mouse brain

Astrocytes are a numerous cell type of the central nervous system. They perform many important functions in synapse formation and maintenance, control of local homeostasis and modulation of synaptic transmission. However, the degree to which specialist astrocyte subtypes fulfil these specific tasks is currently unclear. Here we use single cell transcriptomics to demonstrate that astrocytes, even those lying within the same region of adult mouse brain, show distinct molecular and spatial profiles, with profound implications for local CNS functions, including axon guidance, synaptogenesis and synaptic transmission.

neuroscience↗

bioRxiv2018

Single cell RNA-seq reveals profound transcriptional similarity between Barretts esophagus and esophageal glands

Barretts esophagus is a precursor of esophageal adenocarcinoma. In this common condition, squamous epithelium in the esophagus is replaced by columnar epithelium in response to acid reflux. Barretts esophagus is highly heterogeneous and its relationships to normal tissues are unclear. We investigated the cellular complexity of Barretts esophagus and the upper gastrointestinal tract using RNA-sequencing of 2895 single cells from multiple biopsies from four patients with Barretts esophagus and two patients without esophageal pathology. We found that uncharacterised cell populations in Barretts esophagus, marked by LEFTY1 and OLFM4, exhibit a profound transcriptional overlap with a subset of esophageal cells, but not with gastric or duodenal cells. Additionally, SPINK4 and ITLN1 mark cells that precede morphologically identifiable goblet cells in colon and Barretts esophagus, potentially aiding the identification of metaplasia. Our findings reveal striking transcriptional relationships between normal tissue populations and cells in a premalignant condition, with implications for clinical practice.

genetics↗