Biology subjects

Davidson, N.

Publications and source records attributed to Davidson, N..

9 recordsLinked to original sources

bioRxiv2026

mRNA editing of the Alzheimer's risk gene APOE

Variants in the human APOE gene govern the risk of Alzheimer's disease and other disorders. Three major APOE variants in humans reflect C to T replacements at two positions in a single exon: an upstream variant (AE4 site) that differs between the ancestral APOE epsilon 4 allele (APOE4) (C) and human-specific APOE2/E3 (T), and a downstream variant (AE2 site) that differentiates APOE3/E4 (C) from APOE2 (T). It has long been assumed that APOE allelotypes are genomically encoded, but here we report that multiple individuals express brain APOE C or U/T variant transcripts that differ from genomically templated versions. We demonstrate up to 10% C to U, or U to C nucleotide replacement at AE4 and AE2, but not at other sites, and with no corresponding changes in genomic DNA. Single-cell transcriptomic datasets from brain microglia revealed sporadic (up to ~8%) C to U replacement at AE2. We found 0.4 to 1.6% of brain transcripts in human APOE knock-in mice harbor selective C to U changes at either AE4 or AE2 sites. Transfection of HepG2 or Huh7 cells with either mouse or human APOBEC1 led to efficient (>90%) C to U editing of APOE4 mRNA at the AE4 but not AE2 site, with lower (<10%) C to T editing of genomic DNA at the AE4 site by mouse, but not human, APOBEC1. Furthermore, interrogation of proteomic datasets revealed up to 4% of non-genomically encoded APOE peptides in human plasma, indicating that the edited APOE transcripts are functional in vivo. These data suggest that APOE mRNA is subject to RNA editing that interconverts the different allelic forms of APOE.

genetics↗

bioRxiv2026

Estrogen receptor-positive cell line xenograft models recapitulate metastatic dissemination and endocrine response of invasive lobular breast carcinoma

HighlightsO_LIER+, CDH1-deficient ILC xenografts recapitulate single-file histology in vivo C_LIO_LISpontaneous metastases faithfully mirror unique ILC clinical dissemination patterns C_LIO_LIER+ leptomeningeal metastases confirmed histologically in ILC xenograft models C_LIO_LIFulvestrant inhibits ILC tumor growth and metastatic burden, improving survival C_LIO_LIER signaling is enriched in ILC brain metastases, with upregulation of RET C_LI Invasive lobular breast carcinoma (ILC), the most common special histological subtype of breast cancer, is characterized by nearly universal expression of estrogen receptor alpha (ER) and unique sites of metastases, neither of which is fully recapitulated by genetically engineered mouse models. Using reporter-labeled ILC mouse xenografts, herein we used mammary fat pad, tail vein and intracardiac orthotopic growth to analyze spontaneous and experimental metastasis and gene expression. We observed ER-positive primary tumors with single-file histology and collagen deposition, and spontaneous metastasis from the mammary fat pad to bones, ovaries, and brain including the leptomeninges, thereby closely mirroring the growth and metastatic spread of human ILC. Brain metastases showed strong ER staining, confirmed by sequencing analyses which identified estrogen signaling as top activated pathway, and the lesions exhibited robust response to endocrine therapy. In summary, we report endocrine responsive mammary fat pad, tail vein and intracardiac xenografts that faithfully demonstrate unique ILC features and can serve as invaluable pre-clinical translational platforms for validating candidate ILC genetic drivers and testing novel therapeutics.

cancer biology↗

bioRxiv2025

Adolescent morphine exposure does not alter low-dose lipopolysaccharide-induced sickness behavior in adult mice

Adolescent opioid use in the United States commands attention: millions of twelve- to nineteen-year-olds are exposed to opioids each year by prescription and misuse. Recent findings show that opioids bind not only to canonical opioid receptors but also interact with receptors on immune cells within both the central and peripheral nervous systems. The potential for early life opioid exposure to induce long-term changes in the neuroimmune system is not fully understood, particularly given the adolescent brains high susceptibility to neuroplastic changes. The goal of this study was to investigate the hypothesis that adolescent opioid use potentiates physiological and behavioral responses to pathogen-induced sickness later in life. To achieve this, we treated adolescent mice (PND 35-42) with bi-daily escalating doses of morphine to model dependence and then administered a low dose of lipopolysaccharide (LPS, 0.1 mg/kg) in adulthood (PND 60-76) to induce an immune response. In contrast to our hypotheses, we found that adolescent morphine exposure had no additive effect on low-dose LPS-induced sickness measures when assessed in adulthood. These data suggest that adolescent opioid exposure may have minimal effects on future immune challenges, although further research is needed to confirm this.

neuroscience↗

bioRxiv2025

Distinct yet Overlapping Functions of VMP1 and TMEM41B in Modulating Hepatic Lipoprotein Secretion and Autophagy in MASH

BackgroundTransmembrane protein 41B (TMEM41B) and vacuolar membrane protein 1 (VMP1) are endoplasmic reticulum (ER) scramblases that shuttle phospholipids between the inner and outer leaflets of the ER membrane. Both TMEM41B and VMP1 also play critical roles in regulating hepatic lipoprotein secretion and autophagy. Despite these similarities, whether TMEM41B and VMP1 exhibit different roles in very low-density lipoprotein (VLDL) secretion and autophagy in the pathogenesis of metabolic-associated steatotic liver disease (MASLD) remains unclear. MethodsWe created liver- and hepatocyte-specific single knockout (KO) and double knockout (DKO) mice for Tmem41b and Vmp1, as well as overexpression knock-in (KI) mice with hepatic overexpression of TMEM41B, Tmem41b KO/Vmp1 KI, and Vmp1 KO/Tmem41b KI. We conducted lipidomic, metabolomic, biochemical, and functional studies in these mice, fed either a chow diet or a MASLD diet. ResultsTMEM41B protein levels were decreased in the livers of human subjects with MASLD. The loss of hepatic Tmem41b impaired VLDL secretion, resulting in steatosis, inflammation, and fibrosis. Vmp1 KO mice exhibited similar phenotypes to DKO mice, displaying a more severe defect in VLDL secretion and greater liver injury than Tmem41b KO mice. Lipidomic analysis revealed decreased levels of phosphatidylcholine and phosphatidylethanolamine, along with increased neutral lipids in both Tmem41b KO and Vmp1 KO mice; however, these changes were generally more pronounced in Vmp1 KO mice. VMP1 and TMEM41B localized at the mitochondrial-associated membrane (MAM), and a reduction in mitochondria-ER contact was observed in hepatocytes deficient in either VMP1 or TMEM41B. Ultrastructural electron microscopy analysis showed increased accumulation of "lipid droplet" in the ER membrane bilayer and ER lumen in both Vmp1 KO and Tmem41b KO hepatocytes, with greater ER luminal "lipid droplet" accumulation in Tmem41b KO hepatocytes. The loss of hepatic Vmp1 or Tmem41b led to elevated levels of LC3-II and p62, with significantly higher levels of both markers in Vmp1 KO and DKO mouse livers compared to Tmem41b KO mouse livers. Restoring Vmp1 in Tmem41b KO mice partially improved defective VLDL secretion; however, high expression levels of VMP1 did not correct the hepatic autophagy defect. In contrast, restoring Tmem41b in Vmp1 KO mice dose-dependently enhanced both defective VLDL secretion and autophagy. Importantly, overexpression of hepatic TMEM41B mitigated diet-induced MASLD in mice. ConclusionThe loss of hepatic Vmp1 or Tmem41b decreases hepatic MAM and phospholipid content, leading to decreased VLDL secretion and promoting MASLD. While VMP1 and TMEM41B have overlapping functions, VMP1 appears to play a more critical role in regulating VLDL secretion and autophagy in mouse livers than TMEM41B.

cell biology↗

bioRxiv2024

Targeting Diffuse Midline Glioma with a novel anti-CD99 Antibody

Diffuse midline gliomas (DMGs) are devastating brain tumors that occur primarily in children. The salient feature of these tumors is the presence of a H3K27M mutation (K27M), associated with the worst prognosis. We identified the cell surface antigen CD99 as notably expressed in DMGs, particularly in K27M+DMGs. We found that the increased expression of CD99 in K27M+DMGs was a result of the onco-histone K27M mutation. In K27M+DMG cells, CD99 inactivation impaired tumor growth by inducing cell differentiation, indicating an oncogenic role of CD99 enabled by blocking differentiation. We then developed a novel therapeutic anti-CD99 chimeric antibody, 10D1, with a membrane-proximal binding epitope, and evaluated its antitumor efficacy in preclinical models of K27M+DMG. 10D1 suppressed DMG growth in vitro and in vivo by inducing apoptosis. When combined with radiation treatment, 10D1 exhibited improved antitumor efficiency and xenograft survival, providing a strong justification for its clinical development as a therapy for DMGs. Statement of SignificanceThis study emphasizes that CD99 overexpression occurs due to the H3K27M mutation in Diffuse Midline Gliomas (DMGs). This heightened expression suppresses apoptosis, inhibits differentiation, and induces radio-resistance in DMGs. This research justifies using a novel CD99 antibody alone or combined with radiation therapy in human pediatric clinical trials.

cancer biology↗

bioRxiv2021

A systematic benchmark of Nanopore long read RNA sequencing for transcript level analysis in human cell lines

The human genome contains more than 200,000 gene isoforms. However, different isoforms can be highly similar, and with an average length of 1.5kb remain difficult to study with short read sequencing. To systematically evaluate the ability to study the transcriptome at a resolution of individual isoforms we profiled 5 human cell lines with short read cDNA sequencing and Nanopore long read direct RNA, amplification-free direct cDNA, PCR-cDNA sequencing. The long read protocols showed a high level of consistency, with amplification-free RNA and cDNA sequencing being most similar. While short and long reads generated comparable gene expression estimates, they differed substantially for individual isoforms. We find that increased read length improves read-to-transcript assignment, identifies interactions between alternative promoters and splicing, enables the discovery of novel transcripts from repetitive regions, facilitates the quantification of full-length fusion isoforms and enables the simultaneous profiling of m6A RNA modifications when RNA is sequenced directly. Our study demonstrates the advantage of long read RNA sequencing and provides a comprehensive resource that will enable the development and benchmarking of computational methods for profiling complex transcriptional events at isoform-level resolution.

genomics↗

bioRxiv2021

APOBEC1 mediated C-to-U RNA editing: target sequence and trans-acting factor contribution to 177 RNA editing events in 119 murine transcripts in-vivo

Mammalian C-to-U RNA editing was described more than 30 years ago as a single nucleotide modification in APOB RNA in small intestine, later shown to be mediated by the RNA-specific cytidine deaminase APOBEC1. Reports of other examples of C-to-U RNA editing, coupled with the advent of genome-wide transcriptome sequencing, identified an expanded range of APOBEC1 targets. Here we analyze the cis-acting regulatory components of verified murine C-to-U RNA editing targets, including nearest neighbor as well as flanking sequence requirements and folding predictions. We summarize findings demonstrating the relative importance of trans-acting factors (A1CF, RBM47) acting in concert with APOBEC1. Using this information, we developed a multivariable linear regression model to predict APOBEC1 dependent C-to-U RNA editing efficiency, incorporating factors independently associated with editing frequencies based on 103 Sanger-confirmed editing sites, which accounted for 84% of the observed variance. Co-factor dominance was associated with editing frequency, with RNAs targeted by both RBM47 and A1CF observed to be edited at a lower frequency than RBM47 dominant targets. The model also predicted a composite score for available human C-to-U RNA targets, which again correlated with editing frequency.

bioinformatics↗

bioRxiv2019

Characterization of HIF-dependent alternative isoforms in pancreatic cancer

Intra-tumor hypoxia is a common feature in many solid cancers. Although transcriptional targets of hypoxia-inducible factors (HIFs) have been well characterized, alternative splicing or processing of pre-mRNA transcripts which occurs during hypoxia and subsequent HIF stabilization is much less understood. Here, we identify HIF-dependent alternative splicing events after whole transcriptome sequencing in pancreatic cancer cells exposed to hypoxia with and without downregulation of the aryl hydrocarbon receptor nuclear translocator (ARNT), a protein required for HIFs to form a transcriptionally active dimer. We correlate the discovered hypoxia-driven events with available sequencing data from pan-cancer TCGA patient cohorts to select a narrow set of putative biologically relevant splice events for experimental validation. We validate a small set of candidate HIF-dependent alternative splicing events in multiple human cancer cell lines as well as patient-derived human pancreatic cancer organoids. Lastly, we report the discovery of a HIF-dependent mechanism to produce a hypoxia-dependent, long and coding isoform of the UDP-N-acetylglucosamine transporter SLC35A3.

cell biology↗

bioRxiv2018

Fast and accurate differential transcript usage by testing equivalence class counts

RNA sequencing has enabled high-throughput and fine-grained quantitative analyses of the transcriptome. While differential gene expression is the most widely used application of this technology, RNA-seq data also has the resolution to infer differential transcript usage (DTU), which can elucidate the role of different transcript isoforms between experimental conditions, cell types or tissues. DTU has typically been inferred from exon-count data, which has issues with assigning reads unambiguously to counting bins, and requires alignment of reads to the genome. Recently, approaches have emerged that use transcript quantifications estimates directly for DTU. Transcript counts can be inferred from pseudo or lightweight aligners, which are significantly faster than traditional genome alignment. However, recent evaluations show lower sensitivity in DTU analysis. Transcript abundances are estimated from equivalence classes (ECs), which determine the transcripts that any given read is compatible with. Here we propose performing DTU testing directly on equivalence class read counts. We evaluate this approach on simulated human and drosophila data, as well as on a real dataset through subset testing. We find that ECs counts have similar sensitivity and false discovery rates as exon-level counts but can be generated in a fraction of the time through the use of pseudo-aligners. We posit that equivalent class counts is a natural unit on which to perform many types of analysis.

bioinformatics↗