Biology subjects

Alexander, K. A.

Publications and source records attributed to Alexander, K. A..

8 recordsLinked to original sources

bioRxiv2026

Expanding the HIF-2α proteomic interactome with TurboID proximity labeling.

The transcription factor HIF2 is a central regulator of cellular adaptation to hypoxia, orchestrating gene expression programs that control angiogenesis, erythropoiesis, and metabolic reprogramming, and is famously overexpressed in cancers such as clear cell Renal Cell Carcinoma (ccRCC). While the gene targets of HIF2 have been extensively characterized, the composition and dynamics of its protein interaction network remain less well defined. In this study, we sought to systematically characterize proteins associated with HIF2 using two distinct proteomic approaches, enabling the identification of both stable binding partners and transient or indirect interactors. We integrated affinity purification mass spectrometry with proximity labeling strategies, thus expanding the existing interactome of HIF2 to include uniquely identified proteins and complexes such as members of the nuclear pore complex. Across both immunoprecipitation mass spectrometry (IP MS) and TurboID MS, we identified 888 and 1,048 proteins, respectively. We applied stringent filtering criteria to refine both datatsets, yielding a dataset of 329 HIF2 interacting proteins, approximately 75% of which have yet to be documented as HIF2 interactors. We queried this set across publicly available cancer genomics and proteomics datasets and detected expression of our interactors in breast cancer and ccRCC tumor proteomes. These findings led us to identify GRHL2 and KIF4A as proteomic interactors that contribute to poor patient survival in breast cancer. Taken together, we herein provide a comprehensive resource of HIF2 interacting proteins which provide insights into the mechanisms by which HIF2 drives disease progression.

biochemistry↗

bioRxiv2026

Endotoxemia and TLR4 via tissue resident macrophages triggers anemia in mouse model of colitis

Anemia is one of the most debilitating and frequent complication of inflammatory bowel diseases (IBD) and is often treated with iron supplementation, which has limited efficacy and causes additional co-morbidities. Damaged intestinal barrier function is a hallmark of IBD and causes the translocation of endotoxins from gut bacteria into the bloodstream. A previous study in mice reported that endotoxins suppress erythropoiesis by reprogramming erythroblastic island macrophages (EBI M{varphi}). Here, we show that IBD patients and mice with acute colitis developed endotoxemia associated with anemia. Endotoxemia in IBD patients was negatively correlated with blood erythrocyte counts. In line with this, mice with acute colitis caused by drinking water containing dextrin sodium sulphate (DSS) had endotoxemia together with anemia characterized by reduced red blood cell counts, hemoglobin content and hematocrit, and reduced medullary erythropoiesis which was in part compensated by increased extramedullary erythropoiesis. As the endotoxin receptor TLR4 is expressed by CD169+ gut-resident macrophages as well as erythroid island macrophages in the bone marrow, we tested the hypothesis that TLR4 expressed by these CD169+ macrophages mediate both inflammatory colitis and anemia. Indeed, mice with a conditional deletion of the Tlr4 gene specifically in CD169+ tissue-resident macrophages were protected from DSS-induced anemia, inflammation and colitis. In addition, treatment with the TLR4 inhibitor C34 abated inflammation and anemia in DSS mice. These results suggest that endotoxins leaking from the inflamed gut may play a crucial role in IBD and associated anemia via CD169+ tissue-resident macrophages and that drugs targeting TLR4 may protect against IBD-associated anemia.

immunology↗

bioRxiv2025

SWING domains prime chromatin for nuclear body mediated gene regulation

Nuclear speckles have long been recognized as RNA-rich nuclear bodies, yet their role in genome organization and gene regulation remains incompletely understood. Using a rapid dTAG-mediated degradation system to simultaneously deplete SON and SRRM2--the core structural components of nuclear speckles--we identify a novel class of genomic regions, which we term SWING regions. Upon speckle disruption, SWING regions relocate to the nuclear periphery and acquire repressive histone marks such as H3K9me3, accompanied by gene downregulation, particularly of genes involved in developmental pathways. Consistent with this, depletion of Lamin A reduces lamina association of SWING regions and enhances their association with nuclear speckles, supporting a bidirectional balance between these two nuclear compartments. Notably, human mutations in SON and SRRM2 are associated with neurodevelopmental disorders characterized by intellectual disability and global developmental delay. Patient-derived cells bearing such mutations similarly exhibit SWING-region relocalization and gene repression, underlining a role for speckles in developmental gene regulation. We also report that drug-induced speckle rejuvenation partially rescues aberrant SWING-region localization to the nuclear lamina in patient-derived cells and iPSCs with acute depletion of SON. These findings identify SWING regions as an intermediate chromatin state positioned between nuclear speckles and the lamina, maintained by opposing functions from both structures. Our work reveals a mechanism underlying the contribution of nuclear bodies to 3D genome organization, highlights the importance of nuclear speckles and SWING regions in developmental regulation, and provides a potential therapeutic intervention in speckle dysfunction. Impact StatementIdentification of nuclear speckles as determinants of specific 3D genome organization. Demonstration of functional interactions between opposing nuclear structures (speckle versus lamina) through SWING regions. Establishment of developmental and human disease relevance of speckle-mediated genome organization. Providing potential avenues for therapeutic intervention in speckleopathies.

genetics↗

bioRxiv2025

Deciphering the role of histone modifications in memory and exhausted CD8 T cells

Exhausted CD8 T cells (TEX) arising during chronic infections and cancer have reduced functional capacity and limited fate flexibility that prevents optimal disease control and response to immunotherapies. Compared to memory (TMEM) cells, TEX have a unique open chromatin landscape underlying a distinct gene expression program. How TEX transcriptional and epigenetic landscapes are regulated through histone post-translational modifications (hPTMs) remains unclear. Here, we profiled key activating (H3K27ac and H3K4me3) and repressive (H3K27me3 and H3K9me3) histone modifications in naive CD8 T cells (TN), TMEM and TEX. We identified H3K27ac-associated super-enhancers that distinguish TN, TMEM and TEX, along with key transcription factor networks predicted to regulate these different transcriptional landscapes. Promoters of some key genes were poised in TN, but activated in TMEM or TEX whereas other genes poised in TN were repressed in TMEM or TEX, indicating that both repression and activation of poised genes may enforce these distinct cell states. Moreover, narrow peaks of repressive H3K9me3 were associated with increased gene expression in TEX, suggesting an atypical role for this modification. These data indicate that beyond chromatin accessibility, hPTMs differentially regulate specific gene expression programs of TEX compared to TMEM through both activating and repressive pathways.

immunology↗

bioRxiv2023

Nuclear speckles regulate HIF-2α programs and correlate with patient survival in kidney cancer

Nuclear speckles are membrane-less bodies within the cell nucleus enriched in RNA biogenesis, processing, and export factors. In this study we investigated speckle phenotype variation in human cancer, finding a reproducible speckle signature, based on RNA expression of speckle-resident proteins, across >20 cancer types. Of these, clear cell renal cell carcinoma (ccRCC) exhibited a clear correlation between the presence of this speckle expression signature, imaging-based speckle phenotype, and clinical outcomes. ccRCC is typified by hyperactivation of the HIF-2 transcription factor, and we demonstrate here that HIF-2 drives physical association of a select subset of its target genes with nuclear speckles. Disruption of HIF-2-driven speckle association via deletion of its speckle targeting motifs (STMs)--defined in this study--led to defective induction of speckle-associating HIF-2 target genes without impacting non-speckle-associating HIF-2 target genes. We further identify the RNA export complex, TREX, as being specifically altered in speckle signature, and knockdown of key TREX component, ALYREF, also compromises speckle-associated gene expression. By integrating tissue culture functional studies with tumor genomic and imaging analysis, we show that HIF-2 gene regulatory programs are impacted by specific manipulation of speckle phenotype and by abrogation of speckle targeting abilities of HIF-2. These findings suggest that, in ccRCC, a key biological function of nuclear speckles is to modulate expression of a specific subset of HIF-2-regulated target genes that, in turn, influence patient outcomes. We also identify STMs in other transcription factors, suggesting that DNA-speckle targeting may be a general mechanism of gene regulation. HIGHLIGHTS- Nuclear speckles shown to reproducibly vary in cancer, predicting patient survival in ccRCC - HIF-2 drives DNA/gene-speckle contacts dependent on identified speckle targeting motifs within HIF-2 - Putative speckle targeting motifs are highly enriched among regulators of gene expression - Partitioning of transcription factor functional programs may be a major biological function of nuclear speckles

cancer biology↗

bioRxiv2022

Coursing hyenas and stalking lions: the potential for inter- and intraspecific interactions

Resource partitioning promotes coexistence among guild members, and carnivores reduce interference competition through behavioural mechanisms that promote spatio-temporal separation. We analyzed sympatric lion and spotted hyena movements and activity patterns to ascertain the mechanisms facilitating their coexistence within semi-arid and wetland ecosystems. We identified recurrent high-use (revisitation) and extended stay (duration) areas within home ranges, and correlated environmental variables with movement-derived measures of inter- and intraspecific interactions. Spatial overlaps among lions and hyenas occurred at edges of home ranges, around water-points, along pathways between patches of high-use areas, and expanded during the wet season. Lions shared more of their home ranges with spotted hyenas in arid ecosystems, but shared more of their ranges with conspecifics in mesic environments. Despite shared space use, we found evidence for subtle temporal differences in the nocturnal movement and activity patterns between the two predators, suggesting a fine localized-scale avoidance strategy. Revisitation frequency and duration within home ranges were influenced by interspecific interactions, subsequent to land cover categories and diel cycles. Intraspecific interactions were also important for lions and, for hyenas, moon illumination and ungulates attracted to former anthrax carcass sites in Etosha, with distance to water in Chobe/Linyanti. Recursion and duration according to locales of competitor probabilities were similar among female lions and both sexes of hyenas, but different for male lions. Our results suggest that lions and spotted hyenas mediate the potential for interference competition through subtle differences in temporal activity, fine-scale habitat use differentiation, and localized reactive-avoidance behaviours. These findings enhance our understanding of the potential effects of interspecific interactions among large carnivore space-use patterns within an apex predator system, and show adaptability across heterogeneous and homogeneous environments. Future conservation plans should emphasize the importance of inter- and intraspecific competition within large carnivore communities, particularly moderating such effects within increasingly fragmented landscapes.

ecology↗

bioRxiv2020

The spatial distributions of pre-mRNAs suggest post-transcriptional splicing of specific introns within endogenous genes

Splicing is the stepwise molecular process by which introns are removed from pre-mRNA and exons are joined together to form mature mRNA sequences. The ordering and spatial distribution of these steps remain controversial, with opposing models suggesting splicing occurs either during or after transcription. We used single-molecule RNA FISH, expansion microscopy, and live-cell imaging to reveal the spatiotemporal distribution of nascent transcripts in mammalian cells. At super-resolution levels, we found that pre-mRNA formed clouds around the transcription site. These clouds indicate the existence of a transcription site proximal zone through which RNA move more slowly than in the nucleoplasm. Full-length pre-mRNA undergo continuous splicing as they move through this zone following transcription, suggesting a model in which splicing can occur post-transcriptionally but still within the proximity of the transcription site, thus seeming co-transcriptional by most assays. These results may unify conflicting reports of co-transcriptional versus post-transcriptional splicing.

cell biology↗

bioRxiv2019

Imprinted gene expression at the Dlk1-Dio3 cluster is controlled by both maternal and paternal IG-DMRs in a tissue-specific fashion.

Imprinting at the Dlk1-Dio3 cluster is controlled by the IG-DMR, an imprinting control region differentially methylated between maternal and paternal chromosomes. The maternal IG-DMR is essential for imprinting control, functioning as a cis enhancer element. Meanwhile, DNA methylation at the paternal IG-DMR is thought to prevent enhancer activity. To explore whether suppression of enhancer activity at the methylated IG-DMR requires the transcriptional repressor TRIM28, we analyzed Trim28chatwo embryos and performed epistatic experiments with IG-DMR deletion mutants. We found that while TRIM28 regulates the enhancer properties of the paternal IG-DMR, it also controls imprinting through other mechanisms. Additionally, we found that the paternal IG-DMR, previously deemed dispensable for imprinting, is required in certain tissues, demonstrating that imprinting is regulated in a tissue-specific manner. Using PRO-seq to analyze nascent transcription, we identified 30 novel transcribed regulatory elements, including 23 that are tissue-specific. These results demonstrate that different tissues have a distinctive regulatory landscape at the Dlk1-Dio3 cluster and provide insight into potential mechanisms of tissue-specific imprinting control. Together, our findings challenge the premise that Dlk1-Dio3 imprinting is regulated through a single mechanism and demonstrate that different tissues use distinct strategies to accomplish imprinted gene expression.

genetics↗