Biology subjects

Lee, H. O.

Publications and source records attributed to Lee, H. O..

8 recordsLinked to original sources

bioRxiv2026

Subnuclear cofactor partitioning underlies auxin-dependent transcriptional regulation

Cellular and organismal function relies on the precise activation and repression of gene expression by DNA-binding transcription factors (TFs). Many TFs occur in large gene families, and a key question in biology is how divergent functions emerge in TF families during evolution. Here we discover the biochemical mechanism for transcriptional activation by the Marchantia polymorpha AUXIN RESPONSE FACTOR1 (MpARF1) TF, which relies on direct recruitment of the Mediator complex into subnuclear MpARF1 clusters. We find that the Mediator recruitment region was the evolutionary innovation that converted ARF repressors into activators, switching binding specificity from co-repressor to co-activator. We demonstrate that this evolutionary innovation can be recreated, thereby revealing a deeply conserved mechanism based on competition between ARF clusters at the heart of the transcriptional auxin response.

plant biology↗

bioRxiv2025

Long-read proteogenomic atlas of human neuronal differentiation reveals isoform diversity informing neurodevelopmental risk mechanisms

RNA splicing shapes neuronal identity and disease risk, yet current maps lack the developmental resolution and depth to resolve this complexity. Here, we integrate deep long-read RNA sequencing and proteomics in iPSC-derived cortical neurons to generate a high-resolution proteogenomic atlas of human neuron development. We identify 182,371 mRNA isoforms (over half previously unknown) and provide direct peptide evidence for the translation of hundreds of novel protein-coding sequences. Population genetics demonstrates that variants affecting novel exons and splice sites are under negative selection, underscoring the potential significance of these isoforms. During neuronal maturation, we observe that ASD risk genes undergo dynamic isoform switching, including microexon inclusion and intron retention, that remodel key protein domains and regulatory regions. Furthermore, we uncover widespread, long-range coordination between splicing and polyadenylation. Finally, our atlas enables variant reinterpretation in ASD, highlighting the value of an isoform-centric view for interpreting pathogenic variation in neurodevelopment.

bioinformatics↗

bioRxiv2024

Cytoplasmic protein-free mRNA induces stress granules by two G3BP1/2-dependent mechanisms

Stress granules are cytoplasmic membraneless organelles that sequester proteins and non-translating mRNAs in response to various stressors. To assess the contributions of mRNA and RNA-binding proteins to stress granule formation, we use microinjection to deliver protein-free mRNA into the cytoplasm in a controlled manner. We demonstrate that mRNAs trigger stress granule formation through two mechanisms that are enhanced by the presence of G3BP1 and G3BP2. Low concentrations of in vitro transcribed mRNA activated protein kinase R (PKR), leading to phosphorylation and inhibition of the eukaryotic translation initiation factor eIF2 and stress granule formation. This was inhibited by replacing uridine with pseudouridine in the mRNA or by treating it with RNase III, which cleaves double-stranded RNA. High concentrations of mRNA triggered stress granule formation by a mechanism that was independent of PKR and enhanced by G3BP1/2, highlighting the importance of both protein-free mRNA and RNA-binding proteins in stress granule formation. Graphical Abstract/Model O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=197 SRC="FIGDIR/small/578830v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1b1bcfeorg.highwire.dtl.DTLVardef@1eee33corg.highwire.dtl.DTLVardef@888c9forg.highwire.dtl.DTLVardef@c835aa_HPS_FORMAT_FIGEXP M_FIG C_FIG SummaryMicroinjected mRNA induces stress granules in mammalian cells by two G3BP1/2-dependent mechanisms: one requires the stress-sensing protein kinase PKR to phosphorylate the translation initiation factor eIF2, and the other is independent of PKR and phospho-eIF2 and acts when the cytoplasmic concentration of ribosome-free mRNA is increased acutely.

cell biology↗

bioRxiv2024

PARP1 condensates differentially partition DNA repair proteins and enhance DNA ligation

Poly(ADP-ribose) polymerase 1 (PARP1) is one of the first responders to DNA damage and plays crucial roles in recruiting DNA repair proteins through its activity - poly(ADP-ribosyl)ation (PARylation). The enrichment of DNA repair proteins at sites of DNA damage has been described as the formation of a biomolecular condensate. However, it is not understood how PARP1 and PARylation contribute to the formation and organization of DNA repair condensates. Using recombinant human PARP1 in vitro, we find that PARP1 readily forms viscous biomolecular condensates in a DNA-dependent manner and that this depends on its three zinc finger (ZnF) domains. PARylation enhances PARP1 condensation in a PAR chain-length dependent manner and increases the internal dynamics of PARP1 condensates. DNA and single-strand break repair proteins XRCC1, LigIII, Pol{beta}, and FUS partition in PARP1 condensates, although in different patterns. While Pol{beta} and FUS are both homogeneously mixed within PARP1 condensates, FUS enrichment is greatly enhanced upon PARylation whereas Pol{beta} partitioning is not. XRCC1 and LigIII display an inhomogeneous organization within PARP1 condensates; their enrichment in these multiphase condensates is enhanced by PARylation. Functionally, PARP1 condensates concentrate short DNA fragments and facilitate compaction of long DNA and bridge DNA ends. Furthermore, the presence of PARP1 condensates significantly promotes DNA ligation upon PARylation. These findings provide insight into how PARP1 condensation and PARylation regulate the assembly and biochemical activities in DNA repair foci, which may inform on how PARPs function in other PAR-driven condensates.

biochemistry↗

bioRxiv2023

BrainRBPedia: a resource for RNA-binding proteins relevant to neurodevelopmental disorders

RNA-binding proteins (RBPs) are crucial players in the post-transcriptional regulation of mRNA and play major roles in ensuring proper neuronal development and function. Deficits in RBP function have been implicated in a number of neurodevelopmental disorders including autism spectrum disorder (ASD) and intellectual disability (ID), yet we lack resources that integrate current knowledge of RBP function, tissue expression, and disease association in one place to aid in their experimental characterization. Here we introduce BrainRBPedia - a database of 1072 RBPs with both disease annotations for neurodevelopmental disorders and functional annotations relevant to these disorders, including loss-of-function intolerance and expression specificity to the brain, neurons, and neuronal development. Using these functional annotations, we develop a machine learning model to prioritize RBPs likely to be involved in ASD and ID. Our model indicates that RBPs with high loss-of-function intolerance and those upregulated during neuronal differentiation are disproportionately likely to contribute to ASD and ID etiology. In summary, BrainRBPedia comprises a unique resource for researchers interested in the experimental characterization of RBPs in relation to neurodevelopmental disorders and suggests functional signatures of RBPs likely to play a role in neurodevelopment.

bioinformatics↗

bioRxiv2021

O-GlcNAcylation reduces phase separation and aggregation of the EWS N-terminal low complexity region

Many membraneless organelles are thought to be biomolecular condensates formed by phase separation of proteins and other biopolymers. Post-translational modifications (PTMs) can impact protein phase separation behavior, although for many PTMs this aspect of their function is unknown. O-linked {beta}-D-N-acetylglucosaminylation (O-GlcNAcylation) is an abundant form of intracellular glycosylation whose roles in regulating biomolecular condensate assembly and dynamics have not been delineated. Using an in vitro approach, we found that O-GlcNAcylation reduces the phase separation propensity of the EWS N-terminal low complexity region (LCRN) under different conditions, including in the presence of the arginine-and glycine-rich RNA-binding domains (RBD). O-GlcNAcylation enhances fluorescence recovery after photobleaching (FRAP) within EWS LCRN condensates and causes the droplets to exhibit more liquid-like relaxation following fusion. Following extended incubation times, EWS LCRN+RBD condensates exhibit diminished FRAP, indicating a loss of fluidity, while condensates containing the O-GlcNAcylated LCRN do not. In HeLa cells, EWS is less O-GlcNAcylated following OGT knockdown and more prone to aggregation based on a filter retardation assay. Relative to the human proteome, O-GlcNAcylated proteins are enriched with regions that are predicted to phase separate, suggesting a general role of O-GlcNAcylation in regulation of biomolecular condensates. Insert Table of Contents artwork here O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/443654v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@a09fb6org.highwire.dtl.DTLVardef@1556f47org.highwire.dtl.DTLVardef@1fcd76borg.highwire.dtl.DTLVardef@a2dbda_HPS_FORMAT_FIGEXP M_FIG C_FIG For Table of Contents only.

biochemistry↗

bioRxiv2019

DNA repair by Rad52 liquid droplets

Cellular processes are influenced by liquid phase separation, but its role in DNA repair is unclear. Here, we show that in Saccharomyces cerevisiae, Rad52 DNA repair proteins at different DNA damage sites assemble liquid droplets that fuse into a repair centre droplet. This larger droplet concentrates tubulin and projects short aster-like microtubule filaments, which tether the droplet to longer microtubule filaments mediating the mobilization of damaged DNA to the nuclear periphery for repair.

molecular biology↗

bioRxiv2019

Small molecules for modulating protein driven liquid-liquid phase separation in treating neurodegenerative disease

Neurodegenerave diseases such as amyotrophic lateral sclerosis (ALS) are oten associated with mutaons in proteins that are associated with stress granules. Stress granules are condensates formed by liquid-liquid phase separaon which, when aberrant, can lead to altered condensaon behaviours and disease phenotypes. Here, we identified lipoamide, a small molecule which specifically prevents cytoplasmic condensaon of stress granule proteins. Thermal proteome profiling showed that lipoamide preferentially stabilises intrinsically disordered domain-containing proteins. These include SRSF1 and SFPQ, stress granule proteins necessary for lipoamide activity. The redox state of SFPQ correlates with its condensate-dissolving behaviour, in concordance with the importance of the dithiolane ring for lipoamide activity. In animals, lipoamide ameliorates aging-associated aggregaon of a stress granule reporter, improves neuronal morphology, and recovers motor defects caused by expression of ALS-associated FUS and TDP-43 mutants. In conclusion, lipoamide is a well-tolerated small molecule modulator of stress granule condensaon and dissection of its molecular mechanism identified a cellular pathway for redox regulaon of stress granule formaon.

cell biology↗