Biology subjects

Ryoo, H. D.

Publications and source records attributed to Ryoo, H. D..

8 recordsLinked to original sources

bioRxiv2026

Pathological tau leads to network hyperexcitability through neuronal-subtype-specific functional impairment

Pathological tau disrupts neuronal activity and brain function in Alzheimer s disease and other tauopathies. However, the underlying mechanisms for neuronal network dysfunction remain largely unknown. Using human inducible pluripotent stem cell (iPSC) - derived neurons, we show that the familial MAPT P301L mutation leads to neuronal network hyperexcitability. Imbalanced excitation and inhibition were attributable to neuronal subtype-specific tau pathology that was associated with different alterations of tau interactomes in excitatory versus inhibitory neurons. Suppressing enhanced excitatory synaptic transmission or blocking Ca2+ influx resulting from enhanced P301L tau/AHNAK interaction in inhibitory neurons rescued the neuronal network hyperexcitability. This study expands our understanding on how disease-causing tau mutations alter the excitatory/inhibitory balance, leading to network dysfunction in human neurons.

neuroscience↗

bioRxiv2026

A single-domain antibody targets aggregation-prone region of α-synuclein to reduce synucleinopathy, rescue neurodegeneration and improve function

Synucleinopathies are a group of neurodegenerative disorders characterized by the accumulation of aggregated -synuclein (-syn), including Parkinsons disease, Dementia with Lewy Bodies, and Multiple System Atrophy. These diseases are marked by locomotor and non-motor impairments, as well as mitochondrial dysfunction and the loss of dopaminergic (DA) neurons. We have developed several anti--syn single-domain antibodies (sdAbs) and demonstrated the diagnostic imaging potential of two of them and the acute therapeutic benefit of one in clearing -syn in a mouse model. However, whether these sdAbs can suppress -syn-mediated neuronal loss and locomotor impairment in vivo remains unclear. We evaluated the therapeutic potential of five anti--syn sdAbs to clear pathological -syn in mouse neuronal culture and then demonstrated their in vivo efficacy in a Drosophila model of synucleinopathy. The sdAbs differed in their efficacy to lower levels of phospho-serine 129 -syn, prevent loss of DA neurons, alleviate mitochondrial dysfunction, improve motor function, and prolong survival in synucleinopathy flies. The most effective sdAb, 2H1, has not been reported before. It binds strongly to the aggregation prone region of -syn and robustly improves all these disease parameters. Additionally, that sdAb is associated with -syn in the fly neurons, as shown through proximity dependent turboID biotinylation assays. The sdAb-turboID also biotinylated -syn-associated proteins involved in synapse/vesicle trafficking pathways, pinpointing the location of their intracellular interaction. Our findings provide an insight into the therapeutic mechanism of action of these sdAbs and strongly support their clinical development.

neuroscience↗

bioRxiv2026

NECAP antagonizes light-induced Rhodopsin-1 internalization to promote photoreceptor homeostasis

AP-2 is a key mediator of clathrin-mediated endocytosis (CME) that internalizes cargo from the plasma membrane. NECAP proteins physically bind phosphorylated AP-2 during CME, but their roles during endocytosis remain unresolved, with conflicting reports about their function. Here, we report that Drosophila NECAP is dispensable for development, but antagonizes light-dependent Rhodopsin-1 (Rh1) internalization, a process that occurs through AP-2-mediated endocytosis. Specifically, loss of Drosophila NECAP causes excessive light-dependent Rh1 internalization and an age-related retinal degeneration that can be rescued by photoreceptor-specific expression of a wild-type transgenic NECAP. A Drosophila NECAP mutant transgene, equivalent to a canine NECAP1 variant associated with retinal atrophy, failed to rescue the NECAP loss-of-function phenotype in the eye. Furthermore, overexpression of wild-type NECAP suppressed massive Rh1 internalization in a distinct Drosophila model of light-dependent Rh1 endocytosis and retinal degeneration. These results establish NECAP as a negative regulator of light-dependent Rh1 internalization essential for photoreceptor survival.

cell biology↗

bioRxiv2021

The Transcription Factor Xrp1 is Required for PERK-Mediated Antioxidant Gene Induction in Drosophila

PERK is an endoplasmic reticulum (ER) transmembrane sensor that phosphorylates eIF2 to initiate the Unfolded Protein Response (UPR). eIF2 phosphorylation promotes stress-responsive gene expression most notably through the transcription factor ATF4 that contains a regulatory 5 leader. Possible PERK effectors other than ATF4 remain poorly understood. Here, we report that the bZIP transcription factor Xrp1 is required for ATF4-independent PERK signaling. Cell type-specific gene expression profiling in Drosophila indicated that delta-family glutathione-S-transferases (gstD) are prominently induced by the UPR-activating transgene Rh1G69D. Perk was necessary and sufficient for such gstD induction, but ATF4 was not required. Instead, Perk and other regulators of eIF2 phosphorylation regulated Xrp1 protein levels to induce gstDs. The Xrp1 5 leader has a conserved upstream Open Reading Frame (uORF) analogous to those that regulate ATF4 translation. The gstD-GFP reporter induction required putative Xrp1 binding sites. These results indicate that antioxidant genes are highly induced by a previously unrecognized UPR signaling axis consisting of PERK and Xrp1.

cell biology↗

bioRxiv2021

A protein-trap allele reveals roles for Drosophila ATF4 in photoreceptor degeneration, oocyte maturation and wing development

Metazoans have evolved various stress response mechanisms to cope with cellular stress inflicted by external and physiological conditions. The Integrated Stress Response (ISR) is an evolutionarily conserved pathway that mediates adaptation to cellular stress via the transcription factor, ATF4. Loss of function of Drosophila ATF4, encoded by the gene cryptocephal (crc), results in lethality during pupal development. The roles of crc in Drosophila disease models and adult tissue homeostasis thus remain poorly understood. Here, we report that a protein-trap MiMIC insertion in the crc locus generates a crc-GFP fusion protein that allows visualization of crc activity in vivo, and acts as a hypomorphic mutant that uncovers previously unknown roles for crc. Specifically, the crc protein-trap line shows crc-GFP induction in a Drosophila model for Retinitis Pigmentosa (RP). This crc allele renders photoreceptors more vulnerable to age-dependent retinal degeneration. crc mutant adult animals also show greater susceptibility to amino acid deprivation and reduced levels of known crc transcriptional targets. Furthermore, this mutant allele shows defects in wing veins and oocyte maturation, uncovering previously unknown roles for crc in the development of these tissues. Together, our data establish physiological and pathological functions of crc-mediated ISR in adult Drosophila tissues.

genetics↗

bioRxiv2021

Drosophila fabp is a retinoid-inducible gene required for Rhodopsin-1 homeostasis and photoreceptor survival

Retinoids act as chromophore co-factors for light-detecting rhodopsin proteins. In vertebrates, retinoids also actively regulate gene expression. Whether retinoids regulate gene expression in Drosophila for a specific biological function remains unclear. Here, we report that Drosophila fatty acid binding protein (fabp) is a retinoid-inducible gene required for Rhodopsin-1 (Rh1) protein homeostasis and photoreceptor survival. Specifically, we performed a photoreceptor-specific gene expression profiling study in flies bearing a misfolding-prone Rhodopsin-1 (Rh1) mutant, ninaEG69D, which serves as a Drosophila model for Retinitis Pigmentosa. ninaEG69D photoreceptors showed increased expression of genes that control Rh1 protein levels, along with a poorly characterized gene, fabp. We found that in vivo fabp expression was reduced when the retinoids were deprived through independent methods. Conversely, fabp mRNA was induced when we challenged cultured Drosophila cells with retinoic acid. In flies reared under light, loss of fabp caused an accumulation of Rh1 proteins in cytoplasmic vesicles. fabp mutants exhibited light-dependent retinal degeneration, a phenotype also found in other mutants that block light-activated Rh1 degradation. These observations indicate that a retinoid-inducible gene expression program regulates fabp that is required for Rh1 proteostasis and photoreceptor survival. Author SummaryRhodopsins are light-detecting proteins that use retinoids as chromophore co-factors. In vertebrates, retinoids also actively regulate gene expression. Whether retinoids regulate Rhodopsin function aside from its role as a chromophore remains unclear. Here, we report that Drosophila fatty acid binding protein (fabp) is a retinoid-inducible gene required for Rhodopsin-1 (Rh1) protein homeostasis and photoreceptor survival. Specifically, we found that fabp is among the genes induced by a misfolding-prone Rhodopsin-1 (Rh1) mutant, ninaEG69D, which serves as a Drosophila model for Retinitis Pigmentosa. We further found that fabp induction in ninaEG69D photoreceptors required retinoids. fabp was required in photoreceptors to help degrade light-activated Rh1. In the absence of fabp, Rh1 accumulated in cytoplasmic vesicles in a light-dependent manner, and exhibited light-dependent retinal degeneration. These observations indicate that a retinoid-inducible gene expression program regulates fabp that is required for Rh1 proteostasis and photoreceptor survival.

cell biology↗

bioRxiv2017

highroad is induced by retinoids and clears mutant Rhodopsin-1 in Drosophila Retinitis Pigmentosa models.

The light detecting protein, Rhodopsin, requires retinoid chromophores for their function. In vertebrates, retinoids also serve as signaling molecules, but whether these molecules similarly regulate gene expression in Drosophila remains unclear. Here, we report the identification of a retinoid-inducible gene in Drosophila, highroad, which is required for photoreceptors to clear folding-defective mutant Rhodopsin-1 proteins. Specifically, we identified highroad through an in vivo RNAi based genetic interaction screen with one such folding defective Rhodopsin-1 mutant, ninaEG69D. CRISPR-Cas9-mediated deletion of highroad results in the stabilization of folding-defective mutant Rhodopsin-1 proteins, and acceleration of the age-related retinal degeneration phenotype of ninaEG69D mutants. Elevated highroad transcript levels are detected ninaEG69D flies, and interestingly, deprivation of retinoids in the fly diet blocks this effect. Consistently, mutations in the retinoid transporter santa maria impairs the induction of highroad in ninaEG69D flies. In cultured S2 cells, highroad expression is induced by retinoic acid treatment. These results indicate that cellular quality control mechanism against misfolded Rhodopsin-1 involves regulation of gene expression by retinoids.

genetics↗

bioRxiv2017

The integrated stress response pathway activates 4E-BP to bias mRNA translation and boost antimicrobial peptide synthesis in response to bacterial infection

Pathogenic bacterial infection imposes considerable cellular stress on the host and often leads to attenuation of mRNA translation. In this translation-suppressive environment, it is unclear how the host synthesizes various antimicrobial peptides (AMPs) to mount innate immune response. Here, we use Drosophila as a model to demonstrate that AMP production during infection relies on a translation bias mechanism mediated by the inhibitor of cap-dependent translation 4E-BP (Drosophila Thor), and the AMP 5UTRs that can undergo cap-independent translation. We found that 4E-BP is induced upon infection with the pathogenic bacteria Ecc15 by the stress-responsive transcription factor ATF4, and its upstream kinase GCN2. Moreover, loss of gcn2, atf4 or 4e-bp compromised immunity against Ecc15. In 4E-BP mutants, the transcriptional induction of AMPs after infection was unaffected, while the protein levels of AMPs were substantially reduced in their hemolymph. Analysis of the 5UTRs of AMPs using cell-based bicistronic reporters and in vitro translation analysis indicated that AMPs are translated in a cap-independent mechanism. Analysis of bicistronic reporters in the presence of 4E-BP indicate that infection enhances cap-independent translational activity associated with AMP 5UTRs, accounting for enhanced AMP translation during infection.\n\nHighlights O_LI4E-BP is transcriptionally induced by GCN2/ATF signaling in response to bacterial infection\nC_LIO_LI4E-BP mutants show unaltered antimicrobial peptide (AMP) transcript levels, but have reduced AMP translation\nC_LIO_LIAMP 5UTRs are translated cap-independently\nC_LIO_LITranslation bias by 4E-BP drives cap-independent AMP translation\nC_LI

immunology↗