Biology subjects

Osaka, J.

Publications and source records attributed to Osaka, J..

6 recordsLinked to original sources

bioRxiv2026

PCP-dependent polarity propagation across neuronal columns in the Drosophila medulla

Planar cell polarity (PCP) signaling establishes coordinated tissue polarity through asymmetric localization of core PCP factors and propagation of polarity information between neighboring cells. While PCP mechanisms are well characterized in continuous epithelial tissues, whether PCP-dependent polarity propagation can operate across discontinuous neuronal structures remains unclear. During pupal development of the Drosophila medulla, R8 photoreceptor axon terminals transiently form horseshoe-shaped structures whose orientation reflects neuronal column polarity. Here, we show that Frizzled (Fz) progressively becomes asymmetrically localized within developing horseshoe structures, whereas Van Gogh (Vang) transiently accumulates in adjacent glial cells during early developmental stages. Conditional disruption of Vang in glial cells impaired asymmetric Fz localization and disrupted horseshoe orientation polarity. Glial Vang localization preceded the emergence of robust Fz asymmetry, suggesting that glial Vang functions during an early polarity establishment phase. Furthermore, mosaic knockdown of fz in R8 neurons altered Fz localization in neighboring R8 terminals, suggesting local propagation of polarity information between adjacent neuronal columns. Together, our results suggest that PCP-dependent polarity propagation operates across discontinuous neuronal columns in the developing medulla and provide a framework for understanding coordinated polarity formation in neural tissues lacking continuous epithelial organization.

developmental biology↗

bioRxiv2025

NADPH phosphatase activity of Mesh1 controls sleep in Drosophila

Recent findings have shown that metazoans accumulate the bacterial second messenger guanosine tetraphosphate (ppGpp) and possess Mesh1, a gene encoding a ppGpp hydrolase domain. Mesh1 deficiency affects sleep behavior and eclosion under starvation in Drosopila, and ferroptosis in human cells. However, human Mesh1 also exhibits NADPH/NADP+ phosphatase activity in vitro, making it unclear whether these phenotypes result from loss of ppGpp hydrolysis, NADPH/NADP+ dephosphorylation, or both. To address this, we performed biochemical and genetic analysis of Drosophila Mesh1. We first found that Drosophila Mesh1 dephosphorylates NADPH, but not NADP+, in vitro. We subsequently sought to generate Drosophila Mesh1 point mutants specifically impaired in NADPH phosphatase activity. Based on structural data, we mutated W138 and R142, residues that are predicted to interact with NADPH but not ppGpp. W138 was replaced with phenylalanine results in complete loss of NADPH phosphatase activity with retained ppGpp hydrolase activity. Flies carrying the W138F mutation, introduced via genome editing, exhibited shortened total sleep and increased sleep fragmentation in behavioral assays, without changes in intracellular ppGpp levels. These results indicate that the NADPH phosphatase activity of Mesh1, and specifically the W138 residue, is essential for normal sleep regulation in Drosophila.

molecular biology↗

bioRxiv2025

An Innate Immune Receptor Toll-1 converts chronic light stress into glial phagocytosis

Chronic stress can cause progressive neuronal degeneration, yet the molecular mechanisms linking stress sensing to neuroimmune responses remain elusive. In this study, using a Drosophila model of chronic light-induced stress, we show that photoreceptor neurons accumulate reactive oxygen species (ROS) and exhibit Toll-1 activation which involves Spatzle ligands and receptor endocytosis. Toll-1 activation in neurons promotes axonal degeneration by inducing expression of the glial phagocytic receptor Draper (Drpr), leading to the engulfment of stressed axons. Genetic interaction analyses indicate that Toll-1 functions upstream of Drpr in a stress-responsive signaling cascade. Blocking either Toll-1 or Drpr attenuates axon loss under light stress, while Toll-1 overexpression exacerbates it. Toll-1 also plays a similar pro-degenerative role in an activity-dependent olfactory neuron degeneration paradigm, pointing to a broader role for this mechanism in neural degeneration. Together, these findings identify a neuron-glia signaling axis that converts sustained stress into structural degeneration.

neuroscience↗

bioRxiv2023

Complex Formation of Immunoglobulin Superfamily Molecules Side-IV and Beat-IIb Regulates Synaptic Specificity in the Drosophila Visual System

Neurons establish specific synapses based on the adhesive properties of cell-surface proteins, while also retaining the ability to form synapses in a relatively non-selective manner. However, the comprehensive understanding of the underlying mechanism reconciling these opposing characteristics remains incomplete. Here, we have identified Side-IV/Beat-IIb, members of the Drosophila immunoglobulin superfamily, as a novel combination of cell-surface recognition molecules inducing synapse formation. The Side-IV/Beat-IIb combination transduces bifurcated signaling with Side-IVs co-receptor, Kirre, and a synaptic scaffold protein, Dsyd-1. Genetic experiments and subcellular protein localization analyses showed the newly characterized Side-IV/Beat-IIb/Kirre/Dsyd-1 complex to have two essential functions. First, it narrows neuronal binding specificity through Side-IV/Beat-IIb extracellular interactions. Second, it recruits synapse formation factors, Kirre and Dsyd-1, to restrict synaptic loci and inhibit miswiring. This dual function explains how the combinations of cell-surface molecules enable the ranking of preferred interactions among neuronal pairs to achieve synaptic specificity in complex circuits in vivo.

neuroscience↗

bioRxiv2023

Drosophila model to clarify the pathological significance of OPA1 in autosomal dominant optic atrophy

Autosomal dominant optic atrophy (DOA) is a progressive form of blindness caused by degeneration of retinal ganglion cells and their axons, mainly caused by mutations in the OPA1 mitochondrial dynamin like GTPase (OPA1) gene. OPA1 encodes a dynamin-like GTPase present in the mitochondrial inner membrane. When associated with OPA1 mutations, DOA can present not only ocular symptoms but also multi-organ symptoms (DOA plus). DOA plus often results from point mutations in the GTPase domain, which are assumed to have dominant negative effects. However, the presence of mutations in the GTPase domain does not always result in DOA plus. Therefore, an experimental system to distinguish between DOA and DOA plus is needed. In this study, we found that loss-of-function mutations of the dOPA1 gene in Drosophila can imitate the pathology of optic nerve degeneration observed in DOA. We successfully rescued this degeneration by expressing the human OPA1 (hOPA1) gene, indicating that hOPA1 is functionally interchangeable with dOPA1 in the fly system. However, mutations previously identified did not ameliorate the dOPA1 deficiency phenotype. By expressing both WT and DOA plus mutant hOPA1 forms in the optic nerve of dOPA1 mutants, we observed that DOA plus mutations suppressed the rescue, facilitating the distinction between loss-of-function and dominant negative mutations in hOPA1. This fly model aids in distinguishing DOA from DOA plus and guides initial hOPA1 mutation treatment strategies.

pathology↗

bioRxiv2021

MeDUsA: A novel system for automated axon quantification to evaluate neuroaxonal degeneration

BackgroundDrosophila is an excellent model organism for studying human neurodegenerative diseases (NDs), and the rough eye phenotype (REP) assay is a convenient experimental system for analysing the toxicity of ectopically expressed human disease genes. However, the association between REP and axonal degeneration, an early sign of ND, remains unclear. To address this question, we developed a method to evaluate axonal degeneration by quantifying the number of retinal R7 axons in Drosophila; however, it requires expertise and is time-consuming. Therefore, there is a need for an easy-to-use software that can automatically quantify the axonal degeneration. ResultWe created MeDUsA (a method for the quantification of degeneration using fly axons), which is a standalone executable computer program based on Python that combines a pre-trained deep-learning masking tool with an axon terminal counting tool. This software automatically quantifies the number of axons from a confocal z-stack image series. Using this software, we have demonstrated for the first time directly that axons degenerate when the causative factors of NDs (Syn, Tau, TDP-43, HTT) were expressed in the Drosophila eye. Furthermore, we compared axonal toxicity of the representative causative genes of NDs and their pathological alleles with REP and found no significant correlation between them. ConclusionsMeDUsA rapidly and accurately quantifies axons in Drosophila eye. By simplifying and automating time-consuming manual efforts requiring significant expertise, it enables large-scale, complex research efforts on axonal degeneration, such as screening to identify genes or drugs that mediate axonal toxicity caused by ND disease proteins.

pathology↗