Biology subjects

Kawaguchi, S.

Publications and source records attributed to Kawaguchi, S..

8 recordsLinked to original sources

bioRxiv2026

Microbe-dependent inter-organ communication regulates germline stem cell proliferation in Drosophila

Animals integrate environmental cues with internal physiological states through inter-organ communication to regulate reproduction. However, how environmental microbes are incorporated into these systemic pathways to control reproductive stem cell proliferation remains poorly understood. Here, we demonstrate that environmental microbes colonizing the gut promote stem cell-mediated oogenesis in Drosophila melanogaster by increasing germline stem cell (GSC) number. This process requires microbial activation of gut metabolic pathways, including glycolysis and the pentose phosphate pathway (PPP), linking microbial cues to organismal physiology. We further show that microbial cues modulate circadian clock gene expression in both the gut and brain, and that circadian gene activity in these tissues is required for microbe-induced increases in GSCs. These metabolic changes promote ecdysone and juvenile hormone signaling in ovarian somatic cells, and single-cell transcriptomic analyses further reveal cell type-specific metabolic and hormonal responses across germline and follicle cell populations. Together, our findings establish that microbe-dependent gut-mediated inter-organ communication integrates metabolism, circadian gene expression, and endocrine signaling to regulate stem cell-mediated reproduction in Drosophila.

developmental biology↗

bioRxiv2025

The glomerulus as a selective gate for tumor-derived extracellular vesicles in urine

Urinary small extracellular vesicles (sEVs), which can reflect systemic conditions, hold great promise for non-invasive cancer diagnostics, yet the mechanism by which tumor-derived sEVs reach urine remains unclear. Here, we demonstrate that the glomerulus actively transcytoses circulating tumor-derived sEVs into urine. Using CRISPR gRNA-tagged glioma sEVs and bioluminescent/fluorescent GeNL-tagged lung and pancreatic cancer sEVs, we tracked their journey from tumors to urine in multiple mouse models. In vivo and in vitro analyses revealed endocytic uptake and transcytotic release by glomerular cells, accompanied by changes in sEV size and surface composition. GeNL-tagged sEVs consistently showed higher signals in urine than plasma, indicating selective excretion. These findings redefine the glomerulus as a dynamic regulator of EV processing and establish a mechanistic foundation for urinary liquid biopsy.

cancer biology↗

bioRxiv2025

Transcriptional Repression of reaper by Stand Still Safeguards Female Germline Development in Drosophila

Apoptosis plays a central role in shaping tissues and preserving cellular integrity across developmental stages. In the germline, its precise regulation is critical to ensure both the elimination of aberrant cells and the maintenance of reproductive capacity. However, the molecular mechanisms that control apoptotic susceptibility in germline cells remain poorly defined. Here, we identify stand still (stil) as a female germline-specific regulator of apoptosis in Drosophila. Loss of stil leads to near-complete depletion of germline cells at the time of eclosion, associated with upregulation of the pro-apoptotic gene reaper (rpr) and activation of caspase-dependent cell death. Reporter assays in S2 cells show that Stil directly represses rpr transcription through its N-terminal BED-type zinc finger domain. Despite the absence of stil, undifferentiated germline cells remain resistant to apoptosis. Analysis of publicly available chromatin data reveals that the rpr locus in these cells resides in a closed, H3K9me3-enriched chromatin state, suggesting a Stil-independent mode of transcriptional silencing. Together, our findings uncover two distinct mechanisms that protects the female germline from rpr-dependent apoptosis: Stil-mediated transcriptional repression that operates in both undifferentiated and differentiated germline cells, and an additional chromatin-based silencing mechanism that functions specifically in undifferentiated cells. This work provides new insights into the interplay between transcriptional and chromatin-based regulations that maintain germline cell identity and survival.

developmental biology↗

bioRxiv2024

In silico screening by AlphaFold2 program revealed the potential binding partners of nuage-localizing proteins and piRNA-related proteins

Protein-protein interactions are the fundamental features for understanding the molecular functions and regulations of proteins. Despite extensive databases, many interactions remain uncharacterized due to the intensive labor required for experimental validation. In this study, we utilized the AlphaFold2 program to predict interactions among proteins localized in the nuage, a germline-specific non-membrane organelle critical for piRNA biogenesis and RNA regulation. We screened 20 types of nuage proteins for 1:1 interactions and predicted dimer structures. Among those, five pairs represented novel interaction candidates. Three pairs, including Spn-E_Squ, were validated through co-immunoprecipitation in cultured cells and confirmed the interactions. Disruption of the salt bridges at the Spn-E_Squ interface verified their functional importance, underscoring the predictive models accuracy. Our analysis was extended to include interactions between three representative nuage components, Vas, Squ, and Tej, and approximately 430 oogenesis-related proteins. Following this extended analysis, co-immunoprecipitation in S2 cells verified interactions for three pairs: Mei-W68_Squ, CSN3_Squ, and Pka-C1_Tej. Furthermore, the majority of Drosophila proteins, [~]12,000, were screened for the interaction with Piwi protein, a central player in the piRNA pathway. Approximately 1.5% of the pairs, totaling 164 pairs, with a score above 0.6, were identified as potential binding partners. This in silico approach not only efficiently identifies potential interaction partners but also significantly reduces the gap by facilitating the integration of bioinformatics and experimental biology.

molecular biology↗

bioRxiv2024

HemK2 functions for sufficient protein synthesis and RNA stability through eRF1 methylation during Drosophila oogenesis

HemK2 is a highly conserved methyltransferase spanning from yeast to humans. Despite its conservation, the identification of its genuine substrates has been controversial, and its biological importance in higher organisms remains unclear. In this study, we elucidate the role of HemK2 in the methylation of eukaryotic Release Factor 1 (eRF1), a process essential for female germline development in Drosophila melanogaster. Knockdown of hemK2 in the germline cells (hemK2-GLKD) induces apoptosis in these cells, accompanied by a pronounced decrease in both eRF1 methylation and protein synthesis. The overexpression of a methylation-deficient eRF1 variant recapitulates the defects observed in hemK2-GLKD, suggesting that eRF1 is a primary methylation target of HemK2. Furthermore, hemK2-GLKD leads to significant reduction mRNA levels in germline cell. We demonstrate that these defects in oogenesis and protein synthesis can be partially restored by inhibiting the No-Go Decay pathway. In addition, hemK2 knockdown is associated with increased disome formation, suggesting that disruptions in eRF1 methylation may provoke ribosomal stalling, which subsequently activates translation-coupled mRNA surveillance mechanisms that degrade actively-translated mRNAs. We propose that HemK2-mediated methylation of eRF1 is critical for ensuring efficient protein production and mRNA stability, which are vital for the generation of high-quality eggs.

developmental biology↗

bioRxiv2022

A pathway to produce non-coding piRNAs from endogenous protein-coding regions supports Drosophila spermatogenesis

PIWI-interacting (pi)RNA pathways control transposable elements (TEs) and endogenous genes in animal gonads, playing important roles in gamete formation. Here, we report a mechanism by which endogenous protein-coding regions, that normally provide their sequences for translation, serve as origins of non-coding piRNA biogenesis in Drosophila melanogaster testes. The products, namely endo-piRNAs, formed silencing complexes with Aubergine (Aub) in germ cells. Proximity proteome combined to functional analyses revealed a testis-specialized chaperone, Cyclophilin 40 (Cyp40), selectively increases endo-piRNA occupancy inside Aub-RISCs aside from other TE-related piRNAs. Moreover, Argonaute 2 (Ago2) activities were found critical for endo-piRNA production. We provide evidence that Ago2-bound short interfering (si)RNAs and micro(mi)RNAs specify precursors and direct endo-piRNA biogenesis. Consistently, Aub and Ago2 cooperate in spermatid differentiation and regulate endogenous genes via endo-piRNA-directed mRNA cleavage. Collectively, our data highlight that Drosophila testes employ a unique strategy to expand the diversity of germline piRNAs supporting late spermatogenesis. HeadlinesO_LIEndogenous protein-coding regions derive non-coding endo-piRNAs C_LIO_LIendo-piRNA and TE-piRNA are produced via distinct mechanisms C_LIO_LIsiRNA and miRNA activities direct secondary piRNA biogenesis C_LIO_LIendo-piRNA pathway controls chromatin and sperm formation C_LI

molecular biology↗

bioRxiv2022

Tejas functions as a core component of nuage assembly and precursor processing in Drosophila piRNA biogenesis

Piwi-interacting RNAs (piRNAs), a class of 23- to 29-nt gonad-specific small RNAs, function to combat transposons in gonads. piRNAs are thought to be processed and amplified in membrane-less granules called nuage in germline cells. In Drosophila, two PIWI family proteins, several Tudor-domain containing (Tdrd) proteins and RNA helicases are assembled at perinuclear region of germline cells, forming nuage to process into piRNAs. Among those, Tejas (Tej), a fly homolog of mouse Tdrd5, has been known as a robust nuage component required for piRNA biogenesis in germline cells, yet its molecular functions remained elusive. To understand its molecular basis on nuage assembly and functions for piRNA biogenesis, we investigated subcellular localization of fluorescent-tagged nuage proteins including Tej and monitored the behavior of piRNA precursors. Tej functions as a core component for assembly of Vasa and Spindle-E to nuage granules through distinct motifs, respectively. The loss of Tej function resulted in malformation of nuage and accumulation of piRNA precursors en route in processing, perturbing further piRNA biogenesis in germline cells. Our study also revealed that the low complexity region of Tej regulates the mobility of nuage by phase separation. Collectively, we propose that Tej plays a pivotal role in processing of piRNA precursors by assembling RNA helicases, Vasa and Spindle-E, to nuage, by controlling the dynamics of nuage components.

cell biology↗

bioRxiv2021

Self-organization and information transfer in Antarctic krill swarms

Antarctic krill swarms are one of the largest known animal aggregations. However, despite being the keystone species of the Southern Ocean, little is known about how swarms are formed and maintained, and we lack a detailed understanding of the local interactions between individuals that provide the basis for these swarms. Here we analyzed the trajectories of captive, wild-caught krill in 3D to determine individual level interaction rules and quantify patterns of information flow. Our results suggest krill operate a novel form of collective organization, with measures of information flow and individual movement adjustments expressed most strongly in the vertical dimension, a finding not seen in other swarming species. In addition, local directional alignment with near neighbors, and strong regulation of both direction and speed relative to the positions of groupmates suggest social factors are vital to the formation and maintenance of swarms. This research represents a first step in understanding the fundamentally important swarming behavior of krill.

animal behavior and cognition↗