Biology subjects

Ikeda, H.

Publications and source records attributed to Ikeda, H..

7 recordsLinked to original sources

bioRxiv2026

Developmental prefrontal myelination shapes inhibitory interneuron function and adult social behavior

Early-life adversity and abnormal myelination are implicated in psychiatric disorders, but how developmental myelination influences adult social cognition remains unclear. Here, we tested whether disrupting developmental myelination in the medial prefrontal cortex (mPFC) impairs adult social behavior. Using complementary genetic strategies in male mice, we suppressed Myelin Regulatory Factor (Myrf)-dependent myelination locally in the juvenile mPFC or broadly in oligodendrocyte-lineage cells. Both approaches selectively impaired adult social novelty preference while sparing sociability, locomotion, and affective behaviors. Focal prefrontal dysmyelination also reduced social dominance. Spatial transcriptomics revealed coupling between myelin-related genes and parvalbumin (PV) interneuron markers in the healthy mPFC, which was disrupted by developmental hypomyelination. Consistent with this transcriptional alteration, PV interneurons showed reduced high-frequency firing despite preserved intrinsic excitability. In the human prefrontal cortex, MBP-PV expression was correlated in controls but not in individuals with schizophrenia. These findings indicate that developmental prefrontal myelination contributes to PV interneuron maturation and suggest that disrupted oligodendrocyte-interneuron coordination may contribute to impaired social recognition.

neuroscience↗

bioRxiv2026

Genomic and ecological characterization of unclassified tetraploid Echinochloa plants distributed in northern Japan

Understanding the evolutionary origins of globally noxious weeds provides insights into the genetic background of weediness. Among species of Echinochloa, the hexaploid E. crus-galli was previously thought to have arisen through hybridization and allopolyploidization between tetraploid E. oryzicola and an undiscovered diploid species, although they exhibit marked differences in both ecological and morphological characteristics. Recently, in Japan, unknown tetraploid Echinochloa plants were discovered that exhibit distinct ecological and morphological characteristics from those of E. oryzicola, with some traits showing greater similarity to those of E. crus-galli. In this study, we investigated the relationships between well-known Echinochloa species and these unknown tetraploid plants, hereafter referred to as ''ninja''. Subgenome-based read mapping analysis and phylogenetic analysis revealed that ninja possesses a distinct genomic composition, while showing close relationships to E. oryzicola in both its chloroplast and nuclear genomes. Furthermore, the identification of a very small number of ninja x E. oryzicola hybrids among field-collected individuals suggests that these two species rarely hybridize in the wild. Although ninja and E. oryzicola showed similar genomic compositions, ninja has a broader habitat range, partially overlapping with that of E. oryzicola and extending into areas occupied by E. crus-galli. Our findings indicate the possibility that hexaploid E. crus-galli may have originated from a tetraploid Echinochloa species other than E. oryzicola.

plant biology↗

bioRxiv2026

Identification of Novel Gamma Radiation-Responsive Genes in the Thiosulfate-Oxidizing Bacterium Limnobacter thiooxidans

Ionizing radiation induces DNA damage and oxidative stress; however, the genes and molecular mechanisms involved in bacterial stress responses have not been sufficiently identified. In this study, we used Limnobacter thiooxidans strain CS-K2, which is the closest relative to the bacteria detected in torus room water at the Fukushima Daiichi Nuclear Power Plant according to 16S rRNA gene sequences, and evaluated its response to {gamma}-ray irradiation using integrated transcriptomic and proteomic analyses. We identified three previously uncharacterized genes (LT3105, LT3115, and LT3126) that were strongly induced at the mRNA and protein levels. These genes exhibited low basal expression but were markedly upregulated by {gamma}-ray irradiation. Notably, LT3126 encodes a protein containing VIT (vault protein inter--trypsin) and VWA (von Willebrand factor type A) domains and showed the strongest induction. Overexpression of LT3126 increased survival after 500 Gy irradiation by approximately 200-fold compared with the control bacteria, demonstrating a direct contribution to survival under high-dose stress. Comparative genomic analysis showed that these genes are not widely conserved across bacteria but are unevenly distributed among specific lineages. Taken together, this study identified a novel set of {gamma}-ray-responsive genes and demonstrated a functional role for LT3126 in radiation resistance, providing new insights into molecular adaptation in radiation-associated environments. IMPORTANCEWe identified a novel set of {gamma}-ray-responsive genes (LT3105, LT3115, and LT3126) in the non-model bacterium Limnobacter thiooxidans. These genes are located in relatively close genomic proximity and are coordinately induced upon irradiation, suggesting a shared functional role in stress response. Overexpression of LT3126 increased survival by approximately 200-fold after 500 Gy irradiation compared with the control bacteria, demonstrating a substantial contribution to survival under high-dose stress. These genes were also induced by heat shock and oxidative stress, indicating that their function extends beyond radiation-specific responses to broader environmental stress adaptation. Consistent with this, comparative genomic analysis showed that these genes are not widely conserved across bacteria but are unevenly distributed among specific lineages. Taken together, these findings highlight previously unrecognized molecular strategies that may support bacterial survival in radiation-associated environments.

microbiology↗

bioRxiv2025

Structural basis for color tuning and passive ion conductance in red-shifted pump-fold channelrhodopsin ChR024

ChR024 is a cation-conducting channelrhodopsin with a red-shifted absorption spectrum, recently discovered from a previously unidentified clade through machine-learning-guided gene mining. Due to its unique position in the phylogenetic tree and distinctive spectral properties, it serves as an important model for elucidating rhodopsin evolution and for engineering optogenetic tools with enhanced performance, but its structure and function remain poorly understood. Here, we present cryo-electron microscopy structures of ChR024 in detergent micelles and lipid nanodiscs at resolutions of 3.22 and 2.45 [A], respectively. The structures reveal an architecture strikingly similar to that of ion-pumping rhodopsins, even more so than other pump-like channelrhodopsins such as ChRmine. Structural, theoretical, and spectroscopic analyses uncover a unique color-tuning mechanism, in which charged residues close and distant from the retinal chromophore cooperatively modulate the pKa of the Schiff base counterion and thereby determine the absorption maximum wavelength. Finally, comparative structural analysis of channel- and pump-type rhodopsins, combined with electrophysiology, provides insights into the molecular boundary between these two functional classes and demonstrates the conversion of an outward proton pump into a light-gated channel. Together, these findings illuminate diverse mechanisms of color tuning and functional specification within the rhodopsin family, paving the way for the rational engineering of next-generation optogenetic tools.

biophysics↗

bioRxiv2022

Histology-associated transcriptomic heterogeneity in ovarian folliculogenesis revealed by quantitative single-cell RNA-sequencing for tissue sections with DRaqL

High-quality single-cell RNA-sequencing (RNA-seq) with spatial resolution remains challenging. Laser capture microdissection (LCM) is a widely used, potent approach to isolate arbitrarily targeted cells from tissue sections for comprehensive transcriptomics. Here, we developed DRaqL (direct RNA recovery and quenching for LCM), an experimental approach for efficient lysis of single cells isolated by LCM from alcohol- and formalin-fixed sections without RNA purification. Single-cell RNA-seq combined with DRaqL allowed transcriptomic profiling from alcohol-fixed sections with efficiency comparable to that of profiling from freshly dissociated cells, together with effective exon- exon junction profiling. Furthermore, the combination of DRaqL and protease treatment enabled robust and efficient single-cell transcriptome analysis from tissue sections strongly fixed with formalin. Applying this method to mouse ovarian sections, we revealed a transcriptomic continuum of growing oocytes quantitatively associated with oocyte size, and detected oocyte-specific splice isoforms. In addition, our statistical model revealed heterogeneity of the relationship between the transcriptome of oocytes and their size, resulting in identification of a size-transcriptome relationship anomaly in a subset of oocytes. Finally, we identified genes that were differentially expressed in granulosa cells in association with the histological affiliations of granulosa cells to the oocytes, suggesting distinct epigenetic regulations and cell-cycle activities governing the germ-soma relationship. Thus, we developed a versatile, efficient approach for robust single-cell cDNA amplification from tissue sections and provided an experimental platform conducive to high-quality transcriptomics, thereby revealing histology-associated transcriptomic heterogeneity in folliculogenesis in ovarian tissues.

developmental biology↗

bioRxiv2022

Structural basis for ion selectivity in potassium-selective channelrhodopsins

The KCR channelrhodopsins are recently-discovered light-gated ion channels with high K+ selectivity, a property that has attracted broad attention among biologists- due to intense interest in creating novel inhibitory tools for optogenetics leveraging this K+ selectivity, and due to the mystery of how this selectivity is achieved in the first place. Indeed, the molecular and structural mechanism for K+ selectivity in KCRs has remained especially puzzling since these 7-transmembrane retinal-binding proteins completely lack structural similarity with known K+ channels, which generally coordinate K+ in a precisely symmetric conduction pathway formed by a tight interface among multiple small monomeric channel subunits (presumably not an accessible mechanism for the large KCR rhodopsin proteins). Here we present the cryo-electron microscopy structures of two KCRs from Hyphochytrium catenoides with distinct spectral properties for light absorption and channel actuation, HcKCR1, and HcKCR2, at resolutions of 2.6 and 2.5 [A], respectively. Structural comparison revealed first an unusually-shaped retinal binding pocket which induces rotation of the retinal in HcKCR2, explaining the large spectral difference between HcKCR1 and 2. Next, our combined structural, electrophysiological, computational, and spectroscopic analyses revealed a new solution to the challenging problem of K+-selective transport. KCRs indeed do not exhibit the canonical tetrameric K+ selectivity filter that specifically coordinates dehydrated K+; instead, single KCR monomers form a size exclusion filter using aromatic residues at the extracellular side of the pore which inhibits passage of bulky hydrated ions. This unique feature allows KCRs to function as K+ channels under relevant physiological conditions, providing not only a novel mechanism for achieving high K+ permeability ratios in biological ion channels, but also a framework for designing the next generation of inhibitory optogenetic tools. In BriefThe first structures of K+-selective channelrhodopsins (HcKCR1 and 2) are determined, revealing a K+ selectivity mechanism distinctly different from canonical K+ channels. HighlightsO_LIThe cryo-EM structures of K+-selective channelrhodopsins, HcKCR1 and 2, in nanodisc C_LIO_LIConditions under which naturally-occurring microbial rhodopsins have a 6-s-cis retinal C_LIO_LIIdentification of key residues for high K+ permeability ratios C_LIO_LIThe unique K+ selectivity mechanism of KCRs C_LI

biophysics↗

bioRxiv2020

Lipooligosaccharide, Vag8, and pertussis toxin of Bordetella pertussis cooperatively cause coughing in mice

Whooping cough, a contagious respiratory disease caused by Bordetella pertussis, is characterized by paroxysmal coughing; however, the mechanism has not been studied because of the lack of versatile animal models that reproduce the cough. Here, we present a mouse model that reproduces coughing after intranasal inoculation with the bacteria or its components and demonstrate that lipooligosaccharide (LOS), pertussis toxin (PTx), and Vag8 of the bacteria cooperatively function to cause coughing. LOS-induced bradykinin sensitized a transient receptor potential ion channel, TRPV1, which acts as a sensor to evoke the cough reflex. Vag8 further increased bradykinin levels by inhibiting the C1 esterase inhibitor, the major downregulator of the contact system, which generates bradykinin. PTx inhibits intrinsic negative regulation systems for TRPV1 through inactivation of Gi GTPases. Our findings provide a basis for answering long-standing questions on the pathophysiology of the pertussis cough.

microbiology↗