Biology subjects

Noda, T.

Publications and source records attributed to Noda, T..

At least 19 recordsLinked to original sources

bioRxiv2026

PCDH17 regulates lysosomal degradative capacity to promote autophagy attenuation during prolonged starvation

Autophagy is induced by nutrient starvation to recycle intracellular constituents; however, its activity must subsequently be attenuated during prolonged nutrient deprivation. The mechanisms underlying this attenuation in mammalian cells remain incompletely understood. Here, using complementary HaloTag-based assays, we show that autophagic activity declines during prolonged starvation in HeLa cells. A genome-wide CRISPR/Cas9 knockout screen designed to identify cells that sustain autophagic activity under these conditions identified protocadherin 17 (PCDH17) as a regulator of autophagy attenuation. PCDH17 depletion maintained autophagic activity during prolonged starvation without detectably altering mTORC1 signaling, ULK1 abundance, or the proximal machinery of autophagosome formation. Instead, PCDH17 depletion increased lysosomal abundance, acidification, and proteolytic activity, whereas PCDH17 overexpression produced reciprocal effects. We further identified a lysosome-associated PCDH17 subpopulation that is supplied predominantly through the biosynthetic ER-Golgi pathway. This pool undergoes proteolytic processing and lysosomal turnover, with starvation preferentially accelerating degradation of the C-terminal fragment while preserving a comparatively stable N-terminal fragment. Together, these findings identify PCDH17 as an unexpected negative regulator of lysosomal function and demonstrate that modulation of lysosomal degradative capacity contributes to autophagy attenuation during prolonged starvation.

cell biology↗

bioRxiv2026

Developmental Gfi1 Dynamics Define Hematopoietic Emergenceand Adult Hematopoietic Stem Cell Potency

Gfi1 regulates endothelial-to-hematopoietic transition (EHT) and hematopoietic stem cell (HSC) maintenance; however, its expression dynamics remain unclear. We generated a non-disruptive Gfi1-T2A-mScarlet reporter to track Gfi1 expression. At E10.5, reporter selectively marked EHT in the dorsal aorta, umbilical artery, and vitelline artery. At E9.5, mScarlet-positive endothelial cells were present in the umbilical and vitelline arteries but were scarce in the dorsal aorta, indicating vascular-bed-specific differences in hemogenic activation. Gfi1 was broadly expressed in fetal liver HSCs, while higher expression levels identified HSCs with enhanced multilineage reconstitution and preferential T-cell output. Although Gfi1 expression declined during fetal-to-adult maturation, a subset of adult bone marrow HSCs retained expression and exhibited superior repopulating and self-renewal capacity. Bulk and single-cell transcriptomic analyses linked this subset to dormant and fetal-associated programs, including imprinted genes. Reduced chromatin accessibility at a conserved Gfi1 +26.5kb putative enhancer correlated with developmental Gfi1 downregulation. Thus, Gfi1 dynamics define EHT onset and functionally distinct HSC stemness.

cell biology↗

bioRxiv2026

Age-associated erosion of organ-specific endothelial programs compromises tissue function and resilience

Endothelial cells (ECs) express organ-specific gene programs supporting tissue homeostasis and resilience. However, the mechanisms by which aging reshapes these organ-specific endothelial programs and how the resulting changes affect tissue homeostasis, resilience, and disease susceptibility remain largely unknown. Herein, we performed single-cell RNA sequencing of ECs harvested from five organs across the lifespan and found that aging progressively erodes organ-specific endothelial programs while inducing shared interferon-responsive and antigen-presentation programs across organs. Although vascular subtype identity and conserved capillary subset identity were mostly preserved, these organ-specific transcriptional programs were broadly attenuated with aging, indicating erosion of organ-specific endothelial identity to be a fundamental feature of endothelial aging. Importantly, these alterations were associated with declines in specialized EC functions, including alveolar barrier maintenance in the lung, scavenging activity in the liver, angiogenic capacity in the heart, and homeostatic programs in the kidneys and the brain, suggesting that age-related EC alterations compromise tissue homeostasis and resilience in multiple organs. Furthermore, we established a single-cell aging index for alveolar capillary ECs in mice and humans, revealing stress-associated endothelial activation to potentially be an intermediate state linking functional deterioration to cellular senescence, and also demonstrating marked heterogeneity in aging states even among ECs from animals of the same chronological age. Notably, alveolar capillary ECs exhibited progressive functional decline before reaching a senescent-like state, suggesting endothelial dysfunction to precede overt cellular senescence as the organism ages. Collectively, our findings establish progressive erosion of organ-specific endothelial programs as a central feature of vascular aging and provide a conceptual framework for elucidating how endothelial aging contributes to tissue dysfunction and reduced resilience across organs.

physiology↗

bioRxiv2026

The SPARK complex forms the molecular basis of vertebrate fertilization

Fertilization requires gamete recognition and membrane fusion, yet the molecular basis of this process in vertebrates remains unknown. Here we identify SPARK (sperm protein assembly and receptor-binding key), a conserved multi-protein complex that integrates all known sperm fertilization factors, including TMEM81-IZUMO1-SPACA6 and DCST1/2, together with two newly identified components, TMDD1 and FAM187A. SPARK subunits are mutually dependent for stability in mature sperm, and disruption of any single component causes male sterility in zebrafish and mice. Incubating zebrafish sperm with soluble egg receptor Bouncer partially rescues fertilization of Bouncer-deficient eggs in a SPARK-dependent manner, consistent with egg receptor binding priming the complex for fusion. Thus, we propose SPARK as a con-served molecular machine that couples gamete recognition to membrane fusion.

developmental biology↗

bioRxiv2026

Autophagy induction requires the suppression of potassium influx mediated by phosphatases

Potassium is an essential element for all living organisms. As the most abundant intracellular cation, it is vital for osmoregulation, maintenance of membrane potential, macromolecule transport and enzyme function. In this study, we identify potassium homeostasis as a previously unknown regulator of autophagy through the phosphatase activities of Ppz1 and Ppz2. We find that overexpression of either Ppz1 or Ppz2 triggers autophagy under nutrient-replete conditions, whereas the loss of both causes severe autophagy defects. Strikingly, deletion of the potassium transporters Trk1 and Trk2, which are substrates of Ppz1 and Ppz2-mediated dephosphorylation, restores autophagic activity in ppz1{Delta} ppz2{Delta} cells. Furthermore, intracellular potassium concentrations declined during autophagy induction in wild-type cells but remained stable in ppz1{Delta} ppz2{Delta} mutants. Collectively, these findings establish Ppz1 and Ppz2 as pivotal regulators of autophagy and underscore intracellular potassium reduction as a primary determinant of this process. Summary statementThis study demonstrates that potassium regulation by the phosphatases, Ppz1 and Ppz2, which suppress the major potassium transporters Trk1 and Trk2, is indispensable for autophagy induction in yeast.

molecular biology↗

bioRxiv2026

Rab32/Rab38-positive Lysosome-Related Organelle degrades lipid droplet in hepatocytes by microautophagy

Rab32 and Rab38 are paralogous small GTPases involved in the biogenesis of lysosome-related organelles (LROs), yet their roles in hepatic lipid metabolism remain poorly defined. Here, Rab32 and Rab38 double-knockout (DKO) male mice exhibited an age-dependent increase in body weight accompanied by hepatic lipid accumulation, suggesting impaired hepatic lipid processing. In AML12 hepatocytes, Rab32 and Rab38 localized to ring-like, LAMP1-positive structures characteristic of LROs, whose size increased with cell confluence. Pharmacological inhibition of lysosomal acid lipase with orlistat led to the accumulation of lipid droplets (LDs) within Rab32/38-positive LROs, indicating that LD degradation occurs in these compartments. Additional treatment with bafilomycin A1 revealed invagination-like internal membrane structures within enlarged LROs. These processes were not affected by artificial inhibition of macroautophagy, highlighting the involvement of microautophagy. Ring-like signals positive for phosphatidylinositol 3-phosphate (PI3P) or phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) were detected within or adjacent to LRO membranes, and LDs were frequently associated with these structures, suggesting a role for PI3P and PI(3,5)P2 in internal membrane formation. Vps4B was also required for efficient LD incorporation. Consistently, Rab32/38 double-knockdown (DKD) AML12 cells exhibited increased lipid accumulation, indicating impaired LD engulfment. Together, these findings identify Rab32/38-positive LROs as a structural platform for microautophagy-mediated lipid droplet degradation in hepatocytes.

cell biology↗

bioRxiv2025

Revisiting the in vivo Functions of Coilin in Mice

Cajal bodies (CBs), first identified in the early 20th century, are classic nuclear structures organized primarily by the protein coilin. Although CBs have long been implicated in snRNA modification and maturation, their precise roles in mice remain unclear. Here, we revisit the functions of CBs by using genome editing to generate mice that lack nearly the entire coilin protein, retaining only the first seven amino acids. Mass-spectrometry analyses showed reduced 2'-O-methylation of U2 snRNA in coilin mutant liver; however, these reductions had minimal impact on overall gene expression and pre-mRNA splicing patterns. Additionally, detailed analysis recapitulated previously reported testicular size reductions and newly revealed decreased proportions of high-quality sperm. We also identified novel coilin-containing condensates distinct from genuine CBs in the nuclear pocket of elongating spermatids. Our findings implicate that coilin orchestrates membraneless organelles in various compartments, playing multifunctional roles beyond classical CB formation.

molecular biology↗

bioRxiv2025

Uric acid accumulation in cockroach wings

Cockroaches, embracing some 4,500 species in the world, are found in a variety of environments including human settlements. The ecological success of cockroaches is attributable to the ability to endure long periods of starvation and to thrive on nutritionally poor diets, which is underpinned by the capability of storing their own nitrogenous waste products as uric acid in the fat body and also by the endosymbiosis with bacteriocyte-dwelling bacteria Blattabacterium that recycle the stored uric acid for synthesis of amino acids. Previous histological studies on cockroaches described that uric acid is accumulated within the fat body, especially in urocytes. Here we report that cockroaches also accumulate uric acid in the wings. In our observation of the German cockroach Blattella germanica under different nutritional conditions, we found that well-fed cockroaches exhibited whitish aggregates in the wing veins, which is ascribed to accumulation of uric acid granules. The uric acid granules in the wings disappeared by starvation and were restored by feeding in B. germanica. The uric acid granules in the wings were found not only in B. germanica but also in other diverse cockroach species.

physiology↗

bioRxiv2025

Structural basis for the folding of PINK1 by the HSP90-CDC37 chaperone complex

PTEN-induced kinase 1 (PINK1) is a mitochondrial serine/threonine kinase that plays a central role in Parkin-dependent mitophagy. Mutations in PINK1 are associated with familial Parkinsons disease. PINK1 is a high-affinity client of the HSP90-CDC37 complex and is stabilized by this chaperone system. However, the molecular mechanism by which HSP90-CDC37 facilitates the folding of PINK1 remains unclear. Here, we present a cryogenic electron microscopy structure of the human PINK1-HSP90-CDC37 complex. The {beta}5 strand of the PINK1 N-lobe is accommodated in the central channel of the HSP90 dimer, which holds the PINK1 kinase domain in a partially unfolded state. The C-lobe and unique C-terminal extension (CTE) of PINK1 is folded. HSP90 covers the CTE of PINK1, which overlaps with interaction sites for TOM5, TOM20, and the PINK1 N-helix. The HPNI motif of CDC37 interacts with the C-lobe of PINK1, mimicking the HPNI motif in the N-lobe. The pathogenic mutation L347P is suggested to disrupt these interactions, while H271Q is located within the HPNI motif in the N-lobe of PINK1. These findings provide structural insights into the folding of PINK1 and its dysfunction in Parkinsons disease.

molecular biology↗

bioRxiv2025

Cockroach bacteriocytes migrate into the ovaries for vertical transmission of the bacterial endosymbiont Blattabacterium

Diverse insect groups are obligatorily associated with and dependent on specific microorganisms as essential mutualistic partners that are usually maintained in specialized cells or organs, called bacteriocytes or symbiotic organs. Many organisms with symbiotic microorganisms have developed elaborate vertical transmission mechanisms, which are thought to be important for the evolution of intimate symbiotic relationships with microorganisms. One such case is the cockroach-Blattabacterium endosymbiosis, in which the symbiotic bacteria have been evolutionarily conserved and co-speciated with the host insects with stable vertical symbiont transmission via ovarial passage. While classical histological descriptions and recent electron microscopic observations have reported the vertical symbiont transmission processes in some cockroach-Blattabacterium associations, the full picture of the infection dynamics has not been fully understood. In this study, we conducted detailed histological and cytological observations of the localization of the bacteriocytes and the symbiotic bacteria during the postembryonic development of the German cockroach Blattella germanica. We found that the symbiont-filled bacteriocytes migrate into and associate with nymphal ovaries and are subsequently eliminated from adult ovaries, suggesting that symbiont infection to the ovaries may only occur during nymphal stages. We also found that the symbiotic bacteria are localized in the space between each oocyte and surrounding follicle cells, the symbiont-localized space is interconnected between neighboring oocytes, and therefore the symbiotic bacteria can move across oocytes within the same ovariole, suggesting the possibility that the symbiont-infected oocytes may serve as the source of symbiont supply to developing young oocytes upstream in the same ovariole. Based on these observations, we provide a hypothesis as to how the postembryonic developmental dynamics of the bacteriocytes are integrated into the vertical symbiont transmission and functioning in the cockroach-Blattabacterium endosymbiosis.

developmental biology↗

bioRxiv2025

Structure and assembly of Borna disease virus 1 nucleoprotein-RNA complexes

Structures of nucleoprotein (N)-RNA complexes of the Bornaviridae, a virus family in the order Mononegavirales, have remained unknown. Using cryo-electron microscopy (cryo-EM), we characterized N structures of Borna disease virus 1 (BoDV-1), the type species of the Bornaviridae, which causes fatal human encephalitis. N forms complexes in both RNA-free and RNA-bound states, revealing conserved features throughout the order, as well as BoDV-1-specific stoichiometry, thereby offering insights into viral evolution. We redefine assembly principles governing N-RNA complexes with the discovery of a previously unrecognized, RNA-independent mechanism involving domain-swapping and truncated subunits. Mutational analyses identified residues essential for nucleocapsid formation and RNA synthesis. Cryo-EM of mutant complexes captured RNA-free assemblies, suggesting that initial N oligomerization precedes RNA binding. These findings explain several unknowns in N-RNA complex structure and suggest an alternative to canonical RNA-driven assembly models, offering a new conceptual framework for nucleocapsid formation.

microbiology↗

bioRxiv2025

Molecular insights into nucleocapsid assembly and transport in Marburg and Ebola viruses

Live-cell imaging enables visualization of the spatiotemporal dynamics of signals in cells. The intracytoplasmic movement of nucleocapsids is crucial during the lifecycle of enveloped viruses, but the molecular mechanisms governing their assembly and transport are not fully understood. Using a MARV live-cell imaging system, we identified three nucleocapsid proteins--NP, VP35, and VP24--that are necessary and sufficient to form transport-competent nucleocapsid-like structures (NCLSs). These findings are consistent with observations in Ebola virus (EBOV). Interestingly, despite incompatibility among these proteins, VP30 interacts with nucleocapsid proteins from both MARV and EBOV, supporting viral transcription and replication in heterologous systems. Furthermore, we show that the conserved PPxPxY motif at the C-terminus of NP regulates NP-VP30 interactions in both homologous and heterologous contexts, and is crucial for VP30 association with NCLSs. Because this motif is conserved across filoviruses, it represents a promising target for antiviral development. Our findings advance the understanding of nucleocapsid formation and offer new avenues for therapeutic intervention against MARV and EBOV.

microbiology↗

bioRxiv2025

No association between metabolic rate and an exaggerated sexually selected trait

Exaggerated sexually selected traits are thought to be energetically costly to produce and to maintain. This is especially true of sexually selected weapons, traits that are frequently positively allometric, and therefore likely to be especially energetically costly. However, there have been few studies that directly measure these putative costs. Additionally, metabolic rate, a measure of energy expenditure, is highly variable across individuals, but the causes of this variation are not always well established. Here we tested for the associations between resting metabolic rate, during development and adulthood, and the size of a weapon used during adult male-male competition in the beetle Gnatocerus cornutus. We also tested for genetic variation metabolic rate and weapon size. We found that metabolic rate was not statistically associated with weapon size, but there were effects of genotype and mass during development (pupal size) on weapons. Additionally, age, mass and genotype all affected metabolic rate in various ways. Despite no evidence of energetic costs to weapon development or maintenance, direct predation costs associated with them have been detected previously, and hence enlarged weapons are costly in this system. Significance statementThe large weapons used in competition between males are thought to be energetically costly. However, there are rather few investigations of these putative costs. We investigate these potential costs by testing for associations between metabolic rate and weapon size in a beetle. We found no relationship between weapons and metabolism, indicating weapons are not always energetically costly.

ecology↗

bioRxiv2024

Step-by-Step Maturation Mechanism of Binary Toxin Pore Revealed by Cryo-EM Analysis

Membrane pore-forming proteins (PFPs) form ring-shaped membrane-translocating oligomers on membranes, contributing to infection, immunity, and cell death functions. Binary toxins produced by some bacteria consist of an enzymatic component that acts as a toxin and a membrane-binding component that forms a pore that delivers the enzymatic component into target cells. Cryo-electron microscopy (cryo-EM) has advanced our understanding of these translocation mechanisms by revealing several binary toxin complexes structures. However, the mechanisms underlying the initial pore formation remain unclear. We determined the structures of several oligomeric forms of the membrane-binding component Ib of the Iota toxin from Clostridium perfringens at various stages of pore formation. Structural comparisons revealed how the symmetrically arranged soluble oligomer (prepore) asymmetrically mature into a transmembrane oligomer (pore). These findings enhance our understanding of mechanisms of PFP and provide a structural basis for developing nanodevices using membrane pores. Significance StatementAlthough the mode of action of pore-forming proteins (PFPs) has been increasingly elucidated, the structural mechanisms underlying their maturation into membrane-spanning pores remain elusive. One of the key challenges is the difficulty in capturing the intermediate states between the soluble prepore and the mature pore, and its structural analysis. In this study, we successfully prepared the super-complex formed by a bacterial toxin PFP. The super-complex inhibited the constituting oligomers to maturate into the pore, which enabled structural determination of multiple intermediate state. Comparative structural analysis revealed that the transition from prepore to pore occurs through stepwise, domino-like conformational changes. The analysis workflow and insights from this study are expected to advance the field of PFP research.

molecular biology↗

bioRxiv2024

Isotonic and minimally invasive optical clearing media for live cell imaging ex vivo and in vivo

Tissue clearing has been widely used for fluorescence imaging of fixed tissues, but not for live tissues due to its toxicity. Here we develop minimally invasive optical clearing media for fluorescence imaging of live mammalian tissues. Light scattering is minimized by adding spherical polymers with low osmolarity to the extracellular medium. A clearing medium containing bovine serum albumin (SeeDB-Live) is minimally invasive to live cells, allowing for structural and functional imaging of live tissues, such as spheroids, organoids, acute brain slices, and the mouse brain in vivo. SeeDB-Live minimally affects the electrophysiological properties and sensory responses of neurons. We demonstrate its utility for widefield imaging of subcellular voltage dynamics, such as backpropagating action potentials, in acute brain slices. We also utilize SeeDB-Live for widefield voltage imaging of dozens of dendrites in vivo, demonstrating population dynamics. Thus, SeeDB-Live expands the scale and modalities of fluorescence imaging of live mammalian tissues.

neuroscience↗

bioRxiv2024

Dual expansion routes likely underlie the present-day population structure in a Parnassius butterfly across the Japanese Archipelago

The Japanese Archipelago, comprising a series of isolated yet interconnected islands, had been geographically separated from the Eurasian continent. The linear topography presents a unique biogeographic context for dispersing organisms from the continent. In this study, we utilized mitochondrial DNA (mtDNA) and single nucleotide polymorphism (SNP) variation to elucidate the dispersal history of the Japanese clouded butterfly Parnassius glacialis across the Japanese Archipelago, including North Island (Hokkaido), Main Island (Honshu) and Shikoku Island. Our analysis of mtDNA (COI, COII) at 1192 base pairs (bps) revealed 49 haplotypes and identified three distinct haplotype groups in the network. These groups correspond geographically to East Japan, West Japan, and Chugoku-Shikoku. The Chugoku-Shikoku group is the most ancient lineage. Interestingly, the Chugoku-Shikoku lineage showed a closer network connection to the East Japan lineage than the geographically proximate West Japan lineage. Divergence time estimates suggest that the Chugoku-Shikoku lineage diverged from the continental P. glacialis approximately 3.05 million years ago (MYA). Subsequently, from the Chugoku-Shikoku lineage, the East Japan and West Japan lineages diverged around 1.05 MYA, with the subsequent divergence between the East and West Japan lineages occurring at approximately 0.62 MYA. Based on the 3067 SNP genotypes, population structure analysis revealed five distinct genetic structures within the Japanese Archipelago, indicating geographical differentiation. From the analyses by mtDNA and SNP variations, four primary genetic barriers were identified: between Hokkaido and Honshu, between East and Central Japan, within the Kansai region, and within the Chugoku region. The former three lines corresponded to the Blakiston Line, the Itoigawa-Shizuoka Tectonic Line, and Lake Biwa, respectively. These findings suggest that P. glacialis diverged from the continental P. glacialis and expanded its range across the Japanese Archipelago via the North and South routes, establishing its current distribution.

molecular biology↗

bioRxiv2024

Influenza A virus circumvents the innate immune response through the sequestration of double-stranded RNA

Double-stranded RNA (dsRNA), which induces an innate immune response against viral infections, is rarely detected in influenza A virus (IAV)-infected cells. Nevertheless, we previously reported that the IAV ribonucleoprotein complex (vRNP) generates looped dsRNAs during RNA synthesis in vitro. This finding suggests that IAV possesses a specific mechanism for sequestering dsRNA within infected cells, thereby enabling viral evasion of the innate immune response. Here, we found that dsRNAs were produced in infected cells lacking the expression of viral non-structural protein 1 (NS1) and nuclear export protein (NEP), both encoded by the same RNA segment. Interestingly, NS1 molecules masked the entire looped dsRNA generated by vRNP, implying a potential role for NS1 in segregating viral dsRNA from cytoplasmic dsRNA sensors, including retinoic acid inducible gene-I (RIG-I). Furthermore, dsRNAs were sequestered within the nucleus of infected cells due to the absence of NEP, while their translocation to the cytoplasm occurred only upon NEP expression. Notably, the cytoplasmic translocation of dsRNA triggered the innate immune response in an RIG-I-dependent manner. These findings highlight IAVs distinctive strategy for circumventing innate immunity by sequestration of dsRNAs. Author summaryIt is widely recognized that double-stranded RNA (dsRNA) produced during viral infection triggers an innate immune response. However, the influenza A virus (IAV) has been thought to rarely produce dsRNA within infected cells. Here, we confirmed the limited dsRNA production in the nucleus of IAV-infected cells and found that the cells lacked expressions of viral non-structural protein 1 (NS1) and nuclear export protein (NEP), both derived from a single RNA segment. High-speed atomic force microscopy demonstrated that NS1 entirely concealed dsRNA produced by the viral ribonucleoprotein complexes, thereby segregating it from cytoplasmic dsRNA sensors that trigger the innate immune response. Interestingly, NEP expression caused cytoplasmic translocation of dsRNA, resulting in the nuclear translocation of interferon regulatory factor 3, which initiates an innate immune response. Collectively, our findings suggest that IAV employs a sophisticated strategy to circumvent the innate immune system, wherein the expressions of NS1 and NEP exert considerable influence.

microbiology↗

bioRxiv2024

Frequent and asymmetric cell division in endosymbiotic bacteria of cockroaches

Many insects are obligatorily associated with and dependent on specific microbial species as essential mutualistic partners. In the host insects, such microbial mutualists are usually maintained in specialized cells or organs, called bacteriocytes or symbiotic organs. Hence, potentially exponential microbial growth cannot be realized but must be strongly constrained by spatial and resource limitations within the host cells or tissues. How such endosymbiotic bacteria grow, divide and proliferate is important for understanding the interactions and dynamics underpinning intimate host-microbe symbiotic associations. Here we report that Blattabacterium, the ancient and essential endosymbiont of cockroaches, exhibits unexpectedly high rates of cell division (20-58%) and, in addition, the cell division is asymmetric (average asymmetry index > 1.5) when isolated from the German cockroach Blattella germanica. The asymmetric division of endosymbiont cells at high frequencies was observed irrespective of host tissues (fat bodies vs. ovaries) or developmental stages (adults vs. nymphs vs. embryos) of B. germanica, and also observed in several different cockroach species. By contrast, such asymmetric and frequent cell division was observed neither in Buchnera, the obligatory bacterial endosymbiont of aphids, nor in Pantoea, the obligatory bacterial gut symbiont of stinkbugs. Comparative genomics of cell division-related genes uncovered that the Blattabacterium genome lacks the Min system genes that determine the cell division plane, which may be relevant to the asymmetric cell division. These observations combined with comparative symbiont genomics provide insight into what processes and regulations may underpin the growth, division and proliferation of such bacterial mutualists continuously constrained under within-host conditions. IMPORTANCEDiverse insects are dependent on specific bacterial mutualists for their survival and reproduction. Due to the long-lasting coevolutionary history, such symbiotic bacteria tend to exhibit degenerative genomes and suffer uncultivability. Because of their microbiological fastidiousness, the cell division patterns of such uncultivable symbiotic bacteria have been poorly described. Here, using fine microscopic and quantitative morphometric approaches, we report that, although bacterial cell division usually proceeds through symmetric binary fission, Blattabacterium, the ancient and essential endosymbiont of cockroaches, exhibits frequent and asymmetric cell division. Such peculiar cell division patterns were not observed with other uncultivable essential symbiotic bacteria of aphids and stinkbugs. Gene repertoire analysis revealed that the molecular machineries for regulating the bacterial cell division plane are lost in the Blattabacterium genome, suggesting the possibility that the general trend toward the reductive genome evolution of symbiotic bacteria may underpin their bizarre cytological/morphological traits.

microbiology↗