Biology subjects

Harumoto, T.

Publications and source records attributed to Harumoto, T..

8 recordsLinked to original sources

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

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↗

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↗

bioRxiv2023

Mechanisms underpinning morphogenesis of symbiotic organ specialized for hosting indispensable microbial symbiont in stinkbug

Microbial mutualists are pivotal for insect adaptation, which often entails the evolution of elaborate organs for symbiosis. Addressing what mechanisms underpin the development of such organs is of evolutionary interest. Here we investigated the stinkbug Plautia stali whose posterior midgut is transformed into a specialized symbiotic organ. Despite being a simple tube in newborns, it developed numerous crypts in four rows, whose inner cavity hosts a specific bacterial symbiont, during 1st to 2nd nymphal instar. Visualization of dividing cells revealed that active cell proliferation was coincident with the crypt formation, although spatial patterns of the proliferating cells did not reflect the crypt arrangement. Visualization of visceral muscles in the midgut, consisting of circular muscles and longitudinal muscles, uncovered that, strikingly, circular muscles exhibited a characteristic arrangement running between the crypts specifically in the symbiotic organ. Even in early 1st instar when no crypts were seen, two rows of epithelial areas delineated by bifurcated circular muscles were identified. In 2nd instar, crossing muscle fibers newly appeared and connected the adjacent circular muscles, whereby the midgut epithelium was divided into four rows of crypt-to-be areas. The crypt formation proceeded even in aposymbiotic nymphs, uncovering autonomous nature of the crypt development. We propose a mechanistic model of crypt formation wherein the spatial arrangement of muscle fibers and the proliferation of epithelial cells underpin the formation of crypts as midgut evaginations. IMPORTANCEDiverse organisms are associated with microbial mutualists, in which specialized host organs often develop for retaining the microbial partners. In the light of the origin of evolutionary novelties, it is important to understand what mechanisms underpin the elaborate morphogenesis of such symbiotic organs, which must have been shaped through interactions with the microbial symbionts. Using the stinkbug Plautia stali as a model, we demonstrated that visceral muscular patterning and proliferation of intestinal epithelial cells during early nymphal stages are involved in the formation of numerous symbiont-harboring crypts arranged in four rows in the posterior midgut to constitute the symbiotic organ. Strikingly, the crypt formation occurred normally even in symbiont-free nymphs, uncovering that the crypt development proceeds autonomously. These findings suggest that the crypt formation is deeply implemented into the normal development of P. stali, which must reflect the considerably ancient evolutionary origin of the midgut symbiotic organ in stinkbugs.

microbiology↗

bioRxiv2023

Self-stabilization mechanism encoded by a bacterial toxin facilitates reproductive parasitism

A wide variety of bacterial endosymbionts in insects are associated with reproductive parasitism, whereby they interfere with host reproductive systems to spread within populations. Recent successes in identifying bacterial factors responsible for reproductive parasitism have highlighted the common appearance of deubiquitinase domains, although their functional roles remain unknown. For example, Spiroplasma symbionts in Drosophila selectively kill male progeny with a male-killing toxin Spaid that encodes an OTU deubiquitinase domain. Here I show that without the function of OTU, the male-killing activity of Spaid is attenuated, though not eliminated, since it is polyubiquitinated and degraded through the host ubiquitin-proteasome pathway. Furthermore, I find that Spaid utilizes its OTU domain to deubiquitinate itself in an intermolecular manner. Collectively, the deubiquitinase domain of Spaid serves as a self-stabilization mechanism to facilitate male killing in flies, optimizing a molecular strategy of endosymbionts that enables the efficient manipulation of the host at low-cost.

microbiology↗

bioRxiv2022

Male-killing-associated bacteriophage WO identified from comparisons of Wolbachia endosymbionts of Homona magnanima

The origin and mechanism of male-killing, an advantageous strategy employed by maternally transmitted symbionts such as Wolbachia, remain unclear. We compared genomes of four Wolbachia strains derived from Homona magnanima, a male-killing strain wHm-t (1.5 Mb), and three non-male-killing strains, wHm-a (1.1 Mb), wHm-b (1.3 Mb), and wHm-c (1.4 Mb). A wHm-t-specific 76-kbp prophage region harboured two tandemly arrayed WO-mediated killing (wmk) gene homologs (wmk-1/wmk-2 and wmk-3/wmk-4). Of these, wmk-1 or wmk-3 killed almost all Drosophila melanogaster individuals when transgenically overexpressed. Dual expression of wmk-3 and wmk-4 killed all males and rescued females. We propose a novel hypothesis wherein horizontally transmitted proto-Wolbachia with a single wmk killed both sexes, and tandem duplication of wmk allowed an evolutionary transition to a vertically transmitted symbiont, causing male-killing. Our study highlights the bacteriophage as a critical driver of the evolution of male-killing and argues for a conserved male-killing mechanism in diverse insects.

evolutionary biology↗

bioRxiv2022

MITE infestation of germline accommodated by genome editing in Blepharisma

During a sophisticated developmental process, ciliates excise numerous internally eliminated sequences (IESs) from a germline genome copy, producing a functional somatic genome. Most IESs ultimately originate from transposons but homology is obscured by sequence decay. To obtain more representative perspectives on ciliate genome editing, we assembled forty thousand IESs of Blepharisma stoltei, from a much earlier-diverging lineage than existing models. Short IESs (< 115 bp) were largely non-repetitive, with a pronounced ~10 bp length periodicity, whereas longer IESs (max 7 kbp) were non-periodic and contained abundant interspersed repeats. Contrary to current models, the Blepharisma germline genome encodes few transposases. Instead, its most abundant repeat (8000 copies) was a Miniature Inverted-repeat Transposable Element (MITE), apparently a deletion derivative of a germline-limited Pogo-family transposon. We propose MITEs as an important and eventually self-limiting IES source. Rather than defending germline genomes against mobile elements, we argue that transposase domestication actually facilitates junk DNA accumulation.

genomics↗

bioRxiv2021

The Blepharisma stoltei macronuclear genome: towards the origins of whole genome reorganization

Massive DNA excision occurs regularly in ciliates, ubiquitous microbial eukaryotes with somatic and germline nuclei in the same cell. Tens of thousands of internally eliminated sequences (IESs) scattered throughout a copy of the ciliate germline genome are deleted during development of the streamlined somatic genome. Blepharisma represents one of the two earliest diverging ciliate classes, and, unusually, has dual pathways of somatic nuclear development, making it ideal for investigating the functioning and evolution of these processes. Here, we report the somatic genome assembly of Blepharisma stoltei strain ATCC 30299 (41 Mb), arranged as numerous alternative telomere-capped minichromosomes. This genome encodes eight PiggyBac transposase homologs liberated from transposons. All are subject to purifying selection, but just one, the putative IES excisase, has a complete catalytic triad. We propose PiggyBac homologs were ancestral excisases that enabled evolution of extensive, natural genome editing.

genomics↗