Biology subjects

Nozaki, T.

Publications and source records attributed to Nozaki, T..

At least 19 recordsLinked to original sources

bioRxiv2026

Evolutionary diversification of the nuclear pore complex in Entamoeba histolytica reveals conserved and lineage-specific nucleoporins

Nuclear pore complexes (NPCs) are the gateways for macromolecular exchange between the nucleus and cytoplasm. Although NPC architecture is broadly conserved across eukaryotes, substantial lineage-specific diversification has emerged, particularly among divergent protists. Here, we investigated the NPC of Entamoeba histolytica, an evolutionarily divergent amoebozoan and the causative agent of amebiasis. Using the FG-repeat nucleoporin EhNup98-like as bait in affinity purification coupled with mass spectrometry, we identified various associated proteins, including a previously uncharacterized candidate nucleoporin with similarity to Nup53/Nup35. Reciprocal proteomic analysis of EhNup53-like further recovered a broader repertoire of candidate NPC components, including proteins corresponding to conserved nucleoporins as well as several uncharacterized nuclear pore-associated proteins. Structural analyses indicated that this EhNup53-like protein retains a conserved RNA recognition motif (RRM)-like fold despite extensive primary-sequence divergence, while displaying lineage-specific features, including an expanded repeat-rich region and truncation of the C-terminal region typically associated with Nup155 binding. Together, these findings expand the known candidate nucleoporins in E. histolytica and reveal NPC-associated networks that combines recognizable conserved components with extensively remodeled and poorly characterized proteins. Our study highlights the evolutionary plasticity of the NPC and provides a framework for understanding how nuclear pore architecture has diversified across deeply divergent eukaryotic lineages.

cell biology↗

bioRxiv2026

Global transcriptional rewiring provides recurrent evolutionary routes to insect-Escherichia coli mutualism

Microbial symbionts often evolve specialized functions that compensate for host nutritional deficiencies, yet the evolutionary routes by which such mutualisms arise remain poorly understood. Here, using an experimental symbiosis between the stinkbug Plautia stali and Escherichia coli, we investigated the early evolution of insect-bacterium mutualism. Among 144 independently evolved bacterial lineages, six acquired the ability to improve host performance. Four lineages carried independent disruptive mutations in cyaA, disabling carbon catabolite repression and thereby increasing the essential amino acid tryptophan. The remaining two lineages evolved through nonsynonymous mutations in rpoB or rpoD, encoding core components of the transcriptional machinery. Transcriptomic analyses revealed extensive regulatory rewiring in both mutants, including marked upregulation of biosynthetic pathways for branched-chain essential amino acids. Our results identify global transcriptional regulatory systems as major evolutionary targets for the emergence of mutualism and demonstrate how large-effect regulatory mutations can rapidly generate host-beneficial traits. (146 < 150 words)

evolutionary biology↗

bioRxiv2026

Chromosome organization of Entamoeba histolytica and Entamoeba dispar

Entamoeba histolytica is a clinically important pathogenic eukaryote and the causative agent of amoebic dysentery. Entamoeba dispar, a nonpathogenic commensal species that resides in the human colon, is the closest sibling species, and serves as an appropriate comparator for genome-wide analysis. Although the genome of E. histolytica is approximately 26.9 Mb, and the largest known genome within the genus, that of E. invadens, is approximately 40.9 Mb, obtaining high-quality assemblies in this genus has remained challenging due to extensive repetitive regions, tRNA gene arrays, and aneuploidy. Here, we used PacBio HiFi sequencing to assemble the genomes of the pathogenic E. histolytica and the nonpathogenic E. dispar. We reconstructed all 36 chromosomes of E. histolytica and 35 chromosomes of E. dispar, assembling each as a single continuous DNA sequence (contig). The two species exhibited high genome-wide nucleotide similarity and conserved synteny at the amino acid level. At one end of each chromosome, we identified tRNA arrays, whereas the opposite end lacked such arrays, resulting in an asymmetric chromosomal architecture. Analysis of unique-read depth revealed widespread aneuploidy in both species: E. histolytica is predominantly tetraploid, whereas E. dispar is diploid, a conclusion further supported by SNP allele-frequency distributions. These assemblies provide a robust foundation for comparative genomics in Entamoeba and offer detailed insights into chromosome-end structure and ploidy.

genomics↗

bioRxiv2025

Symbiont replacement and subsequent parallel genome erosion reshape a dual obligate symbiosis in the aphid Lachnus tropicalis

Many insects rely on obligate microbial symbioses, often involving multiple partners. Although symbiont replacement is well-documented, how newly acquired and resident obligate symbionts adapt after such events remains unclear. Here, we investigate the dual obligate symbiosis of the aphid Lachnus tropicalis, where an ancestral Serratia lineage was replaced by a newly acquired another Serratia lineage while the primary symbiont Buchnera remained. Our metagenomic sequencing yielded complete genomes of Buchnera (0.42 Mb) and Serratia (2.8 Mb), revealing developing metabolic complementarity. Although the Serratia genome retained abundant gene sets for amino acid synthesis, it also contained pseudogenes in leucine and methionine pathways, which would be compensated for by Buchnera or the host. Comparison with L. roboris, which harbors the ancestral Serratia lineage, showed that the newly acquired Serratia in L. tropicalis exhibits identical tissue localization and vertical transmission pattern, suggesting the smooth succession of the priors microniche. Notably, Buchnera in L. tropicalis exhibited a slightly more degenerated genome than its counterpart in L. roboris, indicating that symbiont replacement can accelerate gene loss even in ancient symbionts. Overall, our findings provide new insights into the dynamics of novel mutualism establishment and highlight symbiont replacement as a driver of host-symbiont co-evolution.

evolutionary biology↗

bioRxiv2025

Sex mosaic and a rare male in the parthenogenetic stick insect Neohirasea japonica (Phasmatodea, Lonchodidae)

Parthenogenetic species that reproduce solely by females are pivotal for understanding the evolution and diversity of reproductive strategies. Rare males, often resulting from developmental errors, including chromosomal abnormalities, offer valuable insights into reproductive reversibility, although their rarity limits data on morphology, behavior, and fertility. Stick insects (Phasmatodea), with numerous parthenogenetic species, are key taxa for studying these phenomena; however, detailed analyses of rare males remain scarce. In this study, we investigated the spontaneous appearance of male and sexual mosaics within a captive colony of Neohirasea japonica, a widespread stick insect in Japan, where males are typically absent. In total, three individuals exhibiting male characteristics (penis and non-oviposition) were observed during the 8-years rearing. One displayed a typical male abdominal clasper and exhibited mating behavior with conspecific females, with morphological comparisons strongly suggesting that it was an N. japonica male. The other two individuals lacked mating behavior and were identified as sexual mosaics based on their external morphology and the presence of female reproductive systems upon dissection. This study provides foundational morphological and anatomical data on male, female, and sexually mosaic individuals in N. japonica. It also includes quantitative comparisons of key traits, such as the antenna-to-body length ratio, which is 0.78 in males and ranges from 0.52 to 0.53 in females. These findings establish valuable criteria for future identification of rare males and sexual mosaics in this species, ultimately contributing to our understanding of sexual trait degeneration in obligate parthenogenetic lineages.

zoology↗

bioRxiv2025

The gut microbiota-derived metabolite indole regulates cytoskeletal functions and virulence in Entamoeba histolytica

Entamoeba histolytica is a pathogenic amoeba that inhabits the human large intestine and causes amoebiasis. E. histolytica interacts with both the intestinal microbiota and the metabolites they produce. These bacterial metabolites play a crucial role in shaping the virulence and stress resistance of E. histolytica. One such metabolite, indole, is synthesized by bacteria from tryptophan and functions as a key signaling molecule. In this study, we investigated the impact of indole on E. histolytica by incubating trophozoites with the metabolite and performing proteomic analyses under various conditions, including trophozoites adapted to indole. Our results show that indole is toxic to E. histolytica, with an inhibitory concentration (IC) of 1.2 mM; however, the parasite can adapt to this concentration. Proteomic analyses reveal that indole-adapted trophozoites display enhanced resistance to oxidative stress (OS), upregulation of cytoskeletal proteins, and increased virulence. These trophozoites exhibit increased F-actin formation, smaller cell size, stronger adhesion to HeLa cells, enhanced migratory capacity, and more effective colonization of the mouse cecum compared to non-adapted trophozoites. Thus, indole exerts a dual effect on E. histolytica physiology. While indole is initially toxic to the parasite, adaptation to indole confers enhanced resistance to OS and promotes a more virulent phenotype. This duality underscores the complex role of microbiota-derived metabolites in modulating parasite behavior and highlights indole as a key microbial signal. Author summaryEntamoeba histolytica is a unicellular parasite living in the human large intestine and can cause a disease called amoebiasis. Inside the intestine, E. histolytica interacts with the microbiota and with the metabolites they produce. One such metabolite is indole, which is produced by gut bacteria from tryptophan and used by human cells and trophozoites. In this study, we explored how indole affects E. histolytica. We found that indole is toxic to the parasite at first, but over time, the amoeba can adapt and survive in its presence. Using protein analysis techniques, we discovered that indole-adapted amoebas become more resistant to stress and more virulent. They produce more F-actin, leading to improved mobility, degrade more HeLa cells, and colonize the gut of mice more efficiently than wild-type amoebas (WT). These results show that, while indole initially harms the parasite, it also triggers changes that make it more resistant to stress and more virulent. Our work highlights how metabolites produced by bacteria in the large intestine can influence the behavior of E. histolytica.

microbiology↗

bioRxiv2025

Evolution of multi-partner symbiotic systems in the Cerataphidini tribe: genome reduction of Buchnera and frequent turnover of companion symbionts

How multi-partner symbiotic systems originate and diversify within a lineage remains poorly understood. To address this, we investigated the evolutionary dynamics of bacterial symbionts across eight species of the aphid subfamily Hormaphidinae, with detailed molecular, genomic, and microscopic analyses focused on two Cerataphidini species, Ceratovacuna nekoashi and Pseudoregma panicola. Our 16S ribosomal RNA gene amplicon sequencing analysis revealed that Cerataphidini species consistently harbor companion symbionts alongside Buchnera, whereas the examined Hormaphidini and Nipponaphidini species harbor only Buchnera. Notably, Arsenophonus in C. nekoashi and C. japonica have distinct phylogenetic origins, and P. panicola has acquired Symbiopectobacterium instead of Arsenophonus. Microscopic analyses demonstrated that these companion symbionts are maternally transmitted and occupy distinct cell types from those harboring Buchnera. Genome sequencing revealed extreme reduction in Buchnera genomes to [~]0.4 Mbp in both C. nekoashi and P. panicola, comparable to C. japonica but significantly smaller than Buchnera genomes of [~]0.6 Mbp in mono-symbioses. The companion symbiont genomes retain complete riboflavin biosynthesis pathways absent in Buchnera. Our findings suggest that Buchnera genome reduction and companion symbiont acquisition occurred in the common ancestor of Cerataphidini, followed by multiple companion symbiont replacements, demonstrating that ancient obligate symbionts can remain evolutionarily stable while companion symbionts undergo frequent turnover. ImportanceMany insects depend on multiple bacterial symbionts to survive on nutritionally limited diets, yet how such multi-partner symbiotic systems originate and change over evolutionary time is poorly understood. By examining the aphid subfamily Hormaphidinae, particularly Ceratovacuna nekoashi and Pseudoregma panicola, we show that a dramatic reduction in the genome of the ancient symbiont Buchnera and the acquisition of a companion symbiont occurred together in the common ancestor of the tribe Cerataphidini. Strikingly, while Buchnera has been stably maintained across all examined species, the companion symbiont has been repeatedly replaced by phylogenetically diverse bacteria, even among closely related species. These findings reveal an evolutionary asymmetry between ancient and recently acquired symbionts and suggest that companion symbiont turnover is a common consequence in insects harboring genomically degraded obligate symbionts.

microbiology↗

bioRxiv2025

What makes a society dead: accumulation of uric acid increases infectious disease risk in termites

In social insect colonies, the high reproductive output of kings and queens is supported by non-reproductive castes, a division of labour that allows for the rapid recovery of individuals, often including those of the reproductive castes. However, these seemingly permanent colonies eventually face collapse. Studying the mechanisms of colony death is crucial for understanding the maintenance of insect social systems. Here, we show that the accumulation of uric acid (a major product of nitrogen metabolism) in workers increases their infectious disease risk in the Japanese subterranean termite Reticulitermes speratus. In this species, king replacement has been associated with colony demise, and we found that king replacement increases the uric acid contents in worker bodies in the field. Uric acid, which has antioxidant activity, was shown to reduce in vivo levels of reactive oxygen species (ROS), a key player in innate immunity. Workers with decreased ROS levels were more susceptible than those with normal ROS levels to an opportunistic pathogen that causes disease to immunocompromised termites. Our results indicate that regulating the individual oxidant/antioxidant balance through the interactions among colony members plays a pivotal role in the immunity of social insects.

ecology↗

bioRxiv2025

Vertical transmission of Wolbachia bypassing the germ line in an aphid

Wolbachia, a widespread endosymbiotic bacterium that infects a broad range of arthropods and nematodes, relies on vertical transmission from mother to offspring. This process often involves colonization of the host germline, subsequent transfer to developing oocytes, and utilization of host yolk protein transport mechanisms such as vitellogenin uptake. However, the transmission strategies employed by Wolbachia in viviparous insects such as aphids are poorly understood. Here, we demonstrate a novel Wolbachia transmission mode in the cedar bark aphid Cinara cedri that bypasses germline cells. After confirming stable Wolbachia infection in C. cedri, we visualized the localization of Wolbachia, along with the obligate symbionts Buchnera aphidicola and Serratia symbiotica. Consistent with previous reports, Wolbachia in C. cedri were predominantly observed within maternal and embryonic bacteriocytes, the specialized cells housing obligate symbionts. Notably, Wolbachia cells were rarely detected in germline cells or early-stage embryos and were directly transmitted from maternal bacteriocytes to developing embryos, coinciding with obligate symbiont transfer. These results suggest that Wolbachia in C. cedri has evolved a unique "piggybacking" strategy, utilizing the obligate symbiont transmission system. Our study highlights the diversity of endosymbiont maternal transmission strategies and provides new insights into the underlying molecular mechanisms of action.

evolutionary biology↗

bioRxiv2025

How The Transition of Aphid Life Cycles Affect Endosymbiotic Bacteria

How symbiotic bacteria coordinate and respond to their hosts during complex life cycle transitions is a fascinating and unresolved topic, particularly for organisms that exist solely in natural environments, where their intricate life cycles make laboratory cultivation extremely challenging. Complex life cycles are often associated with host alternation in aphids, especially in eriosomatine gall-forming aphids, which exhibit seven distinct morphs throughout their life cycle while shifting their host plants seasonally. Despite these dramatic changes, these aphids maintain the obligate symbiotic bacterium, Buchnera aphidicola, to enhance their nutritional status. The bacterial communities in our wild-derived samples were dominated by aphid symbionts, including Buchnera, Regiella inseticola, Wolbachia, Arsenophonus, and Serratia symbiotica. Buchnera and Regiella prevailed in Tetraneura akinire and Tetraneura sorini, while Buchnera and Arsenophonus were more abundant in Eriosoma harunire. Our study, utilizing 16S rRNA metagenomic sequencing on the aphid Tetraneura akinire, demonstrates that Buchnera plays significant roles during most life cycle stages but is absent during the sexual male stage, where it is replaced by Regiella. Moreover, Buchnera densities exhibit significant variability across the aphids life cycles and are notably lower in gall generations. This result contradicts the previous hypothesis that galls provide superior nutrition compared to aphids in grassroot-feeding generations. In this study, we reveal the dynamics of symbiotic bacteria across the complex life cycles of three eriosomatine aphid species that form galls on the same Japanese elm tree, Ulmus davidiana var. japonica. Within the framework of tripartite symbiosis, the seemingly passive symbiotic bacteria adjust the hosts specific life stages and influence the changing host ecology in a cascading manner.

evolutionary biology↗

bioRxiv2025

Draft genome of the marine Entamoeba species reveals reduction in the gene family repertoire associated with pathogenicity and lateral gene transfer for adaptation to the marine environment

Entamoeba is the amoebozoan parasite commonly found in the intestines of animals. E. marina is the first exception isolated from marine sediments, possibly adapting from animal intestines to the sea. However, the evolutionary process of E. marina remains uncertain due to the lack of a genome sequence. Here, we present the de novo genome and transcriptome of E. marina using Oxford Nanopore MinION and Illumina HiSeq/MiSeq. The genome of E. marina is approximately 37.5 Mbp in length and consisted of 202 contigs, which is the second longest followed by E. invadens. E. marina showed significant reduction in the major virulence-associated gene families, including cysteine proteases, lysosomal enzyme transporters, and surface galactose/N-acetylglucosamine-specific lectins, suggesting diversification, more specifically reduction of pathogenicity-related genes. Genome and RNA-seq analyses also indicated genes either conserved throughout eukaryotes or laterally transferred from prokaryotes, and potentially responsible for salt tolerance. Our study provides insights into the mechanism underlying the lifestyle changes in the evolution of parasitic eukaryotes.

genomics↗

bioRxiv2024

Induction of cell death in U2OS human cancer cells by Ta3N5

Photocatalysts are widely used in modern society, with their applications extending into the field of medicine. Ultraviolet irradiation is used for photocatalysis to generate reactive oxygen species (ROS). Ta3N5 has attracted attention as a next-generation photocatalyst because it produces ROS upon exposure to visible light. Although ROS generation using visible light irradiation is useful in the field of life sciences, the toxicity of Ta3N5 remains unknown. In the present study, we evaluated the cytotoxicity of Ta3N5 using U2OS cells in terms of the intensity, irradiation time, and wavelength of light and Ta3N5 dose. We also investigated the mode and mechanism of cell death induced by Ta3N5. Cytotoxicity increased with increasing light intensity, irradiation time, and Ta3N5 dose. In contrast, high-intensity blue light irradiation induced cytotoxicity with or without Ta3N5, indicating that irradiation to green and red lights, which can selectively toxify Ta3N5-treated cells, is more useful than irradiation to blue light. Moreover, Ta3N5 induced secondary necrotic death of U2OS cells. These results suggest that Ta3N5 can be used as a photocatalyst in medical and life science fields.

cell biology↗

bioRxiv2024

EhRacM differentially regulates macropinocytosis and motility in the enteric protozoan parasite Entamoeba histolytica

Macropinocytosis is an evolutionarily conserved endocytic process that plays a vital role in internalizing extracellular fluids and particles in cells. This non-selective endocytic pathway is crucial for various physiological functions such as nutrient uptake, sensing, signaling, antigen presentation, and cell migration. While macropinocytosis has been extensively studied in macrophages and cancer cells, the molecular mechanisms of macropinocytosis in pathogens are less understood. It has been known that Entamoeba histolytica, the causative agent of amebiasis, exploits macropinocytosis for survival and pathogenesis. Since macropinocytosis is initiated by actin polymerization, leading to the formation of membrane ruffles and the subsequent trapping of solutes in macropinosomes, actin cytoskeleton regulation is crucial. Thus, this study focuses on unraveling the role of well-conserved actin cytoskeleton regulators, Rho small GTPase family proteins, in macropinocytosis in E. histolytica. Through gene silencing of highly transcribed Ehrho/Ehrac genes and following flow cytometry analysis, we identified that silencing EhracM enhances dextran macropinocytosis and affects cellular migration persistence. Live imaging and interactome analysis unveiled the cytosolic and vesicular localization of EhRacM, along with its interaction with signaling and membrane traffic-related proteins, shedding light on EhRacMs multiple roles. Our findings provide insights into the specific regulatory mechanisms of macropinocytosis among endocytic pathways in E. histolytica, highlighting the significance of EhRacM in both macropinocytosis and cellular migration. Author SummaryEntamoeba histolytica is an intestinal protozoan parasite that causes amoebic dysentery and liver abscesses in humans. This organism exploits macropinocytosis, a cellular process that engulfs extracellular fluids and particles, for its survival and pathogenicity. Although macropinocytosis is well-characterized in immune cells and cancer cells as it is essential for nutrient uptake, its mechanisms in pathogens, such as E. histolytica, remain less explored. Our research focused on the molecular mechanisms underpinning macropinocytosis in this parasite, specifically examining the role of Rho small GTPase family proteins. These proteins are critical regulators of the actin cytoskeleton in eukaryotic cells. Our study reveals that one specific Rho small GTPase, EhRacM, is in the maturation of macropinosomes as well as in directing linear cell migration. The physiological significance of EhRacM in regulating both macropinocytosis and migration opens new avenues for understanding the role of Rho small GTPases in these signaling pathways, which could eventually lead to the development of new control measures against diseases caused by this parasite.

cell biology↗

bioRxiv2024

Rapid Homolog Juxtaposition During Meiotic Chromosome Pairing

A central basic feature of meiosis is pairing of homologous maternal and paternal chromosomes ("homologs") intimately along their lengths. Recognition between homologs and their juxtaposition in space are mediated by axis-associated DNA recombination complexes. Additional effects ensure that pairing occurs without ultimately giving entanglements among unrelated chromosomes. Here we examine the process of homolog juxtaposition in real time by 4D fluorescence imaging of tagged chromosomal loci at high spatio-temporal resolution in budding yeast. We discover that corresponding loci start coming together from a quite large distance ([~]1.8 {micro}m) and progress to completion of pairing in a very short time, usually less than six minutes (thus, "rapid homolog juxtaposition" or "RHJ"). Juxtaposition initiates by motion-mediated extension of a nascent interhomolog DNA linkage, raising the possibility of a tension-mediated trigger. In a first transition, homolog loci move rapidly together (in [~]30 sec, at speeds of up to [~]60 nm/sec) into a discrete intermediate state corresponding to canonical [~]400 nm axis distance coalignment. Then, after a short pause, crossover/noncrossover differentiation (crossover interference) mediates a second short, rapid transition that brings homologs even closer together. If synaptonemal complex (SC) component Zip1 is present, this transition concomitantly gives final close pairing by axis juxtaposition at [~]100 nm, the "SC distance". We also find that: (i) RHJ occurs after chromosomes acquire their prophase chromosome organization; (ii) is nearly synchronously over thirds (or more) of chromosome lengths; but (iii) is asynchronous throughout the genome. Furthermore, cytoskeleton-mediated movement is important for the timing and distance of RHJ onset and also for ensuring normal progression. Potential implications for local and global aspects of pairing are discussed.

molecular biology↗

bioRxiv2024

Tetraspanin-enriched microdomains play an important role in pathogenesis in the protozoan parasite Entamoeba histolytica

Tetraspanins (TSPANs) are a family of proteins highly conserved in all eukaryotes. Although protein-protein interactions of TSPANs have been well established in eukaryotes including parasitic protists, the role they play in parasitism and pathogenesis remains largely unknown. In this study, we characterized three representative members of TSPANs, TSPAN4, TSPAN12, and TSPAN13 from the human intestinal protozoan Entamoeba histolytica. Co-immunoprecipitation assays demonstrated that TSPAN4, TSPAN12 and TSPAN13 are reciprocally pulled down together with several other TSPAN-interacting proteins including TSPAN binding protein of 55kDa (TBP55) and interaptin. Blue native PAGE analysis showed that these TSPANs form several complexes of 120-250 kDa. Repression of tspan12 and tspan13 gene expression led to decreased secretion of cysteine proteases. Meanwhile, strains overexpressing HA-tagged TSPAN12 and TSPAN13 demonstrated reduced adhesion to collagen. Altogether, this study reveals that the TSPANs, especially TSPAN12 and TSPAN13, are engaged with complex protein-protein interactions and are involved in the pathogenicity-related biological functions such as protease secretion and adhesion, offering insights into the potential regulatory mechanisms of tetraspanins in protozoan parasites.

cell biology↗

bioRxiv2023

The significance of social interactions in synchronized swarming flight in a termite

In social insect colonies, individuals of working caste coordinate their actions to manage various collective tasks. Such collective behaviors are observed not only in working castes but also in reproductives. During certain seasons, newly emerged winged reproductives (alates) fly from the nest to disperse and find mating partners in a synchronized manner. Although this "swarming" behavior is one of the collective behaviors that involve the greatest number of individuals in social insects, underlying social interactions remain unexplored. Here, we show that synchronized flight among colony members results from collective decision-making. Our simple simulation model suggests that social interactions in a large group of alates enable synchronized flight within a nest under fluctuating environmental conditions. This model is supported by empirical experiments using a termite Reticulitermes kanmonensis. Under the semi-field environment with fluctuating temperatures, alates within the same colony synchronized their dispersal flight under higher air temperatures, while dispersal flight was suppressed under lower temperatures. Furthermore, termites could synchronize their dispersal flights even under laboratory conditions with constant temperature, indicating that environmental cues are not always necessary for synchronization. In either case, higher synchronization happened with a larger number of alates. All these results demonstrate that both environmental and social factors interplay to enable the synchronized swarming flight of social insects.

animal behavior and cognition↗

bioRxiv2023

Mechanistic modeling of amyloid oligomer and protofibril formation

Early phase of amyloid formation, where prefibrillar aggregates such as oligomers and protofibrils are often observed, is crucial for elucidating pathogenesis. However, since oligomers and protofibrils form transiently and heterogeneously, the detailed mechanisms of their formation remain unclear. Here, we have investigated the early aggregation process of bovine and human insulin by static and dynamic light scattering in combination with thioflavin T (ThT) fluorescence and Fourier transform infrared (FTIR) spectroscopy. The time dependence of light scattering has revealed that oligomers and protofibrils form in bovine insulin, in contrast to no significant aggregation in human insulin. By focusing on bovine insulin for kinetic analysis, it has been revealed that the protofibril formation process was divided into two steps with reference to fractal dimension. When modeled the experimental data of static and dynamic light scattering based on the Smoluchowski aggregation kinetics with fractal aggregation and end-to-end association, we found the initial formation of spherical oligomers and their subsequent uniaxial docking. Furthermore, the analysis of temperature and salt concentration dependence revealed that the end-to-end association is the rate-limiting step, where structure organization occurred with dehydration. The established model for protofibril formation where oligomers are incorporated as a precursor provides insight into the molecular mechanism how protein molecules assemble during the early stage of amyloid formation. SignificanceAmyloid oligomers and protofibrils have attracted attention as critical causes of neurodegenerative diseases; however, detailed formation processes of these aggregates have been poorly understood. In this study, we established a mechanistic model of oligomer and protofibril formation of bovine insulin based on Smoluchowski aggregation kinetics in terms of static and dynamic light scattering. It has been demonstrated that early aggregation proceeds by initial fractal-like aggregation to form oligomers, and subsequent their end-to-end docking to form protofibrils. The latter step is a rate-limiting step, where structural organization occurs with dehydration. The established model is expected to broadly applicable to a variety of proteins, and thus will provides valuable insights for accelerating therapeutic development and anti-neurodegenerative drug design.

biophysics↗

bioRxiv2023

Fruitless mating with the exes: the irreversible parthenogenesis in a stick insect

Parthenogenetic lineages, common in many animals, have sparked debate about their evolutionary persistence. While asexuality is expected to ensure reproductive assurance and provide a demographic advantage, parthenogens should suffer from the lack of gene shuffling with other individuals. On the other hand, occasional sexual reproduction has been theoretically predicted to be enough to mitigate the long-term costs of parthenogenesis. Recent studies have revealed instances of cryptic sex in some old parthenogenetic lineages, which is most likely mediated by rarely occurring males. Unlike female traits that rapidly become vestigial under asexuality, traits in males have been predicted to slowly decay due to the accumulation of neutral mutations over long evolutionary times. In fact, rare males often retain sexual functions, raising questions about the asexuality of these long-standing parthenogenetic lineages. Here, we intensively examined the possibility of sexual reproduction in the Japanese common stick insect, Ramulus mikado, which was also suggested to be an old parthenogen in our previous work. While asexual female reproduction appears to be quite predominant throughout Japan, we fortunately obtained the rare males from the field. These males exhibited typical stick insect male morphology and engaged in mating behaviors with conspecific females. However, no paternal-specific alleles were detected in the offspring; all embryos showed genotypes identical to their mothers. Our histological observations on a few males revealed that they had no sperm in their reproductive organs, although the degree of decay may be different among the lineages. We also found that females have sexual organs with signs of degeneration. All these results demonstrate the irreversible asexual reproduction of R. mikado and indicate their long history as a parthenogenetic species. Our present study provides unique insights into the maintenance of parthenogenesis and degenerative evolution of sexual traits in ancient asexual lineages.

evolutionary biology↗