Biology subjects

Fujita, R.

Publications and source records attributed to Fujita, R..

10 recordsLinked to original sources

bioRxiv2026

Combined elevated temperature and CO2 alter Wolbachia abundance and host fitness but not cytoplasmic incompatibility in a stored-product pest

Coinfecting endosymbiont strains may respond differently to environmental change, with consequences for host performance and reproductive incompatibility. We investigated an isofemale line of Callosobruchus chinensis coinfected with the cytoplasmic incompatibility (CI)-inducing Wolbachia strains wBruCon (Con) and wBruOri (Ori), together with derived Con-only and uninfected sublines. Beetles were maintained under control conditions (30{degrees}C, ~500 ppm CO2) or under combined elevated temperature and CO2 (32{degrees}C, ~1000 ppm CO2; eT&CO2). In coinfected adults, Ori relative abundance declined under eT&CO2, whereas Con abundance increased in females. Con responses also depended on host sex and infection status, with singly infected males showing particularly high abundance under control conditions. However, CI expression remained stable across environmental conditions. Coinfected females laid fewer eggs than uninfected females, whereas host life-history responses to eT&CO2 varied among traits and generations. eT&CO2 accelerated development and reduced adult longevity, while reduced egg-adult survival emerged in the F2 generation. It also reduced F1 fecundity but only in the uninfected subline. Strong and partial CI associated with Con and Ori, respectively, remained evident under both environmental conditions. Equilibrium analyses incorporating relative fecundity, CI intensity, and maternal transmission suggested lower infection persistence under eT&CO2 in the F1 generation but higher persistence in the F2 generation. Sensitivity analysis suggested contribution of improved relative fecundity of infected females in the latter. Overall, the two Wolbachia strains exhibited contrasting, sex-dependent abundance responses to eT&CO2, while CI expression remained stable. These findings suggest that climate change may alter symbiont infection dynamics in economically important pests, with potential implications for symbiont-mediated traits, including pesticide resistance.

ecology↗

bioRxiv2026

Continuous Large Maf Activity Maintains Fast Myofiber Identity and Multicellular Homeostasis in Adult Skeletal Muscle

Fast myofibers are preferentially affected during aging, exhibiting atrophy and shifts toward slower myofiber programs, yet the mechanisms preserving established fast-fiber identity remain unclear. Here, we show that the large Maf transcription factors Mafa, Mafb, and Maf are continuously required to maintain type IIb myofiber identity in adult skeletal muscle. Inducible deletion of large Mafs caused near-complete loss of type IIb fibers, a transition toward type IIx/IIa states, reduced strength, and increased fatigue resistance. RNA-seq and ATAC-seq revealed transcriptional and chromatin accessibility remodeling across the fast myosin locus, characterized by persistent loss of Myh4 expression and increased accessibility around Myh1. Single-nucleus RNA-seq identified transient myonuclei co-expressing multiple myosin isoforms before emergence of a Myh1-dominant state, accompanied by remodeling of non-myonuclear cell populations. These changes shared features with aging- and denervation-associated muscle remodeling. Thus, continuous large Maf activity maintains adult fast myofiber identity and coordinates skeletal muscle tissue homeostasis.

cell biology↗

bioRxiv2026

Cardiac-Detargeted MyoAAV Enables Systemic Nrl-Mediated Fast Myofiber Remodeling and Hypertrophy Across Multiple Skeletal Muscles

Inducing fast myofiber programs offers therapeutic potential for skeletal muscle disorders such as sarcopenia, where fast myofibers are preferentially lost. Engineered muscle-specific AAV (MyoAAV) vectors enable efficient transduction of skeletal muscles after systemic administration; however, cardiac transgene expression limits applications requiring skeletal muscle-selective delivery. We generated modified MyoAAV vectors by incorporating cardiac-specific miR-208a target sequences into the transgene 3'UTR. This design markedly suppressed cardiac expression while preserving skeletal muscle output, with target-site variation enabling tunable trade-offs between cardiac detargeting and skeletal muscle expression levels. We validated this platform using neural retina leucine zipper (Nrl), a large Maf transcription factor regulating type IIb myofiber identity. Systemic delivery of conventional MyoAAV-Nrl caused severe cardiac hypertrophy and uniform lethality within one month. Conversely, incorporating miR-208a target sequences prevented detectable hypertrophy and eliminated mortality during the experimental observation period. This modification significantly reduced cardiac Nrl expression while maintaining skeletal muscle levels, successfully promoting type IIb myofiber formation and hypertrophy across multiple skeletal muscles. These findings demonstrate that miR-208a-mediated cardiac detargeting combined with MyoAAV-Nrl enables safe systemic induction of fast myofiber remodeling and hypertrophy, establishing a platform for gene therapies targeting skeletal muscle disorders associated with fast myofiber loss.

cell biology↗

bioRxiv2026

c-MAF transduces motor neuron firing to sustain fast-glycolytic myofibers and neuromuscular junctions

This study examined how motoneuron activity influences transcription factor binding in mouse fast glycolytic Myh4+ muscle fibers. Single nucleus multiomics of innervated versus denervated tibialis anterior muscles revealed altered chromatin accessibility: SIX and c-MAF binding sites decreased while JUN, FOS, and RUNX1 sites increased in denervated Myh4+ myonuclei. c-MAF showed strong nuclear enrichment after 100 Hz stimulation and periods of increased motoneuron activity but was absent following denervation, establishing it as a primary readout of fast motoneuron firing. Genome-wide analysis demonstrated that c-MAF binding site spacing encodes functionally distinct muscle gene programs. Analysis of constitutive and inducible skeletal muscle-specific c-Maf mutants revealed that c-MAF loss caused region-specific MYH4+ fiber atrophy, MYH1/MYH2 fiber type shifts resembling ALS G93A mouse phenotypes, and progressive neuromuscular junction fragmentation with increased motoneuron terminal sprouting and ectopic reinnervation. These findings establish c-MAF as a critical mediator linking motoneuron activity to muscle gene regulation, fiber integrity, and neuromuscular junction maintenance in fast glycolytic fibers.

physiology↗

bioRxiv2024

Large MAF Transcription Factors Reawaken Evolutionarily Dormant Fast-Glycolytic Type IIb Myofibers in Human Skeletal Muscle

Small mammals rely on type IIb myofibers, expressing the fastest myosin IIb (encoded by MYH4), for rapid muscle contraction. In contrast, larger mammals, including humans, show reduced or absent MYH4 expression and type IIb myofibers, favoring slower-contracting myofibers. The evolutionary mechanisms underlying this shift remain unclear. Here, we identify large MAF transcription factors (MAFA, MAFB, MAF) as key regulators of MYH4 expression in large mammals, including human and bovine. Overexpression of large MAFs induces MYH4 expression and enhances glycolytic capacity in human myotubes, supported by RNA-seq and metabolic flux analyses. RNA-seq of human muscle biopsies reveals a positive correlation between MAFA, MAF, and MYH4 expression, with these genes elevated in power-trained individuals. These findings reveal a conserved mechanism across mammals, showing that large MAFs can induce type IIb myofibers even in humans, with potential applications for enhancing athletic performance and addressing age-related muscle weakness associated with the loss of fast-twitch myofibers.

cell biology↗

bioRxiv2023

Dual-specificity phosphatases 13 and 27 as key switches in muscle stem cell transition from proliferation to differentiation

Muscle regeneration depends on muscle stem cell (MuSC) activity. Myogenic regulatory factors, including myoblast determination protein 1 (MyoD), regulate the fate transition of MuSCs. However, the direct target of MYOD in the process is not completely clear. Using previously established MyoD knock-in (MyoD-KI) mice, we revealed that MyoD targets dual-specificity phosphatase (Dusp) 13 and Dusp27. In Dusp13:Dusp27 double knock-out (DKO) mice, the ability for muscle regeneration after injury was reduced. Moreover, single-cell RNA sequencing of MyoD-high expressing MuSCs from MyoD-KI mice revealed that Dusp13 and Dusp27 are expressed only in specific populations within MyoD-high MuSCs, which also express Myogenin. Overexpressing Dusp13 in MuSCs causes premature muscle differentiation. Thus, we propose a model where DUSP13 and DUSP27 contribute to the fate transition of MuSCs from proliferation to differentiation during myogenesis. Significance StatementMYOD protein is not expressed in quiescent muscle stem cells but accumulates rapidly following muscle injury, leading to the proliferation of myogenic progenitors for differentiation. However, the direct targets of MYOD, aside from myogenin, which play roles in myogenic differentiation remain incompletely understood. Using previously established MyoD knock-in mice and single-cell RNA sequencing, we discovered that Dusp13 and Dusp27 are potential target genes of MYOD that promote myogenesis during muscle regeneration in adult mice.

cell biology↗

bioRxiv2023

Heart generation via blastocyst complementation in Mesp1/2-deficient mice

Heart transplantation is the only curative option available for patients with advanced heart failure. However, donor organ shortage and graft rejection remain critical challenges in heart transplantation. Blastocyst complementation using pluripotent stem cells (PSCs) can be used to generate organs such as the pancreas and kidneys in animal models with abnormalities in essential developmental genes. Nonetheless, whether functional adult hearts can be generated with blastocyst complementation remains unclear, and it is unknown if parenchyma, blood vessels, and stroma can be generated concomitantly from PSCs using blastocyst complementation to avoid graft rejection. Here, we show the generation of functional adult hearts in acardiac Mesp1 and Mesp2 double-knockout (Mesp1/2-DKO) mice via blastocyst complementation using mouse PSCs. Our result shows that the generated hearts were structurally and functionally normal and restored embryonic lethality in Mesp1/2-DKO mice. All four cardiovascular lineages, including cardiomyocytes, vascular endothelial cells, smooth muscle cells, and cardiac fibroblasts, were virtually entirely derived from exogenous PSCs in the myocardium. Exogenous rat PSCs also generated rat-derived xenogeneic hearts in Mesp1/2-DKO mice via interspecies blastocyst complementation. Thus, blastocyst complementation is a viable technique for generating hearts derived from PSCs and may represent significant progress toward generating rejection-free hearts.

cell biology↗

bioRxiv2022

Requirement of sequential hydrolysis by CD73 and ALP for uptake of vitamin B2 into cells

Extracellular hydrolysis of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) to riboflavin is thought to be important for cellular uptake of vitamin B2 because FAD and FMN are hydrophilic and do not pass the plasma membrane. However, it is not clear whether FAD and FMN are hydrolyzed by cell surface enzymes for vitamin B2 uptake. Here, we show that in human cells, FAD, a major form of vitamin B2 in plasma, is hydrolyzed by CD73 (also called ecto-5' nucleotidase) to FMN, then FMN is hydrolyzed by alkaline phosphatase to riboflavin, which is efficiently imported into cells. This process is impaired on the surface of glycosylphosphatidylinositol (GPI)-deficient cells due to lack of these GPI-anchored enzymes. During culture of GPI-deficient cells with FAD or FMN, hydrolysis of these forms of vitamin B2, intracellular levels of vitamin B2, vitamin B2-dependent pyridoxal 5'-phosphate formation, and mitochondrial functions were significantly decreased compared with those in GPI-restored cells. These results suggest that inefficient uptake of vitamin B2 might account for mitochondrial dysfunction seen in some cases of inherited GPI deficiency.

biochemistry↗

bioRxiv2020

Satellite cell expansion is mediated by P-eIF2α dependent Tacc3 translation

Translational control of gene expression is an important regulator of adult stem cell quiescence, activation and self-renewal. In skeletal muscle, quiescent satellite cells maintain low levels of protein synthesis, mediated in part through the phosphorylation of eIF2 (P-eIF2). Pharmacological inhibition of the eIF2 phosphatase with the small molecule sal003 maintains P-eIF2 and permits the expansion of satellite cells ex vivo. Paradoxically, P-eIF2 also increases the translation of specific mRNAs, which is mediated by P-eIF2 dependent readthrough of inhibitory upstream open reading frames (uORFs). Here, we ask whether P-eIF2 dependent mRNA translation enables expansion of satellite cells. Using transcriptomic and proteomic analyses, we show a number of genes associated with the assembly of the spindle pole to be upregulated at the level of protein, without corresponding change in mRNA levels, in satellite cells expanded in the presence of sal003. We show that uORFs in the 5UTR of mRNA for the mitotic spindle stability gene Tacc3 direct P-eIF2 dependent translation. Satellite cells deficient for TACC3 exhibit defects in expansion, self-renewal and regeneration of skeletal muscle. SignificanceTranslational control of gene expression has emerged as an important regulator of adult stem cell populations, which maintain low levels of protein synthesis. In adult muscle stem cells, or satellite cells, a portrait of translational control has emerged whereby multiple repression mechanisms prevent the translation of specific mRNAs. It remains unclear how other mRNAs escape repression and are efficiently translated. We show that within the context of low global rates of protein synthesis, satellite cell expansion occurs through the selective translation of Tacc3 mRNA. Tacc3 deficient satellite cells expand poorly, leading to defects in skeletal muscle regeneration. Our study provides a more complete picture of translational control of gene expression in adult stem cell populations.

cell biology↗

bioRxiv2018

The genomic landscape of western South America: Andes, Amazonia and Pacific Coast

Studies of Native South American genetic diversity have helped to shed light on the peopling and differentiation of the continent, but available data are sparse for the major ecogeographic domains. These include the Pacific Coast, a potential early migration route; the Andes, home to the most expansive complex societies and to one of the most spoken indigenous language families of the continent (Quechua); and Amazonia, with its understudied population structure and rich cultural diversity. Here we explore the genetic structure of 177 individuals from these three domains, genotyped with the Affymetrix Human Origins array. We infer multiple sources of ancestry within the Native American ancestry component; one with clear predominance on the Coast and in the Andes, and at least two distinct substrates in neighboring Amazonia, with a previously undetected ancestry characteristic of northern Ecuador and Colombia. Amazonian populations are also involved in recent gene-flow with each other and across ecogeographic domains, which does not accord with the traditional view of small, isolated groups. Long distance genetic connections between speakers of the same language family suggest that languages had spread not by cultural contact alone. Finally, Native American populations admixed with post-Columbian European and African sources at different times, with few cases of prolonged isolation. With our results we emphasize the importance of including under-studied regions of the continent in high-resolution genetic studies, and we illustrate the potential of SNP chip arrays for informative regional scale analysis.

genetics↗