Biology subjects

Ohsugi, M.

Publications and source records attributed to Ohsugi, M..

6 recordsLinked to original sources

bioRxiv2026

Age-dependent accumulation of RAD51 on non-damaged chromosomes prevents chromosome segregation in mammalian oocytes

RAD51 is targeted to single-stranded (ss)DNA for homologous recombination and DNA replication fork homeostasis. However, the physiological consequences of RAD51 binding to intact double-stranded (ds)DNA, which is tightly limited in vivo, remain elusive. Here we revealed an intrinsic property of RAD51 to bind chromosome axes where cohesin and condensin bind, which is actively suppressed by FIGNL1 AAA+ ATPase. In Fignl1-deficient mouse oocytes, an age-dependent RAD51 accumulation with little DNA damage leads to improper chromosomal localization of condensin II and topoisomerase II, failure in chromosome condensation with massive chromosome entanglement, and meiosis I arrest. We propose that promiscuous RAD51 binding to non-damaged chromosomes, which is prevented by a RAD51 remodeler, is a unique type of chromosomal pathology associated with genome instability.

cell biology↗

bioRxiv2025

Balanced DNA-to-Cytoplasm Ratio at the 2-Cell Stage Is Critical for Mouse Preimplantation Development

Vertebrate development typically begins with a diploid fertilized egg but can also be initiated parthenogenetically with a haploid maternal genome, though such development fails to reach completion. Among vertebrates, mammalian haploid embryos are particularly prone to arrest during early preimplantation stages for reasons that remain unclear. Here, using mouse embryos with varying cell sizes and genome ploidy, we show that developmental arrest is primarily caused not by haploidy itself but an imbalance between genome ploidy and cytoplasmic volume. Haploid embryos exhibit cytokinesis failure, frequently accompanied by chromosome segregation failure due to malformed spindles beginning at the second mitosis, with about half of the affected blastomeres subsequently arresting before the morula stage. Strikingly, restoring the DNA-to- cytoplasm (D/C) ratio by halving the cytoplasmic volume alleviates these defects. Similarly, diploid embryos with doubled cytoplasmic volume show mitotic and developmental abnormalities resembling those of haploid embryos, whereas tetraploid embryos with the same volume develop normally. These findings demonstrate that a proper D/C ratio, rather than genome ploidy, is critical for mouse embryos to reach the morula stage. Moreover, halving the D/C ratio at later developmental stages, such as the late G2 phase of the 1-cell stage or during the 2-cell stage, progressively improves developmental outcomes. When the D/C ratio is reduced at the end of the 2-cell stage, development proceeds normally. Our findings identify a critical temporal window during which a balanced D/C ratio is essential for mitotic fidelity and successful preimplantation development. Graphic Abstract O_FIG O_LINKSMALLFIG WIDTH=198 HEIGHT=200 SRC="FIGDIR/small/651589v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@72a664org.highwire.dtl.DTLVardef@10a22c1org.highwire.dtl.DTLVardef@6fbedforg.highwire.dtl.DTLVardef@5c5b1d_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIHalved D/C ratio impairs preimplantation development in mouse embryos C_LIO_LIHalved D/C ratio causes cytokinesis failure from the second mitosis C_LIO_LIDelaying D/C ratio halving to late 2-cell stage alleviates developmental defects C_LI

cell biology↗

bioRxiv2024

Nuclear assembly in giant unilamellar vesicles encapsulating Xenopus egg extract

The reconstitution of a cell nucleus in a lipid bilayer-enclosed synthetic cell makes great strides in bottom-up synthetic biology. In this study, we propose a method for assembling a nucleus in giant unilamellar vesicles (GUVs). To induce reconstitution of the nucleus, we utilize interphase egg extract of African clawed frogs Xenopus laevis, known as a biochemically controllable cell-free system capable of transforming an added sperm chromatin into a nucleus in vitro. We enhanced GUV formation efficiency by the inverted emulsion method through incorporating prolonged waiting time and adding chloroform into lipid-dispersed oil, facilitating subsequent nuclear assembly reactions in the GUVs.Characterization of nucleus-like structures formed in the GUVs revealed the presence of dense DNA and accumulated GFP-NLS in the structure, indicative of functional nuclear import. Immunostaining further validated the presence of nuclear pore complexes on the surfaces of these nucleus-like structures. Our approach offers a versatile platform for constructing artificial cellular systems that closely mimic eukaryotic cells. TeaserA cell nucleus is reconstituted in lipid bilayer-enclosed confinements using egg extract from African clawed frogs.

synthetic biology↗

bioRxiv2024

Ca2+-driven cytoplasmic backflow secures spindle position in fertilized mouse eggs

AbstractFertilization triggers hours-long Ca2+ oscillations in mammalian eggs, but the effects of repeated Ca2+ surges remain unclear. Here, we investigate spindle dynamics and its relationship with cytoplasmic streaming in fertilized mouse eggs. The spindle, initially parallel to the plasma membrane, rotates vertically, in accordance with previously reported results using artificially activated eggs. Intriguingly, it transiently reverses its rotation direction in synchrony with Ca2+ oscillations, regardless of artificially altered frequency. This effect results from cytoplasmic streaming, initially moving from spindle to egg center, displaying a Ca2+-dependent backflow. Streaming also impacts spindle positioning, balancing spindle rotation and cortical localization maintenance. We provide evidence that Ca2+-dependent cortical myosin II activation causes actomyosin contraction, leading to transient streaming towards non-contracting actin cap regions overlaying chromosomes. Our findings underscore the role of Ca2+ oscillations in maintaining spindle position in fertilized eggs, thereby ensuring highly asymmetric division and preservation of maternal stores in zygotes.

cell biology↗

bioRxiv2022

Extensive gut virome variation and its associations with host and environmental factors in a population-level cohort

Indigenous bacteriophage communities (virome) in the human gut have a huge impact on the gut bacterial communities (bacteriome), but virome variation at a population scale is not fully investigated yet. Here, we analyse the gut virome in a population-level cohort of 4,198 deeply phenotyped individuals. We discovered thousands of high-quality phage genomes including previously uncharacterized ones with different bacterial hosts than known major phage clades. The distribution of host bacteria was a strong determinant for the distribution of phages, and virome diversity was highly correlated with anti-viral defence mechanisms of the bacteriome, such as CRISPR-Cas and restriction-modification systems. We identified 97 various intrinsic/extrinsic factors that significantly affect the virome, including age, sex, lifestyle, and diet, most of which showed consistent associations with both phages and their predicted bacterial hosts. Among the metadata categories, disease and medication had the strongest effects on the virome structure. Overall, these results present a basis to understand the symbiotic communities of bacteria and their viruses in the human gut, which will facilitate the medical and industrial applications of indigenous viruses.

microbiology↗

bioRxiv2020

APC mutant cells exploit compensatory chromosome alterations to restore tumour cell fitness

Cancer cells tolerate copy number alterations (CNAs) of genomic regions that are lethal to non-cancer cells. Certain CNAs are preferentially associated with specific cancer types and lineages, but the mechanisms underlying the emergence and selection of specific CNAs remain unclear. Adenomatous polyposis coli (APC) mutations induce mitotic errors, but their impact on tumor evolution remains elusive. We investigated APC function in cultured cells and tumors and found that its loss led to {beta}-catenin accumulation at centrosomes, suppressing its maturation through inhibition of key centrosome regulators, including Aurora kinase A (AURKA) that promotes tumor growth. These defects collectively reduced cellular fitness, leading to impaired mitotic fidelity and delayed cell cycle progression. However, in APC-mutant tumors, AURKA activity was maintained, at least in part, through the amplification of chromosomes harboring AURKA and its activator genes, yet this alone was insufficient to fully restore proliferation: aberrant chromosomal reorganization also emerged and contributed to the adaptive fitness of APC-mutant cells. Such a process of adaptive CNA selection provides a framework for understanding how specific CNAs are selected to counteract disadvantages imposed by genetic alterations during tumor progression, providing one key insight into how specific CNAs are selected in this context.

cell biology↗