Biology subjects

Otsuka, S.

Publications and source records attributed to Otsuka, S..

3 recordsLinked to original sources

bioRxiv2026

Structural mechanism of nuclear membrane sealing by LEM2-ESCRT-III

In open mitosis, re-establishing nucleocytoplasmic compartmentalization requires the LEM2-ESCRT machinery to coordinate spindle clearance with sealing of the remaining nuclear envelope pores. The structural basis of this topologically unique and fundamental membrane-remodeling process is poorly understood. Here, we combine biochemical reconstitution, cryo-electron tomography, subtomogram averaging and large-scale molecular dynamics simulations to define the structural mechanism of nuclear membrane sealing. We structurally resolve that LEM2s winged-helix domain (WH) co-polymerizes with the ESCRT-II/III protein CHMP7 to form a membrane-bound scaffold whose geometry is progressively remodeled by downstream ESCRT-III proteins as it transitions from the flat membrane surrounding the pore towards the negatively curved membrane neck. In parallel, LEM2 positions its intrinsically disordered low-complexity domain within the pore, where condensation around spindle microtubules mechanically couples the membrane-ESCRT-LEM2 scaffold to the spindle and narrows the remaining diffusion path, restoring compartmentalization before membrane closure is complete. Remarkably, the LEM2-WH domain alone forms tightly constricted membrane tubes, coating the negatively curved inner surface, revealing an intrinsic membrane-remodeling activity of the receptor itself. Together, our work establishes a structural framework for how receptor-ESCRT co-polymerization, low complexity domain-mediated sealing and receptor-driven membrane remodeling guide nuclear-envelope pores from spindle-containing openings to terminal constriction and fusion.

molecular biology↗

bioRxiv2018

Soil nutrient stoichiometry affects the initial response of microbial community to trophic perturbation.

Soil microbes are drivers of global ecosystem functionality and are continuously subjected to external perturbations. It is fundamental for ecologists and environmental scientists to understand and further predict the microbes responses to these perturbations. A major and ubiquitous perturbation is the addition of chemical nutrients, including fertilizers and animal urine, to soil. Recent biogeographical studies suggest that soil nutrient stoichiometry (i.e., nutritional balance) determines microbial community structure and its functions with regard to material circulation. Given this information, here, we show that soil nutrient stoichiometry, or the bioavailable C:P ratio, determines the impact of nutrient addition on the soils microbial communities. We sampled two soils with similar carbon and nitrogen concentrations but with a 20-fold difference in phosphorus bioavailability. Soil microcosms with carbon and nitrogen amendments were constructed for both the soils. The phosphorus-depleted soil received prolonged effect from carbon and nitrogen amendments: the phosphatase activity gradually increased over a 24-day incubation period and the microbial community structure did not present recovery to its initial state. In contrast, in the other soil, both phosphatase activity and microbial community structure gradually returned to those of the control samples. Phosphorus depletion mitigated carbon and nitrogen intake; therefore, the effects of carbon and nitrogen amendment lasted longer. Our results demonstrate that nutritional stoichiometry is a strong predictor of microbial community dynamics in response to trophic perturbation, particularly when considering the length of time the trait of perturbation persists in the soil.

ecology↗

bioRxiv2017

Postmitotic Nuclear Pore Assembly Proceeds By Radial Dilation Of Small ER Membrane Openings

The nuclear envelope has to be reformed after mitosis to create viable daughter cells with closed nuclei. How membrane sealing of DNA and assembly of nuclear pore complexes (NPCs) are achieved and coordinated is poorly understood. Here, we reconstructed nuclear membrane topology and structure of assembling NPCs in a correlative three dimensional electron microscopy time-course of dividing human cells. Our quantitative ultrastructural analysis shows that nuclear membranes form from highly fenestrated ER sheets, whose shrinking holes are stabilized and then dilated into NPCs during inner ring complex assembly, forming thousands of transport channels within minutes. This mechanism is fundamentally different from interphase NPC assembly and explains how mitotic cells can rapidly establish a closed nuclear compartment while making it transport-competent at the same time.

cell biology↗