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Eukaryotic cells are packed with many different organelles. In order to respond to environmental cues and coordinate homeostasis, cells need to tightly control the inter-organelle communication. One of the key organelles for the inter-organelle communication is the ER, which is the site of the synthesis and turnover of a major fraction of lipids and membrane proteins. The ER is directly connected to the nucleus by junctions with the outer nuclear membrane. This ER-to-nucleus connectivity is crucial for cellular homeostasis and to supply new lipids and membrane proteins to the nucleus during nuclear growth. However, what the structural nature of the ER-nucleus connection is, and how its size and number is regulated to support the key cellular functions, remains poorly understood. We aim to reveal the structure and function of this major yet poorly characterized inter-organelle connection and uncover the molecular mechanism governing it.
The correlative live imaging with high resolution electron microscopy that I have established previously, allows to visualise intra-cellular structures in situ in human cells in a spatio-temporally-resolved and quantitative manner. By combining this novel correlative imaging technology with quantitative live cell imaging and a microscopy-based loss-of-function screens, we will elucidate systematically how the structure and function of the ER-nucleus connection changes during nuclear growth, identify molecular players regulating them, and reveal how the ER-nucleus connectivity mechanistically controls the ER-to-nucleus communication.
I investigated nucleocytoplasmic transport by single-molecule measurements using atomic force microscopy during my PhD research at Kyoto University. In my postdoctoral research at the European Molecular Biology Laboratory, I established a novel “dynamic” nano-scale imaging approach and revealed that nuclear pores assemble via fundamentally different mechanisms in mitosis and interphase.
A correlative live imaging with electron microscopy was established that allows to examine subcellular structures and protein complexes at nano-meter resolution at specific stages of cell-cycle in a quantitative manner, and therefore can enable to visualize biological processes which have not been able to study due to the limited resolution of conventional microscopy.
The correlative imaging technique was applied to study nuclear envelope (NE) assembly during mitotic exit, and could demonstrate for the first time that the NE forms from highly fenestrated ER sheet whose holes progressively shrink. This finding provides a new approach to explore the ER-NE connectivity and ask how it is regulated to ensure proper ER-nucleus communication.
Postmitotic nuclear pore assembly proceeds by radial dilation of small membrane openings.
Otsuka, Shotaro; Steyer, Anna M; Schorb, Martin; Hériché, Jean-Karim; Hossain, M Julius; Sethi, Suruchi; Kueblbeck, Moritz; Schwab, Yannick; Beck, Martin; Ellenberg, Jan
Nuclear pore assembly proceeds by an inside-out extrusion of the nuclear envelope.
Otsuka, Shotaro; Bui, Khanh Huy; Schorb, Martin; Hossain, M Julius; Politi, Antonio Z; Koch, Birgit; Eltsov, Mikhail; Beck, Martin; Ellenberg, Jan
Imaging the assembly, structure, and function of the nuclear pore inside cells.
Otsuka, Shotaro; Szymborska, Anna; Ellenberg, Jan
This is a collaboration project with Daniel Gerlich's group at IMBA.
Project title: “Elucidating the mechanics of mitotic chromosome assembly by light-, electron-, and atomic force microscopy"
The Otsuka Group participates in the special doctoral program 'Signaling Mechanisms in Cellular Homeostasis (SMICH)', funded by the Austrian Science Fund (FWF).