Person: Oh, Seungeun
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Seungeun
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Oh, Seungeun
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Publication Survival dynamics of starving bacteria are determined by ion homeostasis that maintains plasmolysis(Springer Science and Business Media LLC, 2024-05-23) Schink, Severin; Polk, Marku; Athaide, Edward; Mukherjee, Avik; Ammar, Constantin; Liu, Xili; Oh, Seungeun; Chang, Yu-Fang; Basan, MarkusThe ability to survive starvation is an integral part of bacterial fitness and determines composition, turn-over and biodiversity in microbial ecosystems. Starving bacteria enter a state, in which their cytoplasm is contracted from the cell wall, known as plasmolysis. Plasmolysis is often thought to be a pathological, passive condition, arising automatically from the lack of ATP. Here, we show that contrary to this existing notion, maintaining plasmolysis is an active, ATP-consuming state that is essential for starvation survival. We show that ion homeostasis for maintaining plasmolysis consumes the lion’s share of starving cells’ energy budget and directly determines death rates in starvation. A quantitative mathematical model accurately predicts death rates across diverse starvation conditions and perturbations. This enabled the development of an optimized starvation medium that would be ideally suited for preserving and transplanting natural microbial communities by maintaining viability but preventing outgrowth of a subset of species.Publication Multiple Phases of Chondrocyte Enlargement Underlie Differences in Skeletal Proportions(2013) Cooper, Kimberly L.; Oh, Seungeun; Sung, Yongjin; Dasari, Ramachandra R.; Kirschner, Marc; Tabin, CliffordEven a casual pass through the great halls of mammals in the world’s natural history museums highlights the wide diversity of skeletal proportions that allow us to distinguish between species even when reduced to their calcified components. Similarly each individual is comprised of a variety of bones of differing lengths. The largest contribution to the lengthening of a skeletal element, and to the differential elongation of elements, comes from a dramatic increase in the volume of hypertrophic chondrocytes in the growth plate as they undergo terminal differentiation1–7. Despite this recognized importance, the mechanisms of chondrocyte volume enlargement have remained a mystery8–11. Here we use quantitative phase microscopy12 to show that chondrocytes undergo three distinct phases of volume increase, including a phase of massive cell swelling in which the cellular dry mass is significantly diluted. In light of the tight fluid regulatory mechanisms known to control volume in many cell types13, this stands as a remarkable mechanism for increasing cell size and regulating growth rate. It is, however, the duration of the final phase of volume enlargement by proportional dry mass increase at low density that varies most between rapidly and slowly elongating growth plates. Moreover, we find that this third phase is locally regulated through an Insulin-like Growth Factor-dependent mechanism. This study provides a framework for understanding how skeletal size is regulated and for exploring how cells sense, modify, and establish a volume set point.Publication Resonant microchannel volume and mass measurements show that suspended cells swell during mitosis(The Rockefeller University Press, 2015) Son, Sungmin; Kang, Joon Ho; Oh, Seungeun; Kirschner, Marc; Mitchison, T.J.; Manalis, ScottOsmotic regulation of intracellular water during mitosis is poorly understood because methods for monitoring relevant cellular physical properties with sufficient precision have been limited. Here we use a suspended microchannel resonator to monitor the volume and density of single cells in suspension with a precision of 1% and 0.03%, respectively. We find that for transformed murine lymphocytic leukemia and mouse pro–B cell lymphoid cell lines, mitotic cells reversibly increase their volume by more than 10% and decrease their density by 0.4% over a 20-min period. This response is correlated with the mitotic cell cycle but is not coupled to nuclear osmolytes released by nuclear envelope breakdown, chromatin condensation, or cytokinesis and does not result from endocytosis of the surrounding fluid. Inhibiting Na-H exchange eliminates the response. Although mitotic rounding of adherent cells is necessary for proper cell division, our observations that suspended cells undergo reversible swelling during mitosis suggest that regulation of intracellular water may be a more general component of mitosis than previously appreciated.