Save the Date: Dr. Hyun Youk | November 17, 2023| UMass Chan Medical School

Our next guest speaker for this semester will be, Dr. Hyun Youk, an Associate Professor of Systems Biology at UMass Chan Medical School. He received his B.S. in Physics and Mathematics from the University of Toronto, his M.A. in Astronomy and Physics from Johns Hopkins University, and his Ph.D. in Physics from Massachusetts Institute of Technology. His lab began in January 2015 at the Kavli Institute of Nanoscience in Delft, the Netherlands. After nearly six years, he moved to the University of Massachusetts Medical School (UMass Med).

His passion in life is understanding what it means to “live” and “die.” Is death inevitable? If so, why is that? If not, what are we and all other organisms doing wrong? In our attempt to address these questions, our lab seeks quantitative principles that dictate the dynamics of cellular systems. These systems include cell-signaling circuits, populations of interacting cells, and organisms that appear to be “dead” but are, in fact, merely at the nexus of life and death (e.g., dormant yeast spores).


One of the hallmarks of a living cell is that it can replicate itself. An important question is when and why a cell might permanently lose its ability to proliferate and thereby transition into being a dead cell. The design principles that govern such “life-to-death” transition remain incompletely understood. In this talk, he will describe two experimental studies in which we used the budding yeast, S. cerevisiae, to reveal such design principles in the context of high and frigid temperatures. Temperature is a universal parameter for life in that it controls the speed of all biochemical reactions in all organisms and every habitat.

By either increasing the temperature to sufficiently high values or decreasing the temperature to sufficiently low values, we placed yeast cells at the (apparent) edge of their capacity to duplicate. For both high temperatures (> 38 C) and near-freezing temperatures (0 C – 5 C), we found ways to extend yeast’s ability to duplicate: we could enable more cells to duplicate with drastically shortened doubling times. We constructed “phase diagrams” that describe cell-population growths for both temperature regimes.

The same mathematical model, with one free parameter, reproduced both phase diagrams as well as stochastic proliferation of individual cells. At near-freezing temperatures, we discovered “speed limits” – slowest and fastest possible doubling times – at which a yeast cell’s life can progress: a cell that progresses more slowly than a “low-speed limit” defined for each temperature faces a certain death. A mathematical model and experimental data elucidated how these speed limits arise. These findings establish a quantitative foundation for engineering organisms that can survive extreme temperatures and elucidating fundamental limits to slowing down life.