University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Thursday, May 10th 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker:  Hyun Youk, Kavli Institute of Nanoscience, TU Delft, Netherlands
Subject: Restarting life on demand: Distinguishing dormancy from death by resuming life in yeast

Stopping life indefinitely and then resuming it at the press of a button is an idea that has captivated movie makers, science fiction writers, and the general public. An open question is whether one can indeed completely stop and then resume, after many years, the life of any animals, including humans. Yeast spores are ideal for investigating the halting and resuming of cellular life. Yeast spores do not outwardly appear to be living – they neither move nor divide, exist without any external energy sources, and are believed to maintain faint, if any, intracellular dynamics. While we know how yeasts form spores when they are starved of nutrients and how a newly introduced energy source (glucose) “wakes-up” the spores and cause them to re-enter replicative life, little is known about the processes that occur, if any, inside the spores during dormancy before glucose is added, how long the dormancy can last (and what determines this timeline), and why some spores cannot wake up (thus considered dead) after a long enough time without any nutrients. We explored these questions by investigating how glucose, the necessary energy source, germinates yeast spores (i.e., restart cell replication). In doing so, we discovered that spores that are conventionally thought to be dead are, in fact, merely dormant. We found that not all spores germinate despite encountering abundant glucose. These un-germinated spores are primed so that they germinate faster upon encountering more glucose. Surprisingly, inducing expression of a useless gene that neither aids nor interferes cell growth, in dormant spores promotes germination. Crucially, we quantify an intrinsic ability by dormant spores to express genes – an intrinsic gene-expression rate. By tuning this, we could tune the probability that a spore germinates and even allow spores that glucose could not germinate, to germinate. Finally, we show that causing spores to use their stored resources to make useless proteins, while dormant, dramatically lengthens by months the time that spores escape death by months. We explain these observations with a simple mathematical model. These results provide quantitative insights into differences between death and dormancy.
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Faculty Host: Elias Puchner

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