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Light-sheet microscopy helps reveal cells response to stress

17 Oct 2023

University of Chicago combines techniques for new views of cells undergoing heat shock.

Analyzing the response of cells to heat shock is an established way to study the behavior of cells in changing conditions, and understand their natural survival mechanisms.

A project at the University of Chicago (UChicago) has now developed a new technique for visualizing the inner machinery of cells to see how they respond to heat stress.

Published in Nature Cell Biology, the method combines imaging techniques to understand how cells conserve energy and pick up where they left off after experiencing heat shock.

"Adaptation is a hidden superpower of the cells," said Asif Ali from UChicago. "They don't have to use this superpower all the time, but once they are stuck in a harsh condition, suddenly there's no way out. So they employ this as a survival strategy."

The techniques employed by the team included lattice light-sheet microscopy (LLSM), an approach to imaging based on the use of laser illumination formed into ultrathin sheets that are scanned through a sample. This aims to produce improved signal to noise performance and lower phototoxicity than other fluorescence-based microscopy techniques, which deliver photons to fragile samples with less finesse.

LLSM is proving its versatility in live cell imaging, with variants employing twin or single objective lenses and different illumination angles to enhance the technique's ability to generate fluorescence imaging data from fragile living systems.

UChicago used lattice light-sheet 4D imaging, an approach in which multiple sheets of laser light are used to create fully dimensional images of components inside the living cells.

A new cell biology that was previously invisible

The team's study showed that when yeast and human cells experienced heat shock, their defense mechanisms involved protecting particular ribosomal proteins and preventing them from aggregating as the cell's normal processing shut down. The ribosomal proteins are critical for cell growth, and taking steps to stop the formation of clumps allows them to then successfully return to their task as the cell recovers.

UChicago combined its 4D lattice light-sheet microscopy with use of a labeling protein named HaloTag, and showed that the key ribsomal proteins form into temporary liquid-like droplets, kept mobile and prevented from aggregating by molecular proteins until the cell recovers from heat shock. At that point the condensates disperse and the constituents go back to their natural business.

"I think a very plausible general definition for cellular health and disease is if things are liquid and moving around, you are in a healthy state; and once things start to clog up and form aggregates, that's pathology," commented David Pincus, whose UChicago lab studies how cell heat-shock response is relevant to cancer and neuodegenerative disease. These conditions can likewise involve misfolded or aggregated clumps of proteins.

Now that 4D light-sheet microscopy has helped to reveal the cell behavior, UChicago hopes that it will prove to be a fundamental mechanism of interest for multiple clinical applications or disease diagnosis.

"Like many innovations, it took a technological breakthrough to enable us to see a whole new biology that was invisible to us before but has always been going on in cells that we have been studying for years," said Pinchus.

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