Hungry yeast are tiny, living thermometers

Date:
January 25, 2022
Source:
University of Washington
Summary:
Researchers report that a yeast cells can actively regulate a
process called phase separation in one of their membranes. During
phase separation, the membrane remains intact but partitions
into multiple, distinct zones or domains that segregate lipids
and proteins. The new findings show for the first time that, in
response to environmental conditions, yeast cells precisely regulate
the temperature at which their membrane undergoes phase separation.



FULL STORY ========================================================================== Membranes are crucial to our cells. Every cell in your body is enclosed
by one.

And each of those cells contains specialized compartments, or organelles,
which are also enclosed by membranes.


========================================================================== Membranes help cells carry out tasks like breaking down food for energy, building and dismantling proteins, keeping track of environmental
conditions, sending signals and deciding when to divide.

Biologists have long struggled to understand precisely how membranes
accomplish these different types of jobs. The primary components of
membranes -- large, fat-like molecules called lipids and compact molecules
like cholesterol -- make great barriers. In all but a few cases, it's
unclear how those molecules help proteins within membranes do their jobs.

In a paper published Jan. 25 in the Proceedings of the National
Academy of Sciences, a team at the University of Washington looked at
phase separation in budding yeast -- the same single-celled fungus of
baking and brewing fame - - and reports that living yeast cells can
actively regulate a process called phase separation in one of their
membranes. During phase separation, the membrane remains intact but
partitions into multiple, distinct zones or domains that segregate
lipids and proteins. The new findings show for the first time that,
in response to environmental conditions, yeast cells precisely regulate
the temperature at which their membrane undergoes phase separation. The
team behind this discovery suggests that phase separation is likely a
"switch" mechanism that these cells use to govern the types of work that membranes do and the signals they send.

"Previous work showed that these domains can be seen in the membranes of
living yeast cells," said lead author Chantelle LeveilIe, a UW doctoral
student in chemistry. "We asked: If it's important for a cell to have
these domains, then if we change the cell's environment -- by growing them
at different temperatures -- would the cell 'care' and devote energy to maintaining phase separation in its membranes? The clear answer is yes,
it does!" Past research has shown that when sugar is plentiful, the yeast cell's vacuole -- an important organelle for storage and signaling --
grows large and its membrane appears uniform under a microscope. But
when food supplies dwindle, the vacuole undergoes phase separation,
with many round zones appearing in the organelle's membrane.



==========================================================================
In this new study, Leveille and her co-authors -- UW chemistry professor
Sarah Keller, UW biochemistry professor Alexey Merz and Caitlin Cornell, previously a UW doctoral student in chemistry -- sought to understand
whether yeast can actively regulate phase separation. Leveille grew yeast
at their typical laboratory temperature of 86 F with plenty of food. After
the food dwindled, the yeast cell vacuole membranes underwent phase
separation, as expected. When Leveille briefly raised the temperature
in the yeast's environment by about 25 degrees Fahrenheit, the domains disappeared. Then Leveille grew yeast at a cooler temperature -- 77 F
instead of the normal 86 F -- and discovered that the domains disappeared
about 25 degrees above this new temperature. When she grew yeast in still colder conditions, at 68 F, phase separation yet again disappeared about
25 degrees higher than their growth temperature.

These experiments showed that the yeast cells always maintained phase separation in the vacuole membrane until the temperature rose about 25
degrees above their growth temperature.

"We think this is a clear sign that yeast cells are engineering the
vacuole membrane in different environmental conditions to maintain this consistent state of phase separation," said Leveille.

Phase separation in the vacuole membrane likely serves an important
purpose in yeast, she added.

"This result suggests that membrane phase separation for yeast is likely
a two- way door," said Leveille. "For example, if the cells ever found
food again, they would want to go back to their original state. Yeast do
not want to get too far away from the transition." Future research could identify other membrane components that affect the vacuole membrane's
ability to phase separate, as well as the consequences of its phase
separation. Biologists have known that, when the domains appear in the
yeast vacuole's membrane, the cell stops dividing. These two events may
be linked because the yeast vacuole's membrane contains two complexes
of proteins that are important for cell division. When the complexes
are far apart, cell division stops.



========================================================================== "Phase separation in the vacuole occurs right when the yeast cell needs
to stop dividing because its food supply has run out," said Merz. "One
idea is that phase separation is the mechanism that the yeast cell
'uses' to separate these two protein complexes and stop cell division."
In cells from yeast to humans, protein complexes embedded in membranes
affect cell behavior. If additional research shows that phase separation
in the yeast vacuole regulates cell division, it would likely be the
first rigorous example of cell regulation through this once-overlooked
property of membranes.

"Phase separation could be a common, reversible mechanism to modulate
many, many types of cellular properties," said Keller.

Cornell is now a postdoctoral researcher at the University of California, Berkeley. The research was funded by the National Institutes of Health
and the National Science Foundation.

========================================================================== Story Source: Materials provided by University_of_Washington. Original
written by James Urton. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Chantelle L. Leveille, Caitlin E. Cornell, Alexey J. Merz, Sarah L.

Keller. Yeast cells actively tune their membranes to phase separate
at temperatures that scale with growth temperatures. Proceedings of
the National Academy of Sciences, 2022; 119 (4): e2116007119 DOI:
10.1073/ pnas.2116007119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220125151004.htm

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