"The Role of Septins during Cytoplasmic "Freezing" in S. Pombe "
In response to nutrient starvation, yeast cells enter a quiescent state.
This state is defined by a marked increase in the viscosity of the cell cytoplasm, a phenomenon
we term cell-freezing . Cell-freezing is a novel phenomenon discovered only
recently through measurements of the viscoelastic properties of the cytoplasm of
fission yeast cells. It occurs as a response to carbon starvation and leads to a
dramatic immobilization of all visible sub-cellular structures, which suggests that
the preservation of the internal organization of the cell in this quiescent state is its
main biological function.
Recently we found evidence that the transition of viscosity of the cell cytoplasm
could be reliably reproduced by starving cells of glucose and that septins might be
involved. Septins were known to form fibers in vitro and following this idea, we
hypothesis that a dense and homogeneous network will be formed by septins
when the cell enters the starvation state and that this network is sufficiently fine to
immobilize all major cell components. Moreover, it should be possible to visualize
septin polymers and their interaction with cell organelles by 3-Dimension (3D)
Cryo-Electron Microscopy (EM).
My project will focus on 1) Confirming the cell-freezing in starved fission yeast
cells by light microscopy (LM); 2) Observing sub-cellular structure differences by
EM (plastic embedding sample); 3) Observing septins fibers in vivo by Cryo-EM
and Cryo-Electron Tomography (ET).
By comparing starved and unstarved yeast cells, I will resolve the proposed
cytoplasmic fiber network and other structural changes that seem typical for
starvation; by comparing wild type and septin mutant yeast cells, I will
demonstrate the role of septins in cell-freezing .