Non-invasive technique to map fluctuations in the cell membrane
17 Nov 2017
By Dr Bidisha Sinha, Intermediate Fellow
Indian Institute of Science Education and Research Kolkata
Cells at their boundaries have a plasma membrane (PM) and an underlying layer of a special filamentous protein network called the actin cortex. These provide structural rigidity and deformability to cells while also serving as a platform where cell-cell interactions occur, electrical signals are relayed and foreign entities park before invading the cell.
The question we have addressed in our recently published paper is what kind of undulations are present in the PM, how do they evolve in time and how are they controlled by the metabolic state and actin cortex. It is important to address this because fluctuations of PM are incessant, present in all cells and can define how the membrane functions. However, at the bottom of cells, these fluctuations are tiny and cannot be measured by normal light microscopy.
We used interference reflection microscopy to measure and map local deformations and create movies of these maps. We then studied the differences in fluctuations across localities inside a single cell and the various cellular factors controlling it (see the image below).
We found that even though live cells fluctuate more than dead cells, the actin cortex works extensively to keep the PM smoothened out and reduces the fluctuations. We also report non-uniform deformation across single cells originating from transient localized peaks in deformation.
Finally, we compare the features of these fluctuations with a theoretical model and extract information like how tense the membrane might be, how easy is it to bend, how pressed it is by the surrounding. This work is unique in the sense that it did not need any labelling and yet extracts details about the physical state of the membrane.
The physical state of the membrane not only affects its functions but is also altered when cells are stressed. We, therefore, hope to extend this work in both directions – to understand more about mechanisms of membrane functioning and to test out if this method is useful in quantifying cellular health.
Interference based mapping of cell membrane fluctuations reveal their active regulation and transient heterogeneities. Biswas, Arikta; Alex, Amal and Sinha, Bidisha. 2017. Biophysical Journal, October 2017