University of Minnesota
School of Physics & Astronomy


Cellular signaling networks

Elias Puchner
Elias Puchner
Richard Anderson

A group of researchers at the School of Physics and Astronomy are working to uncover how cells and their signaling networks detect and respond to stimuli. Elias Puchner is new faculty member in the area of experimental biological physics. Through his research he intends to provide “a nano-scale view of cell communication.”

Puchner says,“I find the ability of a cell to act as a sensor absolutely fascinating.” “For example, chemotactic cells (those responsible for movement in response to chemical stimuli) can sense a gradient of molecules.

In general, cells process signals through networks, acting almost like electronic circuits, to control the behavior of the cell in response to the signal it receives.” In the case of chemotactic cells this means either moving toward helpful material like food or away from potentially hurtful material from the higher concentration of molecules.

The group, which currently consists of six members and brings together the expertise from undergraduates, graduate students and the postdoc Elizabeth Smith is currently setting up a lab to do super resolution microscopy at the single molecule level. This is a fairly new technique that received the 2014 Nobel Prize in Chemistry. “The optical resolution of traditional microscopy is held back by the diffraction limit (about half the wavelength of light) which means that objects less than about 200-300 nm cannot be resolved,” he says. This is one of the biggest challenges of Puchner’s research in that the molecular structures he studies are small (less than 80 nm or about 1000 times thinner than a human hair) and densely packed such that they can be located but not resolved with conventional optical microscopy.

Super resolution microscopy allows for visualization of these molecular structures by using pulses of light to sparsely switch individual fluorophores to their fluorescent state, allowing the user to localize their positions and to study structures much smaller than the diffraction limit. One specific way that super resolution microscopy achieves this activation of fluorophores is through photoswitchable dyes. These dyes allow physicists to finely tune the activation rate, allowing densely packed structures to be viewed. In addition, the motion of individual proteins can be tracked resulting in dynamic insights into molecular processes.

The molecular biology portion of the new research lab will be equipped to grow and label cells so that they can be genetically manipulated for observation. The process will take genes from fluorescent corrals and insert them into the yeast genome so that the cell will automatically produce the fluorescent corral protein attached to a protein of interest. Yeast cells have the advantage of growing fast, being robust and easy to genetically manipulate, with one further unexpected advantage: “It always smells like a bakery when you work with yeast cells.” Eventually, Puchner will transfer these techniques to mammalian cells, which are more biomedically relevant. “We will start to investigate these processes in yeast cells, but obviously it is much more useful to study mammalian cells in order to study disease.”

It is also possible to use cell activation mechanisms for therapeutic purposes. In his previous research, Puchner applied imaging techniques in immune T-cells to characterize a new type of receptor that can be externally switched on and off. Such remotely controlled therapeutic T-Cells could be extremely powerful in that they could be finely tuned by a drug and eventually be used in cancer therapy.

Puchner says that understanding how signal cascades are activated is a first step towards re-engineering and manipulating them. Being able to manipulate signaling processes opens up a range of possibilities, some of which sound like science fiction. “There are optogenetic tools that allow researchers to artificially cluster signaling proteins in various cell types by attaching cryptochrome proteins from plants. Structures in plants that sense blue light do so by condensing themselves. This action triggers directional growth towards the light source.” Puchner says that they could conceivably cut out and amplify the light-sensitive condensing gene, take it to a different organism and it will condense in response to light, causing the proteins to cluster. “Since the activity of many signaling proteins is sensitive to their degree of clustering, we should be able to externally control the cell’s behavior with light.”