New imaging technique reveals intense "activity" before cell death

Studying the movement of tiny cells is not a small task. For chromatin, the group of macromolecules of DNA, RNA, and proteins in our genome, motion is an integral part of its active role as a regulator of how our genes are expressed or repressed.

"Understanding the macromolecular movement is essential, but scientists know very little about it," said Vadim Backman, Walter Dill Scott Professor of Biomedical Engineering at Northwestern University. "One reason is that we lack instrumental techniques to observe these processes."

At present, a research team from the McCormick School of Engineering led by Backman has developed a new optical technique to study cell movement without using labels or dyes to track them. The innovative method also revealed an undiscovered phenomenon that could play a role in the early stages of cell death.

The ideas of the team were published April 10 in the newspaper Nature Communications. The document titled "Multimodal interference-based imaging of the nanoscale structure and macromolecular motion uncovers the UV-induced cell paroxysm".

Scientists can currently track the movement of cells with the help of molecular dyes or labels, but this practice has limitations. Dyes are toxic and alter the behavior of cells before killing them. Labels are attached to cells, may be toxic or cause photobleaching and may alert the movement of the molecules they label.

The new technique, called dual-PWS, does not contain a label and allows imaging and measuring macromolecular movement without the use of dye. Based on a quantitative imaging technique previously created by Backman and called Partial Wave Spectroscopy (PWS), the platform uses interference and pattern modifications from backscattered light to monitor both the macromolecular structure of the cells and their dynamic movement.

"Critical processes such as the transcription of a gene or the repair of damaged proteins require the simultaneous displacement of many molecules in a complex and extremely dense environment," said Scott Gladstein, Ph.D. student in the laboratory's laboratory. Backman and first author of the study. "As an imaging platform capable of measuring both intracellular structure and macromolecular dynamics in living cells sensitive to structures as small as 20 nm with time resolution in milliseconds, the dual-PWS is particularly well suited to allow us to study these processes. "

The researchers applied double PWS by studying the structural and dynamic changes at the nanoscale chromatin in eukaryotic cells in vitro. Using ultraviolet light to induce cell death, the team measured how the movement of chromatin cells was altered.

"It makes sense that when cells are about to die, their dynamics diminish," Backman said. "The existing facilitation movement in living cells to help express genes and modify their expression in response to stimuli is disappearing, we expected that."

The researchers did not expect to witness a biological phenomenon for the first time. A cell reaches a "point of no return" upon decay, and even if the source of cellular damage is halted, the cell would be unable to recover, said Backman. With the help of a dual PWS system, the researchers observed that just before this turn, the genomes of cells exploded with rapid and instantaneous movement, with different parts of the cell apparently moving randomly.

"All of the cells we tested that were destined to die knew this paroxysmal reflex, and none of them could return to a viable state after it was put in place," said Backman, who heads the new Cancer Center. Northwestern Physical and Engineering Genomics.

The team does not know why or how this phenomenon occurs, called cell paroxysm. Backman originally wondered if the movement could be due to ions entering the cell, but such a process would have taken too much time. The uncoordinated movements of cellular structures occurred in milliseconds.

"Nothing in biology can go that fast," said Backman. He added that members of his lab were so surprised by the results that they joked that the phenomenon could be explained by the fact that "Mid-Chlorians" are leaving the cell, a reference to the 39, chemical incarnation of "The Force" in Star Wars movies.

If cellular paroxysms remain a mystery for the moment, Backman thinks that the team's findings underscore the importance of studying the macromolecular behavior of living cells. The more researchers will be able to obtain information on chromatin, the more likely they will be to regulate gene expression one day, which could change the way people are treated for diseases such as cancer and disease. d & # 39; Alzheimer's.

"Every biological process you can imagine involves some sort of macromolecular rearrangement," said Backman. "As we develop our research, I can not help but wonder," What are we going to find next? "