Numerous genes and cellular pathways are activated as cells perform their daily tasks. These developmental histories are documented, thanks to the efforts of engineers at MIT, by cells of long protein chains that can be seen with a light microscope. Building blocks encoding specific biological activities are continually added by cells programmed to make these sequences. Fluorescent molecules can then be added to the ordered protein chain and read under a microscope to reconstruct the order of events.
This technique could help shed light on the steps underlying processes such as memory formation, response to drug therapy, and gene expression. “At the scale of organs and bodies, there are many untraceable changes that occur over time, from hours to weeks,” says Y. Eva Tan, professor of bioengineering, brain and cognition and neurotechnology. His professor, Edward Boyden, said: He is an investigator at the Howard Hughes Medical Institute and a member of the Massachusetts Institute of Technology’s McGovern Brain Institute and the Koch Institute for Integrative Cancer.
If the technology can be scaled up to work over time, the researchers say, it could also be used to study processes such as aging and disease progression. Boyden is a senior author on the study, published today in Nature Biotechnology. Former J. Douglas Stan of the McGovern Institute, his postdoctoral fellow and now assistant professor at the University of Michigan, Changyang Linghu, is the lead author of the paper.
Biological systems such as organs contain various types of cells, each with its own characteristic function. One of his ways of studying these functions is by imaging proteins, RNA, or other molecules inside cells, which provide clues as to what the cells are doing. However, most methods for doing this only provide a glimpse of a single moment in time or do not work well with very large cell populations. “Biological systems are often composed of many different types of cells. For example, the human brain has 86 billion cells of his,” Linghu said. “To understand this kind of biological system, we need to observe physiological events in these large cell populations over time.”
To achieve that, the research team came up with the idea of recording cellular events as a series of protein subunits, continually adding to the chain. We used engineered protein subunits not normally found in living cells that can self-assemble into long filaments. The researchers engineered a genetically-encoded system in which one of these subunits is produced continuously within the cell and another subunit is produced only when a specific event occurs. Did. Each subunit also contains a very short peptide called an epitope tag. In this case, the researcher chose tags he called HA and V5. Each of these tags can be conjugated to a different fluorescent antibody, making it easier to later visualize the tags and determine the sequence of the protein subunits.
For this study, the researchers conditionalized the generation of V5-containing subunits on activation of a gene called c-fos, which is involved in encoding new memories. HA-tagged subunits make up the bulk of the chain, but whenever the V5 tag appears in the chain, it means that c-fos was activated during that time. We hope to use self-assembly to record the activity of every cell,” Linghu said. “It is not only a snapshot of time, but also a record of past history, just as tree rings can permanently store information over time as wood grows.”
In this study, researchers first used the system to record c-fos activation in neurons growing in experimental dishes. The c-fos gene was activated by chemically induced neuronal activation and the V5 subunit was added to the protein chain. To test whether this approach works in animal brains, the researchers programmed mouse brain cells to produce protein chains when the animals were exposed to certain drugs. The researchers were then able to detect the exposure by preserving the tissue and analyzing it with a light microscope.
Researchers can design the system modularly to exchange different epitope tags and detect different types of cellular events. This, in principle, involves cell division and the activation of enzymes called protein kinases that help regulate many cellular pathways. Researchers also hope to extend the record duration that can be achieved. In this study, they recorded events for several days before imaging the tissue. Since protein chain length is limited by cell size, there is a trade-off between the time that can be recorded and temporal resolution, or frequency of event recording.
“The total amount of information that can be stored is fixed, but in principle the chain can grow slower or faster,” Linghu says. “If you want to record for a longer period of time, you can slow down the synthesis so that the cell size is reached, say, within two weeks. That way you can record longer, but at the expense of temporal resolution.” The researchers are also working on designing the system so that it can record multiple types of events in the same chain by increasing the number of different subunits that can be incorporated.
(This article is not edited by Devdiscourse staff and is auto-generated from a syndicated feed.)
