Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers make it possible for ultrasound to reveal gene expression in the body

30.09.2019

Some of the most important tools in the toolbox of modern cell biologists are special chunks of DNA that act like spies, reporting on the cell's function. The markers, known as reporter genes, allow researchers to get a sense for what cells are doing by watching genetic programs embedded in their DNA turn on and off.

Reporter genes work by encoding proteins that can be seen from outside the cell. One particularly popular reporter gene encodes something called the green fluorescent protein (GFP), which, true to its name, is a protein that glows bright green. So, if a researcher wants to learn more about how c


This is an artist's representation of a cell expressing proteinaceous gas vesicles.

Credit: Caltech

ells become neurons, they can insert the GFP gene alongside a neuronal gene into an embryo's DNA. When the embryo's cells turn on the neuron gene, they will also express the GFP gene, and the cells will glow green, making it easy for the researcher to see that the genetic program that encodes neuron formation is active.

As useful as this technique has been, it has a big limitation: Because light does not penetrate well through most living tissue, the GFP gene cannot be used for monitoring the activity of cells deep inside an organism. But now, Caltech's Mikhail Shapiro has a solution.

A team consisting of Shapiro, professor of chemical engineering and investigator with the Heritage Medical Research Institute, graduate student Arash Farhadi, and their colleagues, has developed a reporter gene that allows them to see genetic activity using ultrasound, which can penetrate deeply through tissue, instead of light.

They describe the work in a paper in the journal Science.

To develop their "acoustic reporter genes," Farhadi and Shapiro borrowed proteins from a species of buoyant bacteria that form and contain tiny air-filled protein compartments called gas vesicles.

Besides having buoyancy, the gas vesicles have another useful property: they show up strongly in ultrasound imaging, as Shapiro's lab demonstrated in 2014. If researchers could find a way to engineer a cell to form these nanostructures when a specific genetic program was active, the cells would be highlighted when exposed to ultrasound.

To turn the genes that encode gas vesicle proteins into a reporter gene, Shapiro and Farhadi needed to do something that had never before been done: transplant a genetic program of nine genes from bacteria into mammalian cells, in this case, cells derived from human kidneys (HEK cells).

Doing this was not a straightforward process because bacteria and mammals read the genes in their DNA differently. That means that although Shapiro and Farhadi could insert the bacterial DNA into the cells, those cells would not know what to do with that DNA, similar to how a program written for an Apple computer will not run on a Windows computer.

"The translation machinery is very different in the two kinds of cells," Farhadi says. "One of the biggest differences is that in bacteria it is common to have multiple genes arranged in the DNA such that they are transcribed into one shared piece of RNA, which is then translated into all the corresponding proteins, whereas in eukaryotes, every gene is usually on its own."

Shapiro says the solution came from yet another source of DNA: viruses.

"Viruses also need to trick mammalian cells into expressing a bunch of proteins," Shapiro says. "So we used viral elements to trick the cell into producing multiple genes from a shared piece of RNA." In this way, Farhadi and colleagues combined eight genes together on a single piece of RNA.

However, even after inserting working bacterial DNA into the HEK cells, Shapiro and Farhadi still did not have a complete solution. The cells were making gas vesicle proteins, but gas vesicles were not forming. It turned out that proteins not only needed to be produced, but in the right ratios.

Shapiro likens it to a construction site. A building might be made of wood, glass, and bricks, but if workers show up with mostly windows and only a few bricks, they will not be able to construct a building.

In addition to providing the building materials, some proteins encoded by the gas vesicle genes act like construction machinery--the cranes, bulldozers, et cetera--that are used to make the gas vesicles. If a construction site has 50 cranes but only one bulldozer, the project probably will not get finished. Ratios, again, are key.

"The correct ratios of proteins are programmed into the bacterial gene clusters, but when we put them into the mammalian cells, we have to figure out what those ratios need to be and how to get the mammalian cells to make those correctly," Farhadi says.

Figuring that out, Shapiro and Farhadi say, required a systematic process that took several years. Now that they have the genes working, they say they will be able to use them to study gene expression in tumors, immune cells, neurons, and other cell types in living organisms. With further improvements, they hope biologists around the world will be using ultrasound to peer into model organisms to study cells within their natural biological context, and that doctors may someday use ultrasound to monitor the fate of cell-based therapeutics in patients.

"There has been more than 20 years of work improving fluorescent proteins, and we probably have 20 years of work to improve what we've developed, but this is a key proof of concept," Shapiro says.

###

The paper describing their findings, titled, "Ultrasound Imaging of Gene Expression in Mammalian Cells," appears in the September 27 issue of Science. Other co-authors include Gabrielle H. Ho, a former technician in the Shapiro lab who is now at the University of Pennsylvania; Caltech graduate student Daniel P. Sawyer; and Raymond W. Bourdeau, a former postdoctoral fellow in the Shapiro lab who is now at Codiak Biosciences.

Funding for the research was provided by the National Science Foundation, the National Institutes of Health, the Heritage Medical Research Institute, the Packard Fellowship for Science and Engineering, and a Burroughs Wellcome Fund Career Award at the Scientific Interface.

Media Contact

Emily Velasco
evelasco@caltech.edu
626-395-6487

 @caltech

http://www.caltech.edu 

Emily Velasco | EurekAlert!
Further information:
https://www.caltech.edu/about/news/researchers-make-it-possible-ultrasound-reveal-gene-expression-body

Further reports about: DNA GFP RNA bacterial DNA genes mammalian cells multiple genes neurons proteins vesicle

More articles from Life Sciences:

nachricht Turning carbon dioxide into liquid fuel
06.08.2020 | DOE/Argonne National Laboratory

nachricht Tellurium makes the difference
06.08.2020 | Friedrich-Schiller-Universität Jena

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: ScanCut project completed: laser cutting enables more intricate plug connector designs

Scientists at the Fraunhofer Institute for Laser Technology ILT have come up with a striking new addition to contact stamping technologies in the ERDF research project ScanCut. In collaboration with industry partners from North Rhine-Westphalia, the Aachen-based team of researchers developed a hybrid manufacturing process for the laser cutting of thin-walled metal strips. This new process makes it possible to fabricate even the tiniest details of contact parts in an eco-friendly, high-precision and efficient manner.

Plug connectors are tiny and, at first glance, unremarkable – yet modern vehicles would be unable to function without them. Several thousand plug connectors...

Im Focus: New Strategy Against Osteoporosis

An international research team has found a new approach that may be able to reduce bone loss in osteoporosis and maintain bone health.

Osteoporosis is the most common age-related bone disease which affects hundreds of millions of individuals worldwide. It is estimated that one in three women...

Im Focus: AI & single-cell genomics

New software predicts cell fate

Traditional single-cell sequencing methods help to reveal insights about cellular differences and functions - but they do this with static snapshots only...

Im Focus: TU Graz Researchers synthesize nanoparticles tailored for special applications

“Core-shell” clusters pave the way for new efficient nanomaterials that make catalysts, magnetic and laser sensors or measuring devices for detecting electromagnetic radiation more efficient.

Whether in innovative high-tech materials, more powerful computer chips, pharmaceuticals or in the field of renewable energies, nanoparticles – smallest...

Im Focus: Tailored light inspired by nature

An international research team with Prof. Cornelia Denz from the Institute of Applied Physics at the University of Münster develop for the first time light fields using caustics that do not change during propagation. With the new method, the physicists cleverly exploit light structures that can be seen in rainbows or when light is transmitted through drinking glasses.

Modern applications as high resolution microsopy or micro- or nanoscale material processing require customized laser beams that do not change during...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“Conference on Laser Polishing – LaP 2020”: The final touches for surfaces

23.07.2020 | Event News

Conference radar for cybersecurity

21.07.2020 | Event News

Contact Tracing Apps against COVID-19: German National Academy Leopoldina hosts international virtual panel discussion

07.07.2020 | Event News

 
Latest News

Rare Earth Elements in Norwegian Fjords?

06.08.2020 | Earth Sciences

Anode material for safe batteries with a long cycle life

06.08.2020 | Power and Electrical Engineering

Turning carbon dioxide into liquid fuel

06.08.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>