Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Observing proteins and cells in the wild

13.12.2002


’Quantum dots’ may allow researchers to track proteins and cells in their natural environments



Imagine if molecular and cell biologists could watch proteins and cells at work in their natural habitat in the same way that wildlife biologists observe animals in the wild. They’d sit back and witness first hand their microscopic subjects’ daily routines, interactions and movements, and the places they prefer to be.

This fantasy is rapidly becoming a reality thanks to new Rockefeller University research that takes advantage of a technology originally developed in the early 1980s for use in computers. Called "quantum dots," these fluorescent nanocrystals can be made to glow brightly in any desired color and thus for years have glimmered in the eyes of biologists hoping to use them for molecular and cellular imaging. But, while their potential has been clear, scientists have not been able to persuade living biological tissues to explicitly and safely take up the synthetic dots - until now.


In the Jan. issue of Nature Biotechnology, the Rockefeller University researchers demonstrate for the first time how quantum dots can be used to simultaneously track multiple living proteins or cells for up to days at a time. A fluorescent microscope is all that is required to follow the minute-by-minute activities of the color-coded proteins and cells.

"To truly understand the function of proteins and cells in their natural environment, we need to be able to watch them go about their normal business in real time," says Sanford Simon, Ph.D., head of the Laboratory of Cellular Biophysics at Rockefeller and principal investigator of the study.

Quantum dots may have medical applications as well as biological ones. For example, in such diseases as cystic fibrosis and Alzheimer’s, certain proteins travel to the wrong places; like a milk truck delivering its goods to a post office instead of the grocery store, the aberrant proteins disrupt the working community of the cell. By using quantum dots to follow these proteins once they are produced in body cells, scientists can get a better handle on what goes wrong in the sorting process that leads to disease.

"Quantum dots are an incredibly powerful tool. I am sure there are many biological and medical applications we haven’t thought of yet," says Jyoti Jaiswal, Ph.D., a postdoctoral associate at Rockefeller and first author of the paper.

Other authors of this study include Hedi Mattoussi and J. Matthew Mauro of the U.S. Naval Research Laboratory, Washington, D.C.

Spectral clutter

Currently, researchers visualize proteins and cells by labeling them with organic fluorescent dyes, or fluorophores, such as the popular green fluorescent protein (GFP) produced naturally by jellyfish. But this approach has several limitations.

The first has to do with how researchers induce dyes to emit light of a certain color, or spectra. For example, to make GFP produce green light, the scientists must first hit it with a laser light of a shorter wavelength, such as blue. But, if another dye were being used at the same time, one that fluoresces in the blue wavelength, then its signal would be lost in the blue light needed to trigger the first dye. Such spectral overlap limits the use of fluorophores to two, sometimes three, in any given experiment.

A second limitation of fluorophores is that they don’t shine brightly for very long.

The unique physical properties of quantum dots overcome these obstacles. Simply by altering their size, scientists can manufacture them to produce light in any color of the rainbow, and, additionally, only one wavelength of light is required to illuminate all of the different-colored dots. Thus, spectral overlap no longer limits the number of colors that can be used at once in an experiment. In addition, quantum dots do not stop glowing even after being visualized for very long periods of time: compared to most known fluorescent dyes, they shine for an average of 1,000 times longer.

Water-loving coats

But while quantum dots solve these problems, they have limitations of their own - the biggest one being their water-fearing or "hydrophobic" nature. For quantum dots to mix with the watery contents of a cell, they have to possess a water-loving, or "hydrophilic" coat. Three years ago, Simon and Jaiswal’s colleagues at the U.S. Naval Research Laboratory made their dots biocompatible by enveloping them in a layer of the negatively charged dihydroxylipoic acid (DHLA).

In the same study, the researchers overcame a second major obstacle of making quantum dots biologically useful - building protein-specific dots. By linking antibodies specific for an experimental protein to the DHLA-capped dots, they were able to demonstrate protein-specificity in a test tube.

In the present study, the Rockefeller scientists in collaboration with their U.S. Naval Research Laboratory colleagues have again synthesized protein-specific quantum dots, but this time they have shown their efficacy in living cells - a first for this budding technology. To do this, the researchers employed two different methods of synthesizing the quantum dots, both of which involved linking the negatively charged DHLA-capped dots to positively charged molecules - either avidin or protein G bioengineered to bear a positively charged tail. Because avidin and protein G can be made to readily bind antibodies, the researchers could then attach the dots to their protein-specific antibody of choice.

The critical test was to determine specificity: can quantum dots achieve the same exquisite selectivity that occurs when a protein is synthesized fused to GFP? To answer this question, Simon and colleagues engineered a population of cells growing together in a dish to randomly produce different levels of a membrane protein fused to GFP. When these cells were incubated with quantum dots conjugated to an antibody specific for that membrane protein, the pattern of GFP fluorescence matched the fluorescence of the quantum dots. However, the fluorescence of quantum dots lasted immeasurably longer, and the proteins could now be imaged in a rainbow of colors.

"Researchers should now be able to rapidly create an assortment of quantum dots that specifically bind to several proteins of interest," says Jaiswal.

Uncharted cellular terrain

Proteins aren’t the only subjects the researchers successfully lit up with quantum dots: cells too were labeled and observed in their normal setting for very long periods of time. In the Nature Biotechnology paper, the researchers monitored human tissue culture cells tagged with quantum dots over two weeks with no adverse effects on cells. They also continuously observed slime mold cells labeled with quantum dots through 14 hours of growth and development without detecting any damage. This type of cell-tracking approach would allow researchers to study cell fate either outside the body in culture, or in whole developing organisms.

"With quantum dots, you could follow each cell in the worm C. elegans continuously from its birth in an embryo to its final destination in an adult three and a half days later," says Jaiswal.

Interestingly, the researchers discovered that they could label the cells with quantum dots using a natural process known as endocytosis, whereby cells engulf vitamins and nutrients from their outside surroundings.

"By having the cells take up the dots on their own, you reduce the risk of damaging them," says Simon.

Finally, taking advantage of their newfound ability to color-code slime mold cells, the researchers answered a long standing question about their behavior. When starved, slime molds - which typically exist as single-celled creatures - protect themselves by coming together to form one slug-shaped, multicellular organism. Scientists know that the starved cells possess the ability to instruct other nearby cells to take shape around them, while non-starved cells do not. However, they did not know the extent to which starvation differentially affects this ability.

By tagging non-starved, short-term starved and long-term starved slime mold cells with three different colors and watching their behavior under a microscope, the researchers were able to solve this riddle. It turns out that any starved cell, no matter how starved it may be, has the same ability to induce neighboring cells to undergo development.

In this experiment, quantum dots illuminated the answer to a question that heretofore lay hidden in the dark. What other biological and medical problems will yield under the power of their glow? According to Jaiswal, the possibilities are numerous. "We now have the freedom to ask all sorts of new questions."



To view animated movies of the quantum dot-labeled slime molds in action, visit the researchers Web site at: http://www.rockefeller.edu/labheads/simon/simon-lab.html.

Founded by John D. Rockefeller in 1901, The Rockefeller University was this nation’s first biomedical research university. Today it is internationally renowned for research and graduate education in the biomedical sciences, chemistry, bioinformatics and physics. A total of 21 scientists associated with the university have received the Nobel Prize in medicine and physiology or chemistry, 16 Rockefeller scientists have received Lasker Awards, have been named MacArthur Fellows and 11 have garnered the National Medical of Science. More than a third of the current faculty are elected members of the National Academy of Sciences.


Whitney Clavin | EurekAlert!
Further information:
http://www.rockefeller.edu/labheads/simon/simon-lab.html
http://www.rockefeller.edu/

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>