Archive for the ‘biology’ category

New study shines light on how to better engineer fluorescent proteins

September 22, 2017

Researchers have now captured the ultrafast changes of green fluorescent proteins as they transition between a dark and fluorescent state, using an X-ray laser at the SLAC National Accelerator Laboratory.

Green fluorescent proteins (GFPs), originally found in the jellyfish Aequorea victoria, have helped transform biomedical research. Their green glow has acted like a flashlight on the inner workings of cells, illuminating pathways and processes in lab dishes and living animals since it was discovered in 1961. The protein acts as a molecular switch depending on the conditions, flipping from dark to glowing when excited by light. Scientists attach these fluorescent tags to other proteins to track their activity — studying how cancer cells spread, how HIV infections progress, how genes are expressed and much more.

Although researchers have used these proteins for decades, they were unable to observe how GFPs flipped between their dark and glowing states until now. The transition was too fast for traditional X-ray imaging techniques. So an international collaboration of scientists recently used SLAC’s Linac Coherent Light Source, one of the world’s fastest and brightest X-ray lasers, to excite the proteins and take snapshots of the fluorescent molecules in action.

These images were used to investigate what happened as GFP flipped states — with the hope of engineering GFP to make this happen even faster. They found that the protein became momentarily stuck between a dark and glowing state, as reported in Nature Chemistry.

“After a picosecond, a very short time, this molecular switch is stuck between on and off,” said Martin Weik, PhD, a scientist at the Institute of Structural Biology in Grenoble, France, in a recent news release. “People have predicted this, but to actually confirm it experimentally is extremely exciting. It’s as if there is a door and it’s neither closed nor completely open; it’s half open. And now we are learning what can go through the door, what might be blocking it and how it works in real-time.”

The team discovered that an amino acid partially blocked the doorway, slowing the GFP’s ability to flip states. Using this knowledge, they then engineered a mutated version of the protein with a smaller amino acid that could switch more quickly — creating a brighter and more efficient fluorescent tag that can observe cellular processes more precisely.

“We think that this approach will open a world of possibilities to tailor and create proteins,” Weik said in the release. “We not only have the structure of the molecule, but now we can see what is happening between one static state and the other.”

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.

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The skinny on how chickens grow feathers and, perhaps, on how humans grow hair

July 24, 2017

How do skin cells make regularly spaced hairs in mammals and feathers in birds? Scientists had two opposing theories, but new research at the University of California, Berkeley surprisingly links them.

The first theory contends that the timing of specific gene activation dictates a cell’s destiny and predetermines tissue structure — for example, in the skin, gene activation determines whether a skin cell becomes a sweat gland cell or hair cell, or remains a skin cell. The second theory asserts that a cell’s fate is determined instead by interacting with other cells and the material that it grows on.

Now, Berkeley researchers have found that the creation of feather follicles (like hair follicles) is initiated by cells exerting mechanical tension on each other, which then triggers the necessary changes in gene expression to create the follicles. Their results were recently reported in Science.  

“The cells of the skin in the embryo are pulling on each other and eventually pull one another into little piles that each go on to become a follicle,” said first author Amy Shyer, PhD, a post-doctoral fellow in molecular and cell biology at the University of California, Berkeley, in a recent news release. “What is really key is that there isn’t a particular genetic program that sets up this pattern. All of these cells are initially the same and they have the same genetic program, but their mechanical behavior produces a difference in the piled-up cells that flips a switch, forming a pattern of follicles in the skin.”

The research team grew skin taken from week-old chicken eggs on different materials with varying stiffness. They found that the stiffness of the substrate material was critical to forming feather follicles — material that was too stiff or too soft yielded only one follicle, whereas material with intermediate stiffness resulted in an orderly array of follicles.

“The fundamental tension between cells wanting to cluster together and their boundary resisting them is what allows you to create a spaced array of patterns,” said co-author Alan Rodgues, PhD, a biology consultant and former visiting scholar at Berkeley.

The researchers also showed that when the cells cluster together, this activated genes in those cells to generate a follicle and eventually a feather.

Although the study used chicken skin, the researchers suggest that they have discovered a basic mechanism, which may be used in the future to help grow artificial skin grafts that look like normal human skin with hair follicles and sweat pores.

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.


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