A breakthrough discovery into how living cells process and respond to chemical information could help advance the development of treatments for a large number of cancers and other cellular disorders that have been resistant to therapy. An international collaboration of researchers, led by scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley, have unlocked the secret behind the activation of the Ras family of proteins, one of the most important components of cellular signaling networks in biology and major drivers of cancers that are among the most difficult to treat.
Posts Tagged ‘cell biology’
Cells are the basic structural units of all life. They were first observed more than 400 years ago after the invention of the microscope. One of the most studied cells in science is E. coli, a sausage-shaped bacterium that can cause food poisoning.
In fact, cells resemble sausages insofar as both consist of outer envelopes stuffed with an inner mass. For decades biologists have believed that the growth of this inner mass, pressing on the outer membrane, is what caused cell walls to grow.
However, using new techniques to isolate and visualize cells in different environments, the Stanford team proved that cell wall growth occurred regardless of the pressures exerted on the cell – whether from inside or out.
Here it is critical to understand that, unlike a sausage, the outer envelope of a cell is alive, dynamic and porous. It is designed to allow water to seep in or out. This is important because cells live in fluids and hence are subject to the pressure of osmosis.
Osmosis relates to the amount of solid materials dissolved in a liquid solution. Stirring sugar into coffee, for instance, increases its osmotic pressure. The more sugar you stir in, the higher the osmotic pressure of the solution.
Life is based on water, so cells have an internal osmotic pressure. When a cell enters a solution with a higher osmotic pressure – such as a sugary liquid – its porous membrane tries to protect the cell by letting water out. This causes the cell membrane to shrivel up, compacting the cell to withstand the pressure from without. Put the same cell back into a normal solution, and the porous cell wall allows water to seep back in, causing the cell to swell to its former size.
Biologists have long supposed that this same pressure dynamic retarded cell wall growth. It made sense given the prevailing wisdom – if cell wall growth were indeed driven by expansion from inside the cell, and outward pressure forced the cell to contract, how could the outer cell wall continue to grow?
In fact, the Stanford team initially designed its experiment to measure precisely how much osmotic pressure slowed cell wall growth in E. coli.
They used microfluidic devices to trap the bacterial cells in tiny chambers. This allowed them to bathe the confined cells, first in highly concentrated sugars (high osmotic pressure), then in normal solutions (low osmotic pressure), while recording precise images of cell contraction or expansion.
Initially, the results seemed to confirm the prevailing wisdom: cells bathed in a sugar solution appeared to grow more slowly.
But whenever the researchers “shocked” the cells by flushing out the sugars and bathing the cells in normal solution they were surprised to see that the cells expanded rapidly – in a matter of seconds — to a size roughly equivalent to cells growing at full speed in normal solutions. Click here to see the video.
“The cells just didn’t seem to care that they had been subjected to frequent and large (osmotic) insults in the chamber,” Huang said.
The Stanford researchers came to realize that the cell walls had continued to grow in the sugar solution just as fast as in the normal solution – but the extra mass was shriveled like a raisin. When the cell re-entered the normal solution and water seeped back in through the porous membrane, the now-turgid cell smoothed out like a grape, and all the non-apparent growth became visible.
To follow up this surprising finding, Rojas is in Bangladesh, extending the investigations to study how bacterial pathogens such as Vibrio cholerae respond to rapidly changing fluid environments and how to use this knowledge to fight this scourge.
Thanks to Stanford School of Engineering for contributing this story.
Bio-Rad Laboratories, Inc. today announced the launch of its CytoTrack Cell Proliferation Assays that provide unmatched flexibility when designing a multicolor flow cytometry experiment, allowing researchers to efficiently stain and track live cells in four colors for up to 10 generations — two more generations than other currently available methods can follow.
CFDA-SE, the most commonly used reagent for monitoring cell proliferation, is difficult to use in multicolor experiments because it has the same spectra as green fluorescent protein and the most frequently used fluorophore, fluorescein.
Unlike CFDA-SE and other popular cell proliferation assays that are available in only one color, Bio-Rad’s CytoTrack Assays are available in four different emission wavelengths ranging from blue to far red. This allows researchers to choose the one most suitable for their multicolor flow cytometric experiment.
The CytoTrack Assay dye reacts with primary amines using a proprietary chemistry that provides effective labeling of cells without the large efflux usually seen with CFDA-SE.
“This unique feature allows researchers to easily visualize up to 10 cell divisions, making it ideal for those interested in studying the induction and inhibition of cell division in any in vitro experimental model,” said Mary Thao, Bio-Rad Product Manager in the Gene Expression Division.
CytoTrack Assays come in easy-to-use vials with material sufficient for 50 experiments. The dye can be added directly into the culture medium, allowing researchers to save time.
For more information about Bio-Rad’s cell proliferation assays, please visit bio-rad.com/cellproliferation
An international team led by researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a new technique for identifying gene enhancers – sequences of DNA that act to amplify the expression of a specific gene – in the genomes of humans and other mammals. Called SIF-seq, for site-specific integration fluorescence-activated cell sorting followed by sequencing, this new technique complements existing genomic tools, such as ChIP-seq (chromatin immunoprecipitation followed by sequencing), and offers some additional benefits.
“While ChIP-seq is very powerful in that it can query an entire genome for characteristics associated with enhancer activity in a single experiment, it can fail to identify some enhancers and identify some sites as being enhancers when they really aren’t,” says Diane Dickel, a geneticist with Berkeley Lab’s Genomics Division and member of the SIF-seq development team. “SIF-seq is currently capable of testing only hundreds to a few thousand sites for enhancer activity in a single experiment, but can determine enhancer activity more accurately than ChIP-seq and is therefore a very good validation assay for assessing ChIP-seq results.”
Dickel is the lead author of a paper in Nature Methods describing this new technique. The paper is titled “Function-based identification of mammalian enhancers using site-specific integration.”
In a finding that directly contradicts the standard biological model of animal cell communication, UCSF scientists have discovered that typical cells in animals have the ability to transmit and receive biological signals by making physical contact with each other, even at long distance.
The mechanism is similar to the way neurons communicate with other cells, and contrasts the standard understanding that non-neuronal cells “basically spit out signaling proteins into extracellular fluid and hope they find the right target,” said senior investigator Thomas B. Kornberg, PhD, a professor of biochemistry with the UCSF Cardiovascular Research Institute.
The paper was published on January 2, 2014 in Science.