In Scientific First,
Researchers
Visualize Proteins Being Born
Visualize Proteins Being Born
Breakthrough
Technology Allows Einstein Scientists
to Observe Protein
Production at the Root of Diseases
May 5, 2016—(BRONX, NY)—For the first time, scientists at
Albert Einstein College of Medicine have developed a technology allowing them
to “see” single molecules of messenger RNA as they are translated into proteins
in living mammalian cells. Initial findings using this technology that may shed
light on neurological diseases as well as cancer were published online today in
Science.
“Translation is the fundamental biological process for
converting mRNA’s information into proteins,” said Robert Singer, Ph.D., the
paper’s senior author and co-chair of anatomy & structural biology and
co-director of the Gruss
Lipper Biophotonics
Center
The production of the thousands of different proteins made
by our cells starts in the nucleus, when protein-making information encoded in
a gene’s DNA is transcribed into molecules of messenger RNA (mRNA). These mRNA
molecules exit the nucleus and migrate to specific regions of the cytoplasm. In
the next step, called translation, the mRNA molecules hook up with molecular
structures called ribosomes. Using mRNA as their blueprint, the ribosomes
generate proteins by linking together amino acids one at a time. Researchers
can use the Einstein technology to follow single mRNA molecules in real time as
they arrive at their destination in the cytoplasm—and then to observe the
proteins as they are being generated by the ribosomes.
The Einstein scientists observed the translation of single
mRNA molecules in two types of cells: human cancer (osteosarcoma) cells and
mouse neurons. The scientists made a surprising finding in neurons, where mRNA
translation into protein was found to occur in “bursts”—a phenomenon never
before possible to observe.
“Neurons must control protein synthesis very closely,
because nerve transmission depends on synthesizing the right amount of protein
at precisely the right place: the synapses, where neurons form circuits,” said
Dr. Singer. “Bursts of translation activity may be the best way for neurons to
control the amount and location of protein production—and neurological disease
may result from neurons’ inability to control that bursting. So our findings
may have implications for intellectual disorders such as Fragile X Syndrome,
which seem to involve too much protein production, and possibly for
neurodegenerative disorders such as Alzheimer’s in which clumps of beta-amyloid
protein may block neuron-to-neuron signaling at synapses.”
Another surprising observation occurred when the researchers
looked at mRNA translation in cancer cells. In contrast to neurons, cancer
cells displayed a striking inability to regulate the translation of mRNA.
Instead, mRNA translation was a continuous process in these cells. Since
proteins play crucial roles in controlling cell division, the uncontrolled
translation of certain proteins may lead to certain types of cancer. “
With our technology, researchers can now study
disease-causing protein aberrations at a very basic level that was never
possible before,” says Dr. Singer.
The Einstein technology for observing the translation of
single molecules of mRNA was developed primarily by Bin Wu, Ph.D., the lead
author of the study and research assistant professor of anatomy &
structural biology. It involved two challenges: visualize single molecules of
mRNA as well as single molecules of protein translated from the mRNA. In
research published in Molecular Cell in 1998, Dr. Singer’s lab had become the
first to successfully visualize single molecules of mRNA in living cells, so
Dr. Wu adapted that technique here.
To the mRNA that codes for the protein actin, he added mRNA
that codes for red fluorescent protein along with “membrane targeting sequence”
mRNA that helps the mRNA molecule find its way to the endoplasmic reticulum
(ER)—a membranous cellular structure that is a major focus of protein synthesis
and that transports proteins and lipids throughout the cell. This package of
mRNA was inserted into cells by attaching it to a retrovirus used to infect
them. As the mRNA molecules diffused towards the ER, each synthesized a
“nascent peptide” that tethered it to the ER—after which translation began in
earnest.
Next he tackled the second challenge, which was finding a
way to visualize the individual proteins being born as the mRNA was translated.
Here Dr. Wu used a recently published technique in which genetically encoded
single-chain antibodies fused to green fluorescent protein recognize the newly
formed protein and bind to it, making the protein visible. While this first
study looked at translation of single mRNA molecules in neurons and cancer
cells, the technology can potentially be used to study translation in any type
of cell.
The paper is titled “Translation dynamics of single mRNAs in
live cells and neurons.” Other Einstein authors were Carolina Eliscovich,
Ph.D., and Young J. Yoon, Ph.D. The research was supported by the National
Institutes of Health (NS083085).
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