Nature study shows how molecules escape from the nucleus

Sep 15, 2010
Messenger RNA molecules (green structures) pass through the nuclear pore (red) from the nucleus to the cytoplasm. Credit: Albert Einstein College of Medicine

By constructing a microscope apparatus that achieves resolution never before possible in living cells, researchers at Albert Einstein College of Medicine of Yeshiva University have illuminated the molecular interactions that occur during one of the most important "trips" in all of biology: the journey of individual messenger Ribonucleic acid (RNA) molecules from the nucleus into the cytoplasm (the area between the nucleus and cell membrane) so that proteins can be made. The results, published in the September 15 online edition of Nature, mark a major advance in the use of microscopes for scientific investigation (microscopy). The findings could lead to treatments for disorders such as myotonic dystrophy in which messenger RNA gets stuck inside the nucleus of cells.

Robert Singer, Ph.D., professor and co-chair of anatomy and , professor of cell biology and neuroscience and co-director of the Gruss-Lipper Biophotonics Center at Einstein, is the study's senior author. His co-author, David Grünwald, is at the Kavli Institute of Nanoscience at Delft University of Technology, The Netherlands. Prior to their work, the limit of microscopy resolution was 200 nanometers (billionths of a meter), meaning that molecules closer than that could not be distinguished as separate entities in living cells. In this paper, the researchers improved that resolution limit by 10 fold, successfully differentiating molecules only 20 nanometers apart.

Protein synthesis is arguably the most important of all cellular processes. The instructions for making proteins are encoded in the Deoxyribonucleic acid (DNA) of genes, which reside on chromosomes in the nucleus of a cell. In , DNA instructions of a gene are transcribed, or copied, onto ; these molecules of messenger RNA must then travel out of the nucleus and into the cytoplasm, where are linked together to form the specified proteins.

Molecules shuttling between the nucleus and cytoplasm are known to pass through protein complexes called nuclear pores. After tagging messenger RNA molecules with a yellow fluorescent protein (which appears green in the accompanying image) and tagging the nuclear pore with a red fluorescent protein, the researchers used high-speed cameras to film messenger RNA molecules as they traveled across the pores. The Nature paper reveals the dynamic and surprising mechanism by which nuclear pores "translocate" messenger RNA molecules from the nucleus into the cytoplasm: this is the first time their pore transport has been seen in in real time.

"Up until now, we'd really had no idea how messenger RNA travels through nuclear pores," said Dr. Singer. "Researchers intuitively thought that the squeezing of these molecules through a narrow channel such as the nuclear pore would be the slow part of the translocation process. But to our surprise, we observed that messenger RNA molecules pass rapidly through the nuclear pores, and that the slow events were docking on the nuclear side and then waiting for release into the cytoplasm."

More specifically, Dr. Singer found that single messenger RNA molecules arrive at the nuclear pore and wait for 80 milliseconds (80 thousandths of a second) to enter; they then pass through the pore breathtakingly fast—in just 5 milliseconds; finally, the molecules wait on the other side of the pore for another 80 milliseconds before being released into the cytoplasm.

The waiting periods observed in this study, and the observation that 10 percent of messenger RNA molecules sit for seconds at nuclear pores without gaining entry, suggest that messenger RNA could be screened for quality at this point.

"Researchers have speculated that messenger RNA molecules that are defective in some way, perhaps because the genes they're derived from are mutated, may be inspected and destroyed before getting into the cytoplasm or a short time later, and the question has been, 'Where might that surveillance be happening?'," said Dr. Singer. "So we're wondering if those messenger that couldn't get through the nuclear pores were subjected to a quality control mechanism that didn't give them a clean bill of health for entry."

In previous research, Dr. Singer studied myotonic dystrophy, a severe inherited disorder marked by wasting of the muscles and caused by a mutation involving repeated DNA sequences of three nucleotides. Dr. Singer found that in the cells of people with myotonic dystrophy, messenger RNA gets stuck in the nucleus and can't enter the cytoplasm. "By understanding how messenger RNA exits the nucleus, we may be able to develop treatments for myotonic dystrophy and other disorders in which messenger RNA transport is blocked," he said.

Explore further: Scientists create therapy-grade stem cells using new cocktail to reprogram adult cells

More information: The paper, "In Vivo Imaging of Labelled Endogenous β-actin mRNA during Nucleocytoplasmic Transport," was published in the September 15 online edition of Nature.

Related Stories

Researchers find key to messenger RNA control

Jul 26, 2007

Researchers at McGill University have successfully used a class of tiny nucleic acids called microRNAs to control messenger RNA, one of the major gene regulators in life, outside the confines of a living cell for the first ...

Mechanism of microRNAs deciphered

May 16, 2007

Over 30% of our genes are under the control of small molecules called microRNAs. They prevent specific genes from being turned into protein and regulate many crucial processes like cell division and development, but how they ...

Recommended for you

Healthy humans make nice homes for viruses

13 hours ago

The same viruses that make us sick can take up residence in and on the human body without provoking a sneeze, cough or other troublesome symptom, according to new research at Washington University School ...

Unraveling cell division

20 hours ago

CRG researchers shed new light on mitosis. The study published in the Journal of Cell Biology describes how Topo 2 disentangles DNA molecules and is essential for proper cell division

User comments : 0