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Using R2D2 to Understand RNA Folding

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If you love learning more about biology at a fundamental level, I have a great video for you! It simulates the 3D folding of RNA. RNA is a single stranded molecule, but it is still capable of forming internal loops that can be stabilized by base pairing, just like its famously double-stranded parent, DNA. Understanding more about RNA folding may be valuable in many different areas of biomedical research, including developing ways to help people with RNA-related diseases, such as certain cancers and neuromuscular disorders, and designing better mRNA vaccines against infectious disease threats (like COVID-19).

Because RNA folding starts even while an RNA is still being made in the cell, the process has proven hugely challenging to follow closely. An innovative solution, shown in this video, comes from the labs of NIH grantees Julius Lucks, Northwestern University, Evanston, IL, and Alan Chen, State University of New York at Albany. The team, led by graduate student Angela Yu and including several diehard Star Wars fans, realized that to visualize RNA folding they needed a technology platform that, like a Star Wars droid, is able to “see” things that others can’t. So, they created R2D2, which is short for Reconstructing RNA Dynamics from Data.

What’s so groundbreaking about the R2D2 approach, which was published recently in Molecular Cell, is that it combines experimental data on RNA folding at the nucleotide level with predictive algorithms at the atomic level to simulate RNA folding in ultra-slow motion [1]. While other computer simulations have been available for decades, they have lacked much-needed experimental data of this complex folding process to confirm their mathematical modeling.

As a gene is transcribed into RNA one building block, or nucleotide, at a time, the elongating RNA strand folds immediately before the whole molecule is fully assembled. But such folding can create a problem: the new strand can tie itself up into a knot-like structure that’s incompatible with the shape it needs to function in a cell.

To slip this knot, the cell has evolved immediate corrective pathways, or countermoves. In this R2D2 video, you can see one countermove called a toehold-mediated strand displacement. In this example, the maneuver is performed by an ancient molecule called a single recognition particle (SRP) RNA. Though SRP RNAs are found in all forms of life, this one comes from the bacterium Escherichia coli and is made up of 114 nucleotides.

The colors in this video highlight different domains of the RNA molecule, all at different stages in the folding process. Some (orange, turquoise) have already folded properly, while another domain (dark purple) is temporarily knotted. For this knotted domain to slip its knot, about 5 seconds into the video, another newly forming region (fuchsia) wiggles down to gain a “toehold.” About 9 seconds in, the temporarily knotted domain untangles and unwinds, and, finally, at about 23 seconds, the strand starts to get reconfigured into the shape it needs to do its job in the cell.

Why would evolution favor such a seemingly inefficient folding process? Well, it might not be inefficient as it first appears. In fact, as Chen noted, some nanotechnologists previously invented toehold displacement as a design principle for generating synthetic DNA and RNA circuits. Little did they know that nature may have scooped them many millennia ago!


[1] Computationally reconstructing cotranscriptional RNA folding from experimental data reveals rearrangement of non-naïve folding intermediates. Yu AM, Gasper PM Cheng L, Chen AA, Lucks JB, et. al. Molecular Cell 8, 1-14. 18 February 2021.


Ribonucleic Acid (RNA) (National Human Genome Research Institute/NIH)

Chen Lab (State University of New York at Albany)

Lucks Laboratory (Northwestern University, Evanston IL)

NIH Support: National Institute of General Medical Sciences; Common Fund

Welcoming First Lady Jill Biden to NIH!

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Video Event

It was wonderful to have First Lady Jill Biden pay a virtual visit to NIH on February 3, 2021, on the eve of World Cancer Day. Dr. Biden joined me, National Cancer Institute (NCI) Director Ned Sharpless, and several NCI scientists to discuss recent advances in fighting cancer. On behalf of the entire NIH community, I thanked the First Lady for her decades of advocacy on behalf of cancer education, prevention, and research. To view the event, go to 53:20 in this video. Credit: Adapted from White House video.

NIH at 80: Sharing a Timeless Message from President Roosevelt

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This Saturday, October 31, marks an important milestone in American public health: the 80th anniversary of President Franklin Delano Roosevelt’s dedication of the campus of the National Institutes of Health (NIH) in Bethesda, MD. The President’s stirring speech, delivered from the steps of NIH’s brand-new Administration Building (now called Building 1), was much more than a ribbon-cutting ceremony. It gave voice to NIH’s commitment to using the power of science “to do infinitely more” for the health of all people with “no distinctions of race, of creed, or of color.”

“We cannot be a strong nation unless we are a healthy nation. And so, we must recruit not only men and materials, but also knowledge and science in the service of national strength,” Roosevelt told the crowd of about 3,000. To get a sense of what it was like to be there on that historic day, I encourage you to check out the archival video footage above from the National Archives and Records Administration (NARA).

These words from our 32nd President are especially worth revisiting for their enduring wisdom during a time of national crisis. In October 1940, with World War II raging overseas, the United States faced the prospect of defending its shores and territories from foreign forces. Yet, at the same time as he was bolstering U.S. military capacity, Roosevelt emphasized that it was also essential to use biomedical research to shore up our nation’s defenses against the threats of infectious disease. In a particularly prescient section of the speech, he said: “Now that we are less than a day by plane from the jungle-type yellow fever of South America, less than two days from the sleeping sickness of equatorial Africa, less than three days from cholera and bubonic plague, the ramparts we watch must be civilian in addition to military.”

Today, in the midst of another national crisis—the COVID-19 pandemic—a similar vision is inspiring the work of NIH. With the aim of defending the health of all populations, we are supporting science to understand the novel coronavirus that causes COVID-19 and to develop tests, treatments, and vaccines for this disease that has already killed more than 225,000 Americans and infected more than 8.6 million.

As part of the dedication ceremony, Roosevelt thanked the Luke and Helen Wilson family for donating their 70-acre estate, “Tree Tops,” to serve as a new home for NIH. (Visitors to Wilson Hall in Building 1 will see portraits of the Wilsons.) Founded in 1887, NIH had previously been housed in a small lab on Staten Island, and then in two cramped lab buildings in downtown Washington, D.C. The move to Bethesda, with NIH’s first six buildings already dotting the landscape as Roosevelt spoke, gave the small agency room to evolve into what today is the world’s largest supporter of biomedical research.

Yet, as FDR gazed out over our fledging campus on that autumn day so long ago, he knew that NIH’s true mission would extend far beyond simply conducting science to providing much-needed hope to humans around the world. As he put it in his closing remarks: “I voice for America and for the stricken world, our hopes, our prayers, our faith, in the power of man’s humanity to man.”

On the 80th anniversary of NIH’s move to Bethesda, I could not agree more. Our science—and our humanity—will get us through this pandemic and show the path forward to brighter days ahead.


Who We Are: History (NIH)

Office of NIH History and Stetten Museum (NIH)

70 Acres of Science” (Office of NIH History)

Coronavirus (COVID-19) (NIH)

The Amazing Brain: Shining a Spotlight on Individual Neurons

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A major aim of the NIH-led Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative is to develop new technologies that allow us to look at the brain in many different ways on many different scales. So, I’m especially pleased to highlight this winner of the initiative’s recent “Show Us Your Brain!” contest.

Here you get a close-up look at pyramidal neurons located in the hippocampus, a region of the mammalian brain involved in memory. While this tiny sample of mouse brain is densely packed with many pyramidal neurons, researchers used new ExLLSM technology to zero in on just three. This super-resolution, 3D view reveals the intricacies of each cell’s structure and branching patterns.

The group that created this award-winning visual includes the labs of X. William Yang at the University of California, Los Angeles, and Kwanghun Chung at the Massachusetts Institute of Technology, Cambridge. Chung’s team also produced another quite different “Show Us Your Brain!” winner, a colorful video featuring hundreds of neural cells and connections in a part of the brain essential to movement.

Pyramidal neurons in the hippocampus come in many different varieties. Some important differences in their functional roles may be related to differences in their physical shapes, in ways that aren’t yet well understood. So, BRAIN-supported researchers are now applying a variety of new tools and approaches in a more detailed effort to identify and characterize these neurons and their subtypes.

The video featured here took advantage of Chung’s new method for preserving brain tissue samples [1]. Another secret to its powerful imagery was a novel suite of mouse models developed in the Yang lab. With some sophisticated genetics, these models make it possible to label, at random, just 1 to 5 percent of a given neuronal cell type, illuminating their full morphology in the brain [2]. The result was this unprecedented view of three pyramidal neurons in exquisite 3D detail.

Ultimately, the goal of these and other BRAIN Initiative researchers is to produce a dynamic picture of the brain that, for the first time, shows how individual cells and complex neural circuits interact in both time and space. I look forward to their continued progress, which promises to revolutionize our understanding of how the human brain functions in both health and disease.


[1] Protection of tissue physicochemical properties using polyfunctional crosslinkers. Park YG, Sohn CH, Chen R, McCue M, Yun DH, Drummond GT, Ku T, Evans NB, Oak HC, Trieu W, Choi H, Jin X, Lilascharoen V, Wang J, Truttmann MC, Qi HW, Ploegh HL, Golub TR, Chen SC, Frosch MP, Kulik HJ, Lim BK, Chung K. Nat Biotechnol. 2018 Dec 17.

[2] Genetically-directed Sparse Neuronal Labeling in BAC Transgenic Mice through Mononucleotide Repeat Frameshift. Lu XH, Yang XW. Sci Rep. 2017 Mar 8;7:43915.


Chung Lab (Massachusetts Institute of Technology, Cambridge)

Yang Lab (University of California, Los Angeles)

Show Us Your Brain! (BRAIN Initiative/NIH)

Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative (NIH)

NIH Support: National Institute of Mental Health; National Institute of Neurological Disorders and Stroke; National Institute of Biomedical Imaging and Bioengineering

Watch Flowers Spring to Life

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Spring has sprung! The famous Washington cherry blossoms have come and gone, and the tulips and azaleas are in full bloom. In this mesmerizing video, you’ll get a glimpse of the early steps in how some spring flowers bloom.

Floating into view are baby flowers, their cells outlined (red), at the tip of the stem of the mustard plant Arabidopsis thaliana. Stem cells that contain the gene STM (green) huddle in the center of this fast-growing region of the plant stem—these stem cells will later make all of the flower parts.

As the video pans out, slightly older flowers come into view. These contain organs called sepals (red, bumpy outer regions) that will grow into leafy support structures for the flower’s petals.

Movie credits go to Nathanaёl Prunet, an assistant professor at the University of California, Los Angeles, who shot this video while working in the NIH-supported lab of Elliot Meyerowitz at the California Institute of Technology, Pasadena. Prunet used confocal microscopy to display the different ages and stages of the developing flowers, generating a 3D data set of images. He then used software to produce a bird’s-eye view of those images and turned it into a cool movie. The video was one of the winners in the Federation of American Societies for Experimental Biology’s 2018 BioArt competition.

Beyond being cool, this video shows how a single gene, STM, plays a starring role in plant development. This gene acts like a molecular fountain of youth, keeping cells ever-young until it’s time to grow up and commit to making flowers and other plant parts.

Like humans, most plants begin life as a fertilized cell that divides over and over—first into a multi-cell embryo and then into mature parts, or organs. Because of its ease of use and low cost, Arabidopsis is a favorite model for scientists to learn the basic principles driving tissue growth and regrowth for humans as well as the beautiful plants outside your window. Happy Spring!


Meyerowitz Lab (California Institute of Technology, Pasadena)

Prunet Lab (University of California, Los Angeles)

The Arabidosis Information Resource (Phoenix Bioinformatics, Fremont, CA)

BioArt Scientific Image and Video Competition (Federation of American Societies for Experimental Biology, Bethesda, MD)

NIH Support: National Institute of General Medical Sciences

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