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Each time your cells divide, telomeres—complexes of specialized DNA sequences, RNA, and protein that protect the tips of your chromosomes—shorten just a bit.  And, as the video shows, that shortening renders the genomic information on your chromosomes more vulnerable to changes that can drive cancer and other diseases of aging.

Consequently, over the last few decades, much research has focused on efforts to understand telomerase, a naturally occurring enzyme that helps to replace the bits of telomere lost during cell division. But there’s been a major hitch: until recently, scientists hadn’t been able to determine telomerase’s molecular structure in detail—a key step in figuring out exactly how the enzyme works. Now, thanks to better purification methods and an exciting technology called cryo-electron microscopy (cryo-EM), NIH-funded researchers and their colleagues have risen to the challenge to produce the most detailed view yet of human telomerase in its active form [1].

This structural biology advance is a critical step toward learning more about the role of telomerase in cancers, as well as genetic conditions linked to telomerase deficiencies. It’s also an important milestone in the quest for drugs targeting telomerase in different ways, perhaps to slow the growth of cancerous cells or to boost the proliferative capacity of life-giving adult stem cells.

One reason telomerase has been so difficult to study in humans is that the enzyme isn’t produced at detectable levels in the vast majority of our cells. To get around this problem, the team led by Eva Nogales and Kathleen Collins at the University of California, Berkeley, first coaxed human cells in the lab to produce larger quantities of active telomerase. They then used fluorescent microscopy, along with extensive knowledge of the enzyme’s biochemistry, to develop a multi-step purification process that yielded relatively homogenous samples of active telomerase.

The new study is also yet another remarkable example of how cryo-EM microscopy has opened up new realms of scientific possibility. That’s because, in comparison to other methods, cryo-EM enables researchers to solve complex macromolecular structures even when only tiny amounts of material are available. It can also produce detailed images of molecules, like telomerase, that are extremely flexible and hard to keep still while taking a picture of their structure.

As described in Nature, the researchers used cryo-EM to capture the structure of human telomerase in unprecedented detail. Their images reveal two lobes, held together by a flexible RNA tether. One of those lobes contains the highly specialized core enzyme. It uses an internal RNA template as a guide to make the repetitive, telomeric DNA that’s added at the tips of chromosomes. The second lobe, consisting of a complex of RNA and RNA-binding proteins, plays important roles in keeping the complex stable and properly in place.

This new, more-detailed view helps to explain how mutations in particular genes may lead to telomerase-related health conditions, including bone marrow failure, as well as certain forms of anemia and pulmonary fibrosis. For example, it reveals that a genetic defect known to cause bone marrow failure affects an essential protein in a spot that’s especially critical for telomerase’s proper conformation and function.

This advance will also be a big help for designing therapies that encourage telomerase activity. For example, it could help to boost the success of bone marrow transplants by rejuvenating adult stem cells. It might also be possible to reinforce the immune systems of people with HIV infections. While telomerase-targeted treatments surely won’t stop people from growing old, new insights into this important enzyme will help to understand aging better, including why some people appear to age faster than others.

As remarkable as these new images are, the researchers aren’t yet satisfied. They’ll continue to refine them down to the minutest structural details. They say they’d also like to use cryo-EM to understand better how the complex attaches to chromosomes to extend telomeres. Each new advance in the level of atomic detail will not only make for amazing new videos, it will help to advance understanding of human biology in health, aging, and disease.


[1] Cryo-EM structure of substrate-bound human telomerase holoenzyme. Nguyen THD, Tam J, Wu RA, Greber BJ, Toso D, Nogales E, Collins K. Nature. 2018 April 25. [Epub ahead of publication]


High Resolution Electron Microscopy (National Cancer Institute/NIH)

Nogales Lab (University of California, Berkeley)

Collins Lab (University of California, Berkeley)

NIH Support: National Institute of General Medical Sciences   

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Brain Cell Analysis

Caption: While analyzing brain cells, a computer program “thinks” about which cellular structure to identify.
Credit: Steven Finkbeiner, University of California, San Francisco and the Gladstone Institutes

For centuries, scientists have trained themselves to look through microscopes and carefully study their structural and molecular features. But those long hours bent over a microscope poring over microscopic images could be less necessary in the years ahead. The job of analyzing cellular features could one day belong to specially trained computers.

In a new study published in the journal Cell, researchers trained computers by feeding them paired sets of fluorescently labeled and unlabeled images of brain tissue millions of times in a row [1]. This allowed the computers to discern patterns in the images, form rules, and apply them to viewing future images. Using this so-called deep learning approach, the researchers demonstrated that the computers not only learned to recognize individual cells, they also developed an almost superhuman ability to identify the cell type and whether a cell was alive or dead. Even more remarkable, the trained computers made all those calls without any need for harsh chemical labels, including fluorescent dyes or stains, which researchers normally require to study cells. In other words, the computers learned to “see” the invisible!


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MEMOIR cells

Caption: MEMOIR cells variably activate (cyan). The recorded information is then read out to visualize certain RNA transcripts (red).
Credit: Elowitz and Cai Labs, Caltech, Pasadena, CA

One of the most fascinating challenges in biology is understanding how a single cell divides and differentiates to form a complex, multicellular organism. Scientists can learn a lot about this process by tracking time-lapse images through a microscope. But gazing through a lens has its limitations, especially in the brain and other opaque and inaccessible tissues and organs.

With support from a 2017 NIH Director’s Transformative Research Program, a California Institute of Technology (Caltech) team now has a way around this problem. Rather than watching or digging information out of cells, the team has learned how to program cells to write their own molecular memoirs. These cells store the information right in their own genomic hard drives. Even better, that information is barcoded, allowing researchers to read it out of the cells without dissecting tissue. The programming can be performed in many different cell types, including stem or adult cells in tissues throughout the body.


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UW light sheet microscope team

Caption: University of Washington team that developed new light-sheet microscope (center) includes (l-r) Jonathan Liu, Adam Glaser, Larry True, Nicholas Reder, and Ye Chen.
Credit: Mark Stone/University of Washington

After surgically removing a tumor from a cancer patient, doctors like to send off some of the tissue for evaluation by a pathologist to get a better idea of whether the margins are cancer free and to guide further treatment decisions. But for technical reasons, completing the pathology report can take days, much to the frustration of patients and their families. Sometimes the results even require an additional surgical procedure.

Now, NIH-funded researchers have developed a groundbreaking new microscope to help perform the pathology in minutes, not days. How’s that possible? The device works like a scanner for tissues, using a thin sheet of light to capture a series of thin cross sections within a tumor specimen without having to section it with a knife, as is done with conventional pathology. The rapidly acquired 2D “optical sections” are processed by a computer that assembles them into a high-resolution 3D image for immediate analysis.


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Mouse Midbrain

Credit: Michael Shribak, Marine Biological Laboratory, Woods Hole, MA

Birds do it, bees do it, and even educated fleas do it. No, not fall in love, as the late Ella Fitzgerald so famously sang. Birds and insects can see polarized light—that is, light waves transmitted in a single directional plane—in ways that provides them with a far more colorful and detailed view of the world than is possible with the human eye.

Still, thanks to innovations in microscope technology, scientists have been able to tap into the power of polarized light vision to explore the inner workings of many complex biological systems, including the brain. In this image, researchers used a recently developed polarized light microscope to trace the spatial orientation of neurons in a thin section of the mouse midbrain. Neurons that stretch horizontally appear green, while those oriented at a 45-degree angle are pinkish-red and those at 225 degrees are purplish-blue. What’s amazing is that these colors don’t involve staining or tagging the cells with fluorescent markers: the colors are generated strictly from the light interacting with the physical orientation of each neuron.


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