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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.

References:

[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.

Links:

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!

Links:

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


Finding Beauty in the Nervous System of a Fruit Fly Larva

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Wow! Click on the video. If you’ve ever wondered where those pesky flies in your fruit bowl come from, you’re looking at it right now. It’s a fruit fly larva. And this 3D movie offers never-before-seen details into proprioception—the brain’s sixth sense of knowing the body’s location relative to nearby objects or, in this case, fruit.

This live-action video highlights the movement of the young fly’s proprioceptive nerve cells. They send signals to the fly brain that are essential for tracking the body’s position in space and coordinating movement. The colors indicate the depth of the nerve cells inside the body, showing those at the surface (orange) and those further within (blue).

Such movies make it possible, for the first time, to record precisely how every one of these sensory cells is arranged within the body. They also provide a unique window into how body positions are dynamically encoded in these cells, as a segmented larva inches along in search of food.

The video was created using a form of confocal microscopy called Swept Confocally Aligned Planar Excitation, or SCAPE. It captures 3D images by sweeping a sheet of laser light back and forth across a living sample. Even better, it does this while the microscope remains completely stationary—no need for a researcher to move any lenses up or down, or hold a live sample still.

Most impressively, with this new high-speed technology, developed with support from the NIH’s BRAIN Initiative, researchers are now able to capture videos like the one seen above in record time, with each whole volume recorded in under 1/10th of a second! That’s hundreds of times faster than with a conventional microscope, which scans objects point by point.

As reported in Current Biology, the team, led by Elizabeth Hillman and Wesley Grueber, Columbia University, New York, didn’t stop at characterizing the structural details and physical movements of nerve cells involved in proprioception in a crawling larva. In another set of imaging experiments, they went a step further, capturing faint flashes of green in individual labeled nerve cells each time they fired. (You have to look very closely to see them.) With each wave of motion, proprioceptive nerve cells light up in sequence, demonstrating precisely when they are sending signals to the animal’s brain.

From such videos, the researchers have generated a huge amount of data on the position and activity of each proprioceptive nerve cell. The data show that the specific position of each cell makes it uniquely sensitive to changes in position of particular segments of a larva’s body. While most of the proprioceptive nerve cells fired when their respective body segment contracted, others were attuned to fire when a larval segment stretched.

Taken together, the data show that proprioceptive nerve cells provide the brain with a detailed sequence of signals, reflecting each part of a young fly’s undulating body. It’s clear that every proprioceptive neuron has a unique role to play in the process. The researchers now will create similar movies capturing neurons in the fly’s central nervous system.

A holy grail of the BRAIN Initiative is to capture the brain in action. With these advances in imaging larval flies, researchers are getting ever closer to understanding the coordinated activities of an organism’s complete nervous system—though this one is a lot simpler than ours! And perhaps this movie—and the anticipation of the sequels to come—may even inspire a newfound appreciation for those pesky flies that sometimes hover nearby.

Reference:

[1] Characterization of Proprioceptive System Dynamics in Behaving Drosophila Larvae Using High-Speed Volumetric Microscopy. Vaadia RD, Li W, Voleti V, Singhania A, Hillman EMC, Grueber WB. Curr Biol. 2019 Mar 18;29(6):935-944.e4.

Links:

Using Research Organisms to Study Health and Disease (National Institute of General Medical Sciences/NIH)

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

Hillman Lab (Columbia University, New York)

Grueber Lab (Columbia University, New York)

NIH Support: National Institute of Neurological Disorders and Stroke; Eunice Kennedy Shriver National Institute of Child Health and Human Development


World’s Smallest Tic-Tac-Toe Game Built from DNA

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Check out the world’s smallest board game, a nanoscale match of tic-tac-toe being played out in a test tube with X’s and O’s made of DNA. But the innovative approach you see demonstrated in this video is much more than fun and games. Ultimately, researchers hope to use this technology to build tiny DNA machines for a wide variety of biomedical applications.

Here’s how it works. By combining two relatively recent technologies, an NIH-funded team led by Lulu Qian, California Institute of Technology, Pasadena, CA, created a “swapping mechanism” that programs dynamic interactions between complex DNA nanostructures [1]. The approach takes advantage of DNA’s modular structure, along with its tendency to self-assemble, based on the ability of the four letters of DNA’s chemical alphabet to pair up in an orderly fashion, A to T and C to G.

To make each of the X or O tiles in this game (displayed here in an animated cartoon version), researchers started with a single, long strand of DNA and many much shorter strands, called staples. When the sequence of DNA letters in each of those components is arranged just right, the longer strand will fold up into the desired 2D or 3D shape. This technique is called DNA origami because of its similarity to the ancient art of Japanese paper folding.

In the early days of DNA origami, researchers showed the technique could be used to produce miniature 2D images, such as a smiley face [2]. Last year, the Caltech group got more sophisticated—using DNA origami to produce the world’s smallest reproduction of the Mona Lisa [3].

In the latest work, published in Nature Communications, Qian, Philip Petersen and Grigory Tikhomirov first mixed up a solution of nine blank DNA origami tiles in a test tube. Those DNA tiles assembled themselves into a tic-tac-toe grid. Next, two players took turns adding one of nine X or O DNA tiles into the solution. Each of the game pieces was programmed precisely to swap out only one of the tile positions on the original, blank grid, based on the DNA sequences positioned along its edges.

When the first match was over, player X had won! More importantly for future biomedical applications, the original, blank grid had been fully reconfigured into a new structure, built of all-new, DNA-constructed components. That achievement shows not only can researchers use DNA to build miniature objects, they can also use DNA to repair or reconfigure such objects.

Of course, the ultimate aim of this research isn’t to build games or reproduce famous works of art. Qian wants to see her DNA techniques used to produce tiny automated machines, capable of performing basic tasks on a molecular scale. In fact, her team already has used a similar approach to build nano-sized DNA robots, programmed to sort molecules in much the same way that a person might sort laundry [4]. Such robots may prove useful in miniaturized approaches to drug discovery, development, manufacture, and/or delivery.

Another goal of the Caltech team is to demonstrate to the scientific community what’s possible with this leading-edge technology, in hopes that other researchers will pick up their innovative tools for their own applications. That would be a win-win for us all.

References:

[1] Information-based autonomous reconfiguration in systems of DNA nanostructures. Petersen P, Tikhomirov G, Qian L. Nat Commun. 2018 Dec 18;9(1):5362

[2] Folding DNA to create nanoscale shapes and patterns. Rothemund PW. Nature. 2006 Mar 16;440(7082):297-302.

[3] Fractal assembly of micrometre-scale DNA origami arrays with arbitrary patterns. Tikhomirov G, Petersen P, Qian L. Nature. 2017 Dec 6;552(7683):67-71.

[4] A cargo-sorting DNA robot. Thubagere AJ, Li W, Johnson RF, Chen Z, Doroudi S, Lee YL, Izatt G, Wittman S, Srinivas N, Woods D, Winfree E, Qian L. Science. 2017 Sep 15;357(6356).

Links:

Paul Rothemund—DNA Origami: Folded DNA as a Building Material for Molecular Devices (Cal Tech, Pasadena)

The World’s Smallest Mona Lisa (Caltech)

Qian Lab (Caltech, Pasadena, CA)

NIH Support: National Institute of General Medical Sciences


Mammalian Brain Like You’ve Never Seen It Before

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Credit: Gao et. al, Science

Researchers are making amazing progress in developing new imaging approaches. And they are now using one of their latest creations, called ExLLSM, to provide us with jaw-dropping views of a wide range of biological systems, including the incredibly complex neural networks within the mammalian brain.

In this video, ExLLSM takes us on a super-resolution, 3D voyage through a tiny sample (0.0030 inches thick) from the part of the mouse brain that processes sensation, the primary somatosensory cortex. The video zooms in and out of densely packed pyramidal neurons (large yellow cell bodies), each of which has about 7,000 synapses, or connections. You can also see presynapses (cyan), the part of the neuron that sends chemical signals; and postsynapes (magenta), the part of the neuron that receives chemical signals.

At 1:45, the video zooms in on dendritic spines, which are mushroom-like nubs on the neuronal branches (yellow). These structures, located on the tips of dendrites, receive incoming signals that are turned into electrical impulses. While dendritic spines have been imaged in black and white with electron microscopy, they’ve never been presented before on such a vast, colorful scale.

The video comes from a paper, published recently in the journal Science [1], from the labs of Ed Boyden, Massachusetts Institute of Technology, Cambridge, and the Nobel Prize-winning Eric Betzig, Janelia Research Campus of the Howard Hughes Medical Institute, Ashburn, VA. Like many collaborations, this one comes with a little story.

Four years ago, the Boyden lab developed expansion microscopy (ExM). The technique involves infusing cells with a hydrogel, made from a chemical used in disposable diapers. The hydrogel expands molecules within the cell away from each other, usually by about 4.5 times, but still locks them into place for remarkable imaging clarity. It makes structures visible by light microscopy that are normally below the resolution limit.

Though the expansion technique has worked well with a small number of cells under a standard light microscope, it hasn’t been as successful—until now—at imaging thicker tissue samples. That’s because thicker tissue is harder to illuminate, and flooding the specimen with light often bleaches out the fluorescent markers that scientists use to label proteins. The signal just fades away.

For Boyden, that was a problem that needed to be solved. Because his lab’s goal is to trace the inner workings of the brain in unprecedented detail, Boyden wants to image entire neural circuits in relatively thick swaths of tissue, not just look at individual cells in isolation.

After some discussion, Boyden’s team concluded that the best solution might be to swap out the light source for the standard microscope with a relatively new imaging tool developed in the Betzig lab. It’s called lattice light-sheet microscopy (LLSM), and the tool generates extremely thin sheets of light that illuminate tissue only in a very tightly defined plane, dramatically reducing light-related bleaching of fluorescent markers in the tissue sample. This allows LLSM to extend its range of image acquisition and quickly deliver stunningly vivid pictures.

Telephone calls were made, and the Betzig lab soon welcomed Ruixuan Gao, Shoh Asano, and colleagues from the Boyden lab to try their hand at combining the two techniques. As the video above shows, ExLLSM has proved to be a perfect technological match. In addition to the movie above, the team has used ExLLSM to provide unprecedented views of a range of samples—from human kidney to neuron bundles in the brain of the fruit fly.

Not only is ExLLSM super-resolution, it’s also super-fast. In fact, the team imaged the entire fruit fly brain in 2 1/2 days—an effort that would take years using an electron microscope.

ExLLSM will likely never supplant the power of electron microscopy or standard fluorescent light microscopy. Still, this new combo imaging approach shows much promise as a complementary tool for biological exploration. The more innovative imaging approaches that researchers have in their toolbox, the better for our ongoing efforts to unlock the mysteries of the brain and other complex biological systems. And yes, those systems are all complex. This is life we’re talking about!

Reference:

[1] Cortical column and whole-brain imaging with molecular contrast and nanoscale resolution. Gao R, Asano SM, Upadhyayula S, Pisarev I, Milkie DE, Liu TL, Singh V, Graves A, Huynh GH, Zhao Y, Bogovic J, Colonell J, Ott CM, Zugates C, Tappan S, Rodriguez A, Mosaliganti KR, Sheu SH, Pasolli HA, Pang S, Xu CS, Megason SG, Hess H, Lippincott-Schwartz J, Hantman A, Rubin GM, Kirchhausen T, Saalfeld S, Aso Y, Boyden ES, Betzig E. Science. 2019 Jan 18;363(6424).

Links:

Video: Expansion Microscopy Explained (YouTube)

Video: Lattice Light-Sheet Microscopy (YouTube)

How to Rapidly Image Entire Brains at Nanoscale Resolution, Howard Hughes Medical Institute, January 17, 2019.

Synthetic Neurobiology Group (Massachusetts Institute of Technology, Cambridge)

Eric Betzig (Janelia Reseach Campus, Ashburn, VA)

NIH Support: National Institute of Neurological Disorders and Stroke; National Human Genome Research Institute; National Institute on Drug Abuse; National Institute of Mental Health; National Institute of Biomedical Imaging and Bioengineering


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