nervous system
How Neurons Make Connections
Posted on by Lawrence Tabak, D.D.S., Ph.D.
For many people, they are tiny pests. These fruit flies that sometimes hover over a bowl of peaches or a bunch of bananas. But for a dedicated community of researchers, fruit flies are an excellent model organism and source of information into how neurons self-organize during the insect’s early development and form a complex, fully functioning nervous system.
That’s the scientific story on display in this beautiful image of a larval fruit fly’s developing nervous system. Its subtext is: fundamental discoveries in the fruit fly, known in textbooks as Drosophila melanogaster, provide basic clues into the development and repair of the human nervous system. That’s because humans and fruit flies, though very distantly related through the millennia, still share many genes involved in their growth and development. In fact, 60 percent of the Drosophila genome is identical to ours.
Once hatched, as shown in this image, a larval fly uses neurons (magenta) to sense its environment. These include neurons that sense the way its body presses against the surrounding terrain, as needed to coordinate the movements of its segmented body parts and crawl in all directions.
This same set of neurons will generate painful sensations, such as the attack of a parasitic wasp. Paintbrush-like neurons in the fly’s developing head (magenta, left side) allow the insect to taste the sweetness of a peach or banana.
There is a second subtype of neurons, known as proprioceptors (green). These neurons will give the young fly its “sixth sense” understanding about where its body is positioned in space. The complete collection of developing neurons shown here are responsible for all the fly’s primary sensations. They also send these messages on to the insect’s central nervous system, which contains thousands of other neurons that are hidden from view.
Emily Heckman, now a postdoctoral researcher at the Michigan Neuroscience Institute, University of Michigan, Ann Arbor, captured this image during her graduate work in the lab of Chris Doe, University of Oregon, Eugene. For her keen eye, she received a trainee/early-career BioArt Award from the Federation of American Societies for Experimental Biology (FASEB), which each year celebrates the art of science.
The image is one of many from a much larger effort in the Doe lab that explores the way neurons that will partner find each other and link up to drive development. Heckman and Doe also wanted to know how neurons in the developing brain interconnect into integrated neural networks, or circuits, and respond when something goes wrong. To find out, they disrupted sensory neurons or forced them to take alternate paths and watched to see what would happen.
As published in the journal eLife [1], the system has an innate plasticity. Their findings show that developing sensory neurons instruct one another on how to meet up just right. If one suddenly takes an alternate route, its partner can still reach out and make the connection. Once an electrically active neural connection, or synapse, is made, the neural signals themselves slow or stop further growth. This kind of adaptation and crosstalk between neurons takes place only during a particular critical window during development.
Heckman says part of what she enjoys about the image is how it highlights that many sensory neurons develop simultaneously and in a coordinated process. What’s also great about visualizing these events in the fly embryo is that she and other researchers can track many individual neurons from the time they’re budding stem cells to when they become a fully functional and interconnected neural circuit.
So, the next time you see fruit flies hovering in the kitchen, just remember there’s more to their swarm than you think. Our lessons learned studying them will help point researchers toward new ways in people to restore or rebuild neural connections after devastating disruptions from injury or disease.
Reference:
Presynaptic contact and activity opposingly regulate postsynaptic dendrite outgrowth. Heckman EL, Doe CQ. Elife. 2022 Nov 30;11:e82093.
Links:
Research Organisms (National Institute of General Medical Sciences/NIH)
Doe Lab (University of Oregon, Eugene)
Emily Heckman (University of Michigan, Ann Arbor)
BioArt Awards (Federation of American Societies for Experimental Biology, Rockville, MD)
NIH Support: Eunice Kennedy Shriver National Institute of Child Health and Human Development
Understanding Causes of Devastating Neurodegenerative Condition Affecting Children
Posted on by Lawrence Tabak, D.D.S., Ph.D.
A common theme among parents and family members caring for a child with the rare Batten disease is “love, hope, cure.” While inspiring levels of love and hope are found among these amazing families, a cure has been more elusive. One reason is rooted in the need for more basic research. Although researchers have identified an altered gene underlying Batten disease, they’ve had difficulty pinpointing where and how the gene’s abnormal protein product malfunctions, especially in cells within the nervous system.
Now, this investment in more basic research has paid off. In a paper just published in the journal Nature Communications, an international research team pinpointed where and how a key cellular process breaks down in the nervous system to cause Batten disease, sometimes referred to as CLN3 disease [1]. While there’s still a long way to go in learning exactly how to overcome the cellular malfunction, the findings mark an important step forward toward developing targeted treatments for Batten disease and progress in the quest for a cure.
The research also offers yet another excellent example of how studying rare diseases helps to advance our fundamental understanding of human biology. It shows that helping those touched by Batten disease can shed a brighter light on basic cellular processes that drive other diseases, rare and common.
Batten disease affects about 14,000 people worldwide [2]. For those with the juvenile form of this inherited disease of the nervous system, parents may first notice their seemingly healthy child has difficulty saying words, sudden problems with vision or movement, and changes in behavior. Tragically for parents, with no approved treatments to reverse these symptoms, the disease will worsen, leading to severe vision loss, frequent seizures, and impaired motor skills. The disease can be fatal as early as late childhood or the teenage years.
Batten disease also goes by the more technical name of juvenile neuronal ceroid lipofuscinosis. Using this technical name, it represents one of the more than 70 medically recognized lysosomal storage disorders.
These disorders share a breakdown in the ability of membrane-bound cellular components, known as lysosomes, to degrade the molecular waste products of normal cell biology. As a result, all this undegraded material builds up and eventually kills affected cells. In people with Batten disease, the lost and damaged cells cause progressive dysfunction within the nervous system.
Researchers have known for a while that the most common cause of this breakdown in people with Batten disease is the inheritance of two defective copies of a gene called CLN3. As mentioned above, what’s been missing is a more detailed understanding of what exactly a working copy of the CLN3 gene does and how its loss leads to the changes seen in those with this condition.
Hoping to solve this puzzle was an NIH-supported basic research team led by Alessia Calcagni and Andrea Ballabio, Baylor College of Medicine and Texas Children’s Hospital, Houston, and Telethon Institute of Genetics and Medicine, Naples, Italy.
As described in their latest paper, the researchers first generated an antibody that allowed them to visualize where in cells the protein encoded by CLN3 is found. Their studies unexpectedly showed that this protein has a role outside, not inside, the cell’s estimated 50-to-1,000 lysosomes. Before reaching the lysosomes, the protein first moves through another cellular component called the Golgi body, where many proteins are packaged.
They then identified all the other proteins that interact with the CLN3 protein in the Golgi body and elsewhere in the cell. Their data showed that CLN3 interacts with proteins known for transporting other proteins within the cell and forming new lysosomes.
That gave them a valuable clue: the CLN3 gene must be a player in these fundamentally important cellular processes of protein transport and lysosome formation. Among the proteins CLN3 interacts with in the Golgi body is a particular receptor called M6PR. The receptor known for its role in recognizing lysosomal enzymes and delivering them to the lysosomes, where they go to work inside these bubble-like structures degrading cellular waste products.
The researchers found that loss of CLN3 led this important M6PR receptor to be broken down within lysosomes. The breakdown, in turn, altered the normal shape of new lysosomes, and that limits their functionality. The researchers also showed that restoring CLN3 in cells that lacked this gene also restored the production of more functional lysosomes and lysosomal enzymes.
Overall, the findings point to a major role for CLN3 in the formation of lysosomes and their ability to function. Importantly, the findings also offer clues for understanding the mechanisms that underlie other forms of lysosomal storage disease, which collectively affect as many as one in every 40,000 people [3]. The work also may have broader implications for common neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease.
Most of all, this paper demonstrates the power of basic research to define needed molecular targets. It shows how these fundamental studies are helping families affected by Batten disease and supporting their love, hope, and quest for a cure.
References:
[1] Loss of the batten disease protein CLN3 leads to mis-trafficking of M6PR and defective autophagic-lysosomal reformation. Calcagni’ A, Staiano L, Zampelli N, Minopoli N, Herz NJ, Cullen PJ, Parenti G, De Matteis MA, Grumati P, Ballabio A, et al. Nat Commun. 2023 Jul 3;14(1):3911. doi: 10.1038/s41467-023-39643-7. PMID: 37400440; PMCID: PMC10317969.
[2] Batten Disease. Boston Children’s Hospital.
[3] Lysosomal storage diseases. Cleveland Clinic fact sheet, June 27, 2022.
Links:
Batten Disease (National Institute of Neurological Disorders and Stroke/NIH)
Rare Diseases (NIH)
Alessia Calcagni (Baylor College of Medicine, Houston, TX)
Andrea Ballabio (Telethon Institute of Genetics and Medicine, Naples, Italy)
NIH Support: National Institute of Neurological Disorders and Stroke; National Cancer Institute; National Center for Advancing Translational Sciences
3D Neuroscience at the Speed of Life
Posted on by Dr. Francis Collins
This fluorescent worm makes for much more than a mesmerizing video. It showcases a significant technological leap forward in our ability to capture in real time the firing of individual neurons in a living, freely moving animal.
As this Caenorhabditis elegans worm undulates, 113 neurons throughout its brain and body (green/yellow spots) get brighter and darker as each neuron activates and deactivates. In fact, about halfway through the video, you can see streaks tracking the positions of individual neurons (blue/purple-colored lines) from one frame to the next. Until now, it would have been technologically impossible to capture this “speed of life” with such clarity.
With funding from the NIH-led Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative, Elizabeth Hillman at Columbia University’s Zuckerman Institute, New York, has pioneered the pairing of a 3D live-imaging microscope with an ultra-fast camera. This pairing, showcased above, is a technique called Swept Confocally Aligned Planar Excitation (SCAPE) microscopy.
Since first demonstrating SCAPE in February 2015 [1], Hillman and her team have worked hard to improve, refine, and expand the approach. Recently, they used SCAPE 1.0 to image how proprioceptive neurons in fruit-fly larvae sense body position while crawling. Now, as described in Nature Methods, they introduce SCAPE “2.0,” with boosted resolution and a much faster camera—enabling 3D imaging at speeds hundreds of times faster than conventional microscopes [2]. To track a very wiggly worm, the researchers image their target 25 times a second!
As with the first-generation SCAPE, version 2.0 uses a scanning mirror to sweep a slanted sheet of light across a sample. This same mirror redirects light coming from the illuminated plane to focus onto a stationary high-speed camera. The approach lets SCAPE grab 3D imaging at very high speeds, while also causing very little photobleaching compared to conventional point-scanning microscopes, reducing sample damage that often occurs during time-lapse microscopy.
Like SCAPE 1.0, since only a single, stationary objective lens is used, the upgraded 2.0 system doesn’t need to hold, move, or disturb a sample during imaging. This flexibility enables scientists to use SCAPE in a wide range of experiments where they can present stimuli or probe an animal’s behavior—all while imaging how the underlying cells drive and depict those behaviors.
The SCAPE 2.0 paper shows the system’s biological versatility by also recording the beating heart of a zebrafish embryo at record-breaking speeds. In addition, SCAPE 2.0 can rapidly image large fixed, cleared, and expanded tissues such as the retina, brain, and spinal cord—enabling tracing of the shape and connectivity of cellular circuits. Hillman and her team are dedicated to exporting their technology; they provide guidance and a parts list for SCAPE 2.0 so that researchers can build their own version using inexpensive off-the-shelf parts.
Watching worms wriggling around may remind us of middle-school science class. But to neuroscientists, these images represent progress toward understanding the nervous system in action, literally at the speed of life!
References:
[1] . Swept confocally-aligned planar excitation (SCAPE) microscopy for high speed volumetric imaging of behaving organisms. Bouchard MB, Voleti V, Mendes CS, Lacefield C, et al Nature Photonics. 2015;9(2):113-119.
[2] Real-time volumetric microscopy of in vivo dynamics and large-scale samples with SCAPE 2.0. Voleti V, Patel KB, Li W, Campos CP, et al. Nat Methods. 2019 Sept 27;16:1054–1062.
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)
NIH Support: National Institute of Neurological Disorders and Stroke; National Heart, Lung, and Blood Institute
Creative Minds: Reprogramming the Brain
Posted on by Dr. Francis Collins
Caption: Neuronal circuits in the mouse retina. Cone photoreceptors (red) enable color vision; bipolar neurons (magenta) relay information further along the circuit; and a subtype of bipolar neuron (green) helps process signals sensed by other photoreceptors in dim light.
Credit: Brian Liu and Melanie Samuel, Baylor College of Medicine, Houston.
When most people think of reprogramming something, they probably think of writing code for a computer or typing commands into their smartphone. Melanie Samuel thinks of brain circuits, the networks of interconnected neurons that allow different parts of the brain to work together in processing information.
Samuel, a researcher at Baylor College of Medicine, Houston, wants to learn to reprogram the connections, or synapses, of brain circuits that function less well in aging and disease and limit our memory and ability to learn. She has received a 2016 NIH Director’s New Innovator Award to decipher the molecular cues that encourage the repair of damaged synapses or enable neurons to form new connections with other neurons. Because extensive synapse loss is central to most degenerative brain diseases, Samuel’s reprogramming efforts could help point the way to preventing or correcting wiring defects before they advance to serious and potentially irreversible cognitive problems.
Regenerative Medicine: New Clue from Fish about Healing Spinal Cord Injuries
Posted on by Dr. Francis Collins
Caption: Tissue section of zebrafish spinal cord regenerating after injury. Glial cells (red) cross the gap between the severed ends first. Neuronal cells (green) soon follow. Cell nuclei are stained blue and purple.
Credit: Mayssa Mokalled and Kenneth Poss, Duke University, Durham, NC
Certain organisms have remarkable abilities to achieve self-healing, and a fascinating example is the zebrafish (Danio rerio), a species of tropical freshwater fish that’s an increasingly popular model organism for biological research. When the fish’s spinal cord is severed, something remarkable happens that doesn’t occur in humans: supportive cells in the nervous system bridge the gap, allowing new nerve tissue to restore the spinal cord to full function within weeks.
Pretty incredible, but how does this occur? NIH-funded researchers have just found an important clue. They’ve discovered that the zebrafish’s damaged cells secrete a molecule known as connective tissue growth factor a (CTGFa) that is essential in regenerating its severed spinal cord. What’s particularly encouraging to those looking for ways to help the 12,000 Americans who suffer spinal cord injuries each year is that humans also produce a form of CTGF. In fact, the researchers found that applying human CTGF near the injured site even accelerated the regenerative process in zebrafish. While this growth factor by itself is unlikely to produce significant spinal cord regeneration in human patients, the findings do offer a promising lead for researchers pursuing the next generation of regenerative therapies.
Snapshots of Life: Development in Exquisite Detail
Posted on by Dr. Francis Collins
Credit: Shachi Bhatt and Paul Trainor, Stowers Institute for Medical Research, Kansas City, MO
If you’ve ever tried to take photos of wiggly kids, you know that it usually takes several attempts before you get the perfect shot. It’s often the same for biomedical researchers when taking images with microscopes because there are so many variables—from sample preparation to instrument calibration—to take into account. Still, there are always exceptions where everything comes together just right, and you are looking at one of them! On her first try at using a confocal microscope to image this cross-section of a mouse embryo’s torso, postdoc Shachi Bhatt captured a gem of an image that sheds new light on mammalian development.
Bhatt, who works in the NIH-supported lab of Paul Trainor at the Stowers Institute for Medical Research, Kansas City, MO, produced this micrograph as part of a quest to understand the striking parallels seen between the development of the nervous system and the vascular system in mammals. Fluorescent markers were used to label proteins uniquely expressed in each type of tissue: reddish-orange delineates developing nerve cells; gray highlights developing blood vessels; and yellow shows where the nerve cells and blood vessels overlap.
