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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


Students Contribute to Research Through Ovarian Art

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Ovary from fruit fly
Credit: Crystal D. Rogers and Mariano Loza-Coll, California State University, Northridge

Seeing the development of an organ under a microscope for the first time can be a truly unforgettable experience. But for a class taught by Crystal Rogers at California State University, Northridge, it can also be an award-winning moment.

This image, prepared during a biology lab course, was one of the winners in the 2018 BioArt Scientific Image & Video Competition, sponsored by the Federation of American Societies for Experimental Biology (FASEB). This colorful image shows the tip of an ovary from a fruit fly (Drosophila melanogaster), provided by Mariano Loza-Coll. You can see that the ovary is packed with oocytes (DNA stained blue). The orderly connective structure (pink) and signal-transmitting molecules like STAT (yellow) are common to egg maturation and reproductive processes in humans.

What makes this image unique among this year’s BioArt winners is that the prep work was done by undergraduate students just learning how to work in a lab. They did the tissue dissections, molecular labeling, and beautiful stainings in preparation for Rogers to “snap” the photo on her research lab’s optical-sectioning microscope.

What’s also fantastic is that many of Rogers’s students are from groups traditionally underrepresented in biomedicine. Many are considering careers in research and, from the looks of things, they are off to a beautiful start.

After teaching classes, Rogers also has an NIH-supported lab to run. She and her team study salamanders and chickens to determine how biological “glue” proteins, called cadherins, help to create neural crest cells, a critical cell type that arises very early in development [1].

For developmental biologists, it’s essential to understand what prompts these neural crest cells to migrate to locations throughout the body, from the heart to the skin to the cranium, or head. For example, cranial neural crest cells at first produce what appears to be the same generic, undifferentiated facial template in vertebrate species. And yet, neural crest cells and the surrounding ectodermal cells go on to generate craniofacial structures as distinct as the beak of a toucan, the tusk of a boar, or the horn of a rhinoceros.

But if the organ of interest is an ovary, the fruit fly has long been a go-to organism to learn more. Not only does the fruit fly open a window into ovarian development and health issues like infertility, it showcases the extraordinary beauty of biology.

Reference:

[1] A catenin-dependent balance between N-cadherin and E-cadherin controls neuroectodermal cell fate choices. Rogers CD, Sorrells LK, Bronner ME. Mech Dev. 2018 Aug;152:44-56.

Links:

Rogers Lab (California State University, Northridge)

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

NIH Support: Eunice Kennedy Shriver National Institute of Child Health and Human Development


A Fantastic WALS Lecture

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Francis Collins, Gerald Rubin, and Benjamin White
A big thanks to Gerald Rubin (center), vice president of Howard Hughes Medical Institute, Chevy Chase, MD, and executive director of Janelia Research Campus, Ashburn, VA, for taking part in the NIH’s Wednesday Afternoon Lecture Series (WALS). He delivered a fantastic talk titled “What the fly brain can teach us about the neural mechanisms of complex behaviors.” Afterwards, I presented him with a framed WALS certificate of appreciation. Joining us is Benjamin White (right), chief of the Section of Neural Function at NIH’s National Institute of Mental Health. The WALS lecture was held on January 30, 2019.

Creative Minds: Building a CRISPR Gene Drive Against Malaria

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Valentino Gantz

Valentino Gantz/Credit: Erik Jepsen

Researchers have used Drosophila melanogaster, the common fruit fly that sometimes hovers around kitchens, to make seminal discoveries involving genetics, the nervous system, and behavior, just to name a few. Could a new life-saving approach to prevent malaria be next? Valentino Gantz, a researcher at the University of California, San Diego, is on a path to answer that question.

Gantz has received a 2016 NIH Director’s Early Independence Award to use Drosophila to hone a new bioengineered tool that acts as a so-called “gene drive,” which spreads a new genetically encoded trait through a population much faster than would otherwise be possible. The lessons learned while working with flies will ultimately be applied to developing a more foolproof system for use in mosquitoes with the hope of stopping the transmission of malaria and potentially other serious mosquito-borne diseases.


Creative Minds: A New Mechanism for Epigenetics?

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Keith Maggert

Keith Maggert

To learn more about how DNA and inheritance works, Keith Maggert has spent much of his nearly 30 years as a researcher studying what takes place not just within the DNA genome but also the subtle modifications of it. That’s where a stable of enzymes add chemical marks to DNA, turning individual genes on or off without changing their underlying sequence. What’s really intrigued Maggert is these “epigenetic” modifications are maintained through cell division and can even get passed down from parent to child over many generations. Like many researchers, he wants to know how it happens.

Maggert thinks there’s more to the story than scientists have realized. Now an associate professor at the University of Arizona College of Medicine, Tucson, he suspects that a prominent subcellular structure in the nucleus called the nucleolus also exerts powerful epigenetic effects. What’s different about the nucleolus, Maggert proposes, is it doesn’t affect genes one by one, a focal point of current epigenetic research. He thinks under some circumstances its epigenetic effects can activate many previously silenced, or “off” genes at once, sending cells and individuals on a different path toward health or disease.

Maggert has received a 2016 NIH Director’s Transformative Research Award to pursue this potentially new paradigm. If correct, it would transform current thinking in the field and provide an exciting new perspective to track epigenetics and its contributions to a wide range of human diseases, including cancer, cardiovascular disease, and neurodegenerative disorders.


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