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Snapshots of Life

Electricity-Conducting Bacteria May Inspire Next-Gen Medical Devices

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Nanowires
Credit: Edward H. Egelman

Technological advances with potential for improving human health sometimes come from the most unexpected places. An intriguing example is an electricity-conducting biological nanowire that holds promise for powering miniaturized pacemakers and other implantable electronic devices.

The nanowires come from a bacterium called Geobacter sulfurreducens, shown in the electron micrograph above. This rod-shaped microbe (white) was discovered two decades ago in soil collected from an unlikely place: a ditch outside of Norman, Oklahoma. The bug can conduct electricity along its arm-like appendages, and, in the hydrocarbon-contaminated, oxygen-depleted soil in which it lives, such electrical inputs and outputs are essentially the equivalent of breathing.

Scientists fascinated with G. sulfurreducens thought that its electricity had to be flowing through well-studied microbial appendages called pili. But, as the atomic structure of these nanowires (multi-colors, foreground) now reveals, these nanowires aren’t pili at all! Instead, the bacteria have manufactured unique submicroscopic arm-like structures. These arms consist of long, repetitive chains of a unique protein, each surrounding a core of iron-containing molecules.

The surprising discovery, published in the journal Cell, was made by an NIH-funded team involving Edward Egelman, University of Virginia Health System, Charlottesville. Egelman’s lab has had a long interest in what’s called a type 4 pili. These strong, adhering appendages help certain infectious bacteria enter tissues and make people sick. In fact, they enable bugs like Neisseria meningitidis to cross the blood-brain barrier and cause potentially deadly bacterial meningitis. While other researchers had proposed that those same type 4 pili allowed G. sulfurreducens to conduct electricity, Egelman wasn’t so sure.

So, he took advantage of recent advances in cryo-electron microscopy, which involves flash-freezing molecules at extremely low temperatures before bombarding them with electrons to capture their images with a special camera. The cryo-EM images allowed his team to nail down the atomic structure of the nanowires, now called OmcS filaments.

Using those images and sophisticated bioinformatics, Egelman and team determined that OmcS proteins uniquely fit into the nanowires’ long repetitive chains, spacing their iron-bearing cores at regular intervals to transfer electrons and convey electricity. In fact, bacteria unable to produce OmcS proteins make filaments that conduct electricity 100 times less efficiently.

With these cryo-EM structures in hand, Egelman says his team will continue to explore their conductive properties. Such knowledge might someday be used to build biologically-inspired nanowires, measuring 1/100,000th the width of a human hair, to connect miniature electronic devices directly to living tissues. This is one more example of how nature’s ability to invent is pretty breathtaking—surely one wouldn’t have predicted the discovery of nanowires in a bacterium that lives in contaminated ditches.

Reference:

[1] Structure of Microbial Nanowires Reveals Stacked Hemes that Transport Electrons over Micrometers. Wang F, Gu Y, O’Brien JP, Yi SM, Yalcin SE, Srikanth V, Shen C, Vu D, Ing NL, Hochbaum AI, Egelman EH, Malvankar NS. Cell. 2019 Apr 4;177(2):361-369.

Links:

Electroactive microorganisms in bioelectrochemical systems. Logan BE, Rossi R, Ragab A, Saikaly PE. Nat Rev Microbiol. 2019 May;17(5):307-319.

High Resolution Electron Microscopy (National Cancer Institute/NIH)

Egelman Lab (University of Virginia, Charlottesville)

NIH Support: National Institute of General Medical Sciences; National Institute of Allergy and Infectious Diseases; Common Fund


Making Personalized Blood-Brain Barriers in a Dish

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Credit: Vatine et al, Cell Stem Cell, 2019

The blood-brain barrier, or BBB, is a dense sheet of cells that surrounds most of the brain’s blood vessels. The BBB’s tiny gaps let vital small molecules, such as oxygen and water, diffuse from the bloodstream into the brain while helping to keep out larger, impermeable foreign substances that don’t belong there.

But in people with certain neurological disorders—such as amyotrophic lateral sclerosis (ALS) and Huntington’s disease—abnormalities in this barrier may block the entry of biomolecules essential to healthy brain activity. The BBB also makes it difficult for needed therapies to reach their target in the brain.

To help look for solutions to these and other problems, researchers can now grow human blood-brain barriers on a chip like the one pictured above. The high-magnification image reveals some of the BBB’s cellular parts. There are endothelial-like cells (magenta), which are similar to those that line the small vessels surrounding the brain. In close association are supportive brain cells known as astrocytes (green), which help to regulate blood flow.

While similar organ chips have been created before, what sets apart this new BBB chip is its use of induced pluripotent stem cell (iPSC) technology combined with advanced chip engineering. The iPSCs, derived in this case from blood samples, make it possible to produce a living model of anyone’s unique BBB on demand.

The researchers, led by Clive Svendsen, Cedars-Sinai, Los Angeles, first use a biochemical recipe to coax a person’s white blood cells to become iPSCs. At this point, the iPSCs are capable of producing any other cell type. But the Svendsen team follows two different recipes to direct those iPSCs to differentiate into endothelial and neural cells needed to model the BBB.

Also making this BBB platform unique is its use of a sophisticated microfluidic chip, produced by Boston-based Emulate, Inc. The chip mimics conditions inside the human body, allowing the blood-brain barrier to function much as it would in a person.

The channels enable researchers to flow cerebral spinal fluid (CSF) through one side and blood through the other to create the fully functional model tissue. The BBB chips also show electrical resistance and permeability just as would be expected in a person. The model BBBs are even able to block the entry of certain drugs!

As described in Cell Stem Cell, the researchers have already created BBB chips using iPSCs from a person with Huntington’s disease and another from an individual with a rare congenital disorder called Allan-Herndon-Dudley syndrome, an inherited disorder of brain development.

In the near term, his team has plans to model ALS and Parkinson’s disease on the BBB chips. Because these chips hold the promise of modeling the human BBB more precisely than animal models, they may accelerate studies of potentially promising new drugs. Svendsen suggests that individuals with neurological conditions might one day have their own BBB chips made on demand to help in selecting the best-available therapeutic options for them. Now that’s a future we’d all like to see.

Reference:

[1] Human iPSC-Derived Blood-Brain Barrier Chips Enable Disease Modeling and Personalized Medicine Applications. Vatine GD, Barrile R, Workman MJ, Sances S, Barriga BK, Rahnama M, Barthakur S, Kasendra M, Lucchesi C, Kerns J, Wen N, Spivia WR, Chen Z, Van Eyk J, Svendsen CN. Cell Stem Cell. 2019 Jun 6;24(6):995-1005.e6.

Links:

Tissue Chip for Drug Screening (National Center for Advancing Translational Sciences/NIH)

Stem Cell Information (NIH)

Svendsen Lab (Cedars-Sinai, Los Angeles)

NIH Support: National Institute of Neurological Disorders and Stroke; National Center for Advancing Translational Sciences


A Nose for Science

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Mouse Nasal Cavity
Credit: Lu Yang, David Ornitz, and Sung-Ho Huh, Washington University School of Medicine, St. Louis; University of Nebraska Medical Center, Omaha

Our nose does a lot more than take in oxygen, smell, and sometimes sniffle. This complex organ also helps us taste and, as many of us notice during spring allergy season when our noses get stuffy, it even provides some important anatomic features to enable us to speak clearly.

This colorful, almost psychedelic image shows the entire olfactory epithelium, or “smell center,” (green) inside the nasal cavity of a newborn mouse. The olfactory epithelium drapes over the interior walls of the nasal cavity and its curvy bony parts (red). Every cell in the nose contains DNA (blue).

The olfactory epithelium detects odorant molecules in the air, providing a sense of smell. In humans, the nose has about 400 types of scent receptors, and they can detect at least 1 trillion different odors [1].

But this is more than just a cool image captured by graduate student Lu Yang, who works with David Ornitz at Washington University School of Medicine, St. Louis. The two discovered a new type of progenitor cell, called a FEP cell, that has the capacity to generate the entire smell center [2]. Progenitor cells are made by stem cells. But they are capable of multiplying and producing various cells of a particular lineage that serve as the workforce for specialized tissues, such as the olfactory epithelium.

Yang and Ornitz also discovered that the FEP cells crank out a molecule, called FGF20, that controls the growth of the bony parts in the nasal cavity. This seems to regulate the size of the olfactory system, which has fascinating implications for understanding how many mammals possess a keener sense of smell than humans.

But it turns out that FGF20 does a lot more than control smell. While working in Ornitz’s lab as a postdoc, Sung-Ho Huh, now an assistant professor at the University of Nebraska Medical Center, Omaha, discovered that FGF20 helps form the cochlea [3]. This inner-ear region allows us to hear, and mice born without FGF20 are deaf. Other studies show that FGF20 is important for development of the kidney, teeth, mammary gland, and of specific types of hair [4-7]. Clearly, this indicates multi-tasking can be a key feature of a protein, not a trivial glitch.

The image was one of the winners in the 2018 BioArt Scientific Image & Video Competition, sponsored by the Federation of American Societies for Experimental Biology (FASEB). Its vibrant colors help to show the basics of smell, and remind us that every scientific picture tells a story.

References:

[1] Humans can discriminate more than 1 trillion olfactory stimuli. Bushdid C1, Magnasco MO, Vosshall LB, Keller A. Science. 2014 Mar 21;343(6177):1370-1372.

[2] FGF20-Expressing, Wnt-Responsive Olfactory Epithelial Progenitors Regulate Underlying Turbinate Growth to Optimize Surface Area. Yang LM, Huh SH, Ornitz DM. Dev Cell. 2018;46(5):564-580.

[3] Differentiation of the lateral compartment of the cochlea requires a temporally restricted FGF20 signal. Huh SH, Jones J, Warchol ME, Ornitz DM. PLoS Biol. 2012;10(1):e1001231.

[4] FGF9 and FGF20 maintain the stemness of nephron progenitors in mice and man. Barak H, Huh SH, Chen S, Jeanpierre C, Martinovic J, Parisot M, Bole-Feysot C, Nitschke P, Salomon R, Antignac C, Ornitz DM, Kopan R. Dev. Cell. 2012;22(6):1191-1207

[5] Ectodysplasin target gene Fgf20 regulates mammary bud growth and ductal invasion and branching during puberty. Elo T, Lindfors PH, Lan Q, Voutilainen M, Trela E, Ohlsson C, Huh SH, Ornitz DM, Poutanen M, Howard BA, Mikkola ML. Sci Rep. 2017;7(1):5049

[6] Ectodysplasin regulates activator-inhibitor balance in murine tooth development through Fgf20 signaling. D Haara O, Harjunmaa E, Lindfors PH, Huh SH, Fliniaux I, Aberg T, Jernvall J, Ornitz DM, Mikkola ML, Thesleff I. Development. 2012;139(17):3189-3199.

[7] Fgf20 governs formation of primary and secondary dermal condensations in developing hair follicles. Huh SH, Närhi K, Lindfors PH, Häärä O, Yang L, Ornitz DM, Mikkola ML. Genes Dev. 2013;27(4):450-458.

Links:

Taste and Smell (National Institute on Deafness and Other Communication Disorders/NIH)

Ornitz Lab, (Washington University, St. Louis)

Huh Lab, (University of Nebraska Medical Center, Omaha)

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

NIH Support: National Heart, Lung, and Blood Institute; National Institute of Neurological Disorders and Stroke; National Institute on Deafness and Other Communication Disorders


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


Navigating the Sense of Smell

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Olfactory Sensory Axons
Credit: Yu Lab, Stowers Institute for Medical Research, Kansas City, MO

Our ability to distinguish the aroma of freshly baked bread from the sweet fragrance of a rose comes from millions of sensory neurons that line the upper nasal cavity. These so-called olfactory sensory neurons activate when the specific types of odor molecules to which they are attuned enter the nose, prompting them to send their sensory alerts onward to the brain, where we become aware of a distinctive scent.

If you look closely at the striking image above from a young mouse, the thin, fluorescently labeled lines (red, green, white) show the neuronal extensions, or axons, of olfactory sensory neurons. These information-conveying axons stretch right to left from the nose through the smell-mediating olfactory bulb (blue) in the forebrain of all vertebrates, ending in just the right spot (white, pink, or red).

But the axons presented here don’t belong to just any olfactory sensory neurons. They represent newly discovered “navigator” neurons, which are essential to forge life’s very first olfactory connections [1].

The image comes from a recent paper in the journal Neuron from an NIH-supported team led by C. Ron Yu, Stowers Institute for Medical Research, Kansas City, MO. Yu’s team offered the first hints of navigator neurons a few years ago when it showed that young mice could correct errors in their olfactory wiring only when those disruptions occurred within the first week of life [2].

After that, the mice had lifelong abnormalities in their sense of smell. The findings suggested that the olfactory sensory neurons present very early in life had a unique ability to blaze a trail to the brain to establish a coherent olfactory map.

The new study confirms that navigator neurons indeed have a unique molecular identity. During their short lives, they show more extensive axon growth compared to neurons that arise later. Their axons also travel a more circuitous route to the brain, as if exploring the neural tissue before settling on a path to their final destination. As olfactory neurons in older mice regenerate, they simply follow the trail blazed for them by those early scouts.

While the new findings involve mice, the researchers suspect similar processes are at work in humans too. That means images like this one aren’t just fascinating. They could help pave the way toward new approaches for reviving navigator neurons, potentially making it possible to forge new olfactory connections—and bring back the enjoyment of delightful aromas such as freshly baked bread or roses—in those who’ve lost the ability to smell.

References:

[1] A population of navigator neurons is essential for olfactory map formation during the critical period. Wu Y, Ma L, Duyck K, Long CC, Moran A, Scheerer H, Blanck J, Peak A, Box A, Perera A, Yu CR. Neuron. 2018 Dec 5;100(5):1066-1082.

[2] A developmental switch of axon targeting in the continuously regenerating mouse olfactory system. Ma L, Wu Y, Qiu Q, Scheerer H, Moran A, Yu CR. Science. 2014 Apr 11;344(6180):194-197.

Links:

Smell Disorders (National Institute on Deafness and Other Communication Disorders)

Yu Lab (Stowers Institute for Medical Research, Kansas City, MO)

NIH Support: National Institute on Deafness and Other Communication Disorders


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