Previously Unstudied Gene Is Essential for Normal Nerve Development

Our ability to detect heat, touch, tickling and other sensations depends on our sensory nerves. Now, for the first time, researchers at Albert Einstein College of Medicine of Yeshiva University have identified a gene that orchestrates the crucially important branching of nerve fibers that occurs during development. The findings were published online today in the journal Cell.

The research focuses on dendrites, the string-like extensions of sensory nerves that penetrate tissues of the skin, eyes and other sensory organs. “The formation of dendritic branches—‘arbors’ as we call them—is vital for allowing sensory nerves to collect information and sample the environment appropriately,” said Hannes Buelow, Ph.D., senior author of the Cell paper and associate professor of genetics at Einstein. “These arbors vary greatly in shape and complexity, reflecting the different types of sensory input they receive. The loss of dendritic complexity has been linked to a range of neurological problems including Alzheimer’s disease, schizophrenia and autism spectrum disorders.” Dr. Buelow is also associate professor in the Dominick P. Purpura Department of Neuroscience.

The Human Genome Project, completed in 2003, revealed that humans possess some 20,500 genes and determined the DNA sequence of each. But for many of those genes, their function in the body has remained unknown. The newly identified gene falls into this “previously unknown function” category. In fact, the gene belongs to an entire class of genes that had no known function in any organism.

One way to learn what genes do is to study a model organism like the roundworm, which possesses a similar number of genes as people but only 956 cells, of which 302 are nerve cells (neurons). By knocking out or mutating roundworm genes and observing the effects, researchers can obtain insight into how genes influence the animal’s structure or physiology.

The Einstein scientists were looking for genes that organize the structure of the developing nervous system. They focused on a pair of roundworm sensory neurons, known as PVD neurons, which together produce the largest web of dendrites of any neurons in the roundworm—a sensory web that covers almost the entire skin surface of the worm and detects pain and extreme temperatures.

Suspecting that a gene acts in the skin to “instruct” nearby dendrites to branch, the researchers set out to identify the one responsible. To find it, they induced random mutations in the worms, singled out those worms displaying defects in PVD dendrite branching, and then identified the gene mutations that caused the defective branching.

This lengthy procedure, known as a genetic screen, was carried out by Yehuda Salzberg, Ph.D., the study’s lead author and a postdoctoral fellow in Dr. Buelow’s lab. The screen revealed that four mutations in the same gene caused defective branching of PVD dendrites. The researchers showed that this gene’s expression in the skin produces an extracellular protein that triggers normal branching of PVD dendrites during development. The dendritic branches of PVD neurons had previously been described as resembling menorahs, so the Einstein scientists named this gene mnr-1 and dubbed its protein menorin, or MNR-1.

The mnr-1 gene’s newly identified function in orchestrating dendrite branching is presumably not limited to roundworms. Versions of this gene are present in multicellular animals from the simplest to the most complex, including humans. Genes conserved in this way, through millions of years of evolution, tend to be genes that are absolutely necessary for maintaining life.

Further study revealed that menorin synthesized in the skin was necessary but not sufficient to prompt PVD dendrite branching. The menorin protein appears to form a complex with SAX-7/L1CAM, a well-known cell-adhesion protein found in the skin and elsewhere in the roundworm. The researchers found evidence that dendrite branching ensues when this two-protein complex is sensed by DMA-1, a receptor molecule found on growing sensory dendrites.

"A fair amount was already known about factors within sensory neurons that regulate dendrite branching," said Dr. Buelow. "But until now, we knew next to nothing about external cues that pattern the sensory dendrites crucial to the functioning of any of our five senses. Hopefully, our success in finding two skin-derived cues that orchestrate dendrite branching will help in identifying cues involved in other sensory organs and possibly in the brain. Finding such cues could conceivably lead to therapies for replacing dendrite arbors depleted by injury or disease."

Nobel Prize winner reports new model for neurotransmitter release

In a Neuron article published online October 10th, recent Nobel Laureate Thomas C. Südhof challenges long-standing ideas on how neurotransmitter gets released at neuronal synapses. On October 7th, Südhof won the Nobel Prize in Physiology or Medicine, alongside James Rothman and Randy Schekman, for related work on how vesicles—such as those in neurons that contain neurotransmitter—are transported within cells.

Neurotransmitter-containing vesicles are found inside neurons very close to the end of the axon. Here, they can quickly fuse with the neuronal membrane surrounding the axon to spill their contents into the synapse. How these vesicles are able to fuse with the membrane has been controversial, however, and understanding this process would give researchers much greater insight how neurons communicate with each other. Previously, it was thought that proteins found on the outside of the vesicles and on the axon membrane (called SNARE proteins) would come together and physically form a pore through which the contents of the vesicle—the neurotransmitter—could be released into the synapse. Now, the new findings from Südhof suggest that these proteins may not form a pore at all. Instead, their main role may be to physically force the vesicle and the axon membrane to get very close to each other; once they are forced into contact, the two appear able to fuse spontaneously.

"The importance of SNARE transmembrane regions has never been tested in a physiological fusion reaction," says Dr. Südhof. "We show that the SNARE transmembrane regions are dispensible for fusion as such but are important for maintaining the normal efficiency of regulated fusion. These findings rule out an essential participation of the SNARE transmembrane regions in fusion and are consistent with the notion that the SNAREs function in fusion as force generators, i.e., that their function is to force the membranes close together." The results are controversial due to years of research supporting the SNARE-protein pore hypothesis. These provocative findings could change long-held models for how neurotransmitters are released from neurons and suggest that there remain many open questions about the role of SNAREs in neurotransmitter release at synapses.

(Image: This is a molecular model of the active zone protein complex and its relation to the synaptic vesicle fusion machinery, Ca2+ channels, and synaptic cell-adhesion molecules. Credit: Neuron, Volume 75, Issue 1, 11-25, 12 July 2012, Sudhof)

Brain development differs in children who stutter

UAlberta researcher and ISTAR executive director says study results could increase understanding of brain and speech production, improving treatment.

A new study by a University of Alberta researcher shows that children who stutter have less grey matter in key regions of the brain responsible for speech production than children who do not stutter.

The findings not only improve our understanding of how the brain is built for speech production and why people stutter, but also affirm the importance of seeking treatment early, using approaches such as those pioneered by the Institute for Stuttering Treatment and Research in the Faculty of Rehabilitation Medicine at the U of A, said Deryk Beal, ISTAR’s executive director.

Previous research has used MRI scans to look at structural differences between the brains of adults who stutter and those who do not. The problem with that approach is the scans come years after the onset of stuttering, typically between the ages of two and five years, Beal said.

“You can never be quite sure whether the differences in brain structure or function you’re looking at were the result of a lifetime of coping with a speech disorder or whether those brain differences were there from the beginning,” explained Beal, a speech-language pathologist.

For his study, Beal scanned the brains of 28 children ranging from five to 12 years old. Half the children were diagnosed with stuttering; the other half served as a control.

Results showed that the inferior frontal gyrus region of the brain develops abnormally in children who stutter. This is important because that part of the brain is thought to control articulatory coding—taking information our brain understands about language and sounds and coding it into speech movements.

“If you think about the characteristics of stuttering—repetitions of the first sounds or syllables in a word, prolongation of sounds in a word—it’s easy to hypothesize that it’s a speech-motor-control problem,” explained Beal. “The type of stuttering treatment we deliver at ISTAR is delivered with this limitation of the speech system in mind, and we have good success in stuttering treatment.”

Beal initiated the research at the University of Toronto and completed the work upon his arrival at the U of A. He sees the results as a first step toward testing to see how grey matter volumes are influenced by stuttering treatment and understanding motor-sequence learning differences between children who stutter and those who do not.

“The more we know about motor learning in these kids, the more we can adjust our treatment—deliver it in a shorter period of time, deliver it more effectively.”

The study was published in the September issue of the peer-reviewed journal Cortex and received funding from the Canadian Institutes of Health Research Clinical Fellowship and the Hospital for Sick Children’s Clinician Scientist Training Program.

I’m ok, you’re not ok

Egoism and narcissism appear to be on the rise in our society, while empathy is on the decline. And yet, the ability to put ourselves in other people’s shoes is extremely important for our coexistence. A research team headed by Tania Singer from the Max Planck Institute for Human Cognitive and Brain Sciences has discovered that our own feelings can distort our capacity for empathy. This emotionally driven egocentricity is recognised and corrected by the brain. When, however, the right supramarginal gyrus doesn’t function properly or when we have to make particularly quick decisions, our empathy is severely limited.

When assessing the world around us and our fellow humans, we use ourselves as a yardstick and tend to project our own emotional state onto others. While cognition research has already studied this phenomenon in detail, nothing is known about how it works on an emotional level. It was assumed that our own emotional state can distort our understanding of other people’s emotions, in particular if these are completely different to our own. But this emotional egocentricity had not been measured before now.

This is precisely what the Max Planck researchers have accomplished in a complex marathon of experiments and tests. They also discovered the area of the brain responsible for this function, which helps us to distinguish our own emotional state from that of other people. The area in question is the supramarginal gyrus, a convolution of the cerebral cortex which is approximately located at the junction of the parietal, temporal and frontal lobe. “This was unexpected, as we had the temporo-parietal junction in our sights. This is located more towards the front of the brain,” explains Claus Lamm, one of the publication’s authors.

On the empathy trail with toy slime and synthetic fur

Using a perception experiment, the researchers began by showing that our own feelings actually do influence our capacity for empathy, and that this egocentricity can also be measured. The participants, who worked in teams of two, were exposed to either pleasant or unpleasant simultaneous visual and tactile stimuli.

While participant 1, for example, could see a picture of maggots and feel slime with her hand, participant 2 saw a picture of a puppy and could feel soft, fleecy fur on her skin. “It was important to combine the two stimuli. Without the tactile stimulus, the participants would only have evaluated the situation ‘with their heads’ and their feelings would have been excluded,” explains Claus Lamm. The participants could also see the stimulus to which their team partners were exposed at the same time.

The two participants were then asked to evaluate either their own emotions or those of their partners. As long as both participants were exposed to the same type of positive or negative stimuli, they found it easy to assess their partner’s emotions. The participant who was confronted with a stinkbug could easily imagine how unpleasant the sight and feeling of a spider must be for her partner.

Differences only arose during the test runs in which one partner was confronted with pleasant stimuli and the other with unpleasant ones. Their capacity for empathy suddenly plummeted. The participants’ own emotions distorted their assessment of the other person’s feelings. The participants who were feeling good themselves assessed their partners’ negative experiences as less severe than they actually were. In contrast, those who had just had an unpleasant experience assessed their partners’ good experiences less positively.

Particularly quick decisions cause a decline in empathy

The researchers pinpointed the area of the brain responsible for this phenomenon with the help of functional magnetic resonance imaging, generally referred to as a brain scanning. The right supramarginal gyrus ensures that we can decouple our perception of ourselves from that of others. When the neurons in this part of the brain were disrupted in the course of this task, the participants found it difficult not to project their own feelings onto others. The participants’ assessments were also less accurate when they were forced to make particularly quick decisions.

Up to now, the social neuroscience models have assumed that we mainly draw on our own emotions as a reference for empathy. This only works, however, if we are in a neutral state or the same state as our counterpart – otherwise, the brain must counteract and correct.

New Strategy to Treat Multiple Sclerosis Shows Promise in Mice

Scientists at The Scripps Research Institute (TSRI) have identified a set of compounds that may be used to treat multiple sclerosis (MS) in a new way. Unlike existing MS therapies that suppress the immune system, the compounds boost a population of progenitor cells that can in turn repair MS-damaged nerve fibers.

One of the newly identified compounds, a Parkinson’s disease drug called benztropine, was highly effective in treating a standard model of MS in mice, both alone and in combination with existing MS therapies.

“We’re excited about these results, and are now considering how to design an initial clinical trial,” said Luke L. Lairson, an assistant professor of chemistry at TSRI and a senior author of the study, which is reported online in Nature on October 9, 2013.

Lairson cautioned that benztropine is a drug with dose-related adverse side effects, and has yet to be proven effective at a safe dose in human MS patients. “People shouldn’t start using it off-label for MS,” he said.

A New Approach

An autoimmune disease of the brain and spinal cord, MS currently affects more than half a million people in North America and Europe, and more than two million worldwide. Its precise triggers are unknown, but certain infections and a lack of vitamin D are thought to be risk factors. The disease is much more common among those of Northern European heritage, and occurs about twice as often in women as in men.

In MS, immune cells known as T cells infiltrate the upper spinal cord and brain, causing inflammation and ultimately the loss of an insulating coating called myelin on some nerve fibers. As nerve fibers lose this myelin coating, they lose their ability to transmit signals efficiently, and in time may begin to degenerate. The resulting symptoms, which commonly occur in a stop-start, “relapsing-remitting” pattern, may include limb weakness, numbness and tingling, fatigue, vision problems, slurred speech, memory difficulties and depression, among other problems.

Current therapies, such as interferon beta, aim to suppress the immune attack that de-myelinates nerve fibers. But they are only partially effective and are apt to have significant adverse side effects.

In the new study, Lairson and his colleagues decided to try a complementary approach, aimed at restoring a population of progenitor cells called oligodendrocytes. These cells normally keep the myelin sheaths of nerve fibers in good repair and in principle could fix these coatings after MS damages them. But oligodendrocyte numbers decline sharply in MS, due to a still-mysterious problem with the stem-like precursor cells that produce them. “Oligodendrocyte precursor cells (OPCs) are present during progressive phases of MS, but for unknown reasons don’t mature into functional oligodendrocytes,” Lairson said.

A 100,000-Molecule Screen

Using a sophisticated small-molecule screening laboratory that TSRI manages in conjunction with the California Institute of Regenerative Medicine and in collaboration with the California Institute for Biomedical Research (Calibr), Lairson and his team screened a library of about 100,000 diverse compounds for any that could potently induce OPCs to mature or “differentiate.”

Several compounds scored well as OPC differentiation-inducers. Most were compounds of unknown activity —but one, benztropine, had been well characterized and indeed was already FDA-approved for treating Parkinson’s disease. “That was a surprise, and it meant that we could move forward relatively quickly in testing it,” said graduate student Vishal A. Deshmukh, first author of the paper who performed most of these experiments.

With the help of Brian R. Lawson, a senior author of the paper and assistant professor of immunology at TSRI, and his colleague Research Associate Virginie Tardif, Deshmukh set up tests of benztropine in mice with an induced MS-like autoimmune disease—a model commonly used for testing prospective MS drugs.

In these tests, benztropine showed a powerful ability to prevent autoimmune disease and also was effective in treating it after symptoms had arisen—virtually eliminating the disease’s ability to relapse. Although benztropine on its own worked about as well as existing treatments, it also showed a remarkable ability to complement these existing treatments, in particular two first-line immune-suppressant therapies, interferon-beta and fingolimod.

“Adding even a suboptimal level of benztropine effectively allowed us, for example, to cut the dose of fingolimod by 90%—and achieve the same disease-modifying effect as a normal dose of fingolimod,” said Lawson. “In a clinical setting that dose-lowering could translate into a big reduction in fingolimod’s potentially serious side effects.”

In further analyses, the researchers confirmed that benztropine works against disease in this mouse model by boosting the population of mature oligodendrocytes, which in turn restore the myelin sheaths of damaged nerves—even as the immune attack continues. “The benztropine-treated mice showed no change in the usual signs of inflammation, yet their myelin was mostly intact, suggesting that it was probably being repaired as rapidly as it was being destroyed,” said Lawson.

Benztropine is known to have multiple specific effects on brain cells, including the blocking of activity at acetylcholine and histamine receptors and a boosting of activity at dopamine receptors. But Lairson and his colleagues found evidence that the drug stimulates OPCs to differentiate mainly by blocking M1 or M3 acetylcholine receptors on these cells.

In addition to setting up initial clinical trials, Lairson and his team hope to learn more about how benztropine induces OPC maturation, and how its molecular structure might be optimized for this purpose. “We’re also looking at some of the other, relatively unknown molecules that we identified in our initial screen, to see if any of those has better clinical potential than benztropine,” he said.

“This work, like our previous studies with hematopoietic and mesenchymal stem cells, illustrates the power of small molecules to control stem and precursor cells in ways that may ultimately lead to a new generation of drugs for regenerative medicine,” said Peter G. Schultz, the Scripps Family Chair Professor in the Department of Chemistry at TSRI and one of the study’s senior authors.

Enigmatic Neurons Help Flies Get Oriented

Neurons deep in the fly’s brain tune in to some of the same basic visual features that neurons in bigger animals such as humans pick out in their surroundings. The new research is an important milestone toward understanding how the fly brain extracts relevant information about a visual scene to guide behavior.

As a tiny fruit fly navigates through its environment, it relies on visual landmarks to orient itself. Now, researchers at the Howard Hughes Medical Institute’s Janelia Farm Research Campus have identified neurons deep in the fly’s brain that tune in to some of the same basic visual features that neurons in bigger animals such as humans pick out in their surroundings. The new research is an important milestone toward understanding how the fly brain extracts relevant information about a visual scene to guide behavior.

In Vivek Jayaraman’s lab at Janelia, researchers are studying fly neural circuits with the goal of understanding fundamental principles of information processing. “Our hope is that over time we will get a clear picture of the neural transformations and algorithms involved in creating actions from sensory and motor information,” Vivek says. In a study published October 9, 2013, in the journal Nature, Vivek and postdoctoral researcher Johannes Seelig report on visual representations in a region of the fly brain thought to be important for visual learning.

Researchers have gathered compelling evidence that fruit flies recognize and remember visual features in their environment. Flies can use that information to seek out safe spaces or to avoid uncomfortable ones. Genetic studies have indicated that a region deep in the fly brain called the central complex is critical for these behaviors.

The central complex is found in the brains of insects and some crustaceans. “It’s not purely involved in visual learning, and is quite likely to be broadly important for sensory-motor integration in all these critters,” Vivek says, noting that in butterflies and locusts, the central complex may facilitate the use of polarized light for navigation during migration. Also, studies in cockroaches have found that it is important for turning in response to antennal touch. But in flies, no one had yet examined the activity of the neurons in the central complex to characterize their role. “It really was quite a mystery what was going on in this part of the fly brain,” Seelig says, adding that this study is only one step on a long road.

Technical limitations had prevented researchers from measuring neuronal activity in the fly’s central complex, where neurons are far smaller than they are in larger insects. Available techniques required flies to be immobilized, so scientists were limited to studying parts of the nervous system that detected sensory information, rather than those that processed that information or converted it into motor activity. But in 2010, Seelig and colleagues in Vivek’s lab at Janelia developed a method that enabled them to peer into the interior of a fly’s brain with a two-photon microscope, while the insect maintained the freedom to walk and move its wings. The microscope can detect genetically encoded proteins that light up when a nerve cell fires, due to the surge of calcium ions that accompanies a nerve impulse. “Once we had these tools, we really wanted to apply them to this central brain area,” Seelig says.

Using genetically modified strains of flies, Vivek and Seelig focused their experiments on specific classes of neurons and collected more comprehensive data about the activity of those populations than had been done in other species. They chose to zero in on a class of neurons known as ring neurons, on which the dendrites—the branching structures that connect to neighboring cells—were densely concentrated in specific spots within a region neighboring the central complex.

To test the ring neurons’ response to visual stimuli, Seelig placed the flies into a small virtual reality arena in which the flies could be presented with simple patterns of light. By monitoring the calcium-indicating dyes in the cells, Seelig could visualize nerve activity as each fly was exposed to different stimuli.

The researchers found that each neuron responded to visual stimuli in specific regions of the fly’s field of view. “Each cell seemed to have its receptive field in a slightly different area of that space,” Vivek explains. Further, they found that the orientation of the patterns that they projected onto the walls of the arena influenced the ring cells’ response: for example, vertical bars elicited a stronger response than horizontal bars for most cells.

Flies have an innate tendency to walk or fly toward vertically-oriented stimuli, but Vivek and Seelig were nonetheless surprised by the ring neurons’ strong bias towards detecting such patterns. Further, Seelig says, this preference for specific orientations parallels what others have found in larger animals. Neurons in the primary visual cortex of mammalian brains known as simple cells function similarly—identifying basic visual patterns and being tuned to their orientation. “A wide range of visual animals seem to use the same basic feature set when they break down the visual scene,” Vivek says, explaining that in humans, such simple features are combined by later brain regions into increasingly complex ones to eventually produce representations for faces.

He says it is not clear whether fruit flies reassemble the features in their visual field in the same way, or whether basic representations are instead converted directly into guidance for actions. “It’s an open question how complex a shape a fly needs to recognize and respond to,” he says.

The scientists also found that the ring neurons responded similarly to the visual environment regardless of whether the flies were stationary or walking. Flying diminished the response somewhat, but overall, Seelig says, visual patterns influenced the neurons’ activity far more than the insects’ behavior. “These particular neurons seem to filter out visual features, then send that information to other parts of the central complex that may transform that information into a behavioral signal. So this may be one of the major entry points for visual information to the region,” says Seelig.

Determining what happens next to the information received by ring neurons is an important question for Vivek and Seelig, who say they will expand their studies by testing the activity of other neurons in the central complex. “By marching through these networks, we hope to begin to understand how sensory information is integrated to make motor decisions,” Vivek explains.