Zebrafish Model of a Learning and Memory Disorder Shows Better Way to Target Treatment

Using a zebrafish model of a human genetic disease called neurofibromatosis (NF1), a team from the Perelman School of Medicine at the University of Pennsylvania has found that the learning and memory components of the disorder are distinct features that will likely need different treatment approaches. They published their results this month in Cell Reports.

NF1 is one of the most common inherited neurological disorders, affecting about one in 3,000 people. It is characterized by tumors, attention deficits, and learning problems. Most people with NF1 have symptoms before the age of 10. Therapies target Ras, a protein family that guides cell proliferation. The NF1 gene encodes neurofibromin, a very large protein with a small domain involved in Ras regulation.

Unexpectedly, the Penn team showed that some of the behavioral defects in mutant fish are not related to abnormal Ras, but can be corrected by drugs that affect another signaling pathway controlled by the small molecule cAMP. They used the zebrafish model of NF1 to show that memory defects – such as the recall of a learned task — can be corrected by drugs that target Ras, while learning deficits are corrected by modulation of the cAMP pathway. Overall, the team’s results have implications for potential therapies in people with NF1.

“We now know that learning and memory defects in NF1 are distinct and potentially amenable to drug therapy,” says co-senior author Jon Epstein, MD, chair of the department of Cell and Developmental Biology. “Our data convincingly show that memory defects in mutant fish are due to abnormal Ras activity, but learning defects are completely unaffected by modulation of these pathways. Rather these deficits are corrected with medicines that modulate cAMP.”

Over the last 20 years, zebrafish have become great models for studying development and disease. Like humans, zebrafish are vertebrates, and most of the genes required for normal embryonic development in zebrafish are also present in humans. When incorrectly regulated, these same genes often cause tumor formation and metastatic cancers.

Zebrafish have also become an ideal model for studying vertebrate neuroscience and behavior. In fact, co-senior author Michael Granato, PhD, professor of Cell and Developmental Biology, has developed the first high-throughput behavioral assays that measure learning and memory in fish. For example, Granato explains, “normal fish startle with changes in noise and light level by bending and swimming away from the annoying stimuli and do eventually habituate, that is get used to the alternations in their environment. But, NF1 fish mutants fail to habituate. However, after adding cAMP to their water, they do learn, and then behave like the non-mutant fish.”

This clearly indicates that learning deficits in the NF1 mutant fish are corrected by adding various substances that boost cAMP signaling. “Our data also indicate that learning and memory defects are reversible with acute pharmacologic treatments and are therefore not hard-wired, as might be expected for a defect in the development of nerves,” says Epstein. “This offers great hope for therapeutic intervention for NF1 patients.”

Zebrafish help to unravel Alzheimer’s disease

New fundamental knowledge about the regulation of stem cells in the nerve tissue of zebrafish embryos results in surprising insights into neurodegenerative disease processes in the human brain. A new study by scientists at VIB and KU Leuven identifies the molecules responsible for this process.

Zebrafish as a model
The zebrafish is a small fish measuring 3 to 5 cm in length, with dark stripes along the length of its body. They are originally from India, but also a popular aquarium fish. Zebrafish have several unusual characteristics that make them popular for scientific research. Zebrafish eggs are fertilized outside the body, where they develop into embryos. This process occurs very quickly: the most important organs have formed after 24 hours and the young fish have hatched after 3 days. These fish are initially transparent, making them easy to study under the microscope. Zebrafish start reproducing after only 3 months. The genetic code of humans and zebrafish is more than 90 % identical. In addition, the genetic material of these fish is easy to manipulate, meaning that they are often used as a model in the study of all sorts of diseases.

Stem cells in the brain
Evgenia Salta, scientist in the team of Bart De Strooper (VIB – KU Leuven), used zebrafish as a model in molecular brain research and discovered a previously unknown regulatory process for the development of nerve cells. Evgenia Salta explains: “The human brain contains stem cells, which are cells that have not matured into nerve cells yet, but do have the potential to do this.” Stem cells are of course crucial in the development of the brain. Similar stem cells also exist in zebrafish. Therefore, these fish form an ideal model to study the behavior of these cells. A so-called Notch signaling pathway regulates the further ripening of these cells during early embryonic development. Scientists are still largely in the dark about Notch processes in the brains of Alzheimer patients, but the research by Evgenia Salta is changing this situation.

MicroRNA
The expression of genes, which form the basis of the Notch signaling pathway, is regulated in part by microRNAs (miRNAs), which are short molecules that can inhibit or activate genes. Evgenia Salta: “We specifically studied how miRNA-132 regulates the Notch signaling pathway in stem cells.”

MiRNA-132 appears to play a role in maintaining the plasticity of the adult human brain. The adult brain still contains stem cells, but these are limited in number. The activity of miRNA-132 is reduced in diseases of the nervous system that involve the death of nerve cells, such as Alzheimer’s dementia. “We wanted to study the effect of the reduction in miRNA-132 in the nervous system. Zebrafish are an ideal model for this, because we can easily reduce levels of this miRNA in them. The development of stem cells is impaired in these altered fish. We mapped the molecules that play a role in this process”, explains Evgenia Salta.

Relevance
The concentration of miRNA-132 is also reduced in the brains of patients with Alzheimer’s disease. Therefore, the zebrafish allow you to mimic a condition that also occurs in Alzheimer’s dementia. Evgenia Salta: “To our surprise, the reduced activity of miRNA-132 in the zebrafish blocks the further ripening of stem cells into nerve cells. This new knowledge about the molecular signaling pathway that underlies this process gives us an insight into the exact blocking mechanism. Thanks to this work in zebrafish, we can now examine in detail what exactly goes wrong in the brains of patients with Alzheimer’s disease.” The research team has therefore started a follow-up study in mice and the brains of deceased patients.

Questions
As this research can raise many questions, we would you to refer in your report or article to the e-mail address that VIB has made available for this purpose. Anyone with questions about this research and other medically oriented research can contact: patienteninfo@vib.be.

Research team
This research was performed by the research team of Bart De Strooper, who is head of the Leuven Laboratory for Research into Degenerative Diseases and is affiliated with the VIB Center for the Biology of Disease.

Research
A self-organizing miR-132/Ctbp2 circuit regulates bimodal Notch signals and glial progenitor fate choice during spinal cord maturation.Salta E et al. Developmental Cell.

(Image caption: Techniques known as dimensionality reduction can help find patterns in the recorded activity of thousands of neurons. Rather than look at all responses at once, these methods find a smaller set of dimensions — in this case three — that capture as much structure in the data as possible. Each trace in these graphics represents the activity of the whole brain during a single presentation of a moving stimulus, and different versions of the analysis capture structure related either to the passage of time (left) or the direction of the motion (right). The raw data is the same in both cases, but the analyses finds different patterns. Credit: Jeremy Freeman, Nikita Vladimirov, Takashi Kawashima, Yu Mu, Nicholas Sofroniew, Davis Bennett, Joshua Rosen, Chao-Tsung Yang, Loren Looger, Philipp Keller, Misha Ahrens)

New Tools Help Neuroscientists Analyze Big Data

In an age of “big data,” a single computer cannot always find the solution a user wants. Computational tasks must instead be distributed across a cluster of computers that analyze a massive data set together. It’s how Facebook and Google mine your web history to present you with targeted ads, and how Amazon and Netflix recommend your next favorite book or movie. But big data is about more than just marketing.

New technologies for monitoring brain activity are generating unprecedented quantities of information. That data may hold new insights into how the brain works – but only if researchers can interpret it. To help make sense of the data, neuroscientists can now harness the power of distributed computing with Thunder, a library of tools developed at the Howard Hughes Medical Institute’s Janelia Research Campus.

Thunder speeds the analysis of data sets that are so large and complex they would take days or weeks to analyze on a single workstation – if a single workstation could do it at all. Janelia group leaders Jeremy Freeman, Misha Ahrens, and other colleagues at Janelia and the University of California, Berkeley, report in the July 27, 2014, issue of the journal Nature Methods that they have used Thunder to quickly find patterns in high-resolution images collected from the brains of active zebrafish and mice with multiple imaging techniques.

Importantly, they have used Thunder to analyze imaging data from a new microscope that Ahrens and colleagues developed to monitor the activity of nearly every individual cell in the brain of a zebrafish as it behaves in response to visual stimuli. That technology is described in a companion paper published in the same issue of Nature Methods.

Thunder can run on a private cluster or on Amazon’s cloud computing services. Researchers can find everything they need to begin using the open source library of tools at http://freeman-lab.github.io/thunder

New microscopes are capturing images of the brain faster, with better spatial resolution, and across wider regions of the brain than ever before. Yet all that detail comes encrypted in gigabytes or even terabytes of data. On a single workstation, simple calculations can take hours. “For a lot of these data sets, a single machine is just not going to cut it,” Freeman says.

It’s not just the sheer volume of data that exceeds the limits of a single computer, Freeman and Ahrens say, but also its complexity. “When you record information from the brain, you don’t know the best way to get the information that you need out of it. Every data set is different. You have ideas, but whether or not they generate insights is an open question until you actually apply them,” says Ahrens.

Neuroscientists rarely arrive at new insights about the brain the first time they consider their data, he explains. Instead, an initial analysis may hint at a more promising approach, and with a few adjustments and a new computational analysis, the data may begin to look more meaningful. “Being able to apply these analyses quickly — one after the other — is important. Speed gives a researcher more flexibility to explore and get new ideas.”

That’s why trying to analyze neuroscience data with slow computational tools can be so frustrating. “For some analyses, you can load the data, start it running, and then come back the next day,” Freeman says. “But if you need to tweak the analysis and run it again, then you have to wait another night.” For larger data sets, the lag time might be weeks or months.

Distributed computing was an obvious solution to accelerate analysis while exploring the full richness of a data set, but many alternatives are available. Freeman chose to build on a new platform called Spark. Developed at the University of California, Berkeley’s AMPLab, Spark is rapidly becoming a favored tool for large-scale computing across industry, Freeman says. Spark’s capabilities for data caching eliminates the bottleneck of loading a complete data set for all but the initial step, making it well-suited for interactive, exploratory analysis, and for complex algorithms requiring repeated operations on the same data. And Spark’s elegant and versatile application programming interfaces (APIs) help simplify development. Thunder uses the Python API, which Freeman hopes will make it particularly easy for others to adopt, given Python’s increasing use in neuroscience and data science.

To make Spark suitable for analyzing a broad range of neuroscience data – information about connectivity and activity collected from different organisms and with different techniques – Freeman first developed standardized representations of data that were amenable to distributed computing. He then worked to express typical neuroscience workflows into the computational language of Spark.

From there, he says, the biological questions that he and his colleagues were curious about drove development. “We started with our questions about the biology, then came up with the analyses and developed the tools,” he says.

The result is a modular set of tools that will expand as the Janelia team — and the neuroscience community — add new components. “The analyses we developed are building blocks,” says Ahrens. “The development of new analyses for interpreting large-scale recording is an active field and goes hand-in-hand with the development of resources for large-scale computing and imaging. The algorithms in our paper are a starting point.”

Using Thunder, Freeman, Ahrens, and their colleagues analyzed images of the brain in minutes, interacting with and revising analyses without the lengthy delays associated with previous methods. In images taken of a mouse brain with a two-photon microscope, for example, the team found cells in the brain whose activity varied with running speed.

For analyzing much larger data sets, tools such as Thunder are not just helpful, they are essential, the scientists say. This is true for the information collected by the new microscope that Ahrens and colleagues developed for monitoring whole-brain activity in response to visual stimuli.

Last year, Ahrens and Janelia group leader Phillip Keller used high-speed light-sheet imaging to engineer a microscope that captures neuronal activity cell by cell across nearly the entire brain of a larval zebrafish. That microscope produced stunning images of neurons in the zebrafish brain firing while the fish was inactive. But Ahrens wanted to use the technology to study the brain’s activity in more complex situations. Now, the team has combined their original technology with a virtual-reality swim simulator that Ahrens previously developed to provide fish with visual feedback that simulates movement.

In a light sheet microscope, a sheet of laser light scans across a sample, illuminating a thin section at a time. To enable a fish in the microscope to see and respond to its virtual-reality environment, Ahrens’ team needed to protect its eyes. So they programmed the laser to quickly shut off when its light sheet approaches the eye and restart once the area is cleared. Then they introduced a second laser that scans the sample from a different angle to ensure that the region of the brain behind the eyes is imaged. Together, the two lasers image the brain with nearly complete coverage without interfering with the animal’s vision.

Combining these two technologies lets Ahrens monitor activity throughout the brain as a fish adjusts its behavior based on the sensory information it receives. The technique generates about a terabyte of data in an hour – presenting a data analysis challenge that helped motivate the development of Thunder. When Freeman and Ahrens applied their new tools to the data, patterns quickly emerged. As examples, they identified cells whose activity was associated with movement in particular directions and cells that fired specifically when the fish was at rest, and were able to characterize the dynamics of those cells’ activities. Example analyses like these, and example data sets, are available at the website http://research.janelia.org/zebrafish/.

Ahrens now plans to explore more complex questions using the new technology, and both he and Freeman foresee expansion of Thunder. “At every level, this is really just the beginning,” Freeman says.

Division of labour in the fish brain

For a fish to swim forward, the nerve cells, or neurons, in its brain and spine have to control the swishing movements of its tail with very close coordination. However, the posture of the tail, which determines swimming direction somewhat like a rudder, also needs to be fine-tuned by the brain’s activity. Using the innovative method of optogenetics, scientists from the Max Planck Institute of Neurobiology in Martinsried have now identified a group of only about 15 nerve cells which steer the movements of the tail fin. Movements of the human body are also controlled via nerve pathways in the same region of the brain, which may therefore use processing mechanisms similar to those in fish.

For a long time, neurobiologists have been trying to find out how neuronal networks control both animal and human behaviour. In this context, there is controversy as to whether the brain’s organisation is decentralised as opposed to modular. In decentralised organisation, the interaction of a large number of neurons produces a specific behaviour pattern. If this is the case, individual neurons cannot be assigned an exact function. On the other hand, if the brain has a modular structure, individual regions might possess certain competencies, each making a specific contribution to behaviour. These types of neuronal circuit modules could be combined in many ways and influence a broad range of different behavioural responses.

Switches in the fish brain?

Researchers in Herwig Baier’s Group at the Max Planck Institute of Neurobiology want to get to the bottom of the brain’s organisational structure with the aid of zebrafish larvae. A network known as the descending reticular formation is located in the brainstem of these animals. The neurons of that region are optimally suited for studying the organisation of the brain: the cells are in direct contact with motor neurons in the spinal cord of the fish and can thus directly influence tail movements. “The reticular formation is a like a ‘cockpit’ for the fish, and we asked ourselves whether there are individual ‘switches’ or ‘joysticks‘, which are used to control the movements of the tail”, is how Herwig Baier summarises this challenge.

In their search for these switches, the researchers concentrated on a small brain nucleus (nMLF) within the reticular formation. But how can the influence of individual nMLF neurons on tail movements be studied? It is only recently that such investigations even became a possibility. Using the new method of optogenetics, the activity of nerve cells can be influenced with light. Since a zebrafish larva – including its brain – is transparent, scientists can very accurately “switch on” small sets of genetically modified cells by exposing the larva to blue light. Consequently, tail movements that are induced in this way can be attributed to identified neurons.

Neurons and tillers

The first series of tests showed that the cells of the nMLF region seem to be involved in a variety of movements – from forward propulsion to rotational motion. A second experimental series using optogenetic stimulation, however, suggested that the cells control the deflection of the tail in particular. Are the nMLF cells thus part of a multifunctional centre or are they truly specialised to perform certain functions? To resolve this question, the neurobiologists performed another set of trials in which they very specifically removed small sets of nMLF cells from the circuit. “This experiment gave us our breakthrough”, recalls Tod Thiele, lead author of the now published study.

The results show that, while nMLF cells are active in many aspects of swimming, a subset of these neurons contribute to only one part of the movement: they determine swimming direction through the posture of the tail. Thus, this population of neurons in the nMLF region are more akin to a specialised module within a decentralised control system of the swimming apparatus. Herwig Baier explains it like this: “We can compare the whole setup with the propulsion of a motorboat”. The boat’s engine, which drives the propeller, determines the thrust, whereas the tiller steers the boat. It seems that the tasks in the brain are divided up in a very similar way.

Some time ago, Herwig Baier’s team discovered a small region in the hindbrain, which acts like an engine and propels the fish forwards. “With the nMLF cells, we have now also found the tiller in the fish brain”, says Herwig Baier. In the human brain, movements are also controlled by a multitude of nuclei in the reticular formation. The study therefore suggests that the allocation of tasks in our brain could be similar to that of the zebrafish.

Beneath the Surface: What Zebrafish Can Tell Us About Anxiety

The right tool for the job is important. A surgeon wouldn’t use a chainsaw when a scalpel offers more control. But sometimes the best treatments available aren’t precise. For example, anxiety medications available today are too blunt in how they target the brain, according to Ian Woods, assistant professor of biochemistry at Ithaca College.

“If you look at current treatments for anxiety disorders, the approach is a bit like taking a sledgehammer to a mosquito,” he said. “The treatments may work for anxiety, but they can have a lot of side effects.”

Woods researches how genetics influence responses to stimuli that can trigger anxiety, and he’s using zebrafish — a tropical member of the minnow family named for the black stripes on their bodies — to do so. He and his team of student researchers examine how fish with tweaked genes respond to different triggers compared to unmodified fish. The work could someday lead to better, more nuanced medications for anxiety disorders.

Zebrafish make ideal test subjects for several reasons. The embryos are transparent and develop outside the mother’s body, making it easy for Woods and his team to observe their growth under a microscope. They develop rapidly, are easy to care for and easy to breed in large quantities.

Specifically, Woods is looking at neuropeptides, which are the chemical messengers between brain cells. Different neuropeptides deliver different messages, which in turn produce different behaviors.

“Fish have the same neuropeptides as humans, and they mostly do the same things in the brain,” Woods said. “We can never faithfully model a complex human behavior like anxiety, but when we’re trying to figure out how the brain works, it’s useful to see inside a fish.”

Woods and his team isolate specific genes to disrupt, amplify, alter or replace, then analyze the movements of the modified fish with the aid of a computerized camera system. They examine responses to stimuli such as slight changes in water temperature, decreases in light intensity, or mild chemical irritants such as mustard oil.

“By observing the ensuing behavioral changes in the fish, we know how that replaced gene changed the message in the brain,” Woods explained. For example, fish exhibiting anxiety-like behaviors might hug the walls of the tank, while the rest will swim toward the middle. It’s not unlike social experiments in which the room temperature is raised gradually to see how human occupants will react.

“Genes typically don’t cause the anxiety,” Woods said. “But they can make organisms more susceptible to environmental triggers that might elicit what we’d call an anxious behavior.”

Anxiety disorders are the most common mental illness in the United States; over 40 million Americans suffer from some type in their lifetimes. But medications can be overprescribed and abused. For example, emergency room visits related to the use of Xanax and related drugs doubled from 2005 to 2011, according to the U.S. Substance Abuse and Mental Health Services Administration.

(Image caption: Newly discovered neuron type (yellow) helps zebrafish to coordinate its eye and swimming movements. The image shows the blue-stained brain of a fish larva with the suggested position of the eyes. Credit: © Max Planck Institute of Neurobiology/Kubo)

How vision makes sure that little fish do not get carried away

Our eyes not only enable us to recognise objects; they also provide us with a continuous stream of information about our own movements. Whether we run, turn around, fall or sit still in a car – the world glides by us and leaves a characteristic motion trace on our retinas. Seemingly without effort, our brain calculates self-motion from this “optic flow”. This way, we can maintain a stable position and a steady gaze during our own movements. Together with biologists from the University of Freiburg, scientists from the Max Planck Institute of Neurobiology in Martinsried near Munich have now discovered an array of new types of neurons, which help the brain of zebrafish to perceive, and compensate for, self-motion.

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Whole-Brain Activity Maps Reveal Stereotyped, Distributed Networks for Visuomotor Behavior

Most behaviors, even simple innate reflexes, are mediated by circuits of neurons spanning areas throughout the brain. However, in most cases, the distribution and dynamics of firing patterns of these neurons during behavior are not known. We imaged activity, with cellular resolution, throughout the whole brains of zebrafish performing the optokinetic response. We found a sparse, broadly distributed network that has an elaborate but ordered pattern, with a bilaterally symmetrical organization. Activity patterns fell into distinct clusters reflecting sensory and motor processing. By correlating neuronal responses with an array of sensory and motor variables, we find that the network can be clearly divided into distinct functional modules. Comparing aligned data from multiple fish, we find that the spatiotemporal activity dynamics and functional organization are highly stereotyped across individuals. These experiments systematically reveal the functional architecture of neural circuits underlying a sensorimotor behavior in a vertebrate brain.

Full article

Image caption: An image of the left and right sided habenular nuclei of larval zebrafish showing left/right structural asymmetries in the processes of neurons (pink) and their connections (blue). (Credit: Ana Faro/Tom Hawkins/Steve Wilson/UCL)

Brain asymmetry improves processing of sensory information

Fish that have symmetric brains show defects in processing information about sights and smells, according to the results of a new study into how asymmetry in the brain affects processing of sensory information.

It’s widely believed that the left and right sides of the brain have slightly different roles in cognition and in regulating behaviour. However, scientists don’t know whether these asymmetries actually matter for the efficient functioning of the brain.

Now, a team from UCL and KU Leuven, Belgium has shown that, in zebrafish at least, loss of brain asymmetry can have significant consequences on sensory processing, raising the possibility that defects in the development of brain functions on either the left or right on the brain could cause cognitive dysfunction. The study is published today in Current Biology.

Professor Steve Wilson, senior author of the study from the UCL Department of Cell & Developmental Biology, said: “We don’t know whether asymmetries actually matter for the efficient functioning of the brain. For instance, if your brain was symmetric, would it work any less well than it normally does?

“This is potentially an important issue as brain-imaging studies in various neurological conditions have shown alterations in normally asymmetric patterns of neuronal activity.”

In their study the team used two-photon high resolution microscopy to image the activity of individual neurons in a part of the brain called the habenulae in larval zebrafish. This region of the brain shows asymmetries in many different vertebrates and is involved in mediating addiction, fear and reward pathways and probably influences numerous behaviour patterns.

In zebrafish habenulae most neurons responding to a light stimulus are on the left whereas most responding to odour are on the right. Using this knowledge to their advantage, scientists bred fish in which habenular asymmetry was reversed and fish with double-right and double-left sided habenulae. They then asked how the habenular neurons responded to visual or olfactory stimuli in these different conditions. 

They found that if the direction of brain asymmetry was reversed, the functional properties of the habenular neurons were also reversed, whereas double-left and double-right sided brains almost completely lacked habenular responsiveness to odour or light respectively.

Dr Elena Dreosti, first author of the study, also from UCL Department of Cell & Developmental Biology, said: “These results show that loss of brain asymmetry can have significant consequences upon sensory processing and circuit function”.

The research raises the possibility that defects in the establishment of brain lateralization could indeed be causative of cognitive or other symptoms of brain dysfunction.

Findings Could Help Explain Origins of Human Limb Control

We might have more in common with a lamprey than we think, according to a new Northwestern University study on locomotion. At its core, the study of transparent zebrafish addresses a fundamental evolution issue: How did we get here?

Neuroscientists Martha W. Bagnall and David L. McLean have found that the spinal cord circuits that produce body bending in swimming fish are more complicated than previously thought.

Vertebrate locomotion has evolved from the simple left-right bending of the body exemplified by lampreys to the appearance of fins in bony fish to the movement of humans, with the complex nerve and muscle coordination necessary to move four limbs.

Bagnall and McLean report that differential control of an animal’s musculature — the basic template for controlling more complex limbs — is already in place in the spinal networks of simple fish. Neural circuits in zebrafish are completely segregated: individual neurons map to specific muscles.

Specifically, the neural circuits that drive muscle movement on the dorsal (or back) side are separate from the neural circuits activating muscles on the ventral (or front) side. This is in addition to the fish being able to separately control the left and right sides of its body [Video]

Ultimately, understanding more about how fish swim will allow scientists to figure out how humans walk.

“Evolution builds on pre-existing patterns, and this is a critical piece of the puzzle,” McLean said. “Our data help clarify how the transition from water to land could have been accomplished by simple changes in the connections of spinal networks.”

The findings will be published Jan. 10 in the journal Science. McLean, an assistant professor of neurobiology in the Weinberg College of Arts and Sciences, and Bagnall, a postdoctoral fellow in his research group who made the discovery, are authors of the paper.

“This knowledge will put us in a better position to devise more effective therapies for when things go wrong with neural circuits in humans, such as spinal cord damage,” McLean said. “If you want to fix something, you have to know how it works in the first place. Given that the fish spinal cord works in a similar fashion to our own, this makes it a fantastic model system for research.”

McLean and Bagnall studied the motor neurons of baby zebrafish because the fish develop quickly and are see-through. They used state-of-art imaging techniques to monitor and manipulate neuronal activity in the fish.

“You can stare right into the nervous system,” McLean said. “It’s quite remarkable.”

The separate circuits for moving the left and right and top and bottom of the fish allow the animal to twist its body upright when it senses that it has rolled too far to one side or the other.

“This arrangement is perfectly suited to provide rapid postural control during swimming,” Bagnall said. “Importantly, this ancestral pattern of spinal cord organization may also represent an early functional template for the origins of limb control.”

Separate control of dorsal and ventral muscles in the fish body is a possible predecessor to separate control of extensors and flexors in human limbs. By tweaking the connections between these circuits as they elaborated during evolution, it is easier to explain how more complicated patterns of motor coordination in the limbs and trunk could have arisen during dramatic evolutionary changes in the vertebrate body plan, the researchers said.

“We are teasing apart basic components of locomotor circuits,” McLean said. “The molecular mechanisms responsible for building spinal circuits are conserved in all animals, so this study provides a nice hypothesis that scientists can test.”

Study provides new insights into cause of human neurodegenerative disease

A recent study led by scientists from the National University of Singapore (NUS) opens a possible new route for treatment of Spinal Muscular Atrophy (SMA), a devastating disease that is the most common genetic cause of infant death and also affects young adults. As there is currently no known cure for SMA, the new discovery gives a strong boost to the fight against SMA.

SMA is caused by deficiencies in the Survival Motor Neuron (SMN) gene. This gene controls the activity of various target genes. It has long been speculated that deregulation of some of these targets contributes to SMA, yet their identity remained unknown.

Using global genome analysis, the research team, led by Associate Professor Christoph Winkler of the Department of Biological Sciences at the NUS Faculty of Science and Dr Kelvin See, a former A*STAR graduate scholar in NUS who is currently a Research Fellow at the Genome Institute of Singapore (GIS), found that deficiency in the SMN gene impairs the function of the Neurexin2 gene. This in turn limits the neurotransmitter release required for the normal function of nerve cells. The degeneration of motor neurons in the spinal cord causes SMA. This is the first time that scientists establish an association between Neurexin2 and SMA.

Preliminary experimental data also showed that a restoration of Neurexin2 activity can partially recover neuron function in SMN deficient zebrafish. This indicates a possible new direction for therapy of neurodegeneration.

Collaborating with Assoc Prof Winkler and the NUS researchers are Dr S. Mathavan and his team at GIS, as well as researchers from the University of Wuerzburg in Germany. The breakthrough discovery was first published in scientific journal Human Molecular Genetics last month.

Small zebrafish provides insights into human neurodegenerative disease

SMA is a genetic disease that attacks a distinct type of nerve cells called motor neurons in the spinal cord. The disease has been found to be caused by a defect in the SMN gene, a widely used gene that is responsible for normal motor functions in the body.

To study how defects in SMN cause neuron degeneration, the scientists utilised a zebrafish model, as the small fish has a relatively simple nervous system that allows detailed imaging of neuron behaviour.

In laboratory experiments, the researchers showed when SMN activity in zebrafish was reduced to levels found in human SMA patients, Neurexin2 function was impaired. This novel disease mechanism was also discovered in other in vivo models, suggesting that it is applicable to mammals and possibly human patients.

When the scientists measured the activity of nerve cells in zebrafish using laser imaging, they found that nerve cells deficient for Neurexin2 or SMN could not be activated to the same level as healthy nerve cells. This impairment consequently led to the reduction of muscular activity. Interestingly, preliminary data showed that a restoration of Neurexin2 activity can partially recover neuron function in SMN deficient zebrafish.

Further studies

Assoc Prof Winkler, who is also with the NUS Centre for Biolmaging Sciences, explained, “These findings significantly advance our understanding of how the loss of SMN leads to neurodegeneration. A better understanding of these mechanisms will lead to novel therapeutic strategies that could aim at restoring and maintaining functions in deficient nerve cells of SMA patients.”

Dr See added, “Our study provides a link between SMN deficiency and its effects on a critical gene important for neuronal function. It would be interesting to perform follow up studies in clinical samples to further investigate the role of Neurexin2 in SMA pathophysiology.”

Moving forward, the team of scientists will conduct further research to determine if Neurexin2 is an exclusive mediator of SMN induced defects and hence can be used as a target for future drug designs. They hope their findings will contribute towards treatment of neurodegeneration.