Weizmann Institute

Studying social sense

Michael Gliksberg, left, and Prof. Gil Levkowitz are among the researchers who have discovered that oxytocin in a developing zebrafish brain determines later social behaviour. (photo from Weizmann Institute)

Whenever we decide to throw a party, invite in-laws to dinner or embark on a cruise, we are driven by the most basic component of social behaviour: the desire to hang out with other humans. Considering that the drive to form groups with members of one’s own species has been conserved throughout evolution, it’s evident that social behaviour is governed by genes, at least to some degree. But our parents and teachers help us hone our social graces, so teasing apart the effects of nature and nurture on this behaviour is hard, if not impossible. By studying zebrafish, Weizmann Institute of Science researchers, in collaboration with scientists in Portugal, have managed to solve part of the riddle of how social behaviour is hardwired into the developing brain.

Zebrafish are perfect for studying the inborn basis of behaviour because they receive zero nurturing from parents. “Some fish species take care of their young, but not zebrafish,” explained Prof. Gil Levkowitz of the Weizmann Institute’s molecular cell biology and molecular neuroscience departments, who headed the research team together with Prof. Rui F. Oliveira of Instituto Gulbenkian de Ciência in Portugal. “The female zebrafish spawns several hundred eggs, which are fertilized by sperm released into the water by the male. She does provide her offspring with a ‘lunchbox’ – a protein sac, or yolk, that makes up part of the egg – but, otherwise, her message to her children is: manage on your own.”

At about four weeks of age, the centimetre-long juvenile fish, just out of the larval stage, begin to socialize. Though not as exquisitely synchronized as the schools of moonfish in the movie Finding Nemo, they do exhibit a strong tendency to swim together as a group, termed a shoal. Much like humans, they have an incentive to seek company; in their case, the group provides them with advantages in searching for food, overcoming currents, avoiding predators and finding mates. The shoaling behaviour of zebrafish requires sophisticated processing of visual and social cues, very similar to that which takes place in the brains of socializing humans. In particular, the zebrafish must be able to identify other fish as belonging to their own, “friendly” – as opposed to different or, worse yet, predatory – species.

To learn how the social behaviour of zebrafish develops, the researchers focused on the hormone oxytocin, one of the most important neurochemicals known to enhance social interactions, including bonding. Postdoctoral fellow Dr. Ana Rita Nunes and doctoral student Michael Gliksberg created a system for exploring the effects of oxytocin on the developing brains of zebrafish larvae. They produced transgenic larvae whose oxytocin-making neurons harboured a bacterial gene encoding fatal sensitivity to antibiotics. The researchers could then eliminate these neurons from the brains of the larvae at different stages of their development by adding antibiotics to the water, and they later observed the zebrafish behaviour as they became adults.

The scientists discovered that the larvae whose brains lacked oxytocin early on – specifically, in the first two weeks of life – grew into adult fish with an impaired capacity for social interaction, namely, swimming in a shoal. Although their brains regenerated the oxytocin neurons later in life, this capacity was not restored. This meant that, for adults to be capable of social behaviour, their brains had to be organized by oxytocin in a certain manner during a critical time window of brain development in which the social traits are established.

The researchers further discovered the mechanisms by which oxytocin primes the growing brain for socializing. They showed that oxytocin-producing neurons were critical to the birth of another type of neuron, one that releases the neurotransmitter dopamine, which is known to regulate feelings of reward and motivation. Zebrafish whose brains had not been exposed to oxytocin during the first two weeks of life had reduced numbers of dopamine-making neurons, as well as a reduced number of connections to these neurons, in two distinct brain areas.

One of these areas was responsible for processing visual stimuli, apparently of the kind essential for recognizing potential swimming partners. An analogous area in the brains of mammals, including humans, is involved in processing visual cues in social situations. It controls eye movements that scan, for example, different elements of the face in a particular order to decipher facial expressions. This pattern is often absent in people with autism, suggesting that their brains respond to social-based visual cues differently.

The other dopamine-deficient brain area in the zebrafish was analogous to a major reward centre in the mammalian brain, which is involved in the positive reinforcement of social interactions.

A lack of oxytocin in the critical early developmental period also disrupted a system of neuronal connections known as the social decision-making network – a group of brain areas that work together to process social information. In fish whose brains had developed without oxytocin, the synchronization patterns of neuronal activities among these centres were completely different from those of regular fish.

Nunes summarized: “Oxytocin organizes the developing brain in a way that’s essential for responding to social situations.”

– Courtesy Weizmann Institute

Studying the “love hormone”

Oxytocin, a peptide produced in the brain, may bring hearts together – or it can help induce aggression. (image from Weizmann Institute)

During the pandemic lockdown, as couples have been forced to spend days and weeks in each other’s company, some have found their love renewed while others are on their way to divorce court. Oxytocin, a peptide produced in the brain, is complicated in that way: a neuromodulator, it may bring hearts together or it can help induce aggression. This conclusion arises from research led by Weizmann Institute of Science researchers in which mice living in semi-natural conditions had their oxytocin-producing brain cells manipulated in a precise manner. The findings, which were published in Neuron, could shed new light on efforts to use oxytocin to treat a variety of psychiatric conditions, from social anxiety and autism to schizophrenia.

Much of what we know about the actions of neuromodulators like oxytocin comes from behavioural studies of lab animals in standard lab conditions. These conditions are strictly controlled and artificial, in part so that researchers can limit the number of variables affecting behaviour. But a number of recent studies suggest that the actions of a mouse in a semi-natural environment can teach us much more about natural behaviour, especially when we mean to apply those findings to humans.

Prof. Alon Chen’s lab group in the institute’s neurobiology department have created an experimental setup that enables them to observe mice in something approaching their natural living conditions – an environment enriched with stimuli they can explore – and their activity is monitored day and night with cameras and analyzed computationally. The present study, which has been ongoing for the past eight years, was led by research students Sergey Anpilov and Noa Eren, and staff scientist Dr. Yair Shemesh in Chen’s lab group.

The innovation in this experiment was to incorporate optogenetics – a method that enables researchers to turn specific neurons in the brain on or off using light. To create an optogenetic setup that would enable the team to study mice that were behaving naturally, the group developed a compact, lightweight, wireless device with which the scientists could activate nerve cells by remote control. With the help of optogenetics expert Prof. Ofer Yizhar of the same department, the group introduced a protein previously developed by Yizhar into the oxytocin-producing brain cells in the mice. When light from the wireless device touched those neurons, they became more sensitized to input from the other brain cells in their network.

“Our first goal,” said Anpilov, “was to reach that ‘sweet spot’ of experimental setups in which we track behaviour in a natural environment, without relinquishing the ability to ask pointed scientific questions about brain functions.”

Shemesh added that “the classical experimental setup is not only lacking in stimuli, the measurements tend to span mere minutes, while we had the capacity to track social dynamics in a group over the course of days.”

Delving into the role of oxytocin was sort of a test drive for the experimental system. It had been believed that this hormone mediates pro-social behaviour. But findings have been conflicting, and some have proposed another hypothesis, termed “social salience,” stating that oxytocin might be involved in amplifying the perception of diverse social cues, which could then result in pro-social or antagonistic behaviours, depending on such factors as individual character and the environment.

To test the social salience hypothesis, the team used mice in which they could gently activate the oxytocin-producing cells in the hypothalamus, placing them first in the enriched, semi-natural lab environments. To compare, they repeated the experiment with mice placed in the standard, sterile lab setups.

In the semi-natural environment, the mice at first displayed heightened interest in one another, but this was soon accompanied by a rise in aggressive behaviour. In contrast, increasing oxytocin production in the mice in classical lab conditions resulted in reduced aggression.

“In an all-male, natural social setting, we would expect to see belligerent behaviour as they compete for territory or food,” said Anpilov. “That is, the social conditions are conducive to competition and aggression. In the standard lab setup, a different social situation leads to a different effect for the oxytocin.”

If the “love hormone” is more likely a “social hormone,” what does that mean for its pharmaceutical applications?

“Oxytocin is involved, as previous experiments have shown, in such social behaviours as making eye contact or feelings of closeness,” said Eren, “but our work shows it does not improve sociability across the board. Its effects depend on both context and personality.”

This implies that, if oxytocin is to be used therapeutically, a much more nuanced view is needed in research: “If we want to understand the complexities of behaviour, we need to study behaviour in a complex environment. Only then can we begin to translate our findings to human behaviour,” she said.

Participating in this research were scientists at the Max Planck Institute for Psychiatry in Munich, including research students Asaf Benjamin and Stoyo Karamihalev, staff scientist Dr. Julien Dine and postdoctoral fellow Dr. Oren Forkosh of the Chen lab; Prof. Shlomo Wagner and postdoctoral fellow Dr. Hala Harony-Nicolas of Haifa University; Prof. Inga Neumann and research student Vinicius Oliveira of Regensburg University, Germany; and electrical engineer Avi Dagan.

Predicting diabetes risk

A new computer algorithm can predict in the early stages of pregnancy, or even before pregnancy has occurred, which women are at a high risk of gestational diabetes. (photo from Weizmann Institute)

A new computer algorithm can predict in the early stages of pregnancy, or even before pregnancy has occurred, which women are at a high risk of gestational diabetes, according to a study by researchers at the Weizmann Institute of Science.

The study, reported recently in Nature Medicine, analyzed data on nearly 600,000 pregnancies available from Israel’s largest health organization, Clalit Health Services.

“Our ultimate goal has been to help the health system take measures so as to prevent diabetes from occurring in pregnancy,” said senior author Prof. Eran Segal of the institute’s computer science and applied mathematics, and molecular cell biology departments.

Gestational diabetes is characterized by high blood sugar levels that develop during pregnancy in women who did not previously have diabetes. It occurs in three to nine percent of all pregnancies and is fraught with risks for both mother and baby. Typically, gestational diabetes is diagnosed between the 24th and 28th weeks of pregnancy, with the help of a glucose tolerance test in which the woman drinks a glucose solution and then undergoes a blood test to see how quickly the glucose is cleared from her blood.

In the new study, Segal and colleagues started out by applying a machine learning method to Clalit’s health records on some 450,000 pregnancies in women who gave birth between 2010 and 2017. Gestational diabetes had been diagnosed by glucose tolerance testing in about four percent of these pregnancies. After processing the dataset – made up of more than 2,000 parameters for each pregnancy, including the woman’s blood test results and her and her family’s medical histories – the scientists’ algorithm revealed that nine of the parameters were sufficient to accurately identify the women who were at a high risk of developing gestational diabetes. The nine parameters included the woman’s age, body mass index, family history of diabetes and results of her glucose tests during previous pregnancies (if any).

Next, to make sure that the nine parameters could indeed accurately predict the risk of gestational diabetes, the researchers applied them to Clalit’s health records on about 140,000 additional pregnancies that had not been part of the initial analysis. The results validated the study’s findings: the nine parameters helped accurately identify the women who ultimately developed gestational diabetes.

These findings suggest that, by having a woman answer just nine questions, it should be possible to tell in advance whether she is at a high risk of developing gestational diabetes. If this information is available early on – in the early stages of pregnancy or even before the woman has gotten pregnant – it might be possible to reduce her risk of diabetes through lifestyle measures such as exercise and diet. On the other hand, women identified by the questionnaire as being at a low risk of gestational diabetes may be spared the cost and inconvenience of the glucose testing. (Visit weizmann.ac.il/sites/gd-predictor to access the self-assessment questionnaire.)

In more general terms, this study has demonstrated the usefulness of large human-based datasets, specifically electronic health records, for deriving personalized disease predictions that can lead to preventive and therapeutic measures.

The work was led by graduate students Nitzan Shalom Artzi, Dr. Smadar Shilo and Hagai Rossman from Segal’s lab at the Weizmann Institute of Science, who collaborated with Prof. Eran Hadar, Dr. Shiri Barbash-Hazan, Prof. Avi Ben-Haroush and Prof. Arnon Wiznitzer of the Rabin Medical Centre in Petach Tikvah; and Prof. Ran D. Balicer and Dr. Becca Feldman of Clalit Health Services.

Too much food wasted

Millions more could be fed by the same resources if our diets changed. (photo from wis-wander.weizmann.ac.il)

About a third of the food produced for human consumption is estimated to be lost or wasted globally. But the biggest waste, which is not even included in this estimate, may be through dietary choices that result in the squandering of environmental resources. In a study published in the Proceedings of the National Academy of Sciences of the United States of America, researchers at the Weizmann Institute of Science in Rehovot, Israel, and their colleagues have found a novel way to define and quantify this second type of wastage. The scientists have called it “opportunity food loss,” a term inspired by the “opportunity cost” concept in economics, which refers to the cost of choosing a particular alternative over better options.

Opportunity food loss stems from using agricultural land to produce animal-based food instead of nutritionally comparable plant-based alternatives. The researchers report that, in the United States alone, avoiding opportunity food loss – that is, replacing all animal-based items with edible crops for human consumption – would add enough food to feed 350 million additional people, or more than the total U.S. population, with the same land resources.

“Our analysis has shown that favouring a plant-based diet can potentially yield more food than eliminating all the conventionally defined causes of food loss,” said lead author Dr. Alon Shepon, who worked in the lab of Prof. Ron Milo in the plant and environmental sciences department. The Weizmann researchers collaborated with Prof. Gidon Eshel of Bard College and Dr. Elad Noor of ETZ Zürich.

The scientists compared the resources needed to produce five major categories of animal-based food – beef, pork, dairy, poultry and eggs – with the resources required to grow edible crops of similar nutritional value in terms of protein, calories and micronutrients. They found that plant-based replacements could produce two- to 20-fold more protein per acre.

The most dramatic results were obtained for beef. The researchers compared it with a mix of crops – soya, potatoes, cane sugar, peanuts and garlic – that deliver a similar nutritional profile when taken together in the right proportions. The land area that could produce 100 grams of protein from these crops would yield only four grams of edible protein from beef. In other words, using agricultural land for producing beef instead of replacement crops results in an opportunity food loss of 96 grams – that is, a loss of 96% – per unit of land. This means that the potential gain from diverting agricultural land from beef to plant-based foods for human consumption would be enormous.

The estimated losses from failing to replace other animal-based foods with nutritionally similar crops were also huge: 90% for pork, 75% for dairy, 50% for poultry and 40% for eggs – higher than all conventional food losses combined.

“Opportunity food loss must be taken into account if we want to make dietary choices enhancing global food security,” said Milo.

Milo’s research is supported by the Mary and Tom Beck Canadian Centre for Alternative Energy Research, which he heads; the Zuckerman STEM Leadership Program; Dana and Yossie Hollander; and the Larson Charitable Foundation. Milo is the incumbent of the Charles and Louise Gartner Professorial Chair.

For more on the research being conducted at the Weizmann Institute, visit wis-wander.weizmann.ac.il.

Genetics or lifestyle?

Study brings hope for improving our health.

The question of nature versus nurture extends to our microbiome – the personal complement of mostly friendly bacteria we carry around with us. Study after study has found that our microbiome affects nearly every aspect of our health; and its microbial composition, which varies from individual to individual, may hold the key to everything from weight gain to moods.

Some microbiome researchers have suggested that this variation begins with differences in our genes, but a large-scale study conducted at the Weizmann Institute of Science challenges this idea and provides evidence that the connection between microbiome and health may be even more important than we thought.

Indeed, the working hypothesis has been that genetics plays a major role in determining microbiome variation among people. According to this view, our genes determine the environment our microbiome occupies, and each particular environment allows certain bacterial strains to thrive. However, the Weizmann researchers were surprised to discover that the host’s genetics play a very minor role in determining microbiome composition – only accounting for about two percent of the variation between populations.

The research was led by research students Daphna Rothschild, Dr. Omer Weissbrod and Dr. Elad Barkan from the lab of Prof. Eran Segal of the computer science and applied mathematics department, together with members of Prof. Eran Elinav’s group of the immunology department, all at the Weizmann Institute. Their findings, which were published last month in Nature, were based on a unique database of around 1,000 Israelis who had participated in a longitudinal study of personalized nutrition.

Israel has a highly diverse population, which presents an ideal experimental setting for investigating the effects of genetic differences. In addition to genetic data and microbiome composition, the information collected for each study participant included dietary habits, lifestyle, medications and additional measurements. The scientists analyzing this data concluded that diet and lifestyle are by far the most dominant factors shaping our microbiome composition.

If microbiome populations are not shaped by our genetics, how do they nonetheless interact with our genes to modify our health? The scientists investigated the connections between microbiome and the measurements in the database of cholesterol, weight, blood glucose levels and other clinical parameters. The study results were very surprising: for most of these clinical measures, the association with bacterial genomes was at least as strong as, and in some cases stronger than, the association with the host’s human genome.

According to the scientists, these findings provide solid evidence that understanding the factors that shape our microbiome may be key to understanding and treating many common health problems.

“We cannot change our genes,” said Segal, “but we now know that we can affect – and even reshape – the composition of the different kinds of bacteria we host in our bodies. So, the findings of our research are quite hopeful: they suggest that our microbiome could be a powerful means for improving our health.”

The field of microbiome research is relatively young; the database of 1,000 individuals collected at the Weizmann Institute is one of the most extensive in the world. Segal and Elinav believe that, over time, with the further addition of data to their study and those of others, these recent findings may be further validated, and the connection between our microbiome, our genetics and our health will become clearer.

Elinav’s research is supported by the Adelis Foundation; Andrew and Cynthia Adelson; the estate of Bernard Bishin; Valerie and Aaron Edelheit; the European Research Council; Jack N. Halpern; the Leona M. and Harry B. Helmsley Charitable Trust; the Bernard M. and Audrey Jaffe Foundation; the Else Kroener Fresenius Foundation; the Park Avenue Charitable Fund; the Lawrence and Sandra Post

Family Foundation; the Rising Tide Foundation; Vera and John Schwartz; Leesa Steinberg; and Yael and Rami Ungar. Elinav is the incumbent of the Sir Marc and Lady Tania Feldmann Professorial Chair.

Segal’s research is supported by the Adelis Foundation; Judith Benattar; the Carter Chapman Shreve Family Foundation; the Crown Human Genome Centre, which he heads; the European Research Council; Jack N. Halpern; the Else Kroener Fresenius Foundation; Donald and Susan Schwarz; and Leesa Steinberg.

For more on the work being done at the Weizmann Institute, visit wis-wander.weizmann.ac.il.

Betalains boost resistance?

Unripe (top) and ripe (bottom) tomatoes. Regular tomatoes (far left) start out green (far left top) and turn red when ripe (far left bottom). In contrast, genetically engineered tomatoes assume different shades of red-violet, depending on whether they produce betalains (the column second from left), pigments called anthocyanins (second from right) or betalains together with anthocyanins (far right). (photo from wis-wander.weizmann.ac.il)

Colour in the plant kingdom is not merely a joy to the eye. Coloured pigments attract pollinating insects, they protect plants against disease, and they confer health benefits and are used in the food and drug industries. A new study conducted at the Weizmann Institute of Science, published in Proceedings of the National Academy of Sciences, USA, has opened the way to numerous potential uses of betalains, the highly nutritious red-violet and yellow pigments known for their antioxidant properties and commonly used as food dyes.

Betalains are made by cactus fruit, flowers such as bougainvillea and certain edible plants – most notably, beets. They are relatively rare in nature, compared to the two other major groups of plant pigments and, until recently, their synthesis in plants was poorly understood. Prof. Asaph Aharoni of Weizmann’s plant and environmental sciences department and Dr. Guy Polturak, then a research student, along with other team members, used two betalain-producing plants – red beet (Beta vulgaris) and four o’clock flowers (Mirabilis jalapa) – in their analysis. Using next-generation RNA sequencing and other advanced technologies, the researchers identified a previously unknown gene involved in betalain synthesis and revealed which biochemical reactions plants use to convert the amino acid tyrosine into betalains.

To test their findings they genetically engineered yeast to produce betalains. They then tackled the ultimate challenge: reproducing betalain synthesis in edible plants that do not normally make these pigments.

photo - Tomatoes that have been genetically engineered to produce betalains only in the fruit, but not elsewhere in the plant — Tomatoes that have been genetically engineered to produce betalains only in the fruit, but not elsewhere in the plant. *(photo from wis-wander.weizmann.ac.il)*

The success announced itself in living colour. The researchers produced potatoes, tomatoes and eggplants with red-violet flesh and skin. They also managed to control the exact location of betalain production by, for example, causing the pigment to be made only in the fruit of the tomato plant but not in the leaves or stem.

Using the same approach, the scientists caused white petunias to produce pale violet flowers, and tobacco plants to flower in hues varying from yellow to orange pink. They were able to achieve a desired hue by causing the relevant genes to be expressed in different combinations during the course of betalain synthesis. These findings may be used to create ornamental plants with colours that can be altered on demand.

But a change in colour was not the only outcome. Healthy antioxidant activity was 60% higher in betalain-producing tomatoes than in average ones. “Our findings may in the future be used to fortify a wide variety of crops with betalains in order to increase their nutritional value,” said Aharoni.

An additional benefit is that the researchers discovered that betalains protect plants against grey mold, Botrytis cinerea, which annually causes losses of agricultural crops worth billions of dollars. The study showed that resistance to grey mold rose by a whopping 90% in plants engineered to make betalains.

The scientists produced versions of betalain that do not exist in nature. “Some of these new pigments may potentially prove more stable than the naturally occurring betalains,” said Polturak. “This can be of major significance in the food industry, which makes extensive use of betalains as natural food dyes, for example, in strawberry yogurts.”

Furthermore, the findings of the study may be used by the drug industry. When plants start manufacturing betalains, the first step is conversion of tyrosine into an intermediate product, the chemical called L-dopa. Not only is this chemical itself used as a drug, it also serves as a starting material in the manufacture of additional drugs, particularly opiates such as morphine. Plants and microbes engineered to convert tyrosine into L-dopa may, therefore, serve as a source of this valuable material.

The research team included Noam Grossman, Dr. Yonghui Dong, Margarita Pliner and Dr. Ilana Rogachev of Weizmann’s plant and environmental sciences department, and Dr. Maggie Levy, Dr. David Vela-Corcia and Adi Nudel of the Hebrew University of Jerusalem. Aharoni’s research is supported by the John and Vera Schwartz Centre for Metabolomics, which he heads; the Leona M. and Harry B. Helmsley Charitable Trust; the Adelis Foundation; the Lerner Family Plant Science Research Fund; the Monroe and Marjorie Burk Fund for Alternative Energy Studies; the Sheri and David E. Stone Fund for Microbiota Research; Dana and Yossie Hollander, Israel; the AMN Fund for the Promotion of Science, Culture and Arts in Israel; and the Tom and Sondra Rykoff Family Foundation. Aharoni is the recipient of the André Deloro Prize, and the incumbent of the Peter J. Cohn Professorial Chair.

For more on the research being conducted at the Weizmann Institute, visit wis-wander.weizmann.ac.il.

Israel’s BDS website

Featured on israelbds.org are popular articles that describe the history of Israeli-international scientific cooperation, research that has resulted from that cooperation and the people involved, as well as links to scientific papers. (image from israelbds.org)

Building Dialogue through Science, or BDS, is the purpose of a new website, israelbds.org, which features the many and varied scientific studies that rely on close collaboration between Israeli researchers and those in different countries.

These studies range from the SESAME synchrotron, a Middle Eastern facility based in Jordan that serves life-sciences researchers from Egypt to Iran; efforts to discover the processes that lead to the stellar explosions known as supernovae, in which Israeli researchers are alerted to possible events in the California night sky; brain research; quantum physics studies; scientific archeology; and much more.

Featured on the website are popular articles that describe the history of Israeli-international scientific cooperation, research that has resulted from that cooperation and the people involved, as well as links to scientific papers.

“Building dialogue through science, rather than building walls, has always been our way of doing things,” said Weizmann Institute of Science president Prof. Daniel Zajfman. “If we are going to work against the other BDS [boycott, divest from and sanction Israel], we must do so with real information. That is the intent of the site we have created. When scientists cooperate in their research, they bring back to their countries an understanding of the ways people can work together on many levels – over and above the scientific – including respect for other cultures and a desire for peaceful coexistence. That is why we believe that cooperation between Israeli scientists and those in universities and research institutes around the globe must be preserved at all costs.”

The hope, indeed, is that anyone visiting the website will understand what the world stands to lose from cutting off ties to Israel’s researchers and preventing students and labs around the globe from benefiting from Israeli advances.

Valeria Ulisse, an Italian research student studying the development of the nervous system at the Weizmann Institute of Science sums it up: “In Italy, I was in a really good lab but I was missing something internally. I wanted to improve my knowledge, to start a new project, to change my life and I found the place to do it.”

Israeli science is open to collaboration with anyone, independent of their political opinions.

“Research thrives on the meeting of different worldviews, and it is important to preserve that freedom to meet and discuss, even with those with whom we don’t always agree,” said Zajfman.

A potential malaria vaccine

A malaria vaccine based on stabilized proteins could circumvent today’s problems. (photo from wis-wander.weizmann.ac.il)

Despite decades of malaria research, the disease still afflicts hundreds of millions and kills around half a million people each year – most of them children in tropical regions.

Part of the problem is that the malaria parasite is a shape-shifter, making it hard to target. But another part of the problem is that even the parasite’s proteins that could be used as vaccines are unstable at tropical temperatures and require complicated, expensive cellular systems to produce them in large quantities. Unfortunately, the vaccines are most needed in areas where refrigeration is lacking and funds to buy vaccines are scarce. A new approach developed at the Weizmann Institute of Science, recently reported in Proceedings of the National Academy of Science, could, in the future, lead to an inexpensive malaria vaccine that can be stored at room temperature.

The RH5 protein is one of the malaria parasite’s proteins that has been tested for use as a vaccine. This protein is used by the parasite to anchor itself to the red blood cells it infects. Using the protein as a vaccine alerts the immune system to the threat without causing disease, thus enabling it to mount a rapid response when the disease strikes, and to disrupt the parasite’s cycle of infection.

Research student Adi Goldenzweig and Dr. Sarel Fleishman of the institute’s biomolecular sciences department decided to use the computer-based protein design tools they have been developing in Fleishman’s lab to improve the usefulness of this protein.

Based on software they have been creating for stabilizing protein structures, Goldenzweig developed a new way of “programming” proteins used in vaccines against infectious diseases. Such proteins, because they are under constant attack by the immune system, tend to mutate from generation to generation. So, the program she developed uses all the known information on different configurations of the protein sequence in different versions of the parasite. “The parasite deceives the immune system by mutating its surface proteins,” she explained. “Paradoxically, the better the parasite is at evading the immune system, the more clues it leaves for us to use in designing a successful artificial protein.”

The researchers sent the programmed artificial protein to a group in Oxford that specializes in developing malaria vaccines. This group, led by Prof. Matthew Higgins and Simon Draper, soon had good news: the results showed that, in contrast with the natural ones, the programmed protein can be produced in simple, inexpensive cell cultures, and in large quantities. This could significantly lower production costs. In addition, it is stable at temperatures of up to 50°C, so it won’t need refrigeration. Best of all, in animal trials, the proteins provoked a protective immune response.

“The method Adi developed is really general,” said Fleishman. “It has succeeded where others have failed and, because it is so easy to use, it might be applied to emerging infectious diseases like Zika or Ebola, when quick action can stop an epidemic from developing.”

Fleishman and his group are currently using their method to test a different strategy for treating malaria, based on targeting the RH5 protein itself and blocking its ability to mediate the contact between the parasite and human red blood cells.

For more on the research being conducted at the Weizmann Institute, visit wis-wander.weizmann.ac.il.

Forgetting our fright?

An entire mouse brain viewed from above: neuronal extensions connect the two amygdalas (brightest spots on both sides of the brain) with the prefrontal cortex (top). (photo from wis-wander.weizmann.ac.il)

Erasing unwanted memories is still the stuff of science fiction, but Weizmann Institute scientists have now managed to erase one type of memory in mice. In a study reported in Nature Neuroscience, they succeeded in shutting down a neuronal mechanism by which memories of fear are formed in the mouse brain. After the procedure, the mice resumed their earlier fearless behavior, “forgetting” they had previously been frightened.

This research may one day help extinguish traumatic memories in humans – for example, in people with post-traumatic stress disorder, or PTSD.

“The brain is good at creating new memories when these are associated with strong emotional experiences, such as intense pleasure or fear,” said team leader Dr. Ofer Yizhar. “That’s why it’s easier to remember things you care about, be they good or bad; but it’s also the reason that memories of traumatic experiences are often extremely long-lasting, predisposing people to PTSD.”

In the study, postdoctoral fellows Dr. Oded Klavir (now an investigator at the University of Haifa) and Dr. Matthias Prigge, both from Yizhar’s lab in the neurobiology department, together with departmental colleague Prof. Rony Paz and graduate student Ayelet Sarel, examined the communication between two brain regions: the amygdala and the prefrontal cortex. The amygdala plays a central role in controling emotions, whereas the prefrontal cortex is mostly responsible for cognitive functions and storing long-term memories. Previous studies had suggested that the interactions between these two brain regions contribute to the formation and storage of aversive memories, and that these interactions are compromised in PTSD, but the exact mechanisms behind these processes were unknown.

In the new study, the researchers first used a genetically engineered virus to mark those amygdala neurons that communicate with the prefrontal cortex. Next, using another virus, they inserted a gene encoding a light-sensitive protein into these neurons. When they shone a light on the brain, only the neurons containing the light-sensitive proteins became activated. These manipulations, belonging to optogenetics – a technique extensively studied in Yizhar’s lab – enabled the researchers to activate only those amygdala neurons that interact with the cortex, and then to map out the cortical neurons that receive input from these light-sensitive neurons.

Once they had achieved this precise control over the cellular interactions in the brain, they turned to exploring behaviour: mice that are less fearful are more likely to venture farther than others. They found that when the mice were exposed to fear-inducing stimuli, a powerful line of communication was activated between the amygdala and the cortex. The mice whose brains displayed such communication were more likely to retain a memory of the fear, acting frightened every time they heard the sound that had previously been accompanied by the fear-inducing stimuli.

Finally, to clarify how this line of communication contributes to the formation and stability of memory, the scientists developed an optogenetic technique for weakening the connection between the amygdala and the cortex, using a series of repeated light pulses. Indeed, once the connection was weakened, the mice no longer displayed fear upon hearing the sound. Evidently, “tuning down” the input from the amygdala to the cortex had destabilized or perhaps even destroyed their memory of fear.

“Our research,” said Yizhar, “has focused on a fundamental question in neuroscience: How does the brain integrate emotion into memory? But, one day, our findings may help develop better therapies targeting the connections between the amygdala and the prefrontal cortex, in order to alleviate the symptoms of fear and anxiety disorders.”

For more about the research being done at the Weizmann Institute, visit wis-wander.weizmann.ac.il.

An artificial odour test

(image from wis-wander.weizmann.ac.il)

Say someone claims to have developed a system to “capture” any odour in the form of a digital code – one that could be transmitted online or uploaded to the internet and faithfully reproduced at the receiving end. How could we be sure that the system is valid? In other words, how can we know that, for any possible odour someone has captured digitally and transmitted, the smell we receive is indeed a recognizable, fair rendition of the original?

Prof. David Harel of the Weizmann Institute of Science’s computer science and applied mathematics department explains that, as opposed to video and audio, an odour reproduction system is still far from viable, although some of the components already exist.

“We still don’t understand the process by which the numerous combinations of odourants in our environment are identified and sensed as a particular smell in our brains after they enter our noses, attach to the several hundred kinds of odour receptors there and are transferred to the brain as signals,” he said. But he and his colleagues had, already 15 years ago, laid out the basic principles of such a digital smell system.

This system would need a “sniffer” – a sort of artificial nose – to take “snapshots” of the odourous substances in the air. It would also need a “whiffer” that, something like a colour printer, would be able to mix a fixed set of around 50 chemical odourants in precisely given proportions – something in the way a printer mixes a small number of inks – and release measured amounts of the resulting odour into the air accurately, in a controlled manner.

photo - Prof. David Harel of the Weizmann Institute of Science — Prof. David Harel of the Weizmann Institute of Science. *(photo from wis-wander.weizmann.ac.il)*

Harel believes that such systems will eventually exist, pointing out that research is continually improving our understanding of how smell is “encoded” and how we perceive it. Although reasonably good sniffers and whiffers exist, the tantalizing scientific challenge is to work out the algorithm for connecting the sniffer’s reading into the whiffer’s emission; that is, a method is needed for translating any given odour into precise instructions for the whiffer to follow. The output mixtures would have to be experienced by humans in the way that photos are today – as reproductions that our sense recognizes as faithfully capturing the original.

Despite the fact that this challenge appears to be extremely difficult, Harel recently devised a test that could be used to assess the validity of such a system, if and when one is proposed. One of his inspirations was the Turing test proposed by the British father of computer science, Alan Turing, to test claims of human-like intelligence in a machine. A tester sits in one room and holds conversations with entities in two other rooms – one a human and the other the candidate computer. Through questions, chitchat and serious discourse, the tester tries to identify which is which; if repeated tests cannot distinguish the computer from the human, it is said to possess artificial intelligence. “The problem with using such a test for artificial olfaction,” said Harel, “is that such blind comparisons are detached from the element of human recognizability; and there is no adequate language to describe smells in general, meaning verbal discussions would not work either.”

Harel devised a “lineup” test, whose key feature is the immersion of odours with their natural audio-visual references, thus eliminating the need for verbal description. A team of neutral testers is given several short video clips – for example, of a bakery, a zoo, a dusty attic, a flowering meadow, etc. – and is asked to match an odour emitted by the sniffer with its correct clip. The clips are prepared by a team of challengers, whose role is to try to disprove the claim that the proposed system is valid.

To make sure that the test is fair – for example, the subjects won’t be required to identify the odour of a damp cave hidden from view in the clip of a meadow scene – the group is divided into two. One half is exposed to the actual odours collected and preserved at the video sites, and the other to the artificial, chemically reproduced odour created by the sniffer-whiffer system. That way, the second team of participants – those smelling the whiffer output – are required only to correctly match the odour to its clip when the first team – those exposed to the real odour – succeeds. As in the Turing test, the artificial is pitted against the natural in a blinded experiment, but here the test uses odour immersion for recognizability, and the test is asymmetric, requiring from the artificial no more than is required from the real thing in order to be declared successful.

For more on the research being conducted at the Weizmann Institute, visit wis-wander.weizmann.ac.il.