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SMART research enhances dengue vaccination in mice
Singapore-MIT Alliance for Research and Technology
August 13, 2020

Researchers from the Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise in Singapore, have found a practical way to induce a strong and broad immunity to the dengue virus based on proof-of-concept studies in mice. Dengue is a mosquito-borne viral disease with an estimated 100 million symptomatic infections every year. It is endemic in over 100 countries in the world, from the United States to Africa and wide swathes of Asia. In Singapore, over 1,700 dengue new cases were reported recently.

The study is reported in a paper titled “Sequential immunization induces strong and broad immunity against all four dengue virus serotypes,” published in NPJ Vaccines. It is jointly published by SMART researchers Jue Hou, Shubham Shrivastava, Hooi Linn Loo, Lan Hiong Wong, Eng Eong Ooi, and Jianzhu Chen from SMART’s Infectious Diseases and Antimicrobial Resistance (AMR) interdisciplinary research groups (IRGs).

The dengue virus (DENV) consists of four antigenically distinct serotypes and there is no lasting immunity following infection with any of the DENV serotypes, meaning someone can be infected again by any of the remaining three variants of DENVs.

Today, Dengvaxia is the only vaccine available to combat dengue. It consists of four variant dengue antigens, one for each of the four serotypes of dengue, expressed from attenuated yellow-fever virus. The current three doses of immunization with the tetravalent vaccine induce only suboptimal protection against DENV1 and DENV2. Furthermore, in people who have not been infected by dengue, the vaccine induces a more severe dengue infection in the future. Therefore, in most of the world, the vaccination is only given to those who have been previously infected.

To help overcome these issues, SMART researchers tested on mice whether sequential immunization (or one serotype per dose) induces stronger and broader immunity against four DENV serotypes than tetravalent-formulated immunization — and found that sequential immunization induced significantly higher levels of virus-specific T cell responses than tetravalent immunization. Moreover, sequential immunization induced higher levels of neutralizing antibodies to all four DENV serotypes than tetravalent vaccination.

“The principle of sequential immunization generally aligns with the reality for individuals living in dengue-endemic areas, whose immune responses may become protective after multiple heterotypic exposures,” says Professor Eng Eong Ooi, SMART AMR principal investigator and senior author of the study. “We were able to find a similar effect based on the use of sequential immunization, which will pave the way for a safe and effective use of the vaccine and to combat the virus.”

Upon these promising results, the investigators will aim to test the sequential immunization in humans in the near future.

The work was supported by the National Research Foundation (NRF) Singapore through the SMART Infectious Disease Research Program and AMR IRG. SMART was established by MIT in partnership with the NRF Singapore in 2007. SMART is the first entity in the Campus for Research Excellence and Technological Enterprise (CREATE) developed by NRF.  SMART serves as an intellectual and innovation hub for research interactions between MIT and Singapore, performing cutting-edge research of interest to both Singapore and MIT. SMART currently comprises an Innovation Centre and five IRGs: AMR, Critical Analytics for Manufacturing Personalized-Medicine, Disruptive and Sustainable Technologies for Agricultural Precision, Future Urban Mobility, and Low Energy Electronic Systems. SMART research is funded by the NRF Singapore under the CREATE program.

The AMR IRG is a translational research and entrepreneurship program that tackles the growing threat of antimicrobial resistance. By leveraging talent and convergent technologies across Singapore and MIT, they aim to tackle AMR head-on by developing multiple innovative and disruptive approaches to identify, respond to, and treat drug-resistant microbial infections. Through strong scientific and clinical collaborations, they provide transformative, holistic solutions for Singapore and the world.

Iain Cheeseman earns a Global Consortium for Reproductive Longevity & Equality (GCRLE) Scholar Award
Buck Institute
August 10, 2020

The Global Consortium for Reproductive Longevity and Equality (GCRLE) at the Buck Institute for Research on Aging, made possible by the Bia-Echo Foundation, announces its inaugural recipients of its GCRLE Scholar Awards. The 22 recipients comprise a global group who share a vision of advancing research to better understand the underlying causes of female reproductive aging. Grantees were selected by a Scientific Advisory Council composed of leaders in the fields of Aging and Reproductive Biology. Grantees range from early career scientists to established scholars in the field.

“I am incredibly excited by the potential impact for the GCRLE. The ability to convene a diverse community from across institutions will positively and constructively impact this field and move science forward in a way that simply would not be possible otherwise,” says GCRLE Pilot Award recipient Iain Cheeseman, PhD, of the Whitehead Institute for Biomedical Research at MIT. GCRLE Junior Scholar Award recipient Lynae Brayboy, MD of Charité-Universitätsmedizin, Berlin adds, “I think reproductive scientists can often exist in isolation and don’t have the unique experience GCRLE is fostering…I think it also very challenging for physician scientists to find support in the field of reproductive aging and reproductive biology in general.”

The mission of the GCRLE is to support breakthrough research on reproductive aging through funding, training, infrastructure, programs to support women in science, and a collaborative intellectual network. The GCRLE network will enable grantees and all consortium members to pursue support and collaboration across multidisciplinary approaches and institutions, thereby establishing a foundation on which to grow a diverse and sustainable research ecosystem.

Grants totaling $7.4 million will be awarded over 2 years, with flexibility in budgeting for maximum creativity and non-traditional support such as childcare. “We are thrilled to welcome these promising researchers as our very first grant recipients.” says Jennifer Garrison, PhD, GCRLE Faculty Director and Assistant Professor at the Buck Institute for Research on Aging. “The GCRLE unites two disciplines – reproductive science and geroscience – in an unprecedented way to investigate an area of biology that has tangible societal and clinical implications. Our goal is to foster truly bold, innovative scientists with the potential to transform the field. Beyond funding, we are building an infrastructure to grow a vibrant community and developing creative programs to break down gender barriers in scientific research careers. This is the beginning of something big!”

The GCRLE is anchored at the Buck’s Center for Female Reproductive Longevity and Equality which was established in 2018 with a gift from attorney and entrepreneur Nicole Shanahan. The Center is the first research facility in the world focused solely on reproductive equality and ovarian aging, a key determinant not only of fertility but of overall health and longevity. The GCRLE was established in 2019 with a gift from Shanahan’s Bia-Echo Foundation to build the global ecosystem for this new and exciting field of research.

2020 Inaugural GCRLE Scholars

The Senior Scholar Award supports established investigators who are thought leaders in their fields and are recognized for substantial contributions of creative and productive research.

2020 Senior Scholar Award Recipients:

Holly Ingraham, Ph.D.
University of California, San Francisco
“Identifying Novel Drivers in Central Control of Female Reproduction”

Coleen Murphy, Ph.D.
Princeton University
“Defining a “Clock” for Female Reproductive Decline”

Mary Zelinski, Ph.D.
Oregon Health & Science University
“Interventions for Ovarian Aging”

The Junior Scholar Award supports newly independent investigators with outstanding promise as they are establishing their own labs.

2020 Junior Scholar Award Recipients:

Bérénice Benayoun, Ph.D.
University of Southern California
“Establishing new age-relevant mouse models of menopause”

Lynae Brayboy, M.D.
Charité – Universitätsmedizin, Berlin
“Dysfunctional MDR-1 disrupts mitochondrial homeostasis in the oocyte”

Ingrid Fetter-Pruneda, Ph.D.
Universidad Nacional Autónoma de México
“The molecular and cellular basis of high fecundity in social insects”

Amanda Kallen, M.D.
Yale University
“Ovarian Senescence as a Novel Driver of Female Reproductive Aging”

The Pilot Award is designed to foster innovative collaborative or novel research projects that have the potential for high impact and high reward at an accelerated rate.

Pilot Award Recipients:

Ivana Celic, Ph.D.
Tulane University
“LINE1 Retrotransposons in Female Reproductive Aging”

Iain Cheeseman, Ph.D.
Whitehead Institute/MIT
“Analyzing centromere rejuvenation during female reproductive aging”

Marco Conti, M.D.
University of California, San Francisco
“mRNA translation program and oocyte aging”

Arjumand Ghazi, Ph.D.
University of Pittsburgh
“Genetic & Chemical Modulation of Splicing to Combat Reproductive Senescence”

Polina Lishko, Ph.D.
University of California, Berkeley
“Endocannabinoid signaling in the mammalian ovary and reproductive longevity”

Zita Santos, Ph.D., Carlos Ribeiro, Ph.D.
Champalimaud Foundation, Portugal
“Metabolic reprogramming, dietary nutrients and food cravings in ovary aging”

Yousin Suh, Ph.D.
Columbia University
“Genetic Control of Ovarian Aging in Humans”

The Postdoctoral Scholar Award supports training imaginative junior scientists who will lead the next generation of reproductive aging researchers.

2020 Postdoctoral Scholar Award Recipients:

Cristina Quesada Candela, Ph.D.
University of Pittsburg​
“Proteasomal Targets Driving Meiotic Failure During Reproductive Aging”

Ana Milunovic Jevtic, Ph.D., D.V.M.
University of California, Berkeley
“The role of endocannabinoid hydrolase ABHD2 in the ovarian aging”

Gul Bikem Soygur Kaya, Ph.D.
University of California, San Francisco
“How duration of meiotic prophase affects development and aging of oocytes”

Min Hoo Kim, Ph.D.
University of Southern California
“Elucidating causal effects of the microbiome on reproductive aging”

Seungsoo Kim, Ph.D.
Columbia University Medical Center
“Integrative bioinformatic analysis of human ovarian aging and healthspan”

Olfat Malak, Ph.D.
Buck Institute for Research on Aging
“Role of sympathetic transmission in the regulation of ovarian aging”

Farners Amargant i Riera, Ph.D.
Northwestern University
“Targeting fibrosis and inflammation to extend reproductive longevity”

Zijing Zhang, Ph.D.
University of Arkansas for Medical Sciences
“The impact of ovarian macrophage population on mouse ovarian aging”

About the Global Consortium for Reproductive Longevity and Equality

The Buck Institute, through the generous support of the Bia Echo Foundation, has launched a novel, global collaborative Consortium dedicated to facilitating and accelerating research on female reproductive longevity and equality. The end of fertility sets off a cascade of negative health effects in a woman’s body. As a society, every aspect of a woman’s life is influenced by the fact that reproductive capacity is limited — overall health, family planning, career decisions. The downstream consequences are clear, but why women undergo a precipitous decline in fertility at midlife and what sets it in motion are a mystery. Despite its profound impact on health and well-being, female reproductive aging is an understudied topic.

The Global Consortium for Reproductive Longevity and Equality (GCRLE) is advancing research to better understand the underlying causes of female reproductive aging. This has implications for everyone – we think that understanding the limits on reproductive capacity will provide important clues about aging in other tissues.  Through funding, collaboration, and innovation, we hope to accelerate the pace of discovery and inform the path to intervention. We believe we can profoundly alter the societal balance toward equality for women by defining what leads to menopause and developing interventions to slow or reverse it. Our goal is to build the field to understand the basic biological mechanisms that trigger female reproductive senescence, from the earliest stages through to menopause, and ultimately leverage this understanding to intervene and balance the scales.  Contact info@gcrle.org for more information and to find out how to join the GCRLE today! https://buckinstitute.org/gcrle/

About the Buck Institute for Research on Aging

Our success will ultimately change healthcare. At the Buck, we aim to end the threat of age-related diseases for this and future generations by bringing together the most capable and passionate scientists from a broad range of disciplines to identify and impede the ways in which we age. An independent, nonprofit institution, our goal is to increase human health span, or the healthy years of life. Globally recognized as the pioneer and leader in efforts to target aging, the number one risk factor serious diseases including Alzheimer’s, Parkinson’s, cancer, macular degeneration, heart disease, and diabetes, the Buck wants to help people live better longer.  Learn more at: https://buckinstitute.org

About the Bia-Echo Foundation

Bia-Echo Foundation is a private foundation, founded by Nicole Shanahan that aims to accelerate social change in order to establish a fair and equitable society for future generations to thrive. We invest in changemakers at the forefront of innovation who are tackling some of the world’s greatest challenges within our core areas of equality-based investment:  Reproductive Longevity & Equality, Criminal Justice Reform and Healthy and Livable Ecosystems. https://www.biaecho.org

To distinguish contexts, animals think probabilistically, study suggests
Picower Institute
August 3, 2020

Among the many things rodents have taught neuroscientists is that in a region called the hippocampus, the brain creates a new map for every unique spatial context – for instance, a different room or maze. But scientists have so far struggled to learn how animals decide when a context is novel enough to merit creating, or at least revising, these mental maps. In a study in eLife, MIT and Harvard researchers propose a new understanding: The process of “remapping” can be mathematically modeled as a feat of probabilistic reasoning by the rodents.

The approach offers scientists a new way to interpret many experiments that depend on measuring remapping to investigate learning and memory. Remapping is integral to that pursuit, because animals (and people) associate learning closely with context, and hippocampal maps indicate which context an animal believes itself to be in.

“People have previously asked ‘What changes in the environment cause the hippocampus to create a new map?’ but there haven’t been any clear answers,” said lead author Honi Sanders. “It depends on all sorts of factors, which means that how the animals define context has been shrouded in mystery.”

Sanders is a postdoc in the lab of co-author Matthew Wilson, Sherman Fairchild Professor in The Picower Institute for Learning and Memory and the departments of Biology and Brain and Cognitive Sciences at MIT.  He is also a member of the Center for Brains, Minds and Machines. The pair collaborated with Samuel Gershman, a professor of psychology at Harvard on the study.

Fundamentally a problem with remapping that has frequently led labs to report conflicting, confusing, or surprising results, is that scientists cannot simply assure their rats that they have moved from experimental Context A to Context B, or that they are still in Context A, even if some ambient condition, like temperature or odor, has inadvertently changed. It is up to the rat to explore and infer that conditions like the maze shape, or smell, or lighting, or the position of obstacles, and rewards, or the task they must perform, have or have not changed enough to trigger a full or partial remapping.

So rather than trying to understand remapping measurements based on what the experimental design is supposed to induce, Sanders, Wilson and Gershman argue that scientists should predict remapping by mathematically accounting for the rat’s reasoning using Bayesian statistics, which quantify the process of starting with an uncertain assumption and then updating it as new information emerges.

“You never experience exactly the same situation twice. The second time is always slightly different,” Sanders said. “You need to answer the question: ‘Is this difference just the result of normal variation in this context or is this difference actually a different context?’ The first time you experience the difference you can’t be sure, but after you’ve experienced the context many times and get a sense of what variation is normal and what variation is not, you can pick up immediately when something is out of line.”

The trio call their approach “hidden state inference” because to the animal, the possible change of context is a hidden state that must be inferred.

In the study the authors describe several cases in which hidden state inference can help explain the remapping, or the lack of it, observed in prior studies.

For instance, in many studies it’s been difficult to predict how changing some of cues that a rodent navigates by in a maze (e.g. a light or a buzzer) will influence whether it makes a completely new map or partially remaps the current one and by how much. Mostly the data has showed there isn’t an obvious “one-to-one” relationship of cue change and remapping. But the new model predicts how as more cues change, a rodent can transition from becoming uncertain about whether an environment is novel (and therefore partially remapping) to becoming sure enough of that to fully remap.

In another, the model offers a new prediction to resolve a remapping ambiguity that has arisen when scientists have incrementally “morphed” the shape of rodent enclosures. Multiple labs, for instance, found different results when they familiarized rats with square and round environments and then tried to measure how and whether they remap when placed in intermediate shapes, such as an octagon. Some labs saw complete remapping while others observed only partial remapping. The new model predicts how that could be true: rats exposed to the intermediate environment after longer training would be more likely to fully remap than those exposed to the intermediate shape earlier in training, because with more experience they would be more sure of their original environments and therefore more certain that the intermediate one was a real change.

The math of the model even includes a variable that can account for differences between individual animals. Sanders is looking at whether rethinking old results in this way could allow researchers to understand why different rodents respond so variably to similar experiments.

Ultimately, Sanders said, he hopes the study will help fellow remapping researchers adopt a new way of thinking about surprising results – by considering the challenge their experiments pose to their subjects.

“Animals are not given direct access to context identities, but have to infer them,” he said. “Probabilistic approaches capture the way that uncertainty plays a role when inference occurs. If we correctly characterize the problem the animal is facing, we can make sense of differing results in different situations because the differences should stem from a common cause: the way that hidden state inference works.”

The National Science Foundation funded the research.

This molecule helps sweet-toothed protein complex sense sugar
Eva Frederick | Whitehead Institute
July 28, 2020

In order to grow and thrive, cells need sugar. A repertoire of cellular mechanisms turn unwieldy molecules of glucose and fructose into versatile building blocks for making useful molecules such as lipids, and energy to fuel necessary processes in the cell. But for any of these things to happen, the cells need to sense when sugars are present in the first place — and scientists are still unraveling how they do it.

Now, in a new paper online July 27 in Nature Metabolism, researchers in the lab of Whitehead Institute Member David Sabatini, identify a key molecule that signals to the cell’s growth-triggering complex mTORC1 when there is sugar to be had, leading to a metabolic response. “This discovery puts us another step closer to understanding the biology of mTORC1 and its effects on cellular growth and metabolism,” said Sabatini, who is also a professor of biology at Massachusetts Institute of Technology and investigator with the Howard Hughes Medical Institute.

mTORC1 — short for “mechanistic target of rapamycin complex 1” — is a complex of proteins involved in regulating cell growth and metabolism. Jose Orozco, a fifth-year M.D./Ph.D student in Sabatini’s lab, describes mTORC1 as a sort of cellular licensing board. In order for other parts of the cell to grow and create new products, they must first be “approved” by mTORC1. If there are enough building blocks in the cell to create a certain product, mTORC1 will add a phosphate group to the appropriate “builders” — a signal that allows the building to begin.

“The builders in this case are metabolic pathways responsible for the creation of proteins, the regulation of nucleotides, regulation of glycolysis, regulation of fatty acid synthesis,” he says. “None of these builders can sense everything. But mTORC1 can, and it makes this sort of unified decision for the cell, ‘Yes, we have everything we need to grow.’”

One essential component for cellular building is glucose. That means mTORC1 has a sweet tooth by necessity: the complex is only active when there is enough glucose in the cell. When there’s glucose to go around, mTORC1 is “on” and binds to a lysosome, a structure that serves as the cell’s “digestive system”, where it perches to perform its phosphorylation duties. When a cell is starved for glucose, the complex falls off the lysosome, inactive.

Since the early 2010s, scientists have known one way that mTOR proteins sense glucose: when there is no glucose available, the cell inhibits the action of mTORC1 through a pathway involving the protein AMPK. But another study suggested that even without AMPK, mTORC1 can still sense an absence of glucose. “I think a lot of people had written it off as ‘Oh, [the signal] must just be AMPK,’” Orozco says. “But when we tested that hypothesis, we showed that even cells that didn’t have any AMPK were still able to sense glucose availability. That was the observation that started this project.”

To find the mysterious second sugar-sensing process, Orozco and colleagues created cells in which the known signalling protein AMPK was out of the picture. Using these modified cells, they began looking for specific traits of the glucose molecule that might be triggering the response. The team found that sugars that could be broken down by the cell, such as mannose, glucosamine and fructose, were able to activate mTORC1. Non-metabolizable sugars had no effect.

This suggested that the signaling molecule was not glucose itself, but something produced when glucose is taken apart during glycolysis — the biochemical process that breaks down the sugar into usable building blocks. With this in mind, the researchers next combed step by step through glycolysis products to see which ones could be the signal molecule.

The team identified a step of glycolysis that seemed to be key, zeroing  in on a glycolysis product called dihydroxyacetone phosphate, or DHAP. Even in the complete absence of glucose, the researchers could turn on mTORC1 by adding DHAP.

It is difficult to prove exactly why the cell relies on DHAP as a signal, but Orozco has some ideas. For one thing, DHAP later goes on to serve as the backbone of lipids, which are built by a process controlled by mTORC1 — so it would make sense that mTORC1 would respond to its presence or absence. Also, DHAP levels are extremely sensitive to changes in the amount of cellular glucose, more so than any other glycolysis intermediary. Also, DHAP is a product of both glucose and fructose, which are both important sugars in the human diet.

In the future, the team hopes to understand more. “We don’t know the biochemical details of how DHAP [conveys its message],” Orozco says. “We don’t know the sensor, we don’t know what proteins bind it, and we don’t know if that causes conformational changes in [associated proteins]. That we sort of leave as the enticing next question that we want to tackle.”

At the moment, studying the glucose sensing pathway is purely foundational research. But while there are no clear applications yet, surprises could lurk just around the corner. “Targeting nutrient sensing in mTOR has shown some promise in, of all things, regulating depression and mood,” Orozco says. “That’s interesting, and we don’t really understand why that is the case. How is glucose targeting going to be important? We don’t know yet. But we think it has a lot of potential.”

***

Written by Eva Frederick

Citation:

Orozco, J.M., Krawczyk, P.A., Scaria, S.M. et al. Dihydroxyacetone phosphate signals glucose availability to mTORC1. Nat Metab (2020). https://doi.org/10.1038/s42255-020-0250-5

3 Questions: Jonathan King on the future of nuclear weapons testing

Professor of biology discusses a scientist’s responsibility to speak out about important issues that affect our nation and the world.

Raleigh McElvery | Department of Biology
July 29, 2020

In an open letter published on July 16 in Science, four MIT professors and nearly 70 additional scientific leaders called upon fellow researchers to urge U.S. government officials to halt plans to restart nuclear weapons testing. Corresponding author and professor of biology Jonathan King sat down to discuss the history of nuclear testing, his personal ties to the issue, and his responsibilities as a scientist. He also co-chairs the Nuclear Disarmament Working Group of Massachusetts Peace Action, MIT’s annual Reducing the Threat of Nuclear War conference, and the editorial board of the MIT Faculty Newsletter.

Q: What events have made you passionate about the issue of nuclear weapons testing?

A: I grew up in the shadow of nuclear war, participating in drills at school where you would duck under your desk. During the Cold War, the world’s nations exploded hundreds of dangerous nuclear tests, releasing radioactivity into the atmosphere in order to develop these weapons. I was a college student during the Cuban Missile Crisis, and remember vividly the fear of a nuclear exchange.

Around that time, it became clear to our nation’s leaders that this was not the way to go. In his famous speech at American University, President Kennedy reversed direction. Professor of chemistry at Caltech Linus Pauling led an effort with his wife to back Kennedy and collect 9,000 signatures from scientists endorsing the president’s Partial Nuclear Test Ban Treaty. This was before the internet, so getting 9,000 signatures was not easy, and it had a national impact. I was actually a graduate student at Caltech, following up on Pauling’s work on proteins, when the treaty was ratified and he was awarded the Nobel peace prize for his work.

When I arrived at MIT as an assistant professor, Jerome Wiesner was the Institute president. He was also a key player in pushing the Partial Nuclear Test Ban Treaty, and Kennedy had previously named him chair of the President’s Science Advisory Committee (PSAC). MIT was full of world leaders in nuclear disarmament, including physicists who had worked on the bomb and decided it was a mistake. I’m not a physicist, but I was among the generation at MIT that was very vocal about these issues.

Q: What is the current state of nuclear weapon testing and regulation in the United States, and what concerns do you have about renewed testing?

A: The U.S. hasn’t tested a nuclear weapon since 1992. In that period of time, the Comprehensive Test Ban Treaty (CTBT) was developed by many nations, agreeing not to conduct a nuclear weapons test of any yield. The Senate hasn’t ratified it, but in 2016 the U.S. did adopt UN Security Council Resolution 2310, agreeing to uphold the goal of the CTBT and withhold nuclear testing.

However, the current administration is proposing to modernize nuclear weapons and restart testing, which is both provocative and dangerous. Even if these tests are small, contained, and underground, they will still open the door for other nations to restart testing of their own, and possibly lead to a new nuclear weapons arms race.

When a nuclear weapon — either a conventional bomb or hydrogen bomb — explodes, many radioactive isotopes are produced. Some of them are short-lived and decay quickly, but others like strontium-90 are much longer-lived. These ones can make you sick very slowly, and some can mutate or damage DNA. Even underground tests can leak radioactivity into the atmosphere and environment.

Q: What spurred you and your colleagues to write an open letter to Science, and what was your goal in doing so?

A: Our letter was signed by 70 scientific leaders and Nobel Prize winners, and calls upon the scientific community to warn the nation that this is a dangerous way to go. We also urged the Senate to ratify the CTBT, and pass a new bill introduced by Senator Ed Markey called the Preserving Leadership Against Nuclear Explosives Testing (PLANET) Act — which would prevent spending money on the renewal of testing.

I come from a culture that views scientists as public servants. All my research has been funded by taxpayer dollars, and with that comes a responsibility to help address threats to the community. The very history of my department, the MIT Department of Biology, is tied to scientists taking a stand against social and political issues. I was just a young assistant professor when faculty members like David Baltimore and Ethan Signer led demonstrations to oppose the Vietnam War. It was a very open environment and we supported one another.

These days, science is simply a career. You do your work and you keep your eyes to the bench. But the world can be a better place if we take our eyes off the bench occasionally. So this letter is a reminder to our colleagues: Get involved, and consider it our contribution to the general public who support our research.

Bringing RNA into genomics

ENCODE consortium identifies RNA sequences that are involved in regulating gene expression.

Anne Trafton | MIT News Office
July 29, 2020

The human genome contains about 20,000 protein-coding genes, but the coding parts of our genes account for only about 2 percent of the entire genome. For the past two decades, scientists have been trying to find out what the other 98 percent is doing.

A research consortium known as ENCODE (Encyclopedia of DNA Elements) has made significant progress toward that goal, identifying many genome locations that bind to regulatory proteins, helping to control which genes get turned on or off. In a new study that is also part of ENCODE, researchers have now identified many additional sites that code for RNA molecules that are likely to influence gene expression.

These RNA sequences do not get translated into proteins, but act in a variety of ways to control how much protein is made from protein-coding genes. The research team, which includes scientists from MIT and several other institutions, made use of RNA-binding proteins to help them locate and assign possible functions to tens of thousands of sequences of the genome.

“This is the first large-scale functional genomic analysis of RNA-binding proteins with multiple different techniques,” says Christopher Burge, an MIT professor of biology. “With the technologies for studying RNA-binding proteins now approaching the level of those that have been available for studying DNA-binding proteins, we hope to bring RNA function more fully into the genomic world.”

Burge is one of the senior authors of the study, along with Xiang-Dong Fu and Gene Yeo of the University of California at San Diego, Eric Lecuyer of the University of Montreal, and Brenton Graveley of UConn Health.

The lead authors of the study, which appears today in Nature, are Peter Freese, a recent MIT PhD recipient in Computational and Systems Biology; Eric Van Nostrand, Gabriel Pratt, and Rui Xiao of UCSD; Xiaofeng Wang of the University of Montreal; and Xintao Wei of UConn Health.

RNA regulation

Much of the ENCODE project has thus far relied on detecting regulatory sequences of DNA using a technique called ChIP-seq. This technique allows researchers to identify DNA sites that are bound to DNA-binding proteins such as transcription factors, helping to determine the functions of those DNA sequences.

However, Burge points out, this technique won’t detect genomic elements that must be copied into RNA before getting involved in gene regulation. Instead, the RNA team relied on a technique known as eCLIP, which uses ultraviolet light to cross-link RNA molecules with RNA-binding proteins (RBPs) inside cells. Researchers then isolate specific RBPs using antibodies and sequence the RNAs they were bound to.

RBPs have many different functions — some are splicing factors, which help to cut out sections of protein-coding messenger RNA, while others terminate transcription, enhance protein translation, break down RNA after translation, or guide RNA to a specific location in the cell. Determining the RNA sequences that are bound to RBPs can help to reveal information about the function of those RNA molecules.

“RBP binding sites are candidate functional elements in the transcriptome,” Burge says. “However, not all sites of binding have a function, so then you need to complement that with other types of assays to assess function.”

The researchers performed eCLIP on about 150 RBPs and integrated those results with data from another set of experiments in which they knocked down the expression of about 260 RBPs, one at a time, in human cells. They then measured the effects of this knockdown on the RNA molecules that interact with the protein.

Using a technique developed by Burge’s lab, the researchers were also able to narrow down more precisely where the RBPs bind to RNA. This technique, known as RNA Bind-N-Seq, reveals very short sequences, sometimes containing structural motifs such as bulges or hairpins, that RBPs bind to.

Overall, the researchers were able to study about 350 of the 1,500 known human RBPs, using one or more of these techniques per protein. RNA splicing factors often have different activity depending on where they bind in a transcript, for example activating splicing when they bind at one end of an intron and repressing it when they bind the other end. Combining the data from these techniques allowed the researchers to produce an “atlas” of maps describing how each RBP’s activity depends on its binding location.

“Why they activate in one location and repress when they bind to another location is a longstanding puzzle,” Burge says. “But having this set of maps may help researchers to figure out what protein features are associated with each pattern of activity.”

Additionally, Lecuyer’s group at the University of Montreal used green fluorescent protein to tag more than 300 RBPs and pinpoint their locations within cells, such as the nucleus, the cytoplasm, or the mitochondria. This location information can also help scientists to learn more about the functions of each RBP and the RNA it binds to.

“The strength of this manuscript is in the generation of a comprehensive and multilayered dataset that can be used by the biomedical community to develop therapies targeted to specific sites on the genome using genome-editing strategies, or on the transcriptome using antisense oligonucleotides or agents that mediate RNA interference,” says Gil Ast, a professor of human molecular genetics and biochemistry at Tel Aviv University, who was not involved in the research.

Linking RNA and disease

Many research labs around the world are now using these data in an effort to uncover links between some of the RNA sequences identified and human diseases. For many diseases, researchers have identified genetic variants called single nucleotide polymorphisms (SNPs) that are more common in people with a particular disease.

“If those occur in a protein-coding region, you can predict the effects on protein structure and function, which is done all the time. But if they occur in a noncoding region, it’s harder to figure out what they may be doing,” Burge says. “If they hit a noncoding region that we identified as binding to an RBP, and disrupt the RBP’s motif, then we could predict that the SNP may alter the splicing or stability of the gene.”

Burge and his colleagues now plan to use their RNA-based techniques to generate data on additional RNA-binding proteins.

“This work provides a resource that the human genetics community can use to help identify genetic variants that function at the RNA level,” he says.

The research was funded by the National Human Genome Research Institute ENCODE Project, as well as a grant from the Fonds de Recherche de Québec-Santé.

A recipe for cell fitness

Researchers determine how much of an enzyme is ‘just enough’ to keep a cell healthy and growing.

Raleigh McElvery
July 28, 2020

What ratio of ingredients makes a healthy cell? Researchers know which components are required for proper function, but they’re still working to understand what happens when there’s too much of one protein or not enough of another. As a graduate student in Gene-Wei Li’s lab, Darren Parker PhD ’20 spent years tweaking the recipe for a bacterial cell, adding more or less of one enzyme, aminoacyl-tRNA synthetase (aaRS). He wanted to know: How much aaRS is “just right” for bacterial cells? His findings were published in Cell Systems on July 28.

tRNAs, or transfer RNAs, carry amino acids to the ribosome to help produce proteins. But first, aaRSs must “charge” the tRNAs by attaching an amino acid to them. In doing so, aaRSs not only help the cell make proteins and grow; they also ensure the levels of “uncharged” tRNAs lacking amino acids don’t rise too high, as too many of them can trigger stress responses that slow cell growth. Parker and his collaborators predicted that tinkering with aaRS levels would uncover one of two possible scenarios. Perhaps cells tune their aaRS production to minimize the amount of uncharged tRNAs present. Alternatively, aaRS production could be dictated by the rate of protein synthesis necessary for cell growth — even if that means accumulating uncharged tRNAs.

The researchers determined the latter was true: cells make “just enough” aaRSs to optimize protein production and cell growth. This delicate balance was easily upset when too few aaRSs were produced, cueing the stress responses to kick in and slow growth. Although excess aaRSs reduced the amount of uncharged tRNA, it also hindered cell growth. The researchers determined that the cellular circuits in charge of controlling and sensing tRNA charging are collectively tuned to optimize bacterial growth.

“These results demonstrate that cells have delicately balanced the costs and benefits of producing their proteins,” Parker says. “Understanding the driving forces behind protein production is important for better understanding disease processes, and engineering cells to perform new functions.”

Gene-controlling mechanisms play key role in cancer progression

Study finds “epigenomic” alterations evolve as lung tumors become more aggressive and metastasize.

Anne Trafton | MIT News Office
July 22, 2020

As cancer cells evolve, many of their genes become overactive while others are turned down. These genetic changes can help tumors grow out of control and become more aggressive, adapt to changing conditions, and eventually lead the tumor to metastasize and spread elsewhere in the body.

MIT and Harvard University researchers have now mapped out an additional layer of control that guides this evolution — an array of structural changes to “chromatin,” the mix of proteins, DNA, and RNA that makes up cells’ chromosomes. In a study of mouse lung tumors, the researchers identified 11 chromatin states, also called epigenomic states, that cancer cells can pass through as they become more aggressive.

“This work provides one of the first examples of using single-cell epigenomic data to comprehensively characterize genes that regulate tumor evolution in cancer,” says Lindsay LaFave, an MIT postdoc and the lead author of the study.

In addition, the researchers showed that a key molecule they found in the more aggressive tumor cell states is also linked to more advanced forms of lung cancer in humans, and could be used as a biomarker to predict patient outcomes.

Tyler Jacks, director of MIT’s Koch Institute for Integrative Cancer Research, and Jason Buenrostro, an assistant professor of stem cell and regenerative biology at Harvard University, are the senior authors of the study, which appears today in Cancer Cell.

Epigenomic control

While a cell’s genome contains all of its genetic material, the epigenome plays a critical role in determining which of these genes will be expressed. Every cell’s genome has epigenomic modifications — proteins and chemical compounds that attach to DNA but do not alter its sequence. These modifications, which vary by cell type, influence the accessibility of genes and help to make a lung cell different from a neuron, for example.

Epigenomic changes are also believed to influence cancer progression. In this study, the MIT/Harvard team set out to analyze the epigenomic changes that occur as lung tumors develop in mice. They studied a mouse model of lung adenocarcinoma, which results from two specific genetic mutations and closely recapitulates the development of human lung tumors.

Using a new technology for single-cell epigenome analysis that Buenrostro had previously developed, the researchers analyzed the epigenomic changes that occur as tumor cells evolve from early stages to later, more aggressive stages. They also examined tumor cells that had metastasized beyond the lungs.

This analysis revealed 11 different chromatin states, based on the locations of epigenomic alterations and density of the chromatin. Within a single tumor, there could be cells from all 11 of the states, suggesting that cancer cells can follow different evolutionary pathways.

For each state, the researchers also identified corresponding changes in where gene regulators called transcription factors bind to chromosomes. When transcription factors bind to the promoter region of a gene, they initiate the copying of that gene into messenger RNA, essentially controlling which genes are active. Chromatin modifications can make gene promoters more or less accessible to transcription factors.

“If the chromatin is open, a transcription factor can bind and activate a specific gene program,” LaFave says. “We were trying to understand those transcription factor networks and then what their downstream targets were.”

As the structure of tumor cells’ chromatin changed, transcription factors tended to target genes that would help the cells to lose their original identity as lung cells and become less differentiated. Eventually many of the cells also gained the ability to leave their original locations and seed new tumors.

Much of this process was controlled by a transcription factor called RUNX2. In more aggressive cancer cells, RUNX2 promotes the transcription of genes for proteins that are secreted by cells. These proteins help remodel the environment surrounding the tumor to make it easier for cancer cells to escape.

The researchers also found that these aggressive, premetastatic tumor cells were very similar to tumor cells that had already metastasized.

“That suggests that when these cells were in the primary tumor, they actually changed their chromatin state to look like a metastatic cell before they migrated out into the environment,” LaFave says. “We believe they undergo an epigenetic change in the primary tumor that allows them to become migratory and then seed in a distal location like the lymph nodes or the liver.”

A new biomarker

The researchers also compared the chromatin states they identified in mouse tumor cells to chromatin states seen in human lung tumors. They found that RUNX2 was also elevated in more aggressive human tumors, suggesting that it could serve as a biomarker for predicting patient outcomes.

“The RUNX positive state was very highly predictive of poor survival in human lung cancer patients,” LaFave says. “We’ve also shown the inverse, where we have signatures of early states, and they predict better prognosis for patients. This suggests that you can use these single-cell gene regulatory networks as predictive modules in patients.”

RUNX could also be a potential drug target, although it traditionally has been difficult to design drugs that target transcription factors because they usually lack well-defined structures that could act as drug docking sites. The researchers are also seeking other potential targets among the epigenomic changes that they identified in more aggressive tumor cell states. These targets could include proteins known as chromatin regulators, which are responsible for controlling the chemical modifications of chromatin.

“Chromatin regulators are more easily targeted because they tend to be enzymes,” LaFave says. “We’re using this framework to try to understand what are the important targets that are driving these state transitions, and then which ones are therapeutically targetable.”

The research was funded by a Damon Runyon Cancer Foundation postdoctoral fellowship, the Paul G. Allen Frontiers Group, the National Institutes of Health, and the Koch Institute Support (core) Grant from the National Cancer Institute.