Research Area: Genome Engineering

​CRISPR, SHERLOCK, REPAIR, RNA editing, DNA editing, brain disorders, diagnostics, disease models, therapeutics

Neuroscientists reverse some behavioral symptoms of Williams Syndrome

by Anne Trafton |

Williams Syndrome, a rare neurodevelopmental disorder that affects about 1 in 10,000 babies born in the United States, produces a range of symptoms including cognitive impairments, cardiovascular problems, and extreme friendliness, or hypersociability.

In a study of mice, MIT neuroscientists have garnered new insight into the molecular mechanisms that underlie this hypersociability. They found that loss of one of the genes linked to Williams Syndrome leads to a thinning of the fatty layer that insulates neurons and helps them conduct electrical signals in the brain.

The researchers also showed that they could reverse the symptoms by boosting production of this coating, known as myelin. This is significant, because while Williams Syndrome is rare, many other neurodevelopmental disorders and neurological conditions have been linked to myelination deficits, says Guoping Feng, the James W. and Patricia Poitras Professor of Neuroscience and a member of MIT’s McGovern Institute for Brain Research.

“The importance is not only for Williams Syndrome,” says Feng, who is one of the senior authors of the study. “In other neurodevelopmental disorders, especially in some of the autism spectrum disorders, this could be potentially a new direction to look into, not only the pathology but also potential treatments.”

Zhigang He, a professor of neurology and ophthalmology at Harvard Medical School, is also a senior author of the paper, which appears in the April 22 issue of Nature Neuroscience. Former MIT postdoc Boaz Barak, currently a principal investigator at Tel Aviv University in Israel, is the lead author and a senior author of the paper.

Impaired myelination

Williams Syndrome, which is caused by the loss of one of the two copies of a segment of chromosome 7, can produce learning impairments, especially for tasks that require visual and motor skills, such as solving a jigsaw puzzle. Some people with the disorder also exhibit poor concentration and hyperactivity, and they are more likely to experience phobias.

In this study, the researchers decided to focus on one of the 25 genes in that segment, known as Gtf2i. Based on studies of patients with a smaller subset of the genes deleted, scientists have linked the Gtf2i gene to the hypersociability seen in Williams Syndrome.

Working with a mouse model, the researchers devised a way to knock out the gene specifically from excitatory neurons in the forebrain, which includes the cortex, the hippocampus, and the amygdala (a region important for processing emotions). They found that these mice did show increased levels of social behavior, measured by how much time they spent interacting with other mice. The mice also showed deficits in fine motor skills and increased nonsocial related anxiety, which are also symptoms of Williams Syndrome.

Next, the researchers sequenced the messenger RNA from the cortex of the mice to see which genes were affected by loss of Gtf2i. Gtf2i encodes a transcription factor, so it controls the expression of many other genes. The researchers found that about 70 percent of the genes with significantly reduced expression levels were involved in the process of myelination.

“Myelin is the insulation layer that wraps the axons that extend from the cell bodies of neurons,” Barak says. “When they don’t have the right properties, it will lead to faster or slower electrical signal transduction, which affects the synchronicity of brain activity.”

Further studies revealed that the mice had only about half the normal number of mature oligodendrocytes — the brain cells that produce myelin. However, the number of oligodendrocyte precursor cells was normal, so the researchers suspect that the maturation and differentiation processes of these cells are somehow impaired when Gtf2i is missing in the neurons.

This was surprising because Gtf2i was not knocked out in oligodendrocytes or their precursors. Thus, knocking out the gene in neurons may somehow influence the maturation process of oligodendrocytes, the researchers suggest. It is still unknown how this interaction might work.

“That’s a question we are interested in, but we don’t know whether it’s a secreted factor, or another kind of signal or activity,” Feng says.

In addition, the researchers found that the myelin surrounding axons of the forebrain was significantly thinner than in normal mice. Furthermore, electrical signals were smaller, and took more time to cross the brain in mice with Gtf2i missing.

The study is an example of pioneering research into the contribution of glial cells, which include oligodendrocytes, to neuropsychiatric disorders, says Doug Fields, chief of the nervous system development and plasticity section of the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

“Traditionally myelin was only considered in the context of diseases that destroy myelin, such as multiple sclerosis, which prevents transmission of neural impulses. More recently it has become apparent that more subtle defects in myelin can impair neural circuit function, by causing delays in communication between neurons,” says Fields, who was not involved in the research.

Symptom reversal

It remains to be discovered precisely how this reduction in myelination leads to hypersociability. The researchers suspect that the lack of myelin affects brain circuits that normally inhibit social behaviors, making the mice more eager to interact with others.

“That’s probably the explanation, but exactly which circuits and how does it work, we still don’t know,” Feng says.

The researchers also found that they could reverse the symptoms by treating the mice with drugs that improve myelination. One of these drugs, an FDA-approved antihistamine called clemastine fumarate, is now in clinical trials to treat multiple sclerosis, which affects myelination of neurons in the brain and spinal cord. The researchers believe it would be worthwhile to test these drugs in Williams Syndrome patients because they found thinner myelin and reduced numbers of mature oligodendrocytes in brain samples from human subjects who had Williams Syndrome, compared to typical human brain samples.

“Mice are not humans, but the pathology is similar in this case, which means this could be translatable,” Feng says. “It could be that in these patients, if you improve their myelination early on, it could at least improve some of the conditions. That’s our hope.”

Such drugs would likely help mainly the social and fine-motor issues caused by Williams Syndrome, not the symptoms that are produced by deletion of other genes, the researchers say. They may also help treat other disorders, such as autism spectrum disorders, in which myelination is impaired in some cases, Feng says.

“We think this can be expanded into autism and other neurodevelopmental disorders. For these conditions, improved myelination may be a major factor in treatment,” he says. “We are now checking other animal models of neurodevelopmental disorders to see whether they have myelination defects, and whether improved myelination can improve some of the pathology of the defects.”

The research was funded by the Simons Foundation, the Poitras Center for Affective Disorders Research at MIT, the Stanley Center for Psychiatric Research at the Broad Institute of MIT and Harvard, and the Simons Center for the Social Brain at MIT.

Guoping Feng elected to American Academy of Arts and Sciences

by MIT News |

Four MIT faculty members are among more than 200 leaders from academia, business, public affairs, the humanities, and the arts elected to the American Academy of Arts and Sciences, the academy announced today.

One of the nation’s most prestigious honorary societies, the academy is also a leading center for independent policy research. Members contribute to academy publications, as well as studies of science and technology policy, energy and global security, social policy and American institutions, the humanities and culture, and education.

Those elected from MIT this year are:

  • Dimitri A. Antoniadis, Ray and Maria Stata Professor of Electrical Engineering;
  • Anantha P. Chandrakasan, dean of the School of Engineering and the Vannevar Bush Professor of Electrical Engineering and Computer Science;
  • Guoping Feng, the James W. (1963) and Patricia T. Poitras Professor of Brain and Cognitive Sciences; and
  • David R. Karger, professor of electrical engineering.

“We are pleased to recognize the excellence of our new members, celebrate their compelling accomplishments, and invite them to join the academy and contribute to its work,” said David W. Oxtoby, president of the American Academy of Arts and Sciences. “With the election of these members, the academy upholds the ideals of research and scholarship, creativity and imagination, intellectual exchange and civil discourse, and the relentless pursuit of knowledge in all its forms.”

The new class will be inducted at a ceremony in October in Cambridge, Massachusetts.

Since its founding in 1780, the academy has elected leading “thinkers and doers” from each generation, including George Washington and Benjamin Franklin in the 18th century, Maria Mitchell and Daniel Webster in the 19th century, and Toni Morrison and Albert Einstein in the 20th century. The current membership includes more than 200 Nobel laureates and 100 Pulitzer Prize winners.

Scientists engineer new CRISPR platform for DNA targeting

by The Broad Institute |

A team that includes the scientist who first harnessed the revolutionary CRISPR-Cas9 and other systems for genome editing of eukaryotic organisms, including animals and plants, has engineered another CRISPR system, called Cas12b. The new system offers improved capabilities and options when compared to CRISPR-Cas9 systems.

In a study published today in Nature Communications, Feng Zhang and colleagues at the Broad Institute of MIT and Harvard and the McGovern Institute for Brain Research at MIT, with co-author Eugene Koonin at the National Institutes of Health, demonstrate that the new enzyme can be engineered to target and precisely nick or edit the genomes of human cells. The high target specificity and small size of Cas12b from Bacillus hisashii (BhCas12b) as compared to Cas9 (SpCas9), makes this new system suitable for in vivo applications. The team is now making CRISPR-Cas12b widely available for research.

The team previously identified Cas12b (then known as C2c1) as one of three promising new CRISPR enzymes in 2015, but faced a hurdle: Because Cas12b comes from thermophilic bacteria — which live in hot environments such as geysers, hot springs, volcanoes, and deep sea hydrothermal vents — the enzyme naturally only works at temperatures higher than human body temperature.

“We searched for inspirations from nature,” Zhang said. “We wanted to create a version of Cas12b that could operate at lower temperatures, so we scanned thousands of bacterial genetic sequences, looking in bacteria that could thrive in the lower temperatures of mammalian environments.”

Through a combination of exploration of natural diversity and rational engineering of promising candidate enzymes, they generated a version of Cas12b capable of efficiently editing genomes in primary human T cells, an important initial step for therapeutics that target or leverage the immune system.

“This is further evidence that there are many useful CRISPR systems waiting to be discovered,” said Jonathan Strecker, a postdoctoral fellow in the Zhang Lab, a Human Frontiers Science program fellow, and the study’s first author.

The field is moving quickly: Since the Cas12b family of enzymes was first described in 2015 and demonstrated to be RNA-guided DNA endonucleases, several groups have have been exploring this family of enzymes. In 2017 a team from Jennifer Doudna’s lab at UC Berkeley reported that Cas12b from Alicyclobacillus acidoterrestris can mediate non-specific collateral cleavage of DNA in vitro. More recently, a team from the Chinese Academy of Sciences in Beijing reported that another Cas12b, from Alicyclobacillus acidiphilus, was used to edit mammalian cells.

The Broad Institute and MIT are sharing the Cas12b system widely. As with earlier genome editing tools, these groups will make the technology freely available for academic research via the Zhang lab’s page on the plasmid-sharing website Addgene, through which the Zhang lab has already shared reagents more than 52,000 times with researchers at nearly 2,400 labs in 62 countries to accelerate research.

Zhang is a core institute member of the Broad Institute of MIT and Harvard, as well as an investigator at the McGovern Institute for Brain Research at MIT, the James and Patricia Poitras Professor of Neuroscience at MIT, and an associate professor at MIT, with joint appointments in the departments of Brain and Cognitive Sciences and Biological Engineering.

Support for this study was provided by the Poitras Center for Psychiatric Disorders Research, the Hock E. Tan and K. Lisa Yang Center for Autism Research, the National Human Genome Research Institute, the National Institute of Mental Health, the National Heart, Lung, and Blood Institute, and other sources. Feng Zhang is an Investigator with the Howard Hughes Medical Institute.

References:

Strecker J, et al. Engineering of CRISPR-Cas12b for human genome editing. Nature Communications. Online January 22, 2019. DOI: 10.1038/s41467-018-08224-4.

Feng Zhang

Engineering Physiology

The primary focus of Feng Zhang’s work is to improve human health by discovering ways to modify cellular function and activity –  including the restoration of diseased, stressed, or aged cells to a more healthful state. His team is developing new molecular technologies to modify the cell’s genetic information, vehicles to deliver these tools into the correct cells, and larger-scale engineering to restore organ function. Zhang hopes to apply these approaches to neurodegenerative diseases, immune disorders, aging, and other disease states.

Guoping Feng

Listening to Synapses

Guoping Feng is interested in how synapses — the connections between neurons — contribute to neurodevelopmental and psychiatric diseases, including autism spectrum disorder (ASD) and schizophrenia. He leads research that uses molecular genetics combined with behavioral and electrophysiological methods to study the components of the synapse.

Feng is perhaps best known for pioneering a gene-based therapy that could reverse a severe form of autism that is caused by a single mutation in the SHANK3 gene. After genetically engineering the SHANK3 mutation in animal models using CRISPR-based technology, Feng’s gene-correction therapy greatly reduced SHANK3 symptoms, restoring the animals’ cognitive, behavioral, and motor functions.

Additionally, the lab has leveraged genetic technologies to help map the cellular diversity in the brain—a valuable tool in neuroscience research. Through understanding the molecular, cellular, and circuit changes underlying brain diseases and disorders, the Feng lab hopes to eventually inform new and more effective treatments for neurodevelopmental and psychiatric disorders.

Welcoming the first McGovern Fellows

Anne Trafton |

We are delighted to kick off the new year by welcoming Omar Abuddayeh and Jonathan Gootenberg as the first members of our new McGovern Institute Fellows Program. The fellows program is a recently launched initiative that supports highly-talented and selected postdocs that are ready to initiate their own research program.

As McGovern Fellows, the pair will be given space, time, and support to help them follow scientific research directions of their own choosing. This provides an alternative to the traditional postdoctoral research route.

Abudayyeh and Gootenberg both defended their thesis in the fall of 2018, and graduated from the lab of Feng Zhang, who is the James and Patricia Poitras Professor of Neuroscience at MIT, a McGovern investigator and core member of the Broad Institute. During their time in the Zhang lab, Abudayyeh and Gootenberg worked on projects that sought and found new tools based on enzymes mined from bacterial CRISPR systems. Cas9 is the original programmable single-effector DNA-editing enzyme, and the new McGovern Fellows worked on teams that actively looked for CRISPR enzymes with properties distinct from and complementary to Cas9. In the course of their thesis work, they helped to identify RNA-guided RNA editing factors such as the Cas13 family. This work led to the development of the REPAIR system, which is capable of editing RNA, thus providing a CRISPR-based therapeutic avenue that is not based on permanent, heritable changes to the genome. In addition, they worked on a Cas13-based diagnostic system called SHERLOCK that can detect specific nucleic acid sequences. SHERLOCK is able to detect the presence of infectious agents such as Zika virus in an easily-deployable lateral flow format, similar to a pregnancy test.

We are excited to see the directions that the new McGovern Fellows take as they now arrive at the institute, and will keep you posted on scientific findings as they emerge from their labs.

 

What is CRISPR?

by The Brain |

CRISPR (which stands for Clustered Regularly Interspaced Short Palindromic Repeats) is not actually a single entity, but shorthand for a set of bacterial systems that are found with a hallmarked arrangement in the bacterial genome.

When CRISPR is mentioned, most people are likely thinking of CRISPR-Cas9, now widely known for its capacity to be re-deployed to target sequences of interest in eukaryotic cells, including human cells. Cas9 can be programmed to target specific stretches of DNA, but other enzymes have since been discovered that are able to edit DNA, including Cpf1 and Cas12b. Other CRISPR enzymes, Cas13 family members, can be programmed to target RNA and even edit and change its sequence.

The common theme that makes CRISPR enzymes so powerful, is that scientists can supply them with a guide RNA for a chosen sequence. Since the guide RNA can pair very specifically with DNA, or for Cas13 family members, RNA, researchers can basically provide a given CRISPR enzyme with a way of homing in on any sequence of interest. Once a CRISPR protein finds its target, it can be used to edit that sequence, perhaps removing a disease-associated mutation.

In addition, CRISPR proteins have been engineered to modulate gene expression and even signal the presence of particular sequences, as in the case of the Cas13-based diagnostic, SHERLOCK.

Do you have a question for The Brain? Ask it here.

SHERLOCK: A CRISPR tool to detect disease

by Julie Pryor |

This animation depicts how Cas13 — a CRISPR-associated protein — may be adapted to detect human disease. This new diagnostic tool, called SHERLOCK, targets RNA (rather than DNA), and has the potential to transform research and global public health.

 

Feng Zhang wins 2018 Keio Medical Science Prize

Anne Trafton |

Molecular biologist Feng Zhang has been named a winner of the prestigious Keio Medical Science Prize. He is being recognized for the groundbreaking development of CRISPR-Cas9-mediated genome engineering in cells and its application for medical science.

Zhang is the James and Patricia Poitras Professor of Neuroscience at MIT, an associate professor in the departments of Brain and Cognitive Sciences and Biological Engineering, a Howard Hughes Medical Institute investigator, an investigator at the McGovern Institute for Brain Research, and a core member of the Broad Institute of MIT and Harvard.

“We are delighted that Feng is now a Keio Prize laureate,” says McGovern Institute Director Robert Desimone. “This truly recognizes the remarkable achievements that he has made at such a young age.”

Zhang is a molecular biologist who has contributed to the development of multiple molecular tools to accelerate the understanding of human disease and create new therapeutic modalities. During his graduate work, Zhang contributed to the development of optogenetics, a system for activating neurons using light, which has advanced our understanding of brain connectivity.

Zhang went on to pioneer the deployment of the microbial CRISPR-Cas9 system for genome engineering in eukaryotic cells. The ease and specificity of the system has led to its widespread use across the life sciences and it has groundbreaking implications for disease therapeutics, biotechnology, and agriculture. He has continued to mine bacterial CRISPR systems for additional enzymes with useful properties, leading to the discovery of Cas13, which targets RNA, rather than DNA, and may potentially be a way to treat genetic diseases without altering the genome. Zhang has also developed a molecular detection system called SHERLOCK based on the Cas13 family, which can sense trace amounts of genetic material, including viruses and alterations in genes that might be linked to cancer.

“I am tremendously honored to have our work recognized by the Keio Medical Prize,” says Zhang. “It is an inspiration to us to continue our work to improve human health.”

Now in its 23rd year, the Keio Medical Science Prize is awarded to a maximum of two scientists each year. The other 2018 laureate, Masashi Yanagisawa, director of the International Institute for Integrative Sleep Medicine at the University of Tsukuba, is being recognized for his seminal work on sleep control mechanisms.

The prize is offered by Keio University, and the selection committee specifically looks for laureates that have made an outstanding contribution to medicine or the life sciences. The prize was initially endowed by Mitsunada Sakaguchi in 1994, with the express condition that it be used to commend outstanding science, promote advances in medicine and the life sciences, expand researcher networks, and contribute to the wellbeing of humankind. The winners receive a certificate of merit, a medal, and a monetary award of approximately $90,000.

The prize ceremony will be held on Dec. 18 at Keio University in Tokyo.

Feng Zhang named winner of the 2018 Keio Medical Science Prize

Anne Trafton |

Feng Zhang and Masashi Yanagisawa have been named the 2018 winners of the prestigious Keio Medical Science Prize. Zhang is being recognized for the groundbreaking development of CRISPR-Cas9-mediated genome engineering in cells and its application for medical science. Zhang is an HHMI Investigator and the James and Patricia Poitras Professor of Neuroscience at MIT, an associate professor in MIT’s Departments of Brain and Cognitive Sciences and Biological Engineering, an investigator at the McGovern Institute for Brain Research, and a core member of the Broad Institute of MIT and Harvard. Masashi Yanagisawa, Director of the International Institute for Integrative Sleep Medicine at the University of Tsukuba, is being recognized for his seminal work on sleep control mechanisms.

“We are delighted that Feng is now a Keio Prize laureate,” says McGovern Institute Director Robert Desimone. “This truly recognizes the remarkable achievements that he has made at such a young age.”

The Keio Medical Prize is awarded to a maximum of two scientists each year, and is now in its 23rd year. The prize is offered by Keio University, and the selection committee specifically looks for laureates that have made an outstanding contribution to medicine or the life sciences. The prize was initially endowed by Dr. Mitsunada Sakaguchi in 1994, with the express condition that it be used to commend outstanding science, promote medical advances in medicine and the life sciences, expand researcher networks, and contribute to the well-being of humankind. The winners receive a certificate of merit, medal, and a monetary award of 10 million yen.

Feng Zhang is a molecular biologist who has contributed to the development of multiple molecular tools to accelerate our understanding of human disease and create new therapeutic modalities. During his graduate work Zhang contributed to the development of optogenetics, a system for activating neurons using light, which has advanced our understanding of brain connectivity. Zhang went on to pioneer the deployment of the microbial CRISPR-Cas9 system for genome engineering in eukaryotic cells. The ease and specificity of the system has led to its widespread use across the life sciences and it has groundbreaking implications for disease therapeutics, biotechnology, and agriculture. Zhang has continued to mine bacterial CRISPR systems for additional enzymes with useful properties, leading to the discovery of Cas13, which targets RNA, rather than DNA, and may potentially be a way to treat genetic diseases without altering the genome. He has also developed a molecular detection system called SHERLOCK based on the Cas13 family, which can sense trace amounts of genetic material, including viruses and alterations in genes that might be linked to cancer.

“I am tremendously honored to have our work recognized by the Keio Medical Prize,” says Zhang. “It is an inspiration to us to continue our work to improve human health.”

The prize ceremony will be held on December 18th 2018 at Keio University in Tokyo, Japan.