July 2019 – Penn Bioengineering Blog

July 31, 2019July 30, 2019

Brian Chow, Dan Huh, and David Issadore Promoted to Tenured Positions as Associate Professors in Penn Bioengineering

by Sophie Burkholder

We would like to congratulate Penn Bioengineering faculty members Brian Chow, Ph.D., Dongeun (Dan) Huh, Ph.D., and David Issadore, Ph.D., on all of their recent promotions to tenured positions as Associate Professors. Both Chow and Issadore taught the second half of the foundational course in the Penn Bioengineering undergraduate curriculum, Bioengineering Modeling, Analysis, and Design Laboratory, in which students form lab groups to complete modules in microfluidics, synthetic biology, bioelectrical signal analysis, and bioanalytical spectroscopy.

Outside of the classroom, Chow’s research focuses on the creation of dynamic input and output interfaces for cells through the use of optogenetics, synthetic biology, genomics, and device engineering. The Chow lab’s current projects include the exploration of functional diversity of photoreception, engineering optically active genetically encoded tools, and their applications in neuroscience and mammalian synthetic biology. His research is supported by the NIH and he is the recipient of a 2017 NSF CAREER Award. Chow also supports undergraduate innovations in research by hosting the annual Penn team for the International Genetically Engineered Machine (iGEM) competition, a program which he helped to create during his time as a graduate student at MIT. One group of Bioengineering students under Chow’s mentorship used the iGEM project as a springboard to create an accessible, open-source plate reader.

The Issadore lab at Penn focuses on the use of microelectronics and microfluidics for medical diagnostics. In projects that combine elements of bioengineering, electrical engineering, chemical engineering, and applied physics, Issadore and his team use an interdisciplinary approach to create miniaturized low-cost platforms for disease diagnosis. His company Chip Diagnostics received the JPOD @ Philadelphia QuickFire Challenge Award last month. Earlier this year, Issadore taught the Penn Engineering course Appropriate Point of Care Diagnostics (APOC), which culminated in a service trip to Ghana (read blog posts written by participating students here). This fall, he will take over the core Bioengineering undergraduate course in Bioengineering Signals and Systems, which focuses on applications in ECG signaling, cochlear implants, and biomedical imaging.

Dr. Huh is the principal investigator of the BIOLines Lab at Penn, which is best known for its work on bioinspired engineering systems that Huh calls “organs-on-a-chip.” Using design and engineering principles based on microfluidics and biomimicry, the Huh lab creates microengineered systems that can reconstitute the structural and functional complexity of healthy and diseased human physiological systems in ways not possible using traditional cell culture techniques. His research has been featured in TEDx, and he has won several prestigious honors and awards including the Bernard Langer Distinguished Lectureship, Lush Prize, the McPherson Distinguished Lectureship, CRI Technology Impact Award, John J. Ryan Medal, Design of the Year Award and Best Product of the Year Award from London Design Museum, NIH Director’s New Innovator Award, and Analytical Chemistry Young Innovator Award. This fall, Huh will teach a graduate level course in biomicrofluidics that will cover the use of microfluidics for biomedical application.

July 30, 2019July 26, 2019

New data reveals cell size sparks genome awakening in embryos

Awakening of the zygote genome over time as decreasing individual cell size triggers early embryo transcription. (Image: Hui Chen, Penn Medicine; Cell Press)

There is a transition during early development when an embryo undergoes biochemical changes, switching from being controlled by maternal molecules to being governed by its own genome.

For the first time, a team from the Perelman School of Medicine found in an embryo that activation of its genome does not happen all at once, instead it follows a specific pattern controlled primarily by the various sizes of its cells. The researchers published their results as the cover story in Developmental Cell.

In an early embryo undergoing cell division, maternally loaded RNA and proteins regulate the cell cycle. The genomes of the zygote—a term for the fertilized egg—are initially in sleep mode. However, at a point in the early life of the embryo, these zygotic nuclei “wake up” and expression from their genomes takes biochemical control over subsequent embryo development. But how an embryo “recognizes” when to undergo this transition has remained unknown.

“How an embryo ‘hands over’ control of development from mother to zygote is a fundamental question in developmental biology,” says senior author Matthew C. Good, an assistant professor of both cell and developmental biology and bioengineering. “Previously it was not appreciated that different regions of a vertebrate embryo can undergo genome activation at different times, or how directly cell size regulates the awakening of a zygote’s genome.”

Read more at Penn Medicine News.

July 29, 2019July 26, 2019

Ravi Radhakrishnan Named Director of the Penn Institute for Computational Science

Ravi Radhakrishnan, professor in the departments of Bioengineering and Chemical and Biomolecular Engineering, has been named the new Director of the Penn Institute for Computational Science (PICS).

PICS is a cross-disciplinary institute for the advancement, integration, and support of Penn research via the tools and techniques of high-performance computing. It promotes research through a regular seminar series, an annual conference, by hosting joint research projects and through researcher and student training. PICS also enables computational science research by providing an ongoing series of short technical “how to” workshops or bootcamps for Penn researchers and graduate students.

Radhakrishnan’s research interests lie at the interface of chemical physics and molecular biology. He graduated from the Indian Institute of Technology in 1995 and earned his PhD from Cornell University in 2001. He is a member of the Penn Center for Molecular Discovery and the Center for Engineering Cells and Regeneration.

Originally posted on the Penn Engineering Medium blog.

July 26, 2019July 26, 2019

Week in BioE (July 26, 2019)

by Sophie Burkholder

New 3D Tumor Models Could Improve Cancer Treatment

New ways of testing cancer treatments may now be possible thanks to researchers at the University of Akron who developed three-dimensional tumor models of triple-negative breast cancer. Led by Dr. Hossein Tavana, Ph. D., an associate professor of biomedical engineering at the university, the Tissue Engineering Microtechnologies Lab recently received a $1.13 million grant from the prestigious National Cancer Institute (NCI) of the National Institute of Health (NIH) to continue improving these tumor models. Tumors are difficult to fully replicate in vitro, as they are comprised of cancerous cells, connective tissue, and matrix proteins, among several other components. With this new grant, Tavana sees creating a high-throughput system that uses many identical copies of the tumor model for drug testing and better understanding of the way tumors operate. This high-throughput method would allow Tavana and his lab to isolate and test several different approaches at once, which they hope will help change the way tumors are studied and treated everywhere.

Noise-Induced Hearing Loss Poses Greater Threat to Neural Processing

Even though we all know we probably shouldn’t listen to music at high volumes, most of us typically do it anyway. But researchers at Purdue University recently found that noise-induced hearing loss could cause significant changes in neural processing of more complex sound inputs. Led by Kenneth Henry, Ph.D., an assistant professor of otolaryngology at the University of Rochester Medical Center, and Michael Heinz, Ph.D., a professor of biomedical engineering at Purdue University, the study shows that when compared with age-related hearing loss, noise-induced hearing loss will result in a greater decrease in hearing perception even when the two kinds of hearing loss appear to be of the same degree on an audiogram. This is because noise-induced hearing loss occurs because of physical trauma to the ear, rather than the long-term electrochemical degradation of some components that come happen with age. The evidence of this research is yet another reason why we should be more careful about exposing our ears to louder volumes, as they pose a greater risk of serious damage.

Increasing the Patient Populations for Research in Cartilage Therapy and Regenration

Despite the great progress in research of knee cartilage therapy and regeneration, there are still issues with the patient populations that most studies consider. Researchers often want to test new methods on patients that have the greatest chance of injury recovery without complications – often referred to as “green knees” – but this leaves out those patient populations who suffer from conditions or defects that have the potential to cause complications – often referred to as “red knees.” In a new paper published in Regenerative Medicine, the Mary Black Ralston Professor for Education and Research in Orthopaedic Surgery and secondary faculty in the Department of Bioengineering at Penn, Robert Mauck, Ph.D., discusses some cartilage therapies that may be suitable for red knee populations.

Working with James Carey, M.D., the Director of the Penn Center for Cartilage Repair and Osteochondritis, Mauck and his research team realized that even those with common knee cartilage conditions such as the presence of lesions or osteoarthritis were liable to be excluded from most regeneration studies. In discussing alternatives methods and structures of studying cartilage repair and regeneration, Mauck and Carey hope that future therapies will be applicable to a wider range of patient populations, and that there will soon be more options beyond full joint replacement for those with red knee conditions.

Plant-Like Superhydrophobicity Has Applications in Biomedical Engineering

Researchers in the Department of Biomedical Engineering at Texas A&M University recently found ways of incorporating the superhydrophobic properties of some plant leaves into biomedical applications through what they’re calling a “lotus effect.” The Gaharwar Lab, led by principal investigator and assistant professor of biomedical engineering Akhilesh Gaharwar, Ph.D., developed an assembly of two-dimensional atomic layers that they describe as a “nanoflower” to help control surface wetting in a biomedical setting. A recent paper published in Chemical Communications describes Gaharwar and his team’s work as expanding the use of superhydrophobic surface properties in biomedical devices by demonstrating the important role that atomic vacancies play in the wetting characteristic. While Gaharwar hopes to research the impact that controlling superhydrophobicity could have in stem cell applications, his work already allows for innovations in self-cleaning and surface properties of devices involving labs-on-a-chip and biosensing.

People and Places

Nader Engheta, H. Nedwill Ramsey Professor in Electrical and Systems Engineering, Bioengineering and Materials Science and Engineering, has been inducted into the Canadian Academy of Engineering (CAE) as an International Fellow. The CAE comprises many of Canada’s most accomplished engineers and Engheta was among the five international fellows that were inducted this year.

The Academy’s President Eddy Isaacs remarked: “Over our past 32 years, Fellows of Academy have provided insights in the fields of education, infrastructure, and innovation, and we are expecting the new Fellows to expand upon these contributions to public policy considerably.”

Read the full story on Penn Engineering’s Medium Blog.

We would like to congratulate Anthony Lowman, Ph.D., on his appointment as the Provost and Senior Vice President for Academic Affairs at Rowan University. Formerly the Dean of Rowan’s College of Engineering, Lowman helped the college double in size, and helped foster a stronger research community. Lowman also helped to launch a Ph.D. program for the school, and added two new departments of Biomedical Engineering and Experiential Engineering Education in his tenure as the dean. Widely recognized for his research on hydrogels and drug delivery, Lowman was also formerly a professor of bioengineering at Temple University and Drexel University.

Lastly, we would like to congratulate Daniel Lemons, Ph.D., on his appointment as the Interim President of Lehman College of the City University of New York. Lemons, a professor in the Department of Biology at City College, specializes in cardiovascular and comparative physiology, and was also one of the original faculty members of the New York Center for Biomedical Engineering. With prior research funded by both the National Institute of Health (NIH) and the National Science Foundation (NSF), Lemons also holds patents in biomechanics teaching models and mechanical heart simulators.

July 23, 2019July 18, 2019

César de la Fuente Named Penn Presidential Professor

César de la Fuente, assistant professor in the Perelman School of Medicine and in Department of Bioengineering in the School of Engineering and Applied Science, has been awarded a Presidential Professorship by University of Pennsylvania President Amy Gutmann. Presidential Professorships, which have terms lasting five years, are awarded to outstanding scholars who, according to the award announcement, “demonstrably contribute excellence and diversity to Penn’s inclusive community.”

De la Fuente is a synthetic biologist who incorporates a computational approach into his work, attempting to engineer biological systems that can transform medical tools and therapies. His lab studies naturally occurring proteins and uses their discoveries to design artificial antibiotics and living medicines.

De la Fuente has also been named one of MIT Technology Review’s “35 Innovators Under 35” and one of GEN’s “Top 10 Under 40” for his pioneering work on engineered medicines.

Read the Presidential Professorship award announcement at Penn Medicine, and learn more about de la Fuente’s research on his lab website.

Originally published on the Penn Engineering Medium blog.

July 22, 2019July 18, 2019

Penn Engineers at the Forefront of Penn’s ‘Innovation Ecosystem’

By Lauren Salig

Andrei Georgescu, a member of Dan Huh’s bioengineering laboratory, prepares microfluidics for the lab’s work on organ-on-a-chip technology. Their innovative research was one of many Engineering projects featured in a recent video.

The University of Pennsylvania is highlighting its “ecosystem of innovation” in a new video, featuring some of the most cutting-edge work being done on campus and the infrastructure supporting that work. Alongside shots of the Singh Center for Nanotechnology, the Pennovation Center and the coming VentureLab are the familiar faces of Penn Engineers inventing the future.

The video includes the voices of Vijay Kumar, the Nemirovsky Family Dean of the School of Engineering and Applied Science; Dawn Bonnell, Penn’s Vice Provost of Research and the Henry Robinson Towne Professor of Materials Science and Engineering; and Konrad Kording, a Penn Integrates Knowledge Professor of Neurosciences and Bioengineering — each discussing the collaborative environment at the University.

A quick watch of the video reveals glimpses into Penn Engineering labs and projects where much of Penn’s innovation happens: PERCH’s flying robots that swarm together without using GPS, an investigation into 2-D room-temperature platforms for quantum technology, testing mechanical walking algorithms on robotic legs named Cassie, organs-on-a-chip that aid the study of diseases on Earth and in space, President’s Innovation Prize winners’ nanoscale implant company Visiplate aiming to treat blindness, blueprints for nanocrystals that self-assemble into materials with unique properties, Penn Electric Racing’s four-wheel drive competitive racecar, and PERCH lab spin-off Ghost Robotic’s Minitaur robot that senses the ground beneath its metal feet.

See if you can spot these Penn Engineering contributions in the video at Penn Today.

This article was originally posted on the Penn Engineering Medium blog.

July 19, 2019July 19, 2019

Congratulations to Danielle Bassett and Arjun Raj on Their Promotions to Full Professors

We would like to congratulate Penn Bioengineering faculty members Arjun Raj, Ph.D., and Danielle Bassett, Ph.D., on their promotions from associate to full professors.

The Raj lab studies how biological processes work at the level of individual cells. Their work combines quantitative tools from genomics, imaging, biology, math, and computer science to develop models for how individual cells function, and in particular, how these individual cells can behave differently from each other. One major interest is in cancer, in which the lab is studying how individual cells can drive resistance to anti-cancer drugs. He and his lab also have a regularly updated blog discussing general topics related to scientific academia.

The Bassett lab takes an in-depth look at the use of network science and complex systems theory to study computational neuroscience in projects that involve the architecture of knowledge networks, the controllability of brain networks, and the dynamic networks in neuroscience. This fall, she will teach an elective course in network neuroscience open to graduate and undergraduate students that covers the use of network science in understanding overall brain circuitry. Bassett was recently profiled in Science Magazine.

July 18, 2019July 18, 2019

Michael Mitchell Elected Society for Biomaterials Drug Delivery Chair

by Sophie Burkholder

Michael Mitchell, Ph.D., Skirkanich Assistant Professor of Innovation in the Department of Bioengineering at the University of Pennsylvania, was elected Chair of the Drug Delivery Special Interest Group for the Society for Biomaterials at the 2019 Annual Meeting in Seattle, Washington. According to the Society for Biomaterials website:

The Drug Delivery Special Interest Group will deal with the science and technology of controlled release of active agents from delivery systems. Controlled drug release is achieved by the use of diffusion, chemical reactions, dissolutions or osmosis, used either singly or in combination. While the vast majority of such delivery devices are based on polymers, controlled release can also be achieved by the use of mechanical pumps. In a broader sense, controlled release also involves control over the site of action of the active agent, using the active agent using pro-drugs, targetable water soluble polymers or various microparticulate systems. Relevant aspects of toxicology, bioavailability, pharmacokinetics, and biocompatibility are also included.

The Society for Biomaterials is an interdisciplinary organization comprised of academic, industry, health care, and governmental professionals dedicated to promoting advancements in all aspects of biomaterial science and engineering, education, and professional standards to enhance human health and quality of life. The Society for Biomaterials was established in 1974, and is the oldest scientific organization in the field of biomaterials.

Mitchell joined the Department of Bioengineering at Penn in 2018 as Skirkanich Assistant Professor of Innovation. Previously, he was an NIH Ruth L. Kirschstein Postdoctoral Fellow with Institute Professor Robert Langer at the Koch Institute for Integrative Cancer Research at MIT. His research interests include biomaterials, drug delivery, and cellular and molecular bioengineering for applications in cancer research, immunotherapy, and gene therapy. Since joining Penn in 2018, Mitchell has received the NIH Director’s New Innovator Award, the Burroughs Wellcome Fund Career Award at the Scientific Interface, a Rising Star Award from the Biomedical Engineering Society, and the T. Nagai Award from the Controlled Release Society.

Mitchell’s new role as the Chair of the SFB’s Drug Delivery Special Interest Group will allow him to lead conversations across academia on the future of drug delivery as it relates to biomaterials. With his fellow officers, Mitchell will help spread knowledge about the field of controlled drug release by hosting research forums, helping to publish news and activities of the SFB in Biomaterials Forum, and foster connections and mentorship among members of his and other Special Interest Groups. We can’t wait to see where Mitchell’s leadership will help take the community of research on areas like toxicology, pharmacokinetics, and biocompatibility next!

July 12, 2019July 18, 2019

Week in BioE (July 12, 2019)

by Sophie Burkholder

DNA Microscopy Gives a Better Look at Cell and Tissue Organization

A new technique that researchers from the Broad Institute of MIT and Harvard University are calling DNA microscopy could help map cells for better understanding of genetic and molecular complexities. Joshua Weinstein, Ph.D., a postdoctoral associate at the Broad Institute, who is also an alumnus of Penn’s Physics and Biophysics department and former student in Penn Bioengineering Professor Ravi Radhakrishnan’s lab, is the first author of this paper on optics-free imaging published in Cell.

The primary goal of the study was to find a way of improving analysis of the spatial organization of cells and tissues in terms of their molecules like DNA and RNA. The DNA microscopy method that Weinstein and his team designed involves first tagging DNA, and allowing the DNA to replicate with those tags, which eventually creates a cloud of sorts that diffuses throughout the cell. The DNA tags subsequent interactions with molecules throughout the cell allowed Weinstein and his team to calculate the locations of those molecules within the cell using basic lab equipment. While the researchers on this project focused their application of DNA microscopy on tracking human cancer cells through RNA tags, this new method opens the door to future study of any condition in which the organization of cells is important.

Read more on Weinstein’s research in a recent New York Times profile piece.

Penn Engineers Demonstrate Superstrong, Reversible Adhesive that Works like Snail Slime

If you’ve ever pressed a picture-hanging strip onto the wall only to realize it’s slightly off-center, you know the disappointment behind adhesion as we typically experience it: it may be strong, but it’s mostly irreversible. While you can un-stick the used strip from the wall, you can’t turn its stickiness back on to adjust its placement; you have to start over with a new strip or tolerate your mistake. Beyond its relevance to interior decorating, durable, reversible adhesion could allow for reusable envelopes, gravity-defying boots, and more heavy-duty industrial applications like car assembly.

Such adhesion has eluded scientists for years but is naturally found in snail slime. A snail’s epiphragm — a slimy layer of moisture that can harden to protect its body from dryness — allows the snail to cement itself in place for long periods of time, making it the ultimate model in adhesion that can be switched on and off as needed. In a new study, Penn Engineers demonstrate a strong, reversible adhesive that uses the same mechanisms that snails do.

This study is a collaboration between Penn Engineering, Lehigh University’s Department of Bioengineering, and the Korea Institute of Science and Technology.

Read the full story on Penn Engineering’s Medium blog.

Low-Dose Radiation CT Scans Could Be Improved by Machine Learning

Machine learning is a type of artificial intelligence growing more and more popular for applications in bioengineering and therapeutics. Based on learning from patterns in a way similar to the way we do as humans, machine learning is the study of statistical models that can perform specific tasks without explicit instructions. Now, researchers at Rensselaer Polytechnic Institute (RPI) want to use these kinds of models in computerized tomography (CT) scanning by lowering radiation dosage and improving imaging techniques.

A recent paper published in Nature Machine Intelligence details the use of modularized neural networks in low-dose CT scans by RPI bioengineering faculty member Ge Wang, Ph.D., and his lab. Since decreasing the amount of radiation used in a scan will also decrease the quality of the final image, Wang and his team focused on a more optimized approach of image reconstruction with machine learning, so that as little data as possible would be altered or lost in the reconstruction. When tested on CT scans from Massachusetts General Hospital and compared to current image reconstruction methods for the scans, Wang and his team’s method performed just as well if not better than scans performed without the use of machine learning, giving promise to future improvements in low-dose CT scans.

A Mind-Controlled Robotic Arm That Requires No Implants

A new mind-controlled robotic arm designed by researchers at Carnegie Mellon University is the first successful noninvasive brain-computer interface (BCI) of its kind. While BCIs have been around for a while now, this new design from the lab of Bin He, Ph.D., a Trustee Professor and the Department Head of Biomedical Engineering at CMU, hopes to eliminate the brain implant that most interfaces currently use. The key to doing this isn’t in trying to replace the implants with noninvasive sensors, but in improving noisy EEG signals through machine learning, neural decoding, and neural imaging. Paired with increased user engagement and training for the new device, He and his team demonstrated that their design enhanced continuous tracking of a target on a computer screen by 500% when compared to typical noninvasive BCIs. He and his team hope that their innovation will help make BCIs more accessible to the patients that need them by reducing the cost and risk of a surgical implant while also improving interface performance.

People and Places

Daeyeon Lee, professor in the Department of Chemical and Biomolecular Engineering and member of the Bioengineering Graduate Group Faculty here at Penn, has been selected by the U.S. Chapter of the Korean Institute of Chemical Engineers (KIChE) as the recipient of the 2019 James M. Lee Memorial Award.

KIChE is an organization that aims “to promote constructive and mutually beneficial interactions among Korean Chemical Engineers in the U.S. and facilitate international collaboration between engineers in U.S. and Korea.”

Read the full story on Penn Engineering’s Medium blog.

We would also like to congratulate Natalia Trayanova, Ph.D., of the Department of Biomedical Engineering at Johns Hopkins University on being inducted into the Women in Tech International (WITI) Hall of Fame. Beginning in 1996, the Hall of Fame recognizes significant contributions to science and technology from women. Trayanova’s research specializes in computational cardiology with a focus on virtual heart models for the study of individualized heart irregularities in patients. Her research helps to improve treatment plans for patients with cardiac problems by creating virtual simulations that help reduce uncertainty in either diagnosis or courses of therapy.

Finally, we would like to congratulate Andre Churchwell, M.D., on being named Vanderbilt University’s Chief Diversity Officer and Interim Vice Chancellor for Equity, Diversity, and Inclusion. Churchwell is also a professor of medicine, biomedical engineering, and radiology and radiological sciences at Vanderbilt, with a long career focused in cardiology.

July 11, 2019July 10, 2019

Penn Engineers’ ‘LADL’ Uses Light to Serve Up On-demand Genome Folding

Every cell in your body has a copy of your genome, tightly coiled and packed into its nucleus. Since every copy is effectively identical, the difference between cell types and their biological functions comes down to which, how and when the individual genes in the genome are expressed, or translated into proteins.

Scientists are increasingly understanding the role that genome folding plays in this process. The way in which that linear sequence of genes are packed into the nucleus determines which genes come into physical contact with each other, which in turn influences gene expression.

LADL combines CRISPR/Cas9 and optogenetics to bring two distant points in a linear gene sequence into physical contact, forming a folding pattern known as a “loop.” Looping interactions influence gene expression, so the researchers envision LADL as being a powerful tool for studying these dynamics.

Jennifer Phillips-Cremins, assistant professor in Penn Engineering’s Department of Bioengineering, is a pioneer in this field, known as “3-D Epigenetics.” She and her colleagues have now demonstrated a new technique for quickly creating specific folding patterns on demand, using light as a trigger.

The technique, known as LADL or light-activated dynamic looping, combines aspects of two other powerful biotechnological tools: CRISPR/Cas9 and optogenetics. By using the former to target the ends of a specific genome fold, or loop, and then using the latter to snap the ends together like a magnet, the researchers can temporarily create loops between exact genomic segments in a matter of hours.

The ability to make these genome folds, and undo them, on such a short timeframe makes LADL a promising tool for studying 3D-epigenetic mechanisms in more detail. With previous research from the Phillips-Cremins lab implicating these mechanisms in a variety of neurodevelopmental diseases, they hope LADL will eventually play a role in future studies, or even treatments.

Jennifer Phillips-Cremins, Ji Hun Kim and Mayuri Rege

Alongside Phillips-Cremins, lab members Ji Hun Kim and Mayuri Rege led the study, and Jacqueline Valeri, Aryeh Metzger, Katelyn R. Titus, Thomas G. Gilgenast, Wanfeng Gong and Jonathan A. Beagan contributed to it. They collaborated with associate professor of Bioengineering Arjun Raj and Margaret C. Dunagin, a member of his lab.

The study was published in the journal Nature Methods.

“In recent years,” Phillips-Cremins says, “scientists in our fields have overcome technical and experimental challenges in order to create ultra-high resolution maps of how the DNA folds into intricate 3D patterns within the nucleus. Although we are now capable of visualizing the topological structures, such as loops, there is a critical gap in knowledge in how genome structure configurations contribute to genome function.”

In order to conduct experiments on these relationships, researchers studying these 3D patterns were in need of tools that could manipulate specific loops on command. Beyond the intrinsic physical challenges — putting two distant parts of the linear genome in physical contact is quite literally like threading a needle with a thread that is only a few atoms thick — such a technique would need to be rapid, reversible and work on the target regions with a minimum of disturbance to neighboring sequences.

The advent of CRISPR/Cas9 solved the targeting problem. A modification of the gene editing tool allowed researchers to home in on the desired sequences of DNA on either end of the loop they wanted to form. If those sequences could be engineered to seek one another out and snap together under the other necessary conditions, the loop could be formed on demand.

Cremins Lab members then sought out biological mechanisms that could bind the ends of the loops together, and found an ideal one in the toolkit of optogenetics. The proteins CIB1 and CRY2, found in Arabidopsis, a flowering plant that’s a common model organism for geneticists, are known to bind together when exposed to blue light.

“Once we turn the light on, these mechanisms begin working in a matter of milliseconds and make loops within four hours,” says Rege. “And when we turn the light off, the proteins disassociate, meaning that we expect the loop to fall apart.”

“There are tens of thousands of DNA loops formed in a cell,” Kim says. “Some are formed slowly, but many are fast, occurring within the span of a second. If we want to study those faster looping mechanisms, we need tools that can act on a comparable time scales.”

As shown in a 2013 Nature Methods paper by fellow Penn bioengineer Lukasz Bugaj, the optical response of the CRY2 protein is a key component of LADL. When the blue light is turned on, CRY2 proteins in cell immediately find one another and bind together into clumps large enough to be seen under magnification. When the light is turned off, the clumps begin to dissolve away.”

Fast acting folding mechanisms also have an advantage in that they lead to fewer perturbations of the surrounding genome, reducing the potential for unintended effects that would add noise to an experiment’s results.

The researchers tested LADL’s ability to create the desired loops using their high-definition 3D genome mapping techniques. With the help of Arjun Raj, an expert in measuring the activity of transcriptional RNA sequences, they also were able to demonstrate that the newly created loops were impacting gene expression.

The promise of the field of 3D-epigenetics is in investigating the relationships between these long-range loops and mechanisms that determine the timing and quantity of the proteins they code for. Being able to engineer those loops means researchers will be able to mimic those mechanisms in experimental conditions, making LADL a critical tool for studying the role of genome folding on a variety of diseases and disorders.

“It is critical to understand the genome structure-function relationship on short timescales because the spatiotemporal regulation of gene expression is essential to faithful human development and because the mis-expression of genes often goes wrong in human disease,” Phillips-Cremins says. “The engineering of genome topology with light opens up new possibilities to understanding the cause-and-effect of this relationship. Moreover we anticipate that, over the long term, the use of light will allow us to target specific human tissues and even to control looping in specific neuron subtypes in the brain.”

The research was supported by the New York Stem Cell Foundation; Alfred P. Sloan Foundation; the National Institutes of Health through its Director’s New Innovator Award from the National Institute of Mental Health, grant no. 1DP2MH11024701, and a 4D Nucleome Common Fund, grant no. 1U01HL1299980; and the National Science Foundation through a joint NSF-National Institute of General Medical Sciences grant to support research at the interface of the biological and mathematical sciences, grant no. 1562665, and a Graduate Research Fellowship, grant no. DGE-1321851.

Originally published on the Penn Engineering Medium blog.