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Clinical Laboratories and Pathology Groups

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Harvard and Google Scientists Studying Connectomics Create Massive Highly Detailed 3D Nanoscale Model of Human Neural Tissue

Ten year collaboration between Google and Harvard may lead to a deeper understanding of the brain and new clinical laboratory diagnostics

With all our anatomic pathology and clinical laboratory science, we still do not know that much about the structure of the brain. But now, scientists at Harvard University and Google Research studying the emerging field of connectomics have published a highly detailed 3D reconstruction of human brain tissue that allows visualization of neurons and their connections at unprecedented nanoscale resolutions.

Further investigation of the nano-connections within the human brain could lead to novel insights about the role specific proteins and molecules play in the function of the brain. Though it will likely be years down the road, data derived from this study could be used to develop new clinical laboratory diagnostic tests.

The data to generate the model came from Google’s use of artificial intelligence (AI) algorithms to color-code Harvard’s electron microscope imaging of a cubic millimeter of neural tissue—equivalent to a half-grain of rice—that was surgically removed from an epilepsy patient.

“That tiny square contains 57,000 cells, 230 millimeters of blood vessels, and 150 million synapses, all amounting to 1,400 terabytes of data,” according to the Harvard Gazette, which described the project as “the largest-ever dataset of human neural connections.”

“A terabyte is, for most people, gigantic, yet a fragment of a human brain—just a minuscule, teeny-weeny little bit of human brain—is still thousands of terabytes,” said neuroscientist Jeff W. Lichtman, MD, PhD, Jeremy R. Knowles Professor of Molecular and Cellular Biology, whose Lichtman Lab at Harvard University collaborated on the project with researchers from Google. The two labs have been working together for nearly 10 years on this project, the Harvard Gazette reported.

Lichtman’s lab focuses on the emerging field of connectomics, defined “as understanding how individual neurons are connected to one another to form functional networks,” said neurobiologist Wei-Chung Allen Lee, PhD, Assistant Professor of Neurology, Harvard Medical School, in an interview with Harvard Medical News. “The goal is to create connectomes—or detailed structural maps of connectivity—where we can see every neuron and every connection.” Lee was not involved with the Harvard/Google Research study.

The scientists published their study in the journal Science titled, “A Petavoxel Fragment of Human Cerebral Cortex Reconstructed at Nanoscale Resolution.”

“The human brain uses no more power than a dim incandescent light bulb, yet it can accomplish feats still not possible with the largest artificial computing systems,” wrote Google Research scientist Viren Jain, PhD (above), in a blog post. “To understand how requires a level of understanding more profound than knowing what part of the brain is responsible for what function. The field of connectomics aims to achieve this by precisely mapping how each cell is connected to others.” Google’s 10-year collaboration with Harvard University may lead to new clinical laboratory diagnostics. (Photo copyright: Google Research.)

Study Data and Tools Freely Available

Along with the Science paper, the researchers publicly released the data along with analytic and visualization tools. The study noted that the dataset “is large and incompletely scrutinized,” so the scientists are inviting other researchers to assist in improving the model.

“The ability for other researchers to proofread and refine this human brain connectome is one of many ways that we see the release of this paper and the associated tools as not only the culmination of 10 years of work, but the beginning of something new,” wrote Google Research scientist Viren Jain, PhD, in a blog post that included links to the online resources.

One of those tools—Neuroglancer—allows any user with a web browser to view 3D models of neurons, axons, synapses, dendrites, blood vessels, and other objects. Users can rotate the models in xyz dimensions.

Users with the requisite knowledge and skills can proofread and correct the models by signing up for a CAVE (Connectome Annotation Versioning Engine) account.

Researchers Found Several Surprises

To perform their study, Lichtman’s team cut the neural tissue into 5,000 slices, each approximately 30 nanometers thick, Jain explained in the blog post. They then used a multibeam scanning electron microscope to capture high-resolution images, a process that took 326 days.

Jain’s team at Google used AI tools to build the model. They “stitched and aligned the image data, reconstructed the three dimensional structure of each cell, including its axons and dendrites, identified synaptic connections, and classified cell types,” he explained.

Jain pointed to “several surprises” that the reconstruction revealed. For example, he noted that “96.5% of contacts between axons and their target cells have just one synapse.” However, he added, “we found a class of rare but extremely powerful synaptic connections in which a pair of neurons may be connected by more than 50 individual synapses.”

In their Science paper, the researchers suggest that “these powerful connections are not the result of chance, but rather that these pairs had a reason to be more strongly connected than is typical,” Jain wrote in the blog post. “Further study of these connections could reveal their functional role in the brain.”

Mysterious Structures

Another anomaly was the presence of “axon whorls,” as Jain described them, “beautiful but mysterious structures in which an axon wraps itself into complicated knots.”

Because the sample came from an epilepsy patient, Jain noted that the whorls could be connected to the disease or therapies or could be found in all brains.

“Given the scale and complexity of the dataset, we expect that there are many other novel structures and characteristics yet to be discovered,” he wrote. “These findings are the tip of the iceberg of what we expect connectomics will tell us about human brains.”

The researchers have a larger goal to create a comprehensive high-resolution map of a mouse’s brain, Harvard Medical News noted. This would contain approximately 1,000 times the data found in the 1-cubic-millimeter human sample.

Dark Daily has been tracking the different fields of “omics” for years, as research teams announce new findings and coin new areas of science and medicine to which “omics” is appended. Connectomics fits that description.

Though the Harvard/Google research is not likely to lead to diagnostic assays or clinical laboratory tests any time soon, it is an example of how advances in technologies are enabling researchers to investigate smaller and smaller elements within the human body.

—Stephen Beale

Related Information:

Researchers Publish Largest-Ever Dataset of Neural Connections

A Petavoxel Fragment of Human Cerebral Cortex Reconstructed at Nanoscale Resolution

Ten Years of Neuroscience at Google Yields Maps of Human Brain

Groundbreaking Images Reveal the Human Brain at Nanoscale Resolution

A New Field of Neuroscience Aims to Map Connections in the Brain

New CRISPR Gene-editing Approach Under Development at Broad Institute Could Lead to Improved Clinical Laboratory Diagnostics for Genetic Diseases

‘Prime editing’ is what researchers are calling the proof-of-concept research that promises improved diagnostics and more effective treatments for patients with genetic defects

What if it were possible to edit genetic code and literally remove a person’s risk for specific chronic diseases? Such a personalized approach to treating at-risk patients would alter all of healthcare and is at the core of precision medicine goals. Well, thanks to researchers at the Broad Institute of MIT and Harvard, clinical laboratory diagnostics based on precise gene-editing techniques may be closer than ever.

Known as Prime Editing, the scientists developed this technique as a more accurate way to edit Deoxyribonucleic acid (DNA). In a paper published in Nature, the authors claim prime editing has the potential to correct up to 89% of disease-causing genetic variations. They also claim prime editing is more powerful, precise, and flexible than CRISPR.

The research paper describes prime editing as a “versatile and precise genome editing method that directly writes new genetic information into a specified DNA site using a catalytically impaired Cas9 endonuclease fused to an engineered reverse transcriptase, programmed with a prime editing guide RNA (pegRNA) that both specifies the target site and encodes the desired edit.”

And a Harvard Gazette article states, “Prime editing differs from previous genome-editing systems in that it uses RNA to direct the insertion of new DNA sequences in human cells.”

Assuming further research and clinical studies confirm the viability of this technology, clinical laboratories would have a new diagnostic service line that could become a significant proportion of a lab’s specimen volume and test mix.

Multiple Breakthroughs in Gene Editing

In 2015, Dark Daily reported on a breakthrough in gene editing by David Liu, PhD, Director of the Merkin Institute of Transformative Technologies in Healthcare at the Broad Institute, and his team at Harvard.

In that e-briefing we wrote that Liu “has led a team of scientists in the development of a gene-editing protein delivery system that uses cationic lipids and works on animal and human cells. The new delivery method is as effective as protein delivery via DNA and has significantly higher specificity. If developed, this technology could open the door to routine use of genome analysis, worked up by the clinical laboratory, as one element in therapeutic decision-making.”

Now, Liu has taken that development even further.

“A major aspiration in the molecular life sciences is the ability to precisely make any change to the genome in any location. We think prime editing brings us closer to that goal,” David Liu, PhD (above), Director of the Merkin Institute of Transformative Technologies in Healthcare at the Broad Institute, told The Harvard Gazette. “We’re not aware of another editing technology in mammalian cells that offers this level of versatility and precision with so few byproducts.”  (Photo copyright: Broad Institute.)

Cell Division Not Necessary

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. It is considered the most advanced gene editing technology available. However, it has one drawback not found in Prime Editing—CRISPR relies on a cell’s ability to divide to generate desired alterations in DNA—prime editing does not.

This means prime editing could be used to repair genetic mutations in cells that do not always divide, such as cells in the human nervous system. Another advantage of prime editing is that it does not cut both strands of the DNA double helix. This lowers the risk of making unintended, potentially dangerous changes to a patient’s DNA.  

The researchers claim prime editing can eradicate long lengths of disease-causing DNA and insert curative DNA to repair dangerous mutations. These feats, they say, can be accomplished without triggering genome responses introduced by other forms of CRISPR that may be potentially harmful. 

“Prime editors are more like word processors capable of searching for targeted DNA sequences and precisely replacing them with edited DNA strands,” Liu told NPR.

The scientists involved in the study have used prime editing to perform over 175 edits in human cells. In the test lab, they have succeeded in repairing genetic mutations that cause both Sickle Cell Anemia (SCA) and Tay-Sachs disease, NPR reported.

“Prime editing is really a step—and potentially a significant step—towards this long-term aspiration of the field in which we are trying to be able to make just about any kind of DNA change that anyone wants at just about any site in the human genome,” Liu told News Medical.

Additional Research Required, but Results are Promising

Prime editing is very new and warrants further investigation. The researchers plan to continue their work on the technology by performing additional testing and exploring delivery mechanisms that could lead to human therapeutic applications. 

“Prime editing should be tested and optimized in as many cell types as researchers are interested in editing. Our initial study showed prime editing in four human cancer cell lines, as well as in post-mitotic primary mouse cortical neurons,” Liu told STAT. “The efficiency of prime editing varied quite a bit across these cell types, so illuminating the cell-type and cell-state determinants of prime editing outcomes is one focus of our current efforts.”

Although further research and clinical studies are needed to confirm the viability of prime editing, clinical laboratories could benefit from this technology. It’s worth watching.

—JP Schlingman

Related Information:

Scientists Create New, More Powerful Technique to Edit Genes

Search-and-replace Genome Editing without Double-strand Breaks or Donor DNA

New CRISPR Genome “Prime Editing” System

Genome Editing with Precision

You had Questions for David Liu about CRISPR, Prime Editing, and Advice to Young Scientists. He has Answers

A Prime Time for Genome Editing

Prime Editing with pegRNA: A Novel and Precise CRISPR Genome Editing System

Prime Editing: Adding Precision and Flexibility to CRISPR Editing

Gene-Editing Advance Puts More Gene-Based Cures Within Reach

Harvard, MIT Researchers Develop New Gene Editing Technology

Broad Institute’s New Prime Editing Tech Corrects Nearly 90 Percent of Human Pathogenic Variants

Researchers at Several Top Universities Unveil CRISPR-Based Diagnostics That Show Great Promise for Clinical Laboratories

New CRISPR Genetic Tests Offer Clinical Pathologists Powerful Tools to Diagnose Disease Even in Remote and Desolate Regions

Harvard Researchers Demonstrate a New Method to Deliver Gene-editing Proteins into Cells: Possibly Creating a New Diagnostic Opportunity for Pathologists

Harvard Researchers Demonstrate a New Method to Deliver Gene-editing Proteins into Cells: Possibly Creating a New Diagnostic Opportunity for Pathologists

This technology has potential to create a demand for pathologists to do genetic analysis as a companion diagnostic in support of physicians treating patients with gene-editing proteins

Researchers at Harvard University have demonstrated a new method to deliver gene-editing proteins into cells. This breakthrough could eventually trigger a demand for pathologists to do genetic analysis as the companion diagnostic needed to help clinicians select appropriate gene-editing therapies for their patients.

Of course, it will be several years before such a scenario is feasible. The related example are the companion diagnostic tests that clinical laboratories perform to guide a physician’s decision on an appropriate therapeutic drug. Continued development of gene-editing therapies has the potential to increase the need for pathologists and medical laboratory scientists to do genetic analysis as a companion diagnostic for patients who would benefit from a gene-editing therapy.

The Harvard University researchers used commercially available cationic lipids to deliver genome-editing proteins into cells. The system works on living animals and humans, and the technology enables scientists to precisely and easily change DNA sequences at exact locations. The full study was outlined in an October Nature Biotechnology article. (more…)

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