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Clinical Laboratories and Pathology Groups

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Full Genome Sequencing of All Animal Species Continues, but Sequencing of Invertebrate Species Lags Behind That of Vertebrate Species

Scientists working to sequence all 1.66 million animal species say this is a missed opportunity to better understand our own genetics; such research would identify biomarkers useful for clinical laboratory testing

For 23 years, the world’s genomic scientists have been on a mission to sequence the genomes of all animal species. And they’ve made great progress. However, according to a recent study conducted by researchers at Washington State University (WSU) and Brigham Young University (BYU), only a fraction of the sequences are from invertebrate species. And that, according to the study’s authors, is “overlooking huge swathes of diversity and opportunity.”

The push to sequence the whole genomes of all animals began in 1998 with the sequencing of the Caenorhabditis elegans roundworm, according to a WSU news release. It was the first animal genome sequence, but it was not to be the last. Nearly 25 years later, genomic scientists have sequenced about 3,300 animal genomes. And while that’s a lot of genomic sequences, it’s a drop in bucket of the approximately 1.7 million animal species on the planet.

But here’s where the missed opportunity comes in. According to the WSU news release, “Vertebrates account for 54% of all genome sequencing assemblies, despite representing only 3.9% of animal species. In contrast, the invertebrates of the Arthropoda phylum, which includes insects and spiders, comprise only 34% of current datasets while representing 78.5% of all species.”

Paul Frandsen, PhD

“We are interested in ourselves, and that’s not necessarily a bad thing,” said Paul Frandsen, PhD (above), in the news release. Frandsen is Assistant Professor of Genetics, Genomics, and Biotechnology at Brigham Young University and one of the study authors. “But to begin to understand entire ecosystems,” he continued, “we have to start sampling more of the variety of life to gain a clearer picture. Vertebrates are important components of ecosystems, but arguably insects and many other small creatures probably play an even more important role because they’re down at the base of the food web.” (Photo copyright: Brigham Young University.) 

The WSU/BYU researchers described their findings in the journal Proceedings of the National Academy of Sciences (PNAS), titled, “Toward a Genome Sequence for Every Animal: Where Are We Now?

Are Hominids More Charismatic?

The scientists analyzed the best available genome assemblies found in GenBank, the world’s most extensive genetic database. They found that 3,278 unique animal species across 24 phyla, 64 classes, and 258 orders have been sequenced and assembled to date.

They also found that sequencing efforts have focused heavily on species that most resemble humans. The Hominidae, a taxonomic family of primates that includes humans as well as great apes, bonobos, chimpanzees, orangutans, and gorillas, has the most contiguous genome data assembled.

The team discovered that vertebrates account for 54% of the animal genome sequencing that has been performed even though they make up less than four percent of known animal species. By comparison, invertebrates of the Arthropoda phylum, which represent 78.5% of all animal species, comprise only 34% of the completed animal genome sequencing. And yet, the Arthropoda phylum is the largest phylum in the animal kingdom and includes insects, spiders, scorpions, centipedes, millipedes, crabs, crayfish, lobsters, and barnacles.

“With genome assemblies accumulating rapidly, we want to think about where we are putting our efforts. It’s not being spread evenly across the animal tree of life,” said lead author Scott Hotaling, PhD, post-doctoral researcher at WSU, in the news release. “Invertebrates are still very underrepresented, which makes sense given that people seem to care more about vertebrates, the so-called ‘charismatic megafauna.’”

The team discovered that only five arthropod groups: ants, bees, butterflies, fruit flies, and mosquitos, were well represented in genome sequencing. The longest genome sequenced so far belongs to the Australian lungfish, the only surviving member of the family Neoceratodontidae.

1,100 Years to Sequence All Eukaryotic Life

The scientists also discerned that animal genome assemblies have been produced by 52 countries on every continent with permanent inhabitants. The majority of animal genome sequencing (77%) that is being performed is mostly occurring in developed countries located in the Northern Hemisphere, often referred to as the Global North. Nearly 70% of all animal genome assemblies have been produced by just three countries: the United States, China, and Switzerland.

There are geographic differences between regions regarding the types of animals being sequenced and assembled with North America concentrating on mammals and insects, Europe focusing on fish, and birds being the main type of animals sequenced in Asia.

The scientists would like to see more animal genome sequencing happening in countries from the Global South, or Southern Hemisphere, particularly in tropical regions that contain a myriad of diversity among animal species.

“If we want to build a global discipline, we need to include a global people,” Hotaling said. “It’s just basic equity, and from a pure scientific standpoint, the people who live in areas where species are being sequenced have a lot of knowledge about those species and ecosystems. They have a lot to contribute.”

But the WSU/BYU scientists found that many species in GenBank only have low-quality assemblies available. They noted that “the quality of a genome assembly is likely the most important factor dictating its long-term value.”

Fortunately, several animal genome sequencing ventures have been announced in recent years, so the amount of available data is expected to rise exponentially. These projects include:

The authors of the PNAS paper noted that there are currently only about four genome assemblies happening each day and, at that rate, the sequencing of all eukaryotic life will not be completed until the year 3130.

So, microbiologists, clinical laboratory professionals, and genomic scientists have plenty of time to get up to speed.

JP Schlingman

Related Information:

Toward a Genome Sequence for Every Animal: Where are We Now?

Big Gaps in Quest to Sequence Genomes of All Animals

Genomes of Other Organisms: DNA Barcoding and Metagenomics

Biologists Propose to Sequence the DNA of All Life on Earth

‘Barcoding’ Cells in Nematodes Could Bring Advances and New Medical Laboratory Tools for Treatment of Cancer and Other Chronic Diseases

Ongoing research at the University of Washington promises new methods for identifying and cataloging large numbers of cells quickly, which could lead to more individualized treatments in support of precision medicine initiatives

Researchers have found a new method for identifying specific cell types by groups, a breakthrough that some experts say could lead to new and more accurate methods for diagnosing and treating disease in individual patients, and new tools for fighting cancer and other chronic diseases. If this happens, both clinical laboratories and anatomic pathology labs would benefit from this technology.

A study published in the journal Science titled, “Comprehensive Single-Cell Transcriptional Profiling of a Multicellular Organism,” describes advances in cataloging cells that are much faster than the traditional method of using a microscope. The research is still in the experimental stage, but it is being hailed as both exciting and promising by experts in the field.

Barcoding Large Numbers of Cells for Viewing Simultaneously

To test their method, researchers from the University of Washington (UW) sequenced each cell of an individual Caenorhabditis elegans (nematode). Nematodes are transparent roundworms that have been extensively studied making them ideal for the UW study, since much information exists about their cellular structure.

The researchers developed a strategy they dubbed “single-cell combinatorial indexing RNA sequencing,” or “sci-RNA-seq” for short, to profile the transcriptomes of nuclei. A New York Times article on the study describes sci-RNA-seq as a kind of barcoding that shows which genes are active in each cell.

“We came up with this scheme that allows us to look at very large numbers of cells at the same time, without ever isolating a single cell,” noted Jay Shendure, PhD, MD, Professor of Genome Sciences at the University of Washington.

The UW researchers used sci-RNA-seq to measure the activity in 42,035 cells at the same time. Once all of the cells were tagged, or barcoded, the researchers broke them open so the sequences of tags could be read simultaneously.

“We defined consensus expression profiles for 27 cell types and recovered rare neuronal cell types corresponding to as few as one or two cells,” wrote the researchers in their published study.

Because such a rich body of research on nematodes exists, the researchers could easily compare the results that got to those procured in previous studies.

Jay Shendure, MD, PhD (above), Professor of Genomic Sciences at the University of Washington, and an Investigator at the Howard Hughes Medical Institute, was just a graduate student when his work with genetics led to the development of today’s next-generation gene sequencing technologies. His new cell-type identification technology could eventually be used by clinical laboratories and anatomic pathology groups to diagnose disease. (Photo copyright: Howard Hughes Medical Institute.)

One Giant Leap for Medical Diagnostics

Identifying cell types has been a challenge to the medical community for at least 150 years. It is important for scientists to understand the most basic unity of life, but it has only been in the last few years that researchers have been able to measure transcriptomes in single cells. Even though the research so far is preliminary, the scientific community is excited about the results because—should the methods be refined—it could mean a great leap forward in the field of cell-typing.

However, the study did not identify all of the cell types known to exist in a nematode. “We don’t consider this a finished project,” stated Shendure in a New York Times article.

Nevertheless, researchers not associated with the study feel confident about the promise of the work. Cori Bargmann, PhD, a neurobiologist and Torsten N. Wiesel Professor at The Rockefeller University, and an Investigator for the Howard Hughes Medical Institute from 1995 to 2016, states that the results “will be valuable for me and for the whole field,” adding, “Of course, there’s more to do, but I am pretty optimistic that this can be solved.”

“The ability to measure the transcriptomes of single cells has only been feasible for a few years, and is becoming an extremely popular assay,” wrote Valentine Svensson, predoctoral fellow et al, of EMBL-EBI in the UK, in a paper titled, “Exponential Scaling of Single-Cell RNA-Seq in the Last Decade.” He added, “Technological developments and protocol improvements have fueled a consistent exponential increase in the numbers of cells studied in single cell RNA-seq analyses.” The UW research represents another such improvement.

Human Cell Atlas—Understanding the Basis of Life Itself

There are approximately 37-trillion cells in the human body and scientists have long believed there are 200 different cell types. Thus, there is an enormous difference between a nematode and a human body. For medical science to benefit from these studies, massive numbers of human cells must be identified and understood. Efforts are now underway to catalog and map them all.

The Human Cell Atlas (HCA) is an effort to catalog all of those disparate cell types. The mission of HCA is “To create comprehensive reference maps of all human cells—the fundamental units of life—as a basis for both understanding human health and diagnosing, monitoring, and treating disease.”

According to HCA’s website, having the atlas completed will impact our understanding of every aspect of human biology, from immunologic diseases to cancer. Aviv Regev, PhD, of the Broad Institute at MIT, who also is an Investigator with the HHMI and is co-chair of the organizing committee at the Human Cell Atlas notes, “The human cell atlas initiative will work through organs, tissues, and systems.”

One of the many complications of creating the atlas is that the locations of cells vary in humans. “The trick,” Regev noted in the New York Times article, “is to relate cells to the place they came from.” This would seem to be at the heart of the UW researchers’ new method for “barcoding” groups of cells.

Just as sequencing the entire human genome has brought about previously unimagined advances in science, so too will the research being conducted at the University of Washington, as well as the completion of the Human Cell Atlas Project. It is possible that pursuing the goal of quickly identifying and cataloging cells will lead to advances in anatomic pathology, and allow medical laboratory scientists to better interpret genetic variants, ultimately bringing healthcare closer to the delivery of true precision medicine.

—Dava Stewart

Related Information:

Comprehensive Single-Cell Transcriptional Profiling of a Multicellular Organism

A Speedier Way to Catalog Human Cells (All 37 Trillion of Them)

Exponential Scaling of Single-Cell RNA-Seq In the Last Decade

Human Cell Atlas

Genetic Fingerprint Helps Researchers Identify Aggressive Prostate Cancer from Non-Aggressive Types and Determine if Treatment Will Be Effective

Big Data Projects at Geisinger Health Are Beginning to Help Physicians Speed Up Diagnosis and Improve Patient Care

Biomarker Trends Are Auspicious for Pathologists and Clinical Laboratories

Pathologists and Clinical Laboratories May Soon Have a Test for Identifying Cardiac Patients at Risk from Specific Heart Drugs by Studying the Patients’ Own Heart Cells