Amazing Organisms and the Lessons They Can Teach Us

What do you have in common with rodents, birds, and reptiles? A lot more than you might think. These creatures have organs and body systems very similar to our own: a skeleton, digestive tract, brain, nervous system, heart, network of blood vessels, and more. Even so-called “simple” organisms such as insects and worms use essentially the same genetic and molecular pathways we do. Studying these organisms provides a deeper understanding of human biology in health and disease, and makes possible new ways to prevent, diagnose, and treat a wide range of conditions.

Historically, scientists have relied on a few key organisms, including bacteria, fruit flies, rats, and mice, to study the basic life processes that run bodily functions. In recent years, scientists have begun to add other organisms to their toolkits. Many of these newer research organisms are particularly well suited for a specific type of investigation. For example, the small, freshwater zebrafish grows quickly and has transparent embryos and see-through eggs, making it ideal for examining how organs develop. Organisms such as flatworms, salamanders, and sea urchins can regrow whole limbs, suggesting they hold clues about how to improve wound healing and tissue regeneration in humans.

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CRISPR Illustrated

You’ve probably heard news stories and other talk about CRISPR. If you’re not a scientist—well, even if you are—it can seem a bit complex. Here’s a brief recap of what it’s all about.

In 1987, scientists noticed weird, repeating sequences of DNA in bacteria. In 2002, the abbreviation CRISPR was coined to describe the genetic oddity. By 2006, it was clear that bacteria use CRISPR to defend themselves against viruses. By 2012, scientists realized that they could modify the bacterial strategy to create a gene-editing tool. Since then, CRISPR has been used in countless laboratory studies to understand basic biology and to study whether it’s possible to correct faulty genes that cause disease. Here’s an illustration of how the technique works.

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Interview With a Scientist—Julius Lucks: Shape Seeker

While DNA acts as the hard drive of the cell, storing the instructions to make all of the proteins the cell needs to carry out its various duties, another type of genetic material, RNA, takes on a wide variety of tasks, including gene regulation, protein synthesis, and sensing of metals and metabolites. Each of these jobs is handled by a slightly different molecule of RNA. But what determines which job a certain RNA molecule is tasked with? Primarily its shape. Julius LucksLink to external web site, a biological and chemical engineer at Northwestern University, and his team study the many ways in which RNA can bend itself into new shapes and how those shapes dictate the jobs the RNA molecule can take on.

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Best Documentary: Cells Record Their Own Lives Using CRISPR

Suppose you were a police detective investigating a robbery. You’d appreciate having a stack of photographs of the crime in progress, but you’d be even happier if you had a detailed movie of the robbery. Then, you could see what happened and when. Research on cells is somewhat like this. Until recently, scientists could take snapshots of cells in action, but they had trouble recording what cells were doing over time. They were getting an incomplete picture of the events occurring in cells.

Researchers have started solving this problem by combining some old knowledge—that DNA is spectacularly good at storing information—with a popular new research tool called CRISPR. CRISPR (clustered regularly interspaced short palindromic repeats) is an immune system feature in bacteria that helps them to remember and destroy viruses that infect them. CRISPR can change DNA sequences in precise ways; and it’s programmable, meaning that researchers can tell CRISPR where to make a change on a DNA strand, and even what kind of change to make. By linking cellular events to CRISPR, researchers can make something like a movie that captures many pieces of information in the form of DNA changes that researchers can read back later. These pieces of information include timing, duration, and intensity of events, such as the turning on of a specific protein pathway or the exposure of the cell to pathogens (i.e. germs). Here, we look at some of the ways NIGMS-funded research teams and others are using CRISPR to capture these kinds of data within DNA sequences.

Left: Rectangle containing magnetic tape illustrated as a black strip wound on two spools. Closeup of the magnetic tape beneath as a blue strip with orange lines to indicate stored audio signals. Text reads: data in magnetic tape. Center: Four, white capsule-shaped bacteria, with three rows of connected shapes (black diamonds, blue and orange rectangles) beneath to illustrate stored biological signals in bacteria. Text reads: data in CRISPR tape in cells. Right: Numerous capsule-shaped bacteria in different colors, each containing a black strip wound on two spools

An audio recorder stores audio signals into a magnetic tape medium (left). Similarly, a microscopic data recorder stores biological signals into a CRISPR tape in bacteria (middle). An enormous amount of information can be stored across multiple bacterial cells (right). Credit: Wang Lab/Columbia University Medical Center.

Round and Round: mSCRIBE Creates a Continuous Recording Loop

A dark blue-green cell with textured surface containing a round, blue meter with a white dial. The dial reads a magenta ribbon of DNA and records over time the number of cellular events that occur. The cellular events are depicted by purple, green, and smaller magenta clusters moving through the cell.
MIT bioengineers, led by Timothy Lu, have devised a memory storage system illustrated here as a DNA-embedded meter that records the activity of a signaling pathway in a human cell. Credit: Timothy Lu lab, MIT.

CRISPR uses an enzyme called Cas9 like a surgical knife, to slice both strands of a cell’s DNA at precise points. A cut like this sends the cell scrambling to repair the damage. Often, the repair effort results in changes, or errors, in the repaired strand that pile up at a known rate. Timothy Lu Link to external web site and his colleagues at the Massachusetts Institute of Technology (MIT) decided to turn this cut-repair-error system into a way to record certain events inside a cell. They call their method mSCRIBE (mammalian synthetic cellular recorder integrating biological events).

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Interview with a Scientist: Jeramiah Smith on the Genomic Antics of an Ancient Vertebrate

The first known descriptions of cancer come from ancient Egypt more than 3,500 years ago. Early physicians attributed the disease to several factors, including an imbalance in the body’s humoral fluids, trauma, and parasites. Only in the past 50 years or so have we figured out that mutations in critical genes are often the trigger. The sea lamprey, a slimy, snake-like blood sucker, is proving to be an ideal tool for understanding these mutations.

The sea lamprey, often called the jawless fish, is an ancient vertebrate whose ancestor diverged from the other vertebrate lineages (fish, reptiles, birds and mammals) more than 500 million years ago. Jeramiah Smith,Link to external web site associate professor of biology at the University of Kentucky, has discovered that lamprey have two separate genomes: a complete genome specific to their reproductive cells, consisting of 99 chromosomes (humans have 23 pairs) and another genome in which about 20 percent of genes have been deleted after development. Using the lamprey model, Smith and his colleagues have learned that many of these deleted genes—such as those that initiate growth pathways—are similar to human oncogenes (i.e., cancer-causing genes).

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The Skull’s Petrous Bone and the Rise of Ancient Human DNA: Q & A with Genetic Archaeologist David Reich

A macro image of the petrous bone. 3 sections are color coded A (green), B (blue), and C (red)The human petrous bone in the skull protects the inner ear structures. Though it is one of the hardest, densest bones in the body, some portions (such as the area in orange, protecting the cochlea) are denser than others. Possibly because the petrous bone is so dense, DNA within the petrous bone is better preserved than in other bones. In some cases, scientists have extracted more than 100 times more DNA from the petrous bone than other bones, including teeth. Credit: Pinhasi et al., 2015, PLOS ONE.

For the past few decades, new evidence about ancient humans—in the form of skeletal remains, tools, and other artifacts—has trickled in, inching us closer to an understanding of how our species evolved and spread out across the planet. In just the past few years, however, knowledge of our deep past expanded significantly thanks to a series of technological breakthroughs in sequencing of ancient human genomes. This technology can be used to find genetic links among populations of human ancestors dating back hundreds of thousands of years.

In addition to advances in genomic technology, another factor is driving the explosion of new discoveries—an inch-long section of the human skull. Found near our ears, this pyramid-shaped portion of the temporal bone is nicknamed the petrous bone. The bone is very hard, possibly because it needs to protect fragile structures such as the cochlea, which translates sound into brain signals, and the semicircular canals, which help us maintain our balance. Perhaps because the petrous bone is so dense, it also is the bone in the body that best preserves DNA after a person dies. As a result, archaeologists are scrambling to study samples taken from this pyramid-shaped structure to unlock the mysteries of our species’ formative years.

Here’s a sampling of headlines declaring new findings about ancient peoples from around the globe that were based on genetic information obtained from the petrous bone (NIGMS-funded research indicated in black):

“How the introduction of farming changed the human genome” November 2015

“Fourth strand’ of European ancestry originated with hunter-gatherers isolated by Ice Age” November 2015

“Scientists sequence first ancient Irish human genomes” December 2015

“Genetic studies provide insight into ancient Britain’s diversity” January 2016

“The world’s first farmers were surprisingly diverse” June 2016

“Study reveals Asian ancestry of Pacific islanders” October 2016

“Ancient DNA solves mystery of the Canaanites, reveals the biblical people’s fate” July 2017

“Ancient DNA data fills in thousands of years of human prehistory in Africa” September 2017

“European Hunter-Gatherers Interbred With Farmers From the Near East” November 2017

“Surprise as DNA reveals new group of Native Americans: the ancient Beringians” January 2018

“Ancient DNA reveals genetic replacement despite language continuity in the South Pacific” February 2018

“Stone Age Moroccan Genomes Reveal Sub-Saharan African, Near Eastern Ancestry” March 2018

“Some early modern populations in Britain may have had dark skin” March 2018

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Genomic Gymnastics of a Single-Celled Ciliate and How It Relates to Humans

Laura Landweber
Credit: Denise Applewhite.
Laura Landweber
Grew up in: Princeton, New Jersey
Job site: Columbia University, New York City
Favorite food: Dark chocolate and dark leafy greens
Favorite music: 1940’s style big band jazz
Favorite hobby: Swing dancing
If I weren’t a scientist I would be a: Chocolatier (see “Experiments in Chocolate” sidebar at bottom of story)

One day last fall, molecular biologist Laura Landweber Link to external web site surveyed the Princeton University lab where she’d worked for 22 years. She and her team members had spent many hours that day laboriously affixing yellow Post-it notes to the laboratory equipment—microscopes, centrifuges, computers—they would bring with them to Columbia University, where Landweber had just been appointed full professor. Each Post-it specified the machinery’s location in the new lab. Items that would be left behind—glassware, chemical solutions, furniture, office supplies—were left unlabeled.

As Landweber viewed the lab, decorated with a field of sunny squares, her thoughts turned to another sorting process—the one used by her primary research subject, a microscopic organism, to sift through excess DNA following mating. Rather than using Post-it notes, the creature, a type of single-celled organism called a ciliate, uses small pieces of RNA to tag which bits of genetic material to keep and which to toss.

Landweber is particularly fond of Oxytricha trifallax, a ciliate with relatives that live in soil, ponds and oceans all over the world. The kidney-shaped cell is covered with hair-like projections called cilia that help it move around and devour bacteria and algae. Oxytricha is not only bizarre in appearance, it’s also genetically creative.

Unlike humans, whose cells are programmed to die rather than pass on genomic errors, Oxytricha cells appear to delight in genomic chaos. During sexual reproduction, the ciliate shatters the DNA in one of its two nuclei into hundreds of thousands of pieces, descrambles the DNA letters, throws most away, then recombines the rest to create a new genome.

Landweber has set out to understand how—and possibly why—Oxytricha performs these unusual genomic acrobatics. Ultimately, she hopes that learning how Oxytricha rearranges its genome can illuminate some of the events that go awry during cancer, a disease in which the genome often suffers significant reorganization and damage.

Oxytricha’s Unique Features

Oxytricha carries two separate nuclei—a macronucleus and a micronucleus. The macronucleus, by far the larger of the two, functions like a typical genome, the source of gene transcription for proteins. The tiny micronucleus only sees action occasionally, when Oxytricha reproduces sexually.

Oxytricha trifallax cells in the process of mating
Two Oxytricha trifallax cells in the process of mating. Credit, Robert Hammersmith.

What really makes Oxytricha stand out is what it does with its DNA during the rare occasions that it has sex. When food is readily available, Oxytricha procreates without a partner, like a plant grown from a cutting. But when food is scarce, or the cell is stressed, it seeks a mate. When two Oxytricha cells mate, the micronuclear genomes in each cell swap DNA, then replicate. One copy of the new hybrid micronucleus remains intact, while the other breaks its DNA into hundreds of thousands of pieces, some of which are tagged, recombined, then copied another thousand-fold to form a new macronucleus. Continue reading “Genomic Gymnastics of a Single-Celled Ciliate and How It Relates to Humans”

Interview With a Scientist: Joel Kralj, Electromicist

Every one of our thoughts, emotions, sensations, and movements arise from changes in the flow of electricity in the brain. Disruptions to the normal flow of electricity within and between cells is a hallmark of many diseases, especially neurological and cardiac diseases.

The source of electricity within nerve cells (i.e., neurons) is the separation of charge, referred to as voltage, across neuronal membranes. In the past, scientists weren’t able to identify all the molecules that control neuronal voltage. They simply lacked the tools. Now, University of Colorado biologist Joel Kralj Exit icon has developed a way to overcome this hurdle. His new technique—combining automated imaging tools and genetic manipulation of cells—is designed to measure the electrical contribution of every protein coded by every gene in the human genome. Kralj believes this technology will usher in a new field of “electromics” that will be of enormous benefit to both scientists studying biological processes and clinicians attempting to treat disease.

In 2017, Kralj won a New Innovator Award from the National Institutes of Health for his work on studying voltage in neurons. He is using the grant money to develop a new type of microscope that will be capable of measuring neuronal voltage from hundreds of cells simultaneously. He and his research team will then attempt to identify the genes that encode any of the 20,000 proteins in the human body that are involved in electrical signaling. This laborious process will involve collecting hundreds of nerve cells, genetically removing a single protein from each cell, and using the new microscope to see what happens. If the voltage within a cell is changed in any way when a specific protein is removed, the researchers can conclude that the protein is essential to electrical signaling.

In this video, Kralj discusses how he plans to use his electromics platform to study electricity-generating cells throughout the body, as well as in bacterial cells (see our companion blog post “Feeling Out Bacteria’s Sense of Touch” featuring Kralj’s research for more details).

Dr. Kralj’s work is funded in part by the NIH under grant 1DP2GM123458-01.