Many researchers who search for anti-cancer drugs have labs filled with chemicals and tissue samples. Not Rommie Amaro . Her work uses computers to analyze the shape and behavior of a protein called p53. Defective versions of p53 are associated with more human cancers than any other malfunctioning protein.
Imagine if scientists could zap a single cell (or group of cells) with a pulse of light that makes the cell move, or even turns on or off the cell’s vital functions.
Scientists are working toward this goal using a technology called optogenetics. This tool draws on the power of light-sensitive molecules, called opsins and cryptochromes, which are naturally occurring molecules found in the cell membranes of a wide variety of species, from microscopic bacteria and algae to plants and humans. These light-reacting molecules change their shape or activity when they sense light, so they can be used to trigger cellular activity, such as turning on or off ion flow into the cell and other regulatory pathways. The ability to induce changes in cells has a broad range of practical applications, from enabling scientists to see how cells function to providing the basis for potential therapeutic applications for blindness, cancer, and epilepsy.
Opsins first gained a foothold in research about a decade ago when scientists began using them to study specific electrical networks in the brain. This research relied on channelrhodopsins, opsins that could be used to control the flow of charged ions into and out of the cell. Normally, when a neuron reaches a certain ion concentration, it is triggered to fire, but neuron firing can be changed by inserting opsins in the membrane. Neuroscientists figured out how to incorporate light-sensitive opsin proteins by inserting the opsin gene into the host’s DNA. The genetically encoded opsin proteins in the neuronal membranes could be turned on or off by shining light into the brain itself, using optical fibers or micro-LEDs, to switch on or off the flow of ions and neuron firing.
Since those early studies in the brain, the optogenetics field has come a long way. But the leap from brain cells to other cells has been challenging. Scientists first needed to find a way to deliver light into tissues deep in the body. And, unlike stationary brain cells, they needed a way to target cells that are on the move (such as immune cells). They also needed to develop a way to study not only cell networks but also individual cells and cell parts. The NIGMS-funded researchers highlighted below are among the scientists working to overcome these obstacles and are using optogenetics in new and inventive ways.
Yubin Zhou of Texas A&M is using optogenetics to control the way cells communicate and to study immune cell function. In one line of research, Zhou is using light to make it easier for calcium ions to enter cells. The ions carry instructions for the cell and also help tether small cellular structures (called organelles). Those inter-membrane tethers allow for the movement of proteins and lipids back and forth across the cell, and are critical for sending chemical messengers to communicate information (see illustration). When this process is disrupted, it can lead to extreme changes in cell function and even cell death. Using this technology to “switch on” normal pathways enables the scientists to better understand how such processes can be disrupted.
How “membrane-less” organelles help with key cellular functions
Scientists have long known that animal and plant cells have specialized subdivisions called organelles. These organelles are surrounded by a semi-permeable barrier, called a membrane, that both organizes the organelles and insulates them from the rest of the cell’s mix of proteins, salt, and water. This set-up helps to make cells efficient and productive, aiding in energy production and other specialized functions. But, because of their semi-permeable membranes, organelles can’t regroup and reform in response to stress or other outside changes. Cells need a rapid response team working alongside the membrane-bound organelles to meet these fluctuating needs. Until recently, who those rapid responders were and how they worked has been a mystery.
Recent research has led biologists to learn that the inside of a cell or an organelle is not just a lot of different molecules dissolved in water. Instead, we now know that cells contain many pockets of liquid droplets (one type of liquid surrounded by a liquid of different density) with specialized composition and function that are not surrounded by membranes. Because these “membrane-less organelles” are not confined, they can rapidly come together in response to chemical signals, such as those that indicate stress, and equally rapidly fall apart when they are no longer needed, or when the cell is about to divide. This enables membrane-less organelles to be “rapid responders.” They can have complex, multilayered structures that help them to perform many critical cell functions with multiple steps, just like membrane-bound organelles. Scientists even suspect that the way these organelles form as droplets may shed light on how life on Earth first took shape (see sidebar “Could This Be How Life First Took Shape?” at bottom of page).
The Many Membrane-less Organelles
Scientists have identified more than a dozen membrane-less organelles at work in mammalian cells. Several kinds found inside the nucleus—including nuclear speckles, paraspeckles, and Cajal bodies—help with cell growth, stress response, the metabolizing (breaking down) of RNA, and the control of gene expression—the process by which information in a gene is used in the synthesis of a protein. Out in the cytoplasm, P-bodies, germ granules, and stress granules are membrane-less organelles that are involved in metabolizing or protecting messenger RNA (mRNA), controlling which mRNAs are made into proteins, and in maintaining balance, or homeostasis, of the cell’s overall health.
The nucleolus, located inside the nucleus, is probably the largest of the membrane-less organelles. It acts as a factory to assemble ribosomes, the giant molecular machines that “translate” messenger RNAs to make all cellular proteins. Continue reading
It’s back-to-school time. That means learning lots of new facts and figures. In science, terms tend to be several syllables, sometimes with a Latin word thrown into the mix. As a result, many are referred to by their acronyms, such as DNA—short for deoxyribonucleic acid. This makes them easier both to remember and to say.
Researcher Mark Howarth of Oxford University, has taken this a step further. Searching through information stored in the NIGMS-funded Protein Data Bank , he curated a 3-D protein alphabet. It’s a set of 26 protein crystal structures that look like they were fashioned from bits of rainbow-colored curly ribbon. This 3-D alphabet helps us see what different protein strands look like, and explains terms and concepts relating to protein structure and function.
Proteins are molecules that play important roles in virtually every activity in the body. They form hair and fingernails, carry oxygen in the blood, enable muscle movement and much more. Although proteins are made of long strands of small molecules called amino acids, they do not remain as a straight chain. Some proteins are composed of multiple amino acid strands that wind together in the completed protein. The strands twist, bend and fold into a specific shape, and the protein’s structure enables it to perform its task. For instance, the “Y” shape of antibodies helps these immune system proteins bind to foreign molecules such as bacteria or viruses while also drawing in other immune system molecules. Continue reading
Like a successful business networker, a cell’s endoplasmic reticulum (ER) is the structure that reaches out—quite literally—to form connections with many different parts of a cell. In several important ways, the ER enables those other parts, or organelles, to do their jobs. Exciting new images of this key member of the cellular workforce may clarify how it performs its roles. Such knowledge will also help studies of motor neuron and other disorders, such as amyotrophic lateral sclerosis (ALS), that are associated with abnormalities in ER functioning.
Structure Follows Function
The ER is a continuous membrane that extends like a net from the envelope of the nucleus outward to the cell membrane. Tiny RNA- and protein-laden particles called ribosomes sit on its surface in some places, translating genetic code from the nucleus into amino acid chains. The chains then get folded inside the ER into their three-dimensional protein structures and delivered to the ER membrane or to other organelles to start their work. The ER is also the site where lipids—essential elements of the membranes within and surrounding a cell—are made. The ER interacts with the cytoskeleton—a network of protein fibers that gives the cell its shape—when a cell divides, moves or changes shape. Further, the ER stores calcium ions in cells, which are vital for signaling and other work.
To do so many jobs, the ER needs a flexible structure that can adapt quickly in response to changing situations. It also needs a lot of surface area where lipids and proteins can be made and stored. Scientists have thought that ER structure combined nets of tubules, or small tubes, with areas of membrane sheets. However, recent NIGMS PRAT (Postdoctoral Research Associate; see side bar) fellow Aubrey Weigel, working with her mentor and former PRAT fellow Jennifer Lippincott-Schwartz of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (currently at the Howard Hughes Medical Institute in Virginia) and colleagues, including Nobel laureate Eric Betzig, wondered whether limitations in existing imaging technologies were hiding a better answer to how the ER meets its surface-area structural needs in the periphery, the portion of the cell not immediately surrounding the nucleus. Continue reading
This heart-shaped image shows two mouse skin cancer cells connected to each other with actin, a protein that is part of the cellular skeleton. Researchers use mouse cells like these to tease out the molecular methods that cancer uses to invade new tissues in the body. It turns out that actin plays an essential role.
Cells can move as a collective, or independently. Movement of an individual cell requires a series of carefully controlled steps. Among them, a cell must break contacts with its neighbor cells and change its connections to the proteins and fibers around it. In addition, it must sense and follow a chemical path through the tissue it lies in. To do this, a cell changes shape, molding its membrane into flaps or feet called protrusions reaching in the direction it is traveling. Actin, among a variety of other molecules, is involved in all of these steps, but especially the shape change, when it gathers inside the cell membrane to help form the protrusions. Continue reading
Have you ever collected coins, cards, toy trains, stuffed animals? Did you feel the need to complete the set? If so, then you may be a completist. A completist will go to great lengths to acquire a complete set of something.
Scientists can also be completists who are inspired to identify and catalog every object in a particular field to further our understanding of it. For example, a comprehensive parts list of the human body—and of other organisms that are important in biomedical research—could aid in the development of novel treatments for diseases in the same way that a parts list for a car enables auto mechanics to build or repair a vehicle.
More than 15 years ago, scientists figured out how to catalog every gene in the human body. In the years since, rapid advances in technology and computational tools have allowed researchers to begin to categorize numerous aspects of the biological world. There’s actually a special way to name these collections: Add “ome” to the end of the class of objects being compiled. So, the complete set of genes in the body is called the “genome,” and the complete set of proteins is called the “proteome.”
Below are three -omes that NIH-funded scientists work with to understand human health.
The genome is the original -ome. In 1976, Belgium scientists identified all 3,569 DNA bases—the As, Cs, Gs and Ts that make up DNA’s code—in the genes of bacteriophage MS2, immortalizing this bacteria-infecting virus as possessing the first fully sequenced genome.
Over the next two decades, a small handful of additional genomes from other microorganisms followed. The first animal genome was completed in 1998. Just 5 years later, scientists identified all 3.2 billion DNA bases in the human genome, representing the work of more than 1,000 researchers from six countries over a period of 13 years. Continue reading
Scientists have identified a new family of proteins that, like the targets of penicillin, help bacteria build their cell walls. The finding might reveal a new strategy for treating a range of bacterial diseases.
The protein family is nicknamed SEDS, because its members help control the shape, elongation, division and spore formation of bacterial cells. Now researchers have proof that SEDS proteins also play a role in constructing cell walls. This image shows the movement of a molecular machine that contains a SEDS protein as it constructs hoops of bacterial cell wall material.
Any molecule involved in building or maintaining cell walls is of immediate interest as a possible target for antibiotic drugs. That’s because animals, including humans, don’t have cell walls—we have cell membranes instead. So disabling cell walls, which bacteria need to survive, is a good way to kill bacteria without harming patients.
This strategy has worked for the first antibiotic drug, penicillin (and its many derivatives), for some 75 years. Now, many strains of bacteria have evolved to resist penicillins—and other antibiotics—making the drugs less effective.
According to the Centers for Disease Control and Prevention, drug-resistant strains of bacteria infect at least 2 million people, killing more than 20,000 of them in the U.S. every year. Identifying potential new drug targets, like SEDS proteins, is part of a multi-faceted approach to combating drug-resistant bacteria.
If you’ve ever visited an aquarium or snorkeled along a coral reef, you’ve witnessed the dazzling colors and patterns on tropical fish. The iridescent stripes and dots come from pigment cells, which also tint skin, hair and eyes in all kinds of animals, including humans. Typically, bright colors help attract mates, while dull ones provide camouflage. In humans, pigment helps protect skin from DNA-damaging UV light.
Researchers study cellular hues not only to decipher how they color our world, but also to understand skin cancers that originate from pigment cells. Some of these researchers work their way back, developmentally speaking, to focus on the type of cell, known as a neural crest cell, that is the precursor of pigment cells.
Present at the earliest stages of development, neural crest cells migrate throughout an embryo and transform into many different types of cells and tissues, including nerve cells, cartilage, bone and skin. The images here, from research on neural crest cells in fish and salamanders, showcase the beauty and versatility of pigment cells in nature’s palette.
Hard labor might be the very thing we try to avoid on Labor Day. But our cells and their components don’t have the luxury of taking a day off. Their non-stop work is what keeps us going and healthy.
Scientists often compare cells with small factories. Just like a factory, a cell contains specialized compartments and machines—including organelles and other structures—that each play their own roles in getting the job done. In the vignettes below, we give a shout out to some of these tireless cellular workers.