More Than Skin Deep

“I finished a full three years at MIT. What was nice in that last year was that I could plan out exactly what I wanted to do in my own lab. I wrote for and had my NIH grant before I arrived in Chicago. It was a really nice recipe to hit the ground running. Now, looking back, it was kind of a poised-to-succeed situation,” says Fuchs.

“We’re learning that it is the basic mechanisms that stem cells use to make and repair tissue that become hijacked in cancer.”

Since her time in the Green lab almost four decades ago, Fuchs has been hooked on decoding and unraveling the complicated biology of epidermal cells. In her own labs at the University of Chicago and now at Rockefeller University, Fuchs has used the epidermal-cell culture system to define epithelial stem cells, extending her findings to understand basic principles of multipotent cells in general. Her research has also tackled the biology of other cell types within the epidermis, identifying the progenitor cells that give rise to sweat glands and ducts and isolating hair-follicle stem cells. Fuchs’s lab was also among the first to characterize a cancer stem cell.

Here, Fuchs traces her research path from keratins to stem cells, and discusses her work ethic and her love of world travel.

Fuchs Fascinated

Bucolic Chicago. Fuchs grew up in a suburb of Chicago that at the time, in the late 1950s and 1960s, was “less suburb and more cornfields,” she says. At home, her father made furniture for the house, and her mother sewed clothing for Fuchs and her sister and also did oil painting. Her parents kept a large flower and vegetable garden during the spring and summer months. “I grew up in a very active, self-sustaining environment back in the days when we were allowed to stay out from after breakfast until it became dark outside,” says Fuchs. “My mom made us butterfly nets and sent us out to the swamps and fields.”

One-man show. Fuchs’s family lived near Argonne National Laboratory, which is funded by the US Department of Energy. Fuchs learned about how research is conducted from her father, Louis Fuchs, who was a geochemist there, working on identifying novel minerals in meteorite samples. The only mineralogist employed at Argonne, he had discovered 8 of the 13 known extraterrestrial minerals by the time he retired. “My father was well-known in the field, but was really a one-man show. He had an electron microscope and worked largely on his own,” says Fuchs.  

In pursuit of science. “The progression into science in college was natural,” says Fuchs, whose older sister, Jannon Fuchs, is now a neuroscientist at the University of North Texas. Her aunt, a University of Chicago alum, couldn’t get into medical school because she was female. “She was a feminist and encouraged my sister and me to do something meaningful with our lives.” Fuchs entered the University of Illinois in 1968 and majored in chemistry because, according to her, the university’s biology program at the time was not as strong as those in chemistry and physics. She did research while in college—including at Argonne for a summer—and enjoyed performing the experiments, but didn’t feel particularly adept at doing science.  

Scientific control. After graduating in 1972, Fuchs began graduate work at Princeton in the biochemistry department. She gravitated towards the metabolic pathways she was learning about in Gilvarg’s class and joined his lab. Fuchs worked on bacterial cell wall biosynthesis, exploring how dormant spores from Bacillus megaterium become activated and remodel their cell walls to accommodate a rapidly dividing state. “It took my entire graduate career to become comfortable with molecular biology and biochemistry,” she says. “What I gained from my advisor was the ability to carefully design a properly controlled experiment. I realized later that that this is more critical to becoming a good scientist than anything else.”

Fuchs Focuses

Strong cell biology footing. Next, Fuchs decided to study how human cells make tissues, joining Green’s laboratory at MIT in 1977. “I wanted to pick apart the cell’s biology and biochemistry and liked the idea of working with a cell-culture system,” she says. Fuchs had heard a seminar by Green, who had developed the 3T3 fibroblast cell line and was also the first to culture epithelial cells, which required a layer of irradiated “feeder” fibroblast cells in order to grow in the lab. The epithelial cells Green was studying were human keratinocytes, skin cells that make up about 90 percent of the cells of the epidermis, where they occupy the basal layer of the stratified epithelium. “He didn’t call them stem cells, but essentially that is what they were. These were cells that you could take from human skin, passage long term in culture, and induce them to make differentiated tissue,” Fuchs says. “Green basically opened up the door to the stem cell field as we know it.”

Fuchs published three Cell papers, one for each year spent at MIT. First, using an enzymatic protein cleavage reaction, she demonstrated that keratins—the abundant fibrous, structural proteins that protect epithelial cells from mechanical stresses—were likely distinct proteins coming from distinct genes rather than originating from one single protein that is cleaved posttranslationally. For the second paper, Fuchs fractionated RNA species, separated them on methylmercury gels, and showed that human keratins are indeed coded by distinct messenger RNAs. The third paper showed, for the first time, that keratins are differentially expressed not only during terminal differentiation within the epidermis but also in different epithelial tissues. “This is a concept we now take for granted, but at the time, it was a very important finding. The use of specific intermediate filament proteins like keratins to identify a particular cell type and stage of differentiation has been enormously useful to pathologists in the diagnosis of cancers and other human disease states,” explains Fuchs. “The finding also formed the foundation of our understanding of what are now more than 20 human disorders of intermediate filament genes.”

Towards independence. “It was jolting to go from physical chemistry to biochemistry and then cell biology. It took me forever to get it. There were always far too many variables in biology. In chemistry you could always solve equations but you can’t solve equations in biology. It took me my whole graduate career to feel comfortable with that notion,” Fuchs says. “And then, during my postdoc, that is when I started to realize that I didn’t have to rely upon my training or my lab to guide my research. When I needed to learn something, I could find another lab to learn it. Someone at MIT almost always had the expertise I needed to learn to move my research forward. This helped me develop skills to become interactive and to really run a project myself. So I was resourceful and productive, but I still didn’t think I was doing exceptionally well. A Cell paper didn’t really mean much to me at the time. I just thought this was a publication like any other. I was just pleased with what I was doing and what I was finding.”  

Work ethics. Fuchs started her own lab at the University of Chicago in 1980. “I pretty much knew exactly what I wanted to do when I started my lab. I didn’t have a technician or graduate student. I just started doing experiments on my own after I had cleaned up the lab and office I inherited. Two months later, the department chair came down and asked if I was ever going to hire a technician. I was so naive. I knew what I wanted to do and how to do it, and I didn’t want to take out time to interview or train anyone,” says Fuchs. “I hired the first person I interviewed and she was good, and I realized that she was really helpful. The two of us did all the work for the first year. I was very cautious about taking people on and only taking good people, and I highly recommend that route.”

Hitting the ground running. Fuchs’s lab immediately began to clone and characterize the various keratins and their genes. As her lab grew, they began doing in vitro filament assembly studies with recombinant proteins, and they engineered mutations that perturbed keratin filament assembly in a test tube and in cultured keratinocytes. Protein chemists had tried unsuccessfully for years to crystallize keratins, but remained stymied by the proteins’ propensity to self-aggregate. By obtaining the protein sequences through cloning and DNA sequencing, Fuchs overcame these hurdles. Using transgenic techniques, the lab made mice that expressed various keratin mutants to decipher their functions. Point mutations in one of the keratin genes resulted in mice with a disease akin to epidermolysis bullosa simplex (EBS), a human skin disease characterized by severe blistering. From skin biopsies obtained from such patients, her team verified that EBS, and other related skin disorders, stemmed from keratin mutations.

Fuchs Flourishes    

A big move. While still at the University of Chicago, Fuchs began to isolate and characterize the cells from skin that could make new tissue or repair wounded tissue. This included identifying the signaling pathways involved and the cellular context necessary for self-renewal. Fuchs’s team showed that Wnt is a critical signal for activating stem cells to make follicles. After packing up the lab—including three trucks filled with laboratory mice—and moving to Rockefeller University in New York in 2002, the team developed a way to fluorescently tag slow-proliferating cells by labeling a histone, marking stem cells by their unique quiescent property. “It was a clever technique, but also let us demonstrate, in transplantation assays, that these cells were behaving like stem cells,” says Fuchs. “After that, we could monitor their behavior in normal tissue formation, wound repair, and then malignant transformation.” That same year, the lab showed that these stem cells could make epidermis and hair when grafted onto the backs of nude (hairless) mice.  

A delicate balance. In 2011, Fuchs’s lab defined the stem cells that can initiate squamous cell carcinoma, a type of skin cancer, and characterized the signaling pathways that drive malignancy. “Stem cells in their niche are quiescent most of the time. What we’ve learned is that their neighboring cells dictate their behavior. So when you take stem cells out of their niche, they are faced with a new environment and they dramatically change their behavior. That notion has been really instructive in our tackling how stem cells acquire mutations that make them malignant. Malignancy involves intrinsic changes and altered signals from their new neighbors,” say Fuchs.

“Our recent papers point to a better understanding of how stem cells become malignant. What fascinates me most is the parallel of cancer stem cells—the cells that make cancer—with normal stem cells—the cells that make tissue. We’re learning that it is the basic mechanisms that stem cells use to make and repair tissue that become hijacked in cancer,” she says.

Sweating it. “What has been a difficult nut to crack has been the sweat gland stem cell. I am very curious as to why it’s only the higher primates and humans that have eccrine sweat glands that allow us to run marathons and live in extreme climates,” says Fuchs. “We would like to learn how to grow sweat glands because burn patients can be treated with epidermal cell cultures to repair their skin, but the engrafted skin never makes sweat glands, so the patients can’t properly regulate their body temperature. If we can grow sweat stem cells in culture, we might be able to help these patients.”

Travel bug. “Ever since graduate school, I’ve always worked like crazy and then taken a month off to travel. I think you have to have a well-balanced life but everyone balances their life differently. I enjoy working hard and I can’t sit still, so for me, if I am working, I can go 24–7 for months on end, but then I need a month to do something dramatically different. In graduate school I went to Mexico and Guatemala, India, Nepal, Turkey, Egypt, Greece, Panama, Bolivia, Peru, and Ecuador. I think the travel experiences I’ve had for three decades have helped me enormously in running my lab. I have an international lab and I have a real appreciation for different cultures and I think this is very helpful.” 

Greatest Hits

• Showed that keratins found in the epidermis come from distinct genes and are differentially expressed in different parts of the epidermis.  
• Identified mutations in several keratin genes responsible for five human skin diseases, including epidermolysis bullosa simplex.
• Developed a technique to label, track, and purify quiescent, slow-proliferating stem cells.
• Uncovered the pathways necessary for epithelial stem cells to differentiate into the epidermis, hair follicles, and sweat glands.
• Among the first to describe a cancer stem cell, characterizing how squamous cell carcinoma is initiated.