The scurfy gene: From the Mouse House to the Nobel Prize

KASE CLAPP: Hello everyone and welcome to The Sound of Science, the podcast highlighting the voices behind the breakthroughs at Oak Ridge National Laboratory.

MORGAN MCCORKLE: We're your hosts, Morgan McCorkle and-

KASE: -Kase Clapp.

MORGAN: Today we're bringing you a special Soundbite interview with one of last year's Nobel Prize winners, Mary Brunkow.

KASE: Last year's Nobel Prize in Medicine honors three scientists - Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi - for discoveries that revealed how the immune system keeps itself in check. Together, their work uncovered the gene and the cells that stop our defenses from turning on our own bodies.

MORGAN: But to really understand their discovery, we have to travel several decades back - to the late 1940s. After World War II, scientists were trying to understand the effects of radiation - how it might alter genes and impact human health.

To answer those questions, the newly established Clinton Labs - what's now Oak Ridge National Laboratory - created a research program to study radiation's impact on mammals.

KASE: Alexander Hollaender, head of the lab's Biology Division, recruited a husband-and-wife team of geneticists - William and Liane Russell - from Jackson Laboratory in Bar Harbor, Maine. Their mission: build a genetics program from scratch.

MORGAN: In a 2018 oral history interview conducted by the Atomic Heritage Foundation, Liane Russell described what they initially set out to do.

LIANE RUSSELL: The main mission of the program-to start with at least-was to determine radiation-induced mutation rates. Before that, there had been very little work done on anything except fruit flies and corn, maize. Those were the two organisms in which radiation-induced mutations had been studied. Trying to get something closer to man is why mice - that was the original prescribed mission, just to get radiation-induced mutation rates. That was just the very beginning, but it stayed to be a big mission. Over the years, the main purpose became to study the factors that altered both the quantity and quality of mutations.

KASE: Liane Russell, who continued her work at Oak Ridge for decades until her death in 2019, helped build what became a world-leading mouse genetics facility - known simply as the Mouse House.

MORGAN: It was there, in 1949, that she and her husband stumbled upon something unexpected - a fluke mutation that had nothing to do with radiation at all. Mice began appearing with scaly skin, enlarged lymph nodes, and a dramatically shortened lifespan. Here's Liane Russell again.

RUSSELL: We found a spontaneous mutation that we called scurfy, and it made a mouse look crummy, sick. To start with, Bill was just throwing these out, because he thought, "This is a sick mouse." Pretty soon, it appeared that all of them were males. It turned out to be actually the first sex-linked mutation in a mouse.

KASE: In other words, the scurfy mutation was carried on the X chromosome - which meant only the males, with just one X, showed the symptoms.

MORGAN: That chance discovery - made nearly 80 years ago - would turn out to be the foundation of Mary Brunkow's Nobel-winning research.

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KASE: Fast forward to the 1990s. The Human Genome Project was underway, sequencing was speeding up, and a new generation of scientists was eager to bridge basic biology with medicine. Fresh off a postdoctoral appointment in genetics, Mary Brunkow was one of them.

MARY BRUNKOW: I wanted to be part of an effort that ultimately would result in something that really had a direct impact on human lives. And so at the time, the field of genomics and molecular biology, molecular genetics were really coming to the fore, and it seemed like the time was really ripe for these little biotech startups, whose vision was to take advantage of those kind of new technologies to go after novel genes, which would then hopefully turn into novel drug targets and drugs.

MORGAN: She joined a young biotech company called Darwin Molecular - one of many racing to link genetics to new immune therapies. Darwin's president, David Galas, had previously led biological research for the U.S. Department of Energy and was deeply familiar with Oak Ridge and the Russells' mouse genetics program - which was still going strong.

BRUNKOW: He knew that there was this amazing resource of interesting mouse mutations and mutant stocks that had been maintained since the late 40s. And so he had already been in contact with Bill and Liane Russell asking, are there any interesting mutant mice that would serve as fodder for this new idea of using gene cloning and to feed into drug discovery.

KASE: The scurfy mouse caught their attention. Brunkow soon traveled to Oak Ridge to meet the researchers who were still maintaining the line to learn everything she could about its biology.

MORGAN: Her team then brought a few mice back to Darwin and set up their own small breeding space - literally in a closet.

BRUNKOW: We didn't have a mouse colony at the time, or a Mouse House. This was the only mouse project that we had going at that time. And so we didn't need a ton of space. We took over an unused janitor closet and purchased this caging system that you could get. It was this fully self-contained, racking system where the air system was completely self-contained. The mice were kept under really constant conditions.

KASE: With guidance from the Oak Ridge team, Brunkow's group began crossbreeding scurfy mice with a normal strain to help narrow down the mutation's location on the X chromosome.

MORGAN: At the same time, Brunkow was combing through the scientific literature and the rapidly growing Human Genome Project database - to piece together whatever clues she could find about that region of the X chromosome.

BRUNKOW: I was also trying to digest all of the other published information that was available to give us hints as to what that X chromosome region was going to look like when we finally got to the point where we could dive in at the molecular level and start analyzing specific genes.

KASE: Using new tools like artificial chromosomes, which let scientists copy and study large stretches of DNA all at once, the team mapped a region about half a million base pairs long. Inside it, they identified 20 possible targets.

BRUNKOW: And our approach then of course was just to sequence those 20 genes directly from the scurfy DNA and compare it to the wild type DNA sequence, and we finally found, like I said, like Gene #20. We found a little insertion of just two base pairs. So it was a tiny little mutation, but it was in the coding sequence of one of these novel genes.

MORGAN: That meant the normal version of the gene - what scientists call 'wild type' - worked perfectly, but the scurfy mouse carried a minor error.

KASE: That mutation turned out to be the one - a small change in a gene that would later be named FOXP3.

BRUNKOW: I mean, the day we found the mutation was glorious. You know, it was all very exciting. But then comes the real work of, you know, validating and confirming. And there was an awful lot of work after that to really demonstrate that it was truly the right gene.

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MORGAN: At first, the discovery didn't seem like a big deal to company executives. The gene encoded a DNA-binding protein - something located deep in the cell's nucleus, far from the reach of most drug molecules.

BRUNKOW: The biotech industry at the time, of course, the sort of gene-based drug development projects that had all been successful were based on targeting things that were druggable, things like growth factors or cell surface proteins. Things that you could actually access with a small molecule or an antibody type drug. We prioritized our 20 genes that we knew were in the region and then attacked them one by one to sequence and one of the reasons FOXP3 was at the bottom of the list was we suspected it was a DNA-binding protein, which is not a very good drug target because it will reside in the nucleus of the cell.

KASE: FOXP3 turned out to be a protein known as a transcription factor - one that helps turn specific genes on or off by binding to DNA and controlling how much of a gene's instructions get used inside a cell.

BRUNKOW: From a biological point of view, a transcription factor is kind of a cool thing because maybe it's the top part of a big network of effects that define a certain cell type and that has in fact turned out to be the case.

MORGAN: And it wasn't just the scurfy mice. The Darwin team was contacted by pediatric specialists from a nearby hospital who were treating patients with a rare autoimmune disease called IPEX.

KASE: When the team sequenced the children's DNA, they found mutations in FOXP3 - proof that this same gene was vital to the human immune system.

BRUNKOW: This IPEX disease in children can have a range of severity and once you understood the molecular basis of each child's mutation, you could sort of make a prediction between the effect that a certain mutation would have on the gene and how severe the effect would be.

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MORGAN: But what exactly was the mutated gene doing inside the body?

KASE: Around the same time that Brunkow was hunting for the scurfy gene, Japanese immunologist Shimon Sakaguchi proposed a radical idea. He'd found evidence for a special kind of T-cell - white blood cells that help defend the body from infection.

MORGAN: These new cells, which he called regulatory T-cells, seemed to act like peacekeepers, calming down the other T-cells when necessary. At first, many scientists were skeptical. But when Brunkow and her colleagues identified FOXP3, it provided the missing link -- by revealing the genetic blueprint for how regulatory T cells form.

KASE: Fred Ramsdell - Brunkow's colleague at Darwin - and Shimon Sakaguchi helped confirm that FOXP3 is the master switch that turns on regulatory T cells. The cells act as the body's natural brakes, stopping the immune system from attacking its own tissues.

MORGAN: And without it, those brakes fail - exactly what the Russells saw decades earlier in the scurfy mice.

BRUNKOW: So without this critical driver of regulatory T cell development, you get no brakes on the immune system, and you just get this massive autoimmune effect.

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KASE: Though Darwin Molecular eventually closed, the work didn't end there. The discovery of FOXP3 and its link to regulatory T cells became a cornerstone of immunology, unlocking new paths to treat autoimmune disease and cancer.

MORGAN: Today, that discovery is fueling a wave of clinical trials - from therapies that retrain the immune system to fight cancer…

KASE: … to treatments that quiet autoimmune diseases like Type 1 diabetes and lupus.

MORGAN: Researchers are even testing ways to boost regulatory T cells to help organ transplant patients accept new tissues.

BRUNKOW: It's been so humbling and overwhelming to really have every reason to examine very closely just exactly what our work did to kickstart a whole new field - a whole new area of understanding in immunology. I am so proud that while we weren't able to continue it ourselves and end up with things in clinical trials, the discovery has spread worldwide, and other amazing researchers have been able to take it and run with it, and I mean it doesn't get any better than that.

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KASE: Looking back, Brunkow credits foresight - and a bit of luck - for how it all came together.

MORGAN: The Russells' Mouse House may have started as an effort to understand radiation, but their careful stewardship of mutant mouse lines made discoveries like hers possible.

BRUNKOW: We are all so lucky that the whole program was under the command of such obviously, very thoughtful geneticists who saw the value in harvesting every kind of finding that could come out of this endeavor and take such good care of, maintaining these mutant stocks just with the thought that maybe in the future they would be useful.

MORGAN: From a chance mutation in a 1940s mouse colony to a Nobel Prize nearly eighty years later - it's a story of patience, persistence, and the long arc of discovery.

KASE: Thanks for listening to this Soundbite from The Sound of Science. To hear more about the Russells' work and the origins of the Mouse House, check out our episode on the life and legacy of Liane Russell.

MORGAN: Until next time!