PROFILE Profile of Philip Hieter PROFILE Paul Gabrielsen, Science Writer To bakers, yeast is important for leavening dough. To geneticist Philip Hieter, yeast can help unravel human disease. Hieter, a professor at the University of British Columbia’s Michael Smith Laboratories and member of the National Academy of Sciences, believes that model organisms, such as yeast, represent the future of genetics, as discoveries made using such organisms are increasingly linked to human disorders. Hieter, born in 1952, grew up in Garden City, New York, with two older brothers and an older sister. As an undergraduate at The Johns Hopkins University in the early 1970s, Hieter worked in the laboratory of Carl Levy, who worked to isolate ribonuclease en- zymes from soil in an early effort at RNA sequencing. A year after graduating, Hieter attended a semi- nar given by Philip Leder, a molecular biologist at the National Institutes of Health in Bethesda, Maryland. Leder and his colleagues had just cloned mouse antibody genes using bacteriophage cloning vectors, and were studying the phenomenon of genetic recom- bination that endows the immune system with a rich array of antibodies. “The talk blew my mind,” Hieter says. Inspired, Hieter arranged to work as a graduate student in Leder’s laboratory. Mentored by postdoc- “ ” toral scholar John Seidman ( a wizard, Hieter says), Philip Hieter. Image courtesy of Philip Hieter. Hieter cloned the κ and λ light-chain genes that en- code human antibodies. “Cloning the first gene took “ forever,” Hieter says, but once he cloned the κ gene native, he was impressed with his new setting. Stanford ” “ (1), the λ gene soon followed (2). Hieter, Seidman, and looked like a country club, he says. Everyone seems to ” immunologist Stan Korsmeyer worked together to in- have a smile on their face all the time. Hieter found vestigate the nature of B-cell leukemias, blood can- himself in the company of Nobel laureates such as Paul cers that affect immune system cells (3). The work Berg and Arthur Kornberg, and mingling with their grad- led to Hieter’s doctoral dissertation (4) and the 1981 uate students in shared laboratories. “The weather was Council of Graduate Schools/University Microfilms In- amazing, but the science was incredible,” Hieter says. ternational Dissertation Prize. Hieter intended to continue working on mammalian About a year before Hieter’s graduation, Leder cells, but soon discovered that the simple yeast genome suggested that he start exploring options for a post- provided a good model system for eukaryotic cells. He doctoral fellowship. Hieter talked to NIH colleagues, also discovered that his own training in bacterial genetics and learned of Ronald Davis at Stanford University. Davis was almost entirely lacking, unlike other postdoctoral had been developing yeast as a model organism for scholars. His peers helped him get up to speed. “Isaw genetic studies, and had developed techniques for for the first time the power of genetics,” Hieter says. inserting yeast genes into Escherichia coli bacteria (5), allowing for DNA transformation markers and gene re- Chromosomal Elements placement in yeast. Interested in chromosomal elements such as centro- Hieter moved to Stanford, California, in 1982 to meres, which are structures that facilitate the segre- begin his postdoctoral fellowship. As an East Coast gation of chromosomes at mitosis, and origins of This is a Profile of a recently elected member of the National Academy of Sciences to accompany the member’s Inaugural Article on page 9967 in issue 36 of volume 113. www.pnas.org/cgi/doi/10.1073/pnas.1616437113 PNAS | November 8, 2016 | vol. 113 | no. 45 | 12607–12609 Downloaded by guest on September 26, 2021 replication, DNA sequences that initiate genome Focus on Cancer replication, Hieter developed a visual assay (6) for Over the past decade, Hieter and his group have determining the stability of yeast chromosomes. He translated the lessons learned from the yeast model also cloned and sequenced yeast centromeres (7), laying system into discoveries relevant to human cancer. the foundation for his later work as an independent “How do you find candidate genes for any human researcher. disease?” he asks. “If you know the biology of the Hieter met regularly with Nobel laureate Leland human disease, you can guess a pathway and then go Hartwell, who was on sabbatical at Stanford. Hartwell to the model organism and define all the genes in that had discovered the genes responsible for regulating pathway. You then can ask directly: Are the corre- the cell-division cycle in yeast (8). “We would have sponding human genes mutated in patients or not?” talks sitting around fountains at the Stanford Medical The disease that most chromosome stability re- Center,” Hieter says. “I was amazed by the beauty of searchers were focusing on was cancer. Tumor cells his work.” often have altered numbers of chromosomes, sug- Midway through his fellowship at Stanford, Hieter gesting that some cancers may harbor mutations in received a call from Johns Hopkins. The Molecular chromosome separation processes. Since moving to Biology and Genetics Department was hiring five new the University of British Columbia in 1997, Hieter has faculty members, and invited Hieter to apply. Hieter focused on chromosome stability genes, and his group hadn’t expected to be in the job market so early, but systematically identified in yeast around 700 genes found himself drawn back to Johns Hopkins. “The responsible for maintaining genome stability (17). In scientific atmosphere of the department was excit- a collaboration with Hieter, cancer researcher Bert ing,” he says. Vogelstein used the list of yeast genes to identify Hieter continued his work on chromosome stabil- mutations in colon cancer cells in the corresponding ity, introducing an artificial chromosome into yeast (9) human genes in a painstaking gene-resequencing pro- and then testing mutations to see what genes affected cess. They found a set of cohesin genes consistently the segregation of chromosomes during mitosis. In mutated in tumor cells (18). ’ 1990, Hieter s group published a collection of 138 Synthetic Lethality mutants, defining about 50 genes that caused mis- Hieter has been using a concept called “synthetic le- segregation of chromosomes (10). Hieter further thality” to use yeast genetics to identify drug targets identified genes that encoded proteins for the kinet- for human cancers. Synthetic lethality holds that pairs ochore (11), a structure to which spindles attach to of mutations exist in cells that, individually, have little separate chromatids during mitosis. He also explored or no impact on cell function but are fatal together. the genes that arrested the cell cycle after the chro- Synthetic lethality helps identify related genes be- mosomes had been replicated but before they initi- cause searching for genes synthetically lethal with a ated segregation into daughter cells (12). Hieter and kinetochore mutant likely leads to other kinetochore his group found that the cell-division cycle mutants genes. The process can also generate highly specific they had been studying were subunits of a mechanism drug targets. “If the reference mutation is a cancer called the anaphase promoting complex (13). When somatic mutation and the disruption of the second cells detect that chromosomes have successfully gene specifically kills a cell carrying this mutation but aligned during the metaphase of mitosis, the chemical not a cell with the normal gene, it’s a perfect drug brake on anaphase promoting complex is released, target,” Hieter says. Expanding the concept further, allowing chromosome separation and the anaphase Hieter has identified highly conserved networks (19) of “ ’ ” stage of mitosis to proceed. It s a checkpoint, Hieter genes in mammalian cells that can be knocked out “ says, a mechanism for cells ensuring that metaphase through several approaches. ” is complete before you start anaphase. In 2009, Hieter attended a meeting of the American In 1992, Hieter tasked a graduate student with Society of Human Genetics. One presentation de- cloning the human versions of the genes he had scribed an effort to identify the gene responsible for identified as crucial cell-division cycle mutants in a rare disease by directly comparing the genomes “ yeast. We started to clone human orthologs of genes of four patients. A subsequent presentation by ge- we were studying and map them to human chromo- neticist David Altshuler expounded on the problem in somes (14), and then hopefully make a link to human identifying human disease genes. Altshuler had also disease gene mutations,” he says. A collaboration been looking at large cohorts of patients to identify with Francis Collins and Yossi Shiloh aimed to gain genetic variants that were possibly causative of dis- insights into ataxia telangiectasia mutated gene ease. “His point was that finding the gene is just the function immediately after it was positionally cloned, beginning,” Hieter says. “It’s not the end of the story.” by studying the yeast ortholog (15). Hieter expanded The next task, Altshuler argued, is understanding the this concept to a community-wide resource to link biological processes associated with the disease gene’s human and yeast geneticists, by creating a database function. “The way it almost always works is there’s that cross-referenced the human disease gene genetic someone who’s already working on the function of the map with the biology of yeast genes being studied by gene in a model system,” Hieter says. “I had a big smile yeast researchers (16). on my face.” 12608 | www.pnas.org/cgi/doi/10.1073/pnas.1616437113 Gabrielsen Downloaded by guest on September 26, 2021 Amid the rapid development in 2010 of next- genes in yeast that, when overexpressed, lead to generation sequencing, which dramatically lowered chromosome instability. Comparing those genes the cost of sequencing genomes, scientists began with human counterparts, the team found two hu- identifying rare disease genes, with Canadian scien- man genes that, when overexpressed, destabilized tists identifying around 200 genes over a four-year pe- chromosomes.