A long shot pays off
After others said it was impossible, Jeanne Lawrence, PhD, silenced the extra chromosome in Down syndrome in the lab
Jeanne Lawrence, PhD, works at the microscope on her lab's innovative new method to silence the extra chromosome in Down syndrome cells.
Jeanne Lawrence, PhD, is routinely described as an out-of-the-box thinker, someone who looks at the same problem others have long grappled with from an entirely new perspective—where others see the impossibilities, she said, she likes to see the possibilities. That tactic recently helped Dr. Lawrence, professor and interim chair of cell & developmental biology, prove that the extra X that’s found on chromosome 21 and is responsible for Down syndrome can be silenced, a bold endeavor that other scientists either hadn’t considered, or thought too challenging to try. Though it’s not a cure for Down syndrome, it is a step toward one day significantly diminishing the far-reaching effects of that and other chromosomal disorders.
It’s work that in some ways has deep and personal roots. Lawrence points to two early sources of her determination to help those born with disabilities. The first was a summer job at a local pool while she was in college. Asked if she’d be willing to give swimming instructions to eight adults with Down syndrome, Lawrence, who’d had no prior exposure to the disorder, agreed because, she reasoned, there was no reason not to. At the end of the summer, after she’d taught the group the basics and performed a few rescues of over-eager swimmers who’d headed for the deep end, the diminutive Lawrence met with the pool’s director, who thanked her and said of the special request, “I asked
you last because you’re the smallest. But everyone else had said no, and you said yes.”
Reaching further back, to her childhood, Lawrence recalls the second influence: Patsy Sutton, a cousin who was some 20 years her senior and had cerebral palsy. Lawrence and her family routinely drove Sutton to appointments and took her swimming and on outings.
“I never thought I’m helping someone who’s disabled,” said Lawrence. “I just did it because I enjoyed her company. But today, I always have the perspective that if I’m getting up and walking around and have all my faculties, I’m actually very lucky.”
Lawrence went to Stevens College in Columbia, Missouri, intending to teach elementary school. But uninspired by the coursework, she refocused her studies on music before discovering “the intersection of science and society, philosophy and religion” in her junior year. When the dean summoned her to his office right before graduation, she was stunned to learn that she was first in her class. The prize was a fellowship to the University of Missouri, where she enrolled in her first real science courses. That led to a master’s in human genetics and counseling from Rutgers, and a PhD in developmental biology from Brown. Wanting to stay involved in what she calls the “people angle” of science, upon arrival for her postdoctoral fellowship at UMMS, Lawrence quickly signed up to teach human genetics, later going on to direct the entire course. (Among other things, she lectured on the question of nature versus nurture, and was pleased to have a real-life test case in her own house when she gave birth to identical twin sons; she also has a third, older son.) In particular, she taught chromosomal abnormalities, bringing in patients with Down syndrome, sickle cell anemia, Huntington’s disease and their families for special sessions designed to engage students in what it means to live with a given condition. One family whose daughter has Down syndrome attended so regularly that Lawrence was inspired to advocate for the establishment of the Patient as Educator Award, naming them as the first recipients.
At the same time, Lawrence was busy in the lab, where she was studying RNA molecules directly in cells rather than extracting them, in order to fully understand their organization and behavior. To that end, she had spent three years during her first postdoctoral fellowship attempting to develop fluorescent in situ hybridization, or FISH. At the time, it was thought that fluorescence was too insensitive to detect RNA in cells. So she spent years working without a microscope, labeling her probes with radioactivity and rapidly quantifying the radioactivity of multiple cell samples hybridized with those probes, in order to speed up the process of optimizing methods for FISH.
“I look back and I think, I didn’t know that it was ever going to work!” said Lawrence of the three years she spent just studying how to make FISH more successful. Eventually, she published a quantitative analysis of in situ hybridization in Nucleic Acids Research, which in turn led to publication in several high-visibility journals. Her lab then extended the technique to examine RNA from XIST (X inactive specific transcript), a notably large gene that had been identified by Hunt Willard and Carolyn Brown in the early 1990s. While there was initial disappointment that the gene didn’t encode a protein, Lawrence and her team determined that the gene made a unique “chromosomal” RNA that, indeed, controls X inactivation in women—what Lawrence laughingly calls the “first equal opportunity.” But if XIST could silence the X chromosome voluntarily, could it also be redirected to silence a different chromosome? Some literature and studies in her own lab with Lisa Hall, PhD, assistant professor of cell & developmental biology, said that it would be possible to a degree, but no one had shown it was possible to insert XIST into a specific chromosomal site, or tested whether it would be able to silence the chromosome entirely. And if it was able to, could gene therapy control the trisomy of chromosome 21 in individuals with Down syndrome? Extrapolating from there, might scientists then be able to control the entire genome, whose various components are in a perpetual state of silencing and functioning?
The key issue unique to individuals with Down syndrome, however, is that hundreds of the genes are overrepresented, and developing gene therapy that can address a defect in a single gene has been challenge enough. Correcting an entire chromosome would seem nearly impossible. Undeterred, Lawrence and her colleagues looked to XIST. They planned to use genome editing as a sort of scissors and glue to cut and paste DNA at a specified site.
Lawrence applied for and received an Exceptional, Unconventional Research Enabling Knowledge Accelerating (EUREKA) grant from the NIH in 2008. Midway through writing the EUREKA grant, Lawrence met with Provost and School of Medicine Dean Terence R. Flotte, then newly arrived at UMMS, for an honest assessment of the project, and was relieved to get his support.
“The sheer creativity and originality of Jeanne’s ideas was what made them so appealing. If you don’t take crazy chances in research sometimes, you will never make a real breakthrough,” said Dr. Flotte, the Celia and Isaac Haidak Professor of Medical Education and executive deputy chancellor.
Like so much of science, it was not a speedy process, and Lawrence found the genetic engineering aspect daunting. She contacted Sangamo BioSciences, which had developed zinc finger nucleases that could act as scissors, but the company was skeptical that inserting a gene of XIST’s size would be possible. As this was very expensive technology, they agreed to collaborate, but required that Lawrence and her colleagues first prove it could be done, using the technology on a different chromosome, 19. This was a success, which Lawrence credits to Jun Jiang, PhD, instructor of cell & developmental biology, who had joined her laboratory and helped to push the project forward.
One development in stem cell biology, that of induced pluripotent stem (iPS) cells, was fortuitously timed. Lawrence and her team quickly recognized they could bypass the ethical issues surrounding embryonic stem cells but still take advantage of stem cells as an unparalleled resource. Lawrence also appreciated that working with a trisomic cell meant there was no possibility of ill effects from silencing a chromosome, since there was a spare. Lawrence’s lab worked to silence chromosome 21 with XIST for five years.
By April 2013, Lawrence was ready to share on a broad scale the news that attaching XIST to a trisomic chromosome 21 would, indeed, silence it into inactivity and keep it that way, and she did so at the Global Down Syndrome Foundation’s Workshop on Cognition in Down Syndrome. Shortly thereafter, the team published a paper detailing their findings in Nature. The professional response has been uniformly positive; in turn, Lawrence is quick to applaud those scientists who have been working in the field for decades, pleased to at last be able to discuss openly both the work and the next steps, which include reproduction of the experiment in a mouse model.
Still, there’s no real cure for Down syndrome on the horizon, and there may never be. So many genes are affected that it’s almost inconceivable that science could reach them in the embryonic stage. But what the research may mean is that some of the major health associated concerns—congenital heart disease, leukemia, cognitive defects and Alzheimer’s—could one day be significantly mitigated, something that many of Lawrence’s patient families have written to share their relief about. And in the short term, because it’s now possible to compare cells with a chromosome on and then switched off, there is an opportunity to look at what cell pathologies and gene pathways underlie the syndrome, and identify targets for drug therapies, including gene interactions that might be responsible for Alzheimer’s disease in the larger population.
Lawrence’s lab is now busy investigating several potential applications of this “trisomy silencing” technology. She is also pursuing the basic science implications of so-called “junk” DNA, determining whether it plays a role in XIST RNA’s ability to silence an entire genomic region, and expects to soon publish these findings.
The average lifespan of an individual with Down syndrome has already improved from the days of routine institutionalization, when a resulting failure to thrive was commonplace; today, many adults with Down syndrome enjoy some measure of independence, including holding jobs. But others, said Lawrence, exist just under that threshold, and she’s hopeful her work’s legacy will include biomedical therapies that, coupled with the existing educational therapies, will be the difference. It’s a tall order, and one that Lawrence recognizes will take time.
“I’m a big believer in the idea that if you can show the first step, things can work out,” said Lawrence. “You break through one barrier—don’t worry that you have to break through all the barriers, just break through the first, biggest one and then see what you can figure out.”