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by Monica Coenraads
Variations in our genome are what make us unique. It’s also what predisposes or protects us from disease. For example, you may know people who eat high fat diets and yet have low cholesterol or people who, although they have never smoked, succumb to lung cancer, like Christopher Reeve’s wife, Dana.
I’ve had the opportunity to meet girls with MECP2 mutations and normal X chromosome inactivation that are too high functioning to be diagnosed clinically with Rett Syndrome. These are girls who may walk, run, speak, write, draw, and in some rare instances even speak multiple languages and play an instrument. So what is protecting these individuals from having full-blown Rett? You guessed it: modifier genes.
Those of you familiar with RSRT’s efforts know that we have been funding a project in the lab of Monica Justice aimed at identifying protective modifiers in mice. This past summer the Justice lab published the first modifier that suggests that statins (drugs that lower cholesterol) may be treatment options for Rett. More modifiers are likely to follow.
In the last few years a number of factors have coalesced to make the hunt for modifiers possible in people: 1) the identification of a growing number of individuals with MECP2 mutations who are too high functioning to fit the criteria for a clinical diagnosis of Rett 2) dropping costs for exome sequencing 3) improved bioinformatics which allow for better analysis and interpretation of the vast quantify of data generated from sequencing.
In light of these developments RSRT has awarded $314,000 to Jeffrey Neul at Baylor College of Medicine to sequence the exomes (the protein producing portion of the genome) of high-functioning kids/adults in the hopes that some common variables may point to modifiers which can then become drug targets.
Importantly, the sequencing and phenotypic data will be a valuable resource as it will be deposited into the National Database for Autism Research and available to the scientific community.
We need the Rett community’s help to identify high-functioning individuals who Dr. Neul may not be aware of.
If you think your child may qualify please contact me at email@example.com
Watch the interview below with Dr. Neul to learn more about this project.
It seems that cholesterol and the brain is becoming a hot field. Following up on the RSRT-funded results of the Justice lab comes an intriguing (and unpublished) study highlighted by the Simons Foundation.
New autism gene plays key role in cholesterol synthesis
Mutations in a gene that plays a role in producing cholesterol in the body increase the risk for autism, pointing the way toward therapies for some people with the disorder. The research was presented in a poster Tuesday at the Autism Consortium’s 2013 Research Symposium.
Mutations in the gene, DHCR24, are known to result in a severe metabolic disease linked to cholesterol. The gene’s newly discovered role in autism suggests that statins, drugs that lower cholesterol levels, may treat symptoms of autism.
“The potential is exciting,” says Timothy Yu, a neurologist at Massachusetts General Hospital and a researcher at the Broad Institute of the Massachusetts Institute of Technology and Harvard University in Cambridge, Massachusetts.
“If you can find these kids who are swimming around in an otherwise generic autism pool and figure out a way to treat them appropriately, then you actually have the possibility of therapy.”
The researchers screened 2,000 families that have at least one child with autism to identify rare recessive gene variants for the disorder. In one family, they found that a girl diagnosed with pervasive developmental disorder-not otherwise specified and two boys diagnosed with intellectual disability and autism had all inherited two copies of the mutation, one from each parent.
“The gene is involved with the cholesterol synthesis pathway, so it started us thinking about the pathway’s role in autism and intellectual disability,” says Elaine Lim, a graduate student in Mark Daly’s lab at Harvard who presented the research.
Rett Syndrome is a spectrum disorder with a broad range of symptom severity. Some girls can run, have some use of their hands and can speak in short sentences while others cannot even sit or manage to hold their head up. One reason for this variation is the child’s own unique genetic make-up – in other words, variations in other genes that impact the severity of the Rett mutation. Identification of modifier genes has therefore been a critical component of RSRT’s research program as the modifiers may provide alternate pathways to target.
This hypothesis has now been supported in a major study that could lead to treatments for girls and women with Rett Syndrome. Today the journal Nature Genetics publishes data on the first reported modifier, called Sqle, an enzyme involved in the cholesterol pathway.
The research was undertaken by Monica Justice, PhD, of Baylor College of Medicine, with a $1.5 million investment from RSRT. Dr. Justice tested statins (cholesterol-lowering drugs) on Rett mice models with encouraging results. A human clinical trial is now being planned.
RSRT is committed to seeing this project through to completion as many more modifiers, and therefore druggable pathways, are likely to be found. We thank all of our generous supporters and parent organizations who make this important work possible, in particular our funding partners, Rett Syndrome Research Trust UK and the Rett Syndrome Research & Treatment Foundation.
Below are some resources to help you understand today’s announcement.
by Monica Coenraads
For almost 15 years now, I’ve been immersed in the science behind Rett Syndrome. As Executive Director of RSRT I understand that the work is methodical, that good research takes time, that breakthroughs often come after many tiny, incremental steps. And yet, as a mother witnessing my 16-year-old daughter deteriorate a little more each year, I feel a great urgency to push the research harder and faster. All families with intimate, daily experiences of Rett Syndrome’s harsh rule know the longing for their children to be free and well. RSRT is one-hundred-per-cent focused on that ultimate goal – and that’s what guides our choices about where to invest not just our hard-won funds but our hopes and dreams.
2012 gave us reason to be hopeful. We are grateful for the active engagement of our trustees, the unwavering commitment of the families who fundraise for us and the generous contribution of a wide range of people who give their time and talents freely to help us achieve our goal. We wouldn’t be where we are without the unique global partnerships that we enjoy with Rett Syndrome Research Trust UK and the Rett Syndrome Research & Treatment Foundation (Israel), and with national organizations such as GP2C, Kate Foundation, RMRA. Together you have produced an investment in science that will create a better future for our children.
But that future won’t just happen. Before Rett entered my life, I had never given much thought to the drug development process. Like most people, I assumed that academic scientists, industry and government worked together seamlessly to discover effective therapies for the horrible ailments that afflict us. Nothing could be further from the truth.
There is no “Department of Cures.” Laboratory breakthroughs don’t naturally bubble up and become drugs. The reality is that progress must be relentlessly driven, managed, nurtured and prodded, not to mention funded. It’s a messy, difficult and expensive process that can be slowed and derailed by a multitude of hurdles.
Disease-specific organizations such as RSRT cannot afford to be spectators, passively reviewing proposals and granting money. It is incumbent on us to set the research agenda and to facilitate its execution while staying nimble and vigilant to new opportunities.
Two such opportunities would not currently exist without RSRT: reactivating the silent MECP2 on the inactive X chromosome, and gene modifiers. Following the 2007 reversal, RSRT carefully evaluated the state of Rett research and made the decision to champion these explorations before others had even realized they were, in fact, promising approaches.
Will they lead to a cure? Ongoing research and clinical trials will tell. But in the meantime, RSRT will continue to encourage and support the research that holds the greatest promise to truly change our daughter’s lives. For we have the most to win if we succeed, and the most to lose if we fail.
There is no mystery about why a girl suffers from Rett Syndrome. The cause is that mutated copy of the MECP2 gene inhabiting her every cell. But since MECP2 is on the X chromosome and all females have two X’s, beside each mutated gene rests a healthy but silenced twin. What if we could replace the flawed gene with its perfect counterpart?
That’s the question Ben Philpot of the University of North Carolina at Chapel Hill has asked. RSRT has awarded Philpot, Bryan Roth and Terry Magnuson $2.2 million to answer it.
Philpot’s recent paper in Nature describes successful reactivation of the silenced gene in Angelman Syndrome, demonstrating that replacement is possible.
Joining Philpot and Roth in this effort is Terry Magnusson, a world-renowned leader in X-inactivation. The award will fund a team of three full-time post-docs and two technicians.
The goals of the 3-year project include:
- Screening of 24,000 compounds
- Performing whole genome analyses to test for drug specificity to help predict potential side effects (e.g. what other genes might be affected by the drug)
- Identifying the mechanism of MECP2 unsilencing, which will allow the prediction and design of additional therapeutic targets
- Optimizing drug efficacy through medicinal chemistry (e.g. by designing drugs to maximize transit through the blood-brain-barrier while minimizing off-target effects)
- Advancing lead candidates into preclinical trials. The project will be milestone-driven, with a set of pre-established deliverables. This will allow us to monitor progress utilizing a team of advisors with relevant expertise.
Along with activating the silent MECP2, RSRT has championed a second exciting approach.
In her Baylor College of Medicine laboratory, Monica Justice set out to identify modifier genes – altered genes able to dampen the ill effects of an MECP2 mutation.
The common belief has been that these genes would be hard to find. The reality? With the screen just 15% complete, Justice has already found five. What she is seeing in mice implies that Rett-like symptoms are unstable, and consequently easier to revert to a normal state than anyone had suspected.
None of the modifier genes can suppress the disease entirely, but each reduces a subset of Rett-like symptoms. While we had originally thought that the modifiers were specific to the central nervous system, it turns out they may operate elsewhere in the body. At least one of the modifiers suggests an alternative therapeutic target, using drugs already FDA-approved. With RSRT funding Justice is now testing the drugs in mice and has a manuscript currently under review. A clinical trial is being explored.
At RSRT we’re excited about will happen once the screen is completed. Justice is likely to find many more modifiers, some of which may point to tractable pathways. In support of this goal, RSRT has committed an additional $800K to the Justice lab, bringing its total commitment to the modifier screen to $1.5 million. This funding should provide sufficient resources to allow Dr. Justice to reach the 50 percent mark in the screen within two years – at which point she will propose a plan to us for completing the project. Many more modifiers await discovery. Further surprises are likely in store.
We have also awarded funding of $720K to the lab of Jonathan Kipnis at the University of Virginia. Kipnis and colleagues hope to gain better understanding of the immune system’s involvement in Rett by analyzing patient blood. The hope is that immune-based therapies can be developed.
Previous work from the Kipnis lab suggested that bone marrow transplants could be beneficial. Before proceeding to clinical trials with a procedure that is extremely serious and risky, RSRT committed funding in 2012 for independent corroboration of these findings.
We are also supporting Huda Zoghbi’s work to explore whether symptoms of the MECP2 Duplication Syndrome can be reversed once the protein level is normalized. $236K was awarded to this project via the MECP2 Duplication Syndrome Fund through the fundraising efforts of the duplication/triplication families.
RSRT is supporting work at John Bissonnette’s lab at OHSU (Oregon Health & Science University) to explore serotonin 1a agonists for their ability to reduce apneas, and Andrew Pieper’s lab at UTSW (University of Texas – Southwestern) for ongoing drug screening.
Please join me in wishing all of our scientists Godspeed. I look forward to keeping you apprised of their progress. One last heartfelt thank you to everyone who raises research funds for RSRT. These projects are your money and your effort at work.
Photo credit: Kevin Coloton
By Monica Coenraads
Last week the trustees of RSRT voted to award continued funding to Monica Justice of Baylor College of Medicine. Dr. Justice is a mouse geneticist (yes…there really is such a thing) who is spearheading one of the most unique projects in the Rett research arena today. For background information please read the September 2009 blog interview with Dr. Justice.
This project is a mammoth undertaking – the kind that requires a certain sense of fearlessness on the part of the investigator (and the funding agency). The risks are high but are in line with the potential rewards.
I feel a certain sense of attachment to this particular project as I was present when the idea was first suggested. At the time I was the Director of Research at the Rett Syndrome Research Foundation (RSRF) and I organized the annual Rett Syndrome Symposiums that spanned three days at the end of every June. At the 2006 meeting I cajoled two dozen of the brightest and most creative scientists to join me for an early morning, pre-meeting gathering I called the “knowledge gap meeting”. I posed the following challenge: develop a prioritized list of high-impact experiments that no one was currently undertaking and that was unlikely to be funded by traditional agencies. After a two-hour discussion the group delivered their top contender: a modifier screen to identify genes that suppress the effects of an MECP2 mutation.
My next task was to find the best possible person to undertake the screen and talk them into taking it on. I organized a Rett workshop a few months later at a “Mouse Genetics Meeting” (yes…they have those) in Charleston, SC, which attracted a number of candidates. Bottom line – I courted Dr. Justice and she enthusiastically agreed to pursue the project.
Fast-forward almost five years and I’m delighted that the project is thriving and yielding a wealth of information. I recently caught up with Dr. Justice to discuss how the project is faring.
MC: Dr. Justice, thank you for taking time away from your work to bring our readers up to date on your fascinating project. Please tell us how things are going.
MJ: My pleasure, Monica. I want to start by saying that this project would never have been funded by the NIH [editor’s note: National Institutes of Health] nor would I have proposed this to your foundation, had you not approached me about it. I knew little about Rett Syndrome when I started this project.
MC: Tell us a bit about modifiers. Do you think they exist for every disease?
MJ: I think that most diseases can be influenced by mutations but I don’t think every disease necessarily has modifiers.
MC: Do you have a sense of how many screens like yours are ongoing right now?
MJ: I know of only a few in the mouse.
MC: Do you know of any screens that have yielded modifiers that suggest a drug for the particular disease?
MJ: That’s a great question, Monica. I do not. The goal of most of the modifier screens is not to identify drugs but rather to understand some developmental or biochemical pathway. I think with our screen we are learning a lot about the biology of the pathway, but our hope is to find a drug-targetable pathway.
MC: Can you summarize the progress and the ups and downs of the project?
MJ: At the inception of the project we encountered several problems. We really had no idea that the Mecp2 mutant females would be such poor breeders. We tried all sorts of tricks to improve their breeding capacity, because we needed a lot of them to do the screen, and nothing worked. We kept at it, though, just with basic mouse breeding, and eventually got up to speed. Also, in the beginning we had some communication issues within the lab. I’m not sure we were expecting quite as many modifiers as we found. But we then developed a system, and that system worked very well; then things started moving along beautifully. I also realized early on that I needed to participate in a very hands-on way with this project.
As we isolated each modifier line, we realized that each one was different: that is, none suppressed the disease entirely, but each modifier line appeared to suppress a subset of Rett symptoms. Even so, each line allowed the mice to live longer, function better and be healthier. However some of them developed other symptoms, such as inflammation and susceptibility to infection, which could also shorten their lifespan. So, we worked with our veterinarians who helped us decide how to treat these mice. For example, we found that putting them on antibiotics worked extremely well.
And so, there were some unforeseen glitches in the beginning that are moving very smoothly now. We have isolated five modifier lines. We have put the screen on hold for now and are concentrating on understanding these five modifier lines. We have identified three suppressor genes so far and have candidates for the other two. We feel that the screen and the gene identification have gone extremely well. Each of the modifiers has a different phenotype in that they rescue different symptoms, and we find that each modifier locus is affecting a different gene. For example, in one line that we named “Romeo,” the suppressor delays the onset of Rett-like symptoms, and the mice have no inflammatory lesions, but eventually, the mice succumb with symptoms. Therefore, the onset of neurological symptoms is later in their life, making their lifespan longer. Another line, “Henry” develops almost no Rett-like symptoms, and lives nearly a full long life, with only a few mild inflammatory skin lesions late in life. Another line, “Cletus”, rescues some of the neurological symptoms so the mice live longer, but the long-lived mice have severe inflammatory lesions, even early in life. Remember that each of these lines carries the Mecp2 (Bird) null allele, along with a second site mutation that alleviates its symptoms.
MC: It’s possible to figure out statistically how many mice you have to go through so that you’ve saturated the genome – in other words, ensure that you have a mutation in every gene. What percentage of the genome has your screen hit so far?
MJ: I think we are between ten and twenty percent of the way through.
MC: So there is a way to go.
MJ: Based on our work thus far we could find another 25 modifiers.
MC: The ideal situation is that the suppressors you find are in pathways that are somewhat known and, ideally, for which there are already drugs associated. But you also have to figure out just how the suppressor inhibits the ill effects of having an MeCP2 mutation.
MJ: Yes, there are many steps that we have to take after we find a modifier gene, to understand what’s going on.
MC: One of the surprising things that have already come out of your screen is the mere fact that MeCP2 has so many modifiers. Why do you think that is the case?
MJ: My hypothesis is that the biological system in Rett is sort of poised on the edge, and it’s not so detrimental that it, for instance, causes death immediately. It’s very easy to tip the scale toward a little bit better—– or a little bit worse. And my feeling after doing the screens is that MeCP2 creates that kind of situation in the cells, that they’re poised to go one direction or another pretty easily.
MC: Your hypothesis suggests that there could be lots of things that improve Rett symptoms.
MJ: Absolutely. And maybe combining them will provide an amazing improvement.
MC: What is your time frame for restarting the screen?
MJ: I’m usually an optimist about time; my hope would be that, within a year, we could start the screen again.
MC: One of my favorite things about the screen is that it is completely unbiased. Preconceptions and favored hypothesis don’t play a role here. The animal tells you what is important and you simply go where the data leads you. I find that very reassuring.
MJ: I completely agree. Often, we have been totally surprised, then after generating more data, the mode of suppression makes complete sense. We are learning a lot from these animals.
MC: I will leave our readers with one last comment. Over the past 12 years I’ve overseen peer-review for well over a thousand research applications for funding. So I’ve read my fair share of reviewer comments. Typically reviewers are a conservative bunch; even if they are enthusiastic about a project they tend to be cautious. Your recent proposal, however, generated comments like “Wow”. That’s truly unusual and a real tribute to your creativity, risk-taking and perseverance. I am thrilled that RSRT can partner with you and hope that together we can deliver some much-needed treatments to kids and adults who are in such desperate need.
Anyone who keeps up with Rett research knows that the different mouse models of the disease have given us a rich knowledge base. But have you ever stopped to think of how scientists get access to these crucial models? Today we share with you a conversation between Cathleen Lutz of The Jackson Laboratory in Bar Harbor, Maine, and Monica Coenraads, Executive Director of the Rett Syndrome Research Trust. Jackson is the gold standard for the colonization and distribution of mouse models of disease.
MC: Thank you, Dr. Lutz, for spending some time with us. Tell us a bit about the background behind Jackson Laboratories.
CL: Jackson Laboratories was established by Clarence Cooks Little and Roscoe B. Jackson in 1929 as a genetics institute. Financial support came from Detroit industrialists such as Edsel Ford and Roscoe Jackson, president of the Hudson Motorcar Company, with land donated by family friend George B. Dorr. Of course, Bar Harbor has a long history of philanthropic summer residents who supported the Laboratory, for example the Rockefellers had settled on Bar Harbor.
Off the coast of Maine may seem like a strange place to have a genetics facility. The advantage to the location is that at the time there wasn’t any air conditioning, so the ocean breezes really kept the animal facilities cool. In the early years we didn’t have the ability to do genetic engineering, so essentially we relied on spontaneous mutations that resulted in interesting things to study.
MC: I’ve recently learned of veterinary schools setting up facilities to diagnose animals with spontaneous genetic mutations. For example, it’s possible that a dog with a mutation in MECP2 would be taken to vet and a bright geneticist might be able to diagnose the animal. This would allow different species to be studied without having to do all the expensive and time consuming genetic engineering involved with making models.
CL: In fact I just attended a seminar on this. Recently a naturally occurring form of ALS was identified in dogs. What is particularly interesting is that the canine form of ALS progresses slowly, unlike the human ALS where patients usually die within 5 years of diagnosis. The key question is what is genetically protecting these dogs?
MC: The hope is that genetic modifiers are protecting these dogs from their mutations in SOD1, an ALS gene. And if you can identify these modifiers it may open up avenues for intervention. We have the same situation in Rett. Currently RSRT is funding a project in the lab of Monica Justice at Baylor to look for genetic modifiers in the Rett mice models.
How many disease models would you estimate that Jackson has?
CL: We have over 5000 different strains here at the Jackson Laboratory.
MC: How many new strains are imported every year?
CL: We’re importing about 600 new strains every year.
MC: Is Jackson struggling to keep up given such large numbers?
CL: We have over 1300 strains live on the shelf and over the years have worked to meticulously manage the supply and demand of the strains so investigators can get a jump start on their experiments. We also scale up our colony sizes for individual investigators who need a larger supply of animals than we currently may have. For strains that have low demand, those mice are available from our cryopreserved stocks. Cryopreservation involves either freezing embryos or sperm. Dr. Robert Taft at Jackson has been on the cutting edge of that technology and recently published his technique that helps recover sperm much more easily. Animals can then be recovered from cryopreserved stocks as needed.
So instead of having to super ovulate 50 or 60 females, fertilize, and bring embryos to the two cell stage for cryopreservation, all we have to do is take two males and freeze down the sperm and that particular model is completely archived. We cut down on shelf space and cost.
MC: When a laboratory needs a particular strain which is cryopreserved, that means you don’t have a live colony; what do you actually send them?
CL: It depends on where the requesting laboratory is physically located and the level of their expertise. Cryopreservation is still a rather novel technology so some labs are not equipped to handle the technique of thawing sperm and doing in vitro fertilization (IVF). In those cases we can take the sperm, thaw it and do an IVF to donor females and then we’ll send them live mice. Alternatively we can send frozen viable embryos. This works well especially if the lab is an international customer because we have all kinds of handcuffs regarding transportation of live animals and tissues outside the country.
MC: How many scientists do you estimate have purchased from Jackson?
CL: Last year over 19,000 investigators from 50 countries purchased 2.7 million mice.
MC: That is unbelievable! How is Jackson funded?
CL: We are a not for profit organization with three prongs. We are a research organization; a resource organization, that’s the mouse distribution portion of our institution; and we run courses and conferences where we teach people the latest technologies.
Most of the research and courses are funded mainly through NIH grants. A large portion of our Mouse Repository is also funded through NIH program grants. The rest of the funding required for running the Repository comes from the fees we charge for the mice we distribute. The proceeds go right back into the operation to acquire more mice and outfit new facilities to expand the program. It’s very expensive to distribute mice because we have to maintain high health standards so that any institutions can receive mice knowing that they are free of viruses and pathogens that could contaminate their facility. We also have philanthropic donations.
MC: When I was the Director of Research at the Rett Syndrome Research Foundation we financially supported the importation and colonization of several Rett animal models at Jackson. That was money very well spent as those mice have now been distributed to hundreds of labs and have formed the foundation of much of what we have learned about Rett Syndrome.
You shared that in 2009, 95 different labs ordered Rett mice. The first Rett mouse model made by Adrian Bird was published in 2001, so Jackson had it ready for purchase in 2002. So eight years later almost 100 researchers bought this mouse.
CL: Yes, there is still a lot of demand for that animal, partly because it’s one of the better models of neurological disease. But it’s always going to take more than one model to really dissect what it is that you’re looking for. So if you want to ask specific questions it’s very helpful to be able to utilize more than one type of mouse model. So one model may have a point mutation, another may have a complete exon deleted, yet another may be a conditional mutation so you can just make that mouse gene defective in certain tissues and not others. When you put the collection all together it makes for a really good research resource…your toolbox, so to speak.
MC: I want to acknowledge the scientists who have developed the Rett mouse models: Adrian Bird, Rudolf Jaenisch and Huda Zoghbi. All of them quickly deposited their mice with either Jackson or the Mutant Mouse Regional Resource Center, thereby giving the research community at large access to the mice. This type of sharing does not always happen and I’m so grateful that they set a high standard for our community in terms of accessibility to these models. I hope that it’s a standard that others will follow.
MC: The recent ability to manipulate rat embryonic cells now makes it possible to create rat models of genetic disease. Does Jackson plan to expand into rat models?
CL: We’ve really talked about it a lot as genetic engineering in rats has come a long way in the last few years. One problem is that sperm cryopreservation in rats is still not as efficient as it is in mice. And the housing of rats is so much more expensive because they are so much bigger than mice.
So we have to realize analyze what the advantages of working in rats versus mice are.
MC: Rats are considered smarter than mice.
CL: Yes, they are. They are probably a better model for studying behavior, as well as learning and memory, which will be important in many neurological diseases. But the advantages of studying diabetes in a rat versus mice, for example, is less clear. There is a rat repository in Missouri run by John Critser. I think that Jackson will basically rely on the Missouri repository, working with them when and if needed.. But certainly we’d like to see the cryopreservation and the sperm recovery be just as easy and cost effective and efficient for rats as it is for mice so that we could we could cut the cost and make the process feasible.
MC: I wonder then how many labs would purchase rats. It would be a big learning curve to switch and the costs would be so much higher.
CL: Yes. That’s absolutely true. So there again I think researchers will really need to ask themselves what the advantage to using rats is for their particular research.
MC: Jackson also does its own research and has some high profile scientists on staff.
CL: We have 35 staff scientists on site working right now in a variety of areas. We have cancer biologists, neuroscientists, bioinformaticians. We have investigators who specialize in metabolic diseases like diabetes and obesity. We try to be as diverse as we possibly can in that respect.
MC: And why do you think the scientists would choose to work at Jackson and not at an academic institution?
CL: There are many factors but I think one of the attractions is the availability on site of all of the different mouse models. Also the sheer size of our operation means we can offer economies of scale. The per diem costs of mouse experiments are much lower than they would be at other institutions. That is a very attractive feature for scientists. If researchers need large numbers for their studies then this is the place to do it.
MC: Is there anything you would like to say to families of children with Rett Syndrome?
CL: I’d Iike to let people know that our mission at the Jackson Laboratories is really for the families, for the patients, and for biomedical research. We have, as I described, the repository and the disease model resources. It is quite an undertaking and we really feel that it is within our scientific mission to be collecting these animals and to be making them as readily available to the scientific community as we possibly can. That’s why we’re here and we feel that over the years we’ve really developed the expertise to do that and to manage the sheer numbers of strains that we have live on the shelf.
MC: Jackson truly provides an important resource for the scientific community. Thank you, Dr. Lutz, for sharing some of your knowledge with us today.
by Monica Coenraads
Last week I attended a scientific meeting held in Stresa, Italy and organized by a parent group, Pro Rett Ricerca. One of the most well received talks of the speaking program was presented by Monica Justice, PhD of Baylor College of Medicine, who discussed data collected from her RSRT-funded project. What follows is an excerpt from a recent conversation between the two Monicas following the Italian meeting.
MC: Dr. Justice, it was great to see you in Italy. I thought it might be helpful to give our readers some insight into your project. But first I’d like to start with you, the soul behind this impressive undertaking. How did you end up in science?
MJ: My grandfather was a vet and I had an uncle who was a physician. I have always had a deep love for animals so as a child and young adult I wanted to be a vet. My father thought that was not an appropriate career for a woman and he and my uncle encouraged me towards the medical field. Early on, however, I realized that my true passion was in basic research. I went to graduate school thinking I would focus on immunology and microbiology but my very first class would change my career path forever. My professor was switching into the mouse genetics field and invited me to join his lab. I loved mouse genetics from the very start and knew immediately this was exactly where I wanted to be.
MC: Most lay readers of this blog will not have realized that mouse genetics as a field exists. Can you elaborate on this specialty?
MJ: When I entered the field most mouse genetics was being carried out in a few labs, The Jackson Laboratories being the primary one in the US, and research centered around a few mouse mutations that primarily altered mouse coat color. I think the perception from the science community at large was that we weren’t doing particularly important work. That perception changed with the introduction of very powerful research tools. One such tool was the ability to alter genes in mouse embryonic stem cells to engineer DNA mutations at will. The second was the ability to use a strong mutagen, called N-ethyl-N-nitrosurea or ENU, to do forward genetics – more on that later. This was also the time when molecular biology was exploding. Rather quickly the mouse became THE model organism of choice. I’ve ridden that wave since my graduate student days. Today nearly every institution that is doing cutting edge research has a mouse genetics core. I suspect there are now about 2000 true mouse geneticists worldwide. Nearly every person who works on human disease now works with mouse models.
MC: Please tell our readers the basics behind your Rett project.
MJ: Our Rett project is based on two discoveries: 1) that you could make the symptoms of Mecp2 mutant mice better if you introduced brain derived neurotrophic factor (BDNF) and 2) Adrian Bird’s finding that you could actually reverse very severe symptoms in the mice by reintroducing the gene. Because of those two findings I believe that Rett symptoms can be altered by other genetic mutations. I felt strongly that the genetic approach that I was familiar with would be an ideal strategy to try and identify suppressors of the symptoms of Mecp2 knockout (ko) mice.
So let me tell you a bit about the screen. I use a powerful mutagen, ENU, that induces mutations in mouse sperm at a very high rate. We give the mutagen to wildtype (normal) male mice and then mate them to female Mecp2 knockout mice. A certain percentage of their offspring will have no Mecp2 and a sporadic mutation somewhere in their genome. We then analyze the mice very closely and look for any that appear healthier than your typical Mecp2 ko mouse. For example, a Mecp2 male ko mouse is dead by 6-14 weeks. If a mouse in our screen lives much longer than that, we hypothesize that there is a mutation in another gene that suppresses the ill effects of having no Mecp2. We currently have mice that are over a year old and still do not show signs of Rett.
MC: How many mice has your project generated?
MJ: We have used about 10,000 mice at this point and envision needing 5,000 more to find and understand the current genes of interest. To reach saturation for our screen, meaning that we are confident that the mutagen has generated mutations in every gene that could potentially be a suppressor, we would need to screen through five times the number of males that we have done thus far. Statistically, I estimate that there are 25-50 suppressor genes that we would expect to find were we to hit saturation.
MC: What kind of precedents are there for success using ENU modifier screens?
MJ: The first successful modifier screens were done in bacteria and yeast. The technique gained momentum in the late 1980’s early 1990’s when Gerry Rubin carried out a modifier screen in the fruit fly for genes that would interfere with a particular pathway. Dr. Rubin is a famous scientist who now is the Director of the Howard Hughes Medical Institute Janelia Farm Research Campus. Historically, people thought that fruit flies were the only organism that you could do this with. It’s clear now that the mouse is an equally powerful organism. My graduate mentor, Vernon Bode, did a screen in mice for PKU modifiers, which was finished by Bill Dove at the University of Wisconsin Madison. And an Australian group that works on diseases of the blood did an ENU mouse screen looking for genes that influence platelet counts. Each of these screens was very successful.
MC: Is there data to show that modifier genes are the rule or the exception in disease?
MJ: That’s a very interesting question. I work in the Department of Human and Molecular Genetics at Baylor. What I see from many of my colleagues’ work is that genetic modification of disease is the rule and not the exception.
MC: Can you envision a situation where you find modifiers in the Mecp2 ko mice but those genes are not implicated in the human disorder?
MJ: I do not think that we will find modifiers that are mouse specific only. I believe that because the mouse model for Rett Syndrome is amazingly similar to the human disease. Also, DNA methylation (which is critical to MECP2) and some of the possible functions of the MECP2 gene are highly conserved between species. So it’s very likely that the MECP2 gene in people and in mice is doing the same thing.
MC: What do you foresee as the best possible outcome?
MJ: I foresee finding a molecule that would help forge neuronal connections, and help these connections be maintained and molded.
Furthermore, whatever molecules we find that suppress Rett symptoms may also give us important biochemical information on other genes that may interact with Mecp2.
MC: Did being at Baylor, a Rett hotspot, impact your decision of taking on this Rett project?
MJ: I have been very much aware of Rett since I moved to Baylor in 1998, a year before Huda Zoghbi identified the gene. I have been on the student committee of some of Dr. Zoghbi’s students, which kept me up- to- date on the ongoing work. MECP2 is a transcription factor and I’ve always been interested in transcriptional regulation. What really brought me into the project was when you called me up with a proposition.
MC: When I was the Director of Research at the Rett Syndrome Research Foundation (several years before the merger with IRSA to form IRSF) I piggybacked an early morning think tank during the RSRF Rett Syndrome Symposium in Chicago. About two dozen creative thinkers were kind enough to drag themselves out of bed and brainstorm with me about potential key experiments that could significantly move the field forward. At the top of that list was an ENU mouse modifier screen. The group also gave me a list of potential people who could undertake such a laborious and intense project…it was a small list and your name was on it. As you well know, RSRF then organized a workshop at the Mouse Genetics meeting, which took place in Charleston, SC in 2006. Those discussions led to the funding of your project.
MJ: I was so thrilled when you called. There was a time when I would have turned down this project. But the timing of your call was perfect. The project appealed to me very strongly as a geneticist but also as a compassionate person who wants to make a difference in the life of others.
Your readers should also know that this is a project that the NIH would never have funded. It was too risky and too “out there”. I knew this was a viable technique and I was confident with the expertise of my lab with regards to mouse breeding, husbandry and handling that would move this project along quickly so I am very grateful to have had the funding to pursue this. People should be aware of how much private foundations such as RSRT move the field forward by funding high risk, but high impact projects.
MC: Speaking of compassionate person, at the end of your talk in Italy you got a little emotional. I was quite touched by that. Can you tell our readers what was going through your mind?
MJ: Yes, I got a little “verklempt” and I got teased quite a bit at dinner for that. I take this project very seriously because I feel that what we are doing could have an impact on people’s lives – an impact that perhaps wouldn’t happen without the screen – I guess as I was up there in front of scientists and the organizers of this meeting who have children suffering from Rett – the importance of our efforts hit me hard.
MC: Are you able to give our readers a hint at the data that your project has thus far yielded?
MJ: The project is at an exciting point. We are close to identifying our first suppressor gene and we have a few more potential genes that we are pursuing as well. Once they are identified we will begin experiments to confirm that they are indeed interacting with Mecp2m, first in the mice and then in people. I also think the modifiers we have so far are just the tip of the iceberg. So we have a lot more screening ahead of us.
I love this project, it’s fun, it’s exciting, and each new piece of data that we identify brings us closer to our goal.
MC: On behalf of families everywhere who love a child with Rett Syndrome we wish you Godspeed. We look forward to hearing about future progress. Thank you also to Pro Rett Ricerca and especially Rita Negri and Laura Rassetti for their tireless work to organize this meeting.
MJ: It was my pleasure and honor to attend the meeting in this most beautiful area of Italy, near where you were born.