Marisa Bartolomei is a professor of Cell and Developmental Biology and codirector of Epigenetics Institute at the University at Pennsylvania Perelman School of Medicine. As a postdoctoral fellow in Dr Shirley Tilghman's lab, she identified one of the first imprinted genes, H19, and fell in love with genomic imprinting. She remained faithful and contributed to this relationship by unveiling many of its secrets, and specifically elucidating the mechanisms governing expression of imprinted/epigenetic genes, how their regulation is altered by assisted reproduction technologies (ART) and adverse environmental insults, and what role epigenetic regulation plays in embryos. Dr Bartolomei is a recipient of numerous awards, including the Society for Women's Health Research Medtronics Prize for Contributions to Women's Health and the Jane Glick Graduate School Teaching Award at University of Pennsylvania. She was elected as a fellow of the American Association for the Advancement of Science in 2014 and as a Member-At-Large of the Section on Biological Sciences for AAAS (2016–2020 term). She is also a recipient of the 2017 Genetics Society Medal from the UK Genetics Society. She has served on numerous editorial boards and grant review panels. We asked Dr Bartolomei to reflect about her life as a scientist and her life-long romantic relationship with genomic imprinting. When did you first become interested in genomic imprinting and why this field captivates you so much? My entry into genomic imprinting was largely an accident. During my postdoctoral work, we examined this weird gene, H19, that nobody knew much about. H19 was cloned because it was expressed at high levels during development. We tried to generate mice transgenically overexpressing H19 and found out that it led to embryonic lethality. My postdoctoral advisor, Shirley Tilghman, thought that H19 might be imprinted. So we decided to do experiments to test if it was. We designed an old fashion approach using RNAse protection assays to examine allelic expression in F1 hybrids. I got the answer late at night a few days later and it was the most exciting finding that I ever had . I called Shirley to tell her what happened and we were both ecstatic. The next morning I overslept and appeared in the lab later than usually. When I entered, all lab members were gathered around the autoradiograph showing the H19 result and were busily discussing it. The next steps were already planned! This is what keeps us, scientists, going. One awesome experiment! Did you have any role models that inspired you? I was the first in my family who graduated from college so I did not have role models among relatives. When considering a broader scientific community, my postdoctoral advisor, Shirley Tilghman, is definitely a role model. She was the first woman scientist and probably the smartest person I have ever worked with. She was really brave. She was always thinking outside of the box and was ready to get involved. It felt good to see someone trying to do the right thing. What was the most unexpected and exciting finding in your research to-date? Definitely discovering that H19 was an imprinted gene, which I told you about earlier. But also, when my group deleted the imprinting control region of H19 and observed phenotypes that depended upon the transmitting parent, it was also quite exciting . This was the first substantial result of my own lab so it is a special result. Which aspect of your work do you consider the most impactful? It depends. The deletions and mutations that we made helped us to show that H19 and Igf2 are involved in Beckwith–Wiedemann and Silver–Russell syndrome [3, 4]. The fact that our basic science work impacted on human health is really important. Clinicians working with Silver–Russell syndrome patients did not know where to look, what region/gene was involved. Our work with Igf2 pointed them in the right direction. Therefore, they could develop screening assays for patients. Also, it opens the doors for developing therapies to treat these syndromes. One of your research interests is X chromosome inactivation. This seems like a slight detour from your genomic imprinting love. How did you get involved with it? I became involved with X inactivation primarily because of students and postdocs who approached me to study the phenomenon. Trainees approached me because they considered X inactivation sexy and easy to understand: one X is active one X is not. So we did some work on that, published a paper, which of course brought more questions . Another interested student appeared and continued this work, and so on it went. X inactivation is a very complex phenomenon and this is also a very competitive field. For me, X inactivation is an inadvertently planned but interesting side venture, from which I always happily return to genomic imprinting. One of your research themes is to investigate the effects of ART on epigenetic regulation. How do you think your findings will benefit infertile couples for whom ART is the only option of reproduction? Our work on ART was unintentional. After we identified H19 as an imprinted gene, we wanted to know if the gene was imprinted from the first moment it was expressed. My group performed experiments and demonstrated that it was . However, at the same time Azim Surani's group published that H19 was not imprinted in the early embryo. First, we could not understand why our results were different. But then we realized that our embryos were naturally conceived and Azim generated his embryos by in vitro fertilization (IVF). When we compared our data and performed more experiments, we found out that the difference was indeed caused by the method of conception . Later, we realized that we could use the system as a model for ART. About that time, I attended an American Society of Human Genetics meeting in Philadelphia and heard a series of talks about patients with Angelman syndrome. It emerged that one of these patients was conceived by IVF and had a rare DNA methylation defect. During discussion, another clinician stated he had patients with the imprinting disorder Beckwith–Wiedemann syndrome, who were also conceived with IVF. From that point, we started looking into the relationship between imprinting and ART, and the mouse model really predicted what ended up being observed in humans [8, 9]. Our ultimate goal with this work is to understand which ART procedures may be causing the observed epigenetic errors . Although the work is ongoing, our current data strongly point to culture conditions as the major contributing factor. My involvement with ART is a good example of how you end up being in a place where you did not think you will be. In my case, science took me there and my true love, genomic imprinting, was agreeable for this new branch of our special relationship. The effects of environmental exposures on development is another interest of yours. It is a hot topic these days with many groups tackling it. What in your opinion is the most challenging aspect of this work and how do you see overcoming it? My involvement with environmental exposure research was also not planned. There was an internal pilot project announcement at Penn, which was very specific and called for studying imprinting and epigenetics in environmental exposures. I was the only person on the campus who really studied imprinting, and I had just hired a new postdoc who did her PhD work in Pat Hunt's lab and therefore had experience with environmental exposures, but who wanted to learn epigenetics . So, that fit well with this announcement. I thought it will be pretty straightforward to see how chemicals cause epigenetic changes, but I vastly underestimated the complexity of the field. When we see a phenotype after environmental exposure, the key question always is how long ago the insult happened and what effects it had then, what pathway it affected, and how did it lead to the phenotype observed now? So the major challenge of this field is the duration of time between the insult and its effect. If we see a phenotype in adult mice and the insult could have happened before the mouse was even born, where do we look? It is very hard to decipher that. We have to go to the beginning and see if it is DNA methylation, or perhaps RNA, or perhaps chromatin changes… As if it was not enough, it can take months to have the phenotype manifest itself. I really underestimated how complex it is to study environmental exposures from epigenetic standpoint. It is a fascinating field, but very complex and it requires a lot of time investment. What is your dream project? Do you have any crazy ideas that you have thought of but have not yet put to testing? I have to think about it…. Maybe, once we figure out what genes are imprinted and how, we can make a synthetic imprinted gene. Alternatively, for imprinting disorders, you either have both copies of the gene being expressed or you have a mutation in an expressed copy. So if we find a way to activate and repress a chosen allele, this will be a holy grail for this field, and also for other fields, including X inactivation gene disorders, such as Rett syndrome. You are a mother of two children and clearly a very involved one. I recall you talking about your kids at meetings. How do you balance work and family life? Do you have a recipe for success with that? I am fortunate that my husband is a partner and a lot of times he does more than I do with our children, which allows me to travel. Traveling and sharing your ideas, giving talks and meeting people, is part of being a scientist. My mother is also very helpful. She lives 2 h away, and when the girls were very young she would come and help out. So having someone to help you is a good recipe for balancing science and family. But it is not easy. My children like to talk about the things that I miss when I am out of town, all their sporting and music events. The thing that seemed to bother them most was Young Authors Day, when they would write a story and present it to their elementary school classes. All the parents come to these events and I missed many of them. One day we were sitting at the dinner table and my two daughters (18 and 15 now) started arguing whose writing presentations I missed more. It digressed to a debate: she missed mine more, no, she missed mine more…!!!. My response was excuse me, she is right here!! And we just laughed. It is different for everyone, but for me having a family is important and balances well with work. What advice will you offer next generation of inspiring reproductive biologist to help them succeed? To succeed, in anything really, you have to do what you love. So you have to love science. Everyday I am excited about possibilities and new experiments and results, and being a scientist is very rewarding for me. If you do not have fun doing science, you will not get far with it. The other thing is to never be afraid to ask for help or advice. Have people read your grants. Practice your communication skills with them. Oh, and you also have to be creative about how to sell your science. But that is fun, too. If you are passionate about your science and enjoy being challenged, you can be successful and happy in this career. References 1. Bartolomei MS, Zemel S, Tilghman SM. Parental imprinting of the mouse H19 gene. Nature 1991; 351: 153– 155. Google Scholar CrossRef Search ADS PubMed 2. Thorvaldsen JL, Duran KL, Bartolomei MS. Deletion of the H19 differentially methylated domain results in loss of imprinted expression of H19 and Igf2. Genes Dev 1998; 12: 3693– 3702. Google Scholar CrossRef Search ADS PubMed 3. Engel N, Thorvaldsen JL, Bartolomei MS. CTCF binding sites promote transcription initiation and prevent DNA methylation on the maternal allele at the imprinted H19/Igf2 locus. Hum Mol Genet 2006; 15( 19): 2945– 2954. Google Scholar CrossRef Search ADS PubMed 4. Engel NI, West AE, Felsenfeld G, Bartolomei MS. Antagonism between DNA hypermethylation and enhancer-blocking activity at the H19 DMD is uncovered by CpG mutations. Nat Genet 2004; 36: 883– 888. Google Scholar CrossRef Search ADS PubMed 5. Percec I, Plenge RM, Nadeau JH, Bartolomei MS, Willard HF. Autosomal dominant mutations affecting X inactivation choice in the mouse. Science 2002; 296( 5570): 1136– 1139. Google Scholar CrossRef Search ADS PubMed 6. Tremblay KD, Saam JR, Ingram RS, Tilghman SM, Bartolomei MS. A paternal-specific methylation imprint marks the alleles of the mouse H19 gene. Nat Genet 1995; 9: 407– 413. Google Scholar CrossRef Search ADS PubMed 7. Doherty AS, Mann MRW, Tremblay KD, Bartolomei MS, Schultz RM. Differential effects of culture on imprinted H19 expression in the preimplantation mouse embryo. Biol Reprod 2000; 62: 1526– 1535. Google Scholar CrossRef Search ADS PubMed 8. Mann MR, Lee SS, Doherty AS, Verona RI, Nolen LD, Schultz RM, Bartolomei MS. Selective loss of imprinting in the placenta following preimplantation development in culture. Development 2004; 131( 15): 3727– 3735. Google Scholar CrossRef Search ADS PubMed 9. Rivera RM, Stein P, Weaver JR, Mager J, Schultz RM, Bartolomei MS. Manipulations of mouse embryos prior to implantation result in aberrant expression of imprinted genes on day 9.5 of development. Hum Mol Genet 2008; 17: 1– 14. Google Scholar CrossRef Search ADS PubMed 10. de Waal E, Vrooman LA, Fischer E, Ord T, Mainigi MA, Coutifaris C, Schultz RM, Bartolomei MS. The cumulative effect of assisted reproduction procedures on placental development and epigenetic perturbations in a mouse model. Hum Mol Genet 2015; 15: 6975– 6985. 11. Susiarjo M, Sasson I, Mesaros C, Bartolomei MS. Bisphenol a exposure disrupts genomic imprinting in the mouse. PLoS Genet 2013; 9( 4): e1003401. Google Scholar CrossRef Search ADS PubMed © The Author(s) 2017. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail: firstname.lastname@example.org
Biology of Reproduction – Oxford University Press
Published: Feb 1, 2018
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