The Perelman School of Medicine at the University of Pennsylvania
Department of Cell and Developmental Biology
9-123 Smilow Center for Translational Research
3400 Civic Center Blvd
Philadelphia, PA 19104-6059
Office: 215-898-9063
Lab: 215 898-9277
bartolom@pennmedicine.upenn.edu
The research in the Bartolomei laboratory focuses epigenetic control of genomic imprinting. They also study how the environment can perturb genomic imprinting and other epigenetic processes important in reproduction and health.
Mechanism of Genomic Imprinting: As a postdoctoral fellow in the laboratory of Dr. Shirley Tilghman, I identified the one of the first imprinted genes—the H19 gene and also determined that this gene was adjacent to the imprinted Igf2 gene, representing the first evidence of imprinted gene clusters. In my own laboratory, we study the mechanisms governing imprinted gene expression and have determined that imprinted genes and clusters are regulated by differentially methylated imprinting control regions [ICRs]. In the case of H19 and Igf2, the ICR is a paternally methylated CTCF-dependent insulator. Through the use of cis-acting mutations we have characterized imprinting at the H19 locus and have elucidated elements that are important for setting the DNA methylation imprint in the germline and maintaining imprinting in the embryo after fertilization. Our mouse models contributed to the discovery that epigenetic mutations in the H19 ICR caused Silver-Russell Syndrome in a subset of patients. Additionally, microdeletions in the H19 ICR have been identified in Beckwith-Wiedemann Syndrome. We are generating mouse models as well as using iPS cells to study patient-derived mutations.
Discovery that mouse models epigenetic perturbations identified in Assisted Reproductive Technologies (ART): In the imprinting field, experiments performed in the 1990’s were aimed at elucidating when monoallelic expression was initially set for imprinted genes. Two studies in our laboratory and in the Surani laboratory gave contrasting results for the H19 gene, with our lab showing maternal-specific expression when the gene was activated in the blastocyst and the Surani lab describing biallelic expression at this time. We subsequently determined that culturing mouse preimplantation embryos was associated with loss of imprinted gene expression. It was later shown that ART was associated with a higher than expected number of imprinting syndromes, including Beckwith-Wiedemann Syndrome and Angelman Syndrome, with almost all documented cases caused by loss of DNA methylation of the ICR. The mouse, which has the added benefit of normal fertility, has proven a valuable model to address these observations and determine mechanisms with the eventual goal of improving ART outcomes. We have shown that in vitro culture, embryo transfer, in vitro fertilization and hormonal hyperstimulation contribute to errors in epigenetic gene regulation. We have also determined that placental tissues are especially sensitive to the manipulations involved in ART.
Generation of a mouse model to study endocrine disrupting compounds (EDCs): Numerous experiments in mouse model systems as well as human studies have suggested that exposure to EDCs is associated with aberrant DNA methylation. Because imprinted genes are regulated by DNA methylation, we tested whether imprinting could be disrupted when pregnant dams were exposed to levels of BPA that are comparable to human exposure. We demonstrated that genomic imprinting and DNA methylation of ICRs and repetitive DNA were perturbed in offspring exposed in utero, with a pronounced effect in placenta. We have also shown that metabolic phenotypes observed in F1 offspring exposed in utero were transmitted to their F2 offspring, thus exhibiting multigenerational transmission of the phenotype.
CTCF and insulators: CTCF was initially described as a factor that functioned in transcriptional repression and activation. The first demonstration of its insulator activity was by the Felsenfeld laboratory at the globin locus. It soon became apparent that there were CTCF sites in the H19/Igf2 ICR and that this ICR exhibited insulator activity on the maternal allele. To study the role of CTCF at H19 we generated a knockdown line and showed that in the absence of CTCF, H19 became hypermethylated, and also that embryos died early in development. This study was the first that reported the essential role for CTCF in development. Further experiments demonstrated the extensive role of CTCF in gene activity as well as a role for CTCF interacting with cohesins at a number of developmentally important insulators and regulatory regions. We have also studied CTCF binding in an ES cell differentiation model and elucidated sequence preferences both genomically and biochemically, contributing to the knowledge of the role of CTCF in early developmental decisions, as suggested by the knockdown studies.
Role of DNA methylation in epigenetic gene regulation in the mouse embryo: In early work as a postdoctoral fellow with Dr. Shirley Tilghman, I demonstrated that DNA methylation was critical for conferring parental identity of imprinted genes. Subsequently, my laboratory demonstrated that DNA methylation was erased in primordial germ cells by the time they enter the gonad and established in a sex-specific manner. We and others have also demonstrated that loss of the maintenance methyltransferase DNMT1 disrupts imprinted gene expression in the embryo as well as the placenta. More recently we have collaborated with a number of groups to understand the mechanism by which DNA methylation imprints are established and erased in the germline, including studies on the role of TDG and unpublished studies on the Tet enzyme family.
FIRST NAME: | LAST NAME: | TITLE: | EMAIL: |
---|---|---|---|
Marisa | Bartolomei | PI | bartolom@pennmedicine.upenn.edu |
Nana Yaa | Amoh | Graduate Student | nyamoh@pennmedicine.upenn.edu |
Eric Rhon | Calderon | Postdoc | eric.rhoncalderon@pennmedicine.upenn.edu |
Blake | Caldwell | Graduate Student | blakec@pennmedicine.upenn.edu |
Suhee | Chang | Graduate Student | suheech@pennmedicine.upenn.edu |
Asha | Dahiya | Research Tech | dahiya@sas.upenn.edu |
Yee Hoon | Foong | Undergrad | yfoong@pennmedicine.upenn.edu |
Aimee | Juan | Administrative Assistant | aimjuan@pennmedicine.upenn.edu |
Christopher | Krapp | Research Associate | krappc@pennmedicine.upenn.edu |
Duy | Nguyen | Research Specialist | duyng@pennmedicine.upenn.edu |
Rexxi | Prasaya | Graduate Student | rexxi.prasasya@pennmedicine.upenn.edu |
Jimmy | Ren | Undergrad | jimmyren@seas.upenn.edu |
Nicole | Robels-Matos | Graduate Student | nroble@pennmedicine.upenn.edu |
Kashviya | Suri | Undergrad | kashviya@sas.upenn.edu |
Joanne | Thorvaldsen | Postdoc | thorvald@pennmedicine.upenn.edu |
Lisa | Vrooman | Postbac | lvrooman@pennmedicine.upenn.edu |
Kashish | Wadhwa | Undergrad | kwadhwa@sas.upenn.edu |