Our lab is broadly interested in the mechanisms by which both somatic and embryonic stem cells acquire and maintain developmental potency. We are also exploring how deregulation of these mechanisms can contribute to oncogenic transformation and tumorigenesis, and how we can learn to manipulate these mechanisms for application in disease modeling and regenerative medicine
Nuclear reprogramming during iPS cell generation
Recent advances in the field of epigenetic reprogramming have changed what was previously a highly controversial and technically challenging experimental system (nuclear transfer, or cloning) into a simple and robust methodology (iPS cell generation). The generation of induced pluripotent stem cells (iPSCs) can be accomplished simply by ectopic expression of four transcription factors, Oct4, Sox2, Klf4, and c-Myc, in somatic cells. This process reverts the somatic genome into a pluripotent epigenetic state that is indistinguishable from that of an embryonic stem cell. We have previously shown that this process is relatively efficient and largely independent of the origin of the somatic donor cell. It is also known that this process is accompanied by dramatic changes in the gene expression program and chromatin organization of the somatic nucleus. Using gain and loss of function approaches in genetically modified primary somatic cells harboring both drug-inducible reprogramming alleles and pluripotency reporter alleles coupled with genomic analyses, we are investigating the influence of chromatin-modifying proteins and nuclear organization on the dynamics of the epigenetic reprogramming process.
Somatic stem cells, symmetry of cell division, and oncogenic transformation
In the mammalian soma, tissue-specific stem cells capable of maintaining organization and function during homeostasis and of regenerating damaged tissue upon insult are commonly thought to exist in a state of multipotency (the ability to generate any cell type of that particular tissue, in contrast to the pluripotent state embodied by embryonic stem cells capable of generating all cell types of the mammalian organism). We have recently demonstrated that the genetic pathway governing pluripotency in embryonic stem cells does not contribute to somatic stem cell potency. Therefore, we have performed several screens aimed at identifying factors that may govern somatic stem cell multipotency in a broad range of tissues and have identified the Msi family of RNA binding proteins as attractive candidates. Msi proteins are expressed in putative somatic stem cell compartments, are frequently found to be overexpressed in advanced cancers, and are known to govern asymmetric cell division in Drosophila melanogaster (a process thought to maintain the somatic stem cell niche in mammals). Using mouse genetic approaches integrated with human patient sample data, we have recently demonstrated that human MSI2 contributes to maintaining the stem cell state in hematopoietic stem cells (HSCs) and acts as a cooperating oncogene in chronic and acute myelogenous leukemias by conferring a stem cell-like state to the transformed cells. We are currently pursuing the role of Msi proteins in epithelial stem cell compartments using tissue-specific gene ablation and drug-inducible gene activation. We are relating the effects of Msi proteins on stem cell maintenance and oncogenic transformation to their RNA binding capacity using CLIP-Seq analysis and will ultimately determine how these functions affect asymmetric stem cell division using both mouse and cell culture models.
Gaining an understanding of the mechanisms that govern somatic stem cell potency and how these mechanisms are linked to oncogenic transformation will provide the impetus for harnessing these pathways for the generation of potential therapeutic cell types in vitro and may enable more effective, targeted approaches for intervention during the progression of various cancers.
Zhengquan Yu, Research Associate
Ning Li, Postdoctoral Fellow
Angela Ddamba, Research Specialist
Ryan Cedeno, Graduate Student
Maryam Yousefi, Graduate Student
Shang Wang, Visiting Graduate Student.
Kharas Michael G*, Lengner Christopher J*, Al-Shahrour Fatima, Bullinger Lars, Ball Brian, Zaidi Samir, Morgan Kelly, Tam Winnie, Paktinat Mahnaz, Okabe Rachel, Gozo Maricel, Einhorn William, Lane Steven W, Scholl Claudia, Fröhling Stefan, Fleming Mark, Ebert Benjamin L, Gilliland D Gary, Jaenisch Rudolf, Daley George Q
*equally contributing authors Musashi-2 regulates normal hematopoiesis and promotes aggressive myeloid leukemia. Nature medicine 16: 903-8, 2010.Lengner Christopher J, Gimelbrant Alexander A, Erwin Jennifer A, Cheng Albert Wu, Guenther Matthew G, Welstead G Grant, Alagappan Raaji, Frampton Garrett M, Xu Ping, Muffat Julien, Santagata Sandro, Powers Doug, Barrett C Brent, Young Richard A, Lee Jeannie T, Jaenisch Rudolf, Mitalipova Maisam Derivation of pre-X inactivation human embryonic stem cells under physiological oxygen concentrations. Cell 141: 872-83, 2010.Hanna Jacob, Cheng Albert W, Saha Krishanu, Kim Jongpil, Lengner Christopher J, Soldner Frank, Cassady John P, Muffat Julien, Carey Bryce W, Jaenisch Rudolf Human embryonic stem cells with biological and epigenetic characteristics similar to those of mouse ESCs. Proceedings of the National Academy of Sciences of the United States of America 107: 9222-7, 2010.Lengner Christopher J iPS cell technology in regenerative medicine. Annals of the New York Academy of Sciences 1192: 38-44, 2010.Hanna Jacob, Saha Krishanu, Pando Bernardo, van Zon Jeroen, Lengner Christopher J, Creyghton Menno P, van Oudenaarden Alexander, Jaenisch Rudolf Direct cell reprogramming is a stochastic process amenable to acceleration. Nature 462: 595-601, 2009.Hanna Jacob, Markoulaki Styliani, Mitalipova Maisam, Cheng Albert W, Cassady John P, Staerk Judith, Carey Bryce W, Lengner Christopher J, Foreman Ruth, Love Jennifer, Gao Qing, Kim Jongpil, Jaenisch Rudolf Metastable pluripotent states in NOD-mouse-derived ESCs. Cell stem cell 4: 513-24, 2009.Markoulaki Styliani, Hanna Jacob, Beard Caroline, Carey Bryce W, Cheng Albert W, Lengner Christopher J, Dausman Jessica A, Fu Dongdong, Gao Qing, Wu Su, Cassady John P, Jaenisch Rudolf Transgenic mice with defined combinations of drug-inducible reprogramming factors. Nature biotechnology 27: 169-71, 2009.Wernig Marius*, Lengner Christopher J*, Hanna Jacob, Lodato Michael A, Steine Eveline, Foreman Ruth, Staerk Judith, Markoulaki Styliani, Jaenisch Rudolf
*equally contributing authors A drug-inducible transgenic system for direct reprogramming of multiple somatic cell types. Nature biotechnology 26: 916-24, 2008.Lengner Christopher J, Camargo Fernando D, Hochedlinger Konrad, Welstead G Grant, Zaidi Samir, Gokhale Sumita, Scholer Hans R, Tomilin Alexey, Jaenisch Rudolf Oct4 expression is not required for mouse somatic stem cell self-renewal. Cell stem cell 1: 403-15, 2007.Lengner Christopher J, Steinman Heather A, Gagnon James, Smith Thomas W, Henderson Janet E, Kream Barbara E, Stein Gary S, Lian Jane B, Jones Stephen N Osteoblast differentiation and skeletal development are regulated by Mdm2-p53 signaling. The Journal of cell biology 172: 909-21, 2006.