Krill Prize Laureate 2017
Dr. Yossi Buganim
The Hebrew University of Jerusalem
Research Vision :
Regenerative medicine is a new and expanding area that aims to replace lost or damaged cells, tissues or organs in the human body through cellular transplantation. Embryonic stem cells (ESCs) are pluripotent cells that are capable of long-term growth; self-renewal and can give rise to every cell, tissue and organ in the fetus’s body. The “hyperdynamic” chromatin state, which characterizes the ESC epigenetic state, facilitates a rapid and efficient reaction to external and internal cues that lead to the activation of key master regulators that drive the cells into their developmental fate. Thus, ESCs hold great promise for cell therapy as a source of diverse differentiated cell types. Two major bottlenecks to realizing such potential are allogenic immune rejection of ESC-derived cells by recipients and ethical issues. In 2006, two Japanese scientists, Takahashi and Yamanaka, changed the way we used to think about cell plasticity when they showed that introduction of four transcription factors, Oct4, Sox2, Klf4 and Myc (OSKM), can reprogram adult fibroblasts into functional embryonic stem-like cells (also termed induced pluripotent stem cells (iPSCs)). The notion that as little as four factors are sufficient to reset the epigenome of a cell, opened a new avenue where scientists have attempted to convert different adult cells into other somatic cell types from ontogenetically different lineages, by avoiding the pluripotent state, using a specific subset of key master regulators. Several subsets of cell types such as hematopoietic cells, different neuronal cells cardiomyocytes, hepatocytes, embryonic Sertoli cells, endothelial cells and RPE were converted from different somatic cells by employing the direct conversion approach. Importantly, the generation of iPSCs and directly converted cells resolve the problems of allogenic immune rejection of ESC-derived cells by recipients and ethical issues. However, the majority of the directly converted cells are not stable and represent mostly incomplete reprogramming state and the vast majority of the resulting iPSCs, although could activate their endogenous circuitry, exhibit poor developmental potential in mice. This suggests that the current prevailing reprogramming methods are not ideal and must be improved before considering applying the converted cells and iPSCs in the clinic.
To overcome these barriers, my lab is focused on identifying and investigating the components (e.g. transcription factors, chromatin remodelers, epigenetic marks and metabolites) that determine cellular identity and the elements that can force cells to acquire an alternative fate. To that end, we study two major cell fate decision processes in the embryo: (i) Embryo vs placenta [i.e. inner cell mass (ICM) vs trophectoderm (TE)] and (ii) sex determination during gonadal development [i.e. Sertoli cells (male) vs Granulosa cells (female)]. To identify key elements that play a role in these two fascinating processes we take advantage of our expertise in nuclear reprogramming, embryo manipulation and single-cell technologies, to generate engineered cells that can be captured and examined during embryonic development and following various nuclear reprogramming processes driven by defined factors. We study four somatic cell conversion models, which recapitulate, at least partially, the changes that occur in vivo during the above mentioned two cell fate decision processes: (i) fibroblasts into induced pluripotent stem cells [(iPSCs), an in vitro equivalent to ICM], (ii) fibroblasts into induced trophoblast stem cells (iTSCs), an in vitro equivalent to TE], (iii) induced embryonic Sertoli-like cells [(ieSCs), an in vitro equivalent to embryonic Sertoli cells] and (iv) induced embryonic Granulose cells (ieGCs), an in vitro equivalent to embryonic Granulosa cells]. Our overarching goal is to uncover and explore the elements that are shared among the in vivo and in vitro processes, to shed light on basic cell fate decision processes during embryonic development and to decipher the mechanisms underlying intact somatic nuclear reprogramming. Highlighted elements (e.g. gene, enhancer, miRNA, LincRNA and metabolite) that are discovered by the single-cell analyses are eventually subjected to gain and loss of function experiments within a developing embryo, using gene editing techniques such CRISPR/Cas9, to validate the in vitro results. Pursuing these goals will enable the generation of high quality converted cells and iPSCs for regenerative medicine and fertility treatment.