Identifying genetic and epigenetic processes that initiate and establish mesoderm progenitor identity from human pluripotent stem cells

• Applicant: Professor Dr. Micha Drukker, Ph.D.
• Subject Area: Developmental Biology
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279807181

During human embryonic development, pluripotent cells, which can potentially differentiate into any cell type in the forming body, give rise to progenitor cells with more restricted developmental potential. In the very first point of no return in this process, pluripotent cells form progenitors that are hereby termed clade progenitors (CPs), the very first defined progenitors that can only contribute to the generation of certain organs, tissues or cell lineages. Subsequent differentiation of CPs produces progenitors that exhibit higher degree of specialization, e.g. progenitors of the cardiovascular system.The derivation of human pluripotent stem cells (PSCs) has opened the possibility of inducing their differentiation into specific cell type like cardiomyocytes or neurons, with the prospect of using them in regenerative medicine to replace and/or replenish damaged organs. Typically, researchers expose PSCs to various differentiation conditions that are either empiric or deduced from the signaling pathways that are known to function during natural embryonic development of the relevant organs in model organisms. Others and we were successful in inducing differentiation of human PSCs to mesoderm progenitors, which we purified and further differentiated to form cardiomyocyte progenitors. Despite these achievements however, we noted and numerous other studies have indicated that the efficiencies of differentiation protocols leading to specific cell types are often highly variable. In our opinion, this exemplifies that the precise mechanisms that mediate differentiation of human PSCs are far from being completely understood.Increasing the efficacy of directed differentiation of human PSCs depends considerably on our ability to steer the initial differentiation route towards specific CPs, for example, towards mesoderm CPs that subsequently can give rise to cells harboring cardiac properties. This proposal is focused on the question of identifying the various types of CPs that emerge from human PSCs, and deciphering the mechanisms that govern their emergence. The specific objective of this proposal is to identify gene activation cascades that operate to initiate and establish human mesoderm CP identity.As a first step to discover the complex mechanisms that govern transcript abundance and as a result determine the respective cell identities, we will rely on a combined genetic and epigenetic approach for identifying the components of gene activation cascades underlying mesoderm CP specification. Two factors make our proposal unique in approaching the question of CP specification: our ability to purify very early developmental progenitors emerging from PSC cultures using specific cell surface markers, and our focus on characterizing the initial transcriptome changes that take place in the cells upon exposure to differentiation conditions.

• DFG Programme: Research Grants