Understanding the Role of SCL in Early Mammalian Development Using Mouse Embryonic Stem Cell Differentiation as a Model

How a complete organism develops from a single cell is among the most complicated questions in life sciences. Early experimental studies on the development of animals were performed on amphibians and birds due to the size and accessibility of their embryos, while studies in placental mammals have been limited by the difficulty posed by in utero development. In vitro differentiation of ES cells provides a convenient model for the study of the mammalian development. Since ES cells can be grown and maintained in a pluripotent state virtually forever, ample amount of research material for molecularbiological studies can be produced; differentiating ES cells are easily accessible and they can also be manipulated genetically. I have used the ES cell differentiation model to study the bHLH factor SCL, a critical regulator of the formation of the hematopoietic lineage in the early embryo and the maturation of erythrocytes and megakaryocytes later on. The latter function of the protein has been studied extensively, but a complete molecular analysis of the former function has been lacking. My work shows that SCL can skew the patterning of the mesoderm towards the hematopoietic lineage. This function required the interaction of SCL with LMO2. Transcriptional profiling revealed organizer genes FoxA2 and Chordin as novel downregulated targets of SCL during this time. Differentiation of human pluripotent cells to be used in cellular therapy or to generate replacement tissues; is considered to be one of the most promising branches of medical research. Considering the importance of SCL in hematopoiesis, we hypothesized that SCL can direct differentiation of pluripotent cells to this lineage in a simple culture system. Ectopic expression of SCL induced hematopoiesis at low levels. Co-expression of LMO2 and GATA2 increased efficiency of the programming significantly.