We examine the roles of growth factors on ES cell differentiation. In order to optimize ES cell differentiation procedures, microfluiditic platforms are used to create specialized microenvironments (e.g., gradient) for stem cells.
Manipulation of ES Cell Differentiation
Stem cell niche biology attempts to understand the microenvironment that is necessary to support stem cells proliferation and differentiation. While the importance of the field is recognized, it is a relatively unexplored, emerging stem cell biology field. Recent work suggests that activin and BMPs play critical roles in regulating the differentiation of ES cells into different cell types. However, current approach to regulate ES cell differentiation is rather crude in a sense that these growth factors are normally dumped into the medium. Consequently, the ES cells differentiate into different cell types, but the process is often inefficient, heterogeneous and unpredictable. In order to better define the niche for ES cell differentiation, microfluiditic platforms are used to create specialized microenvironments (e.g., gradient) for stem cells. We find that the usage of microfluiditic platforms improve the efficacy of ES cell response to growth factor stimulation and reduces the amount of growth factor usage.
Albumin-GFP makred ES cells
Conversion of Hepatic Cells into Pancreatic Cells.
It has been suggested that both liver and pancreas actually arise from a common precursor. We take advantage of the closeness in developmental lineage between these cells, and attempt to identify the stem cell population that retains this bipotential activity. We have utilized Xenopus embryos to screen for the molecules capable of converting liver cells into the pancreas tissue types via a transgenic approach. We drive the expression of a given gene by the TTR promoter (transthyretin) that is transcriptionally active only in the liver. Adjacent to the gene is a GFP reporter gene whose expression is under the control of a minimal elastase promoter, which is only active in the pancreas. Normally, GFP would be expressed only in the pancreas with the construct. However, when the given protein is capable of converting liver cells into a pancreatic lineage, the liver cells will become pancreatic cells, resulting in the expression of GFP in the liver in addition to the normal GFP expression in the pancreas. We have identified transcription factors that are capable of converting liver cells into the pancreatic cell using this approach. We have also generated ES cell lines that contain a pALB-EGFP reporter construct. These cells are subjected to a series of growth factor cocktail treatments to differentiate into hepatic cells, followed by ectopic expression of these transcription factors. We found that some of these molecules can convert differentiating liver cells into pancreatic cells.
GFP positive Xenopus pancreas
