Reprogramming somatic gene expression through communication with blastomeres

The program of a differentiated somatic cell can be altered by nuclear transplantation, cell fusion or co-culture. This work demonstrates that somatic gene function can be manipulated in vitro. We developed two novel strategies by which reprogramming of gene expression in a differentiated somatic cell can take place. Our first approach relies on the establishment of connections through gap junctions between somatic cells and blastomeres. We show that mouse epithelial cells are capable of forming gap junctions with blastomeres following injection into cleavage stage mouse embryos. In contrast, fibroblasts adhere but do not form gap junctions with blastomeres. Adhesion of the somatic cells to blastomeres was assessed by electron microscopy and immunological procedures using cell adhesion markers. Transfer of a fluorescent soluble dye from somatic cells to the adherent blastomeres demonstrated formation of functional gap junctions. Establishment of connections between epithelial cells and blastomeres correlated with induction of expression of the embryonic and ES cell-specific transcription factor, Oct-4, in the epithelial cells. We argue that communication between epithelial cells and blastomeres results in changes in somatic cell gene expression. Our second approach relies on the production of cell extracts to which permeabilized fibroblasts are exposed. The resulting fibroblasts are reprogrammed and thus take on characteristics and functions typical of the cell type from which the extract was derived, including the induction of Oct-4. The development of these reprogramming systems can be used to define the factors necessary for reprogramming somatic cells. Ultimately, these strategies for altering genome function could be applied to develop cell therapeutics.