Chapter 5 - Plasticity of Somatic Nucleus by Epigenetic Reprogramming Via Cell Hybridization

Abstract

This chapter presents various studies that focus on the ability of pluripotential stem cells to reprogram somatic nuclei in hybrid cells. The pluripotential stem cells such as the embryonic stem (ES) and gEG cells are capable of reprogramming the somatic nuclei by cell fusion, similar to the nuclear reprogramming represented by the transplantation of somatic nuclei into enucleated oocytes in various animal species. This plasticity of the somatic nucleus is induced by trans-acting factors derived from the ES and gEG cells. Nuclear reprogramming of somatic cells in hybrid cells is demonstrated by the reactivation of the inactive X chromosome present in a female somatic cell, contribution of the ES and gEG hybrid cells to the primary germ layers of chimeric embryos, and reactivation of the somatic-cell-derived Oct4–GFP marker gene, which is specifically expressed in pluripotent cells. Apart from the ability of both the ES and gEG cells to confer pluripotency to somatic nuclei, the gEG cells have an additional capacity not found in the ES cells, which is the ability to erase DNA methylation associated with imprinted genes. Nuclear reprogramming of the somatic nuclei in the gEG hybrid cells corresponds to the germ-cell-type reprogramming, and nuclear reprogramming of somatic nuclei in the ES hybrid cells corresponds to the preimplantation embryo type. Nuclear reprogramming of somatic nuclei in the ES hybrid cells is perhaps similar to what occurs during the process of somatic cell cloning via nuclear transplantation.