Nuclei of Embryonic Stem Cells Reprogram Somatic Cells

Abstract

The restricted potential of a differentiated cell can be reverted back to a pluripotent state by cell fusion; totipotency can even be regained after somatic cell nuclear transfer. To identify factors involved in resetting the genetic program of a differentiated cell, we fused embryonic stem cells (ESCs) with neurosphere cells (NSCs). The fusion activated Oct4, a gene essential for pluripotency, in NSCs. To further identify whether cytoplasmic or nuclear factors are responsible for its reactivation, we fused either karyoplasts or cytoplasts of ESCs with NSCs. Our results show that ESC karyoplasts could induce Oct4 expression in the somatic genome, but cytoplasts lacked this ability. In addition, mitomycin C–treated ESCs, although incapable of DNA replication and cell division, could reprogram 5‐azacytidine–treated NSCs. We therefore conclude that the Oct4 reprogramming capacity resides in the ESC karyoplast and that gene reactivation is independent of DNA replication and cell division.

Induction of pluripotency by defined factors

“…The karyoplasts of ES cells could induce the expression of Oct3/4 and a partially reprogrammed state in these differentiated cells. 19) On the other hand, another group succeeded in establishing human ES cells in which the nuclei were completely replaced by the nuclei of somatic cells. 20) They showed that a partially pluripotent state was obtained.…”

High-efficiency somatic reprogramming induced by intact MII oocytes

“…Oct4 expression begins at the four-to eight-cell stage in mouse parthenogenetic embryos and could start reprogramming the somatic nucleus in the reconstructed embryos. Fourth, undefined nuclear factors present in the CSC of oocytes, in the nuclei of the blastomeres of a parthenogenetic embryo [27,28] and in the nuclei of parthenogenetic ES cells [7] may have important roles in conferring pluripotency to the somatic nucleus present in the reconstructed oocyte, in the reconstructed embryo and in the 4N or 3N ES cells, respectively. Activated intact oocytes show stronger re- programming ability than enucleated oocytes, possibly indicating that oocyte nuclei contain extra factors for reprogramming somatic nuclei.…”

“…The fact that pluripotent 4N hybrid cells can be generated from the fusion of somatic cells with embryonic stem (ES) [3,4], embryonic germ (EG) [5] and embryonic carcinoma [6] cells suggests that nuclear factors or pluripotent genes expressed in these cells are responsible for somatic reprogramming [7]. Derivation of induced pluripotent stem (iPS) cells from somatic cells indicates that overexpression of key transcription factors can drive somatic reprogramming [8,9].…”

Cell reprogramming: expectations and challenges for chemistry in stem cell biology and regenerative medicine

“…32 These approaches include somatic cell nuclear transfer (SCNT, often referred to as somatic cloning), [33][34][35][36] which not only raised numerous ethical debates, but so far has been shown to be too inefficient to be practicable. 37 Other techniques include fusion of adult cells to ES cells [38][39][40] and treatment of differentiated cells with newt blastema extracts, 41 but they have yet to be further developed. At the same time, a different strategy has been quite successful, the so-called transdifferentiation process, which consist of the direct reprogramming of a somatic cell into a different cell type, possibly without going back and forth in the differentiation hierarchy.…”