27 - 30 May 2005

THE OOCYTE - EMBRYONIC STEM CELL CIRCUIT Hans R Schöler, Jeong Tae Do, Luca Gentile, Karin Hübner, Michele Boiani Department for Cell and Developmental Biology Max Planck Institute for Molecular Biomedicine Mendelstrasse 7 D- 48149 Münster Germany

Mouse embryonic stem cells (ESCs) in culture can develop into oogonia, which then enter meiosis and recruit adjacent cells to form follicle-like structures that subsequently develop into blastocysts (1). Insight into the process of oogenesis should elucidate important concepts, such as somatic cell nuclear transfer.

The concept of reprogramming, in regard to the transfer of a differentiated nucleus into an oocyte, can be defined as the transformation of a somatic cell nucleus into a functional embryonic nucleus capable of giving rise to a viable organism. The expression of embryonic genes according to the wild-type, or normal, pattern is necessary for embryonic development, and is indicative of nuclear reprogramming.

Oct4 has been used as a marker for gene reprogramming in relation to the developmental potential of somatic cell clones (2). The re-activation of Oct4 expression in neuroplast cells upon fusion with ESCs has been shown to be contingent on the presence of yet unidentified nuclear factors in ESCs, and is independent of DNA replication and cell division (3).

Recent evidence indicates that reprogramming is independent of the somatic cell type (neuroplasts or cumulus cells), and begins to occur two days after fusion. Clone-clone aggregates from genetically identical, but epigenetically different, embryos do not form more blastocysts, but the majority exhibit normal Oct4 expression and have higher rates of fetal and postnatal development (4).

(1) Hübner, K et al. Science: 300, 1251, 2003
(2) Boiani M, et al. Genes Dev16: 1209, 2002
(3) Do J.-T. and H.R. Schöler. Stem Cells: 22, 941 2004
(4) Boiani M, et al. EMBO J. 22: 5304, 2003.

List of abstracts from the 3rd International Conference on the Female Reproductive Tract