Our contribution discusses the potential use of cell therapies (nucleus replacement) in mammalian oocytes. It is assumed that these approaches may be used, for example, for the elimination of mutated maternally transmitted mitochondrial DNA (mtDNA) as well as for the reconstruction of normal oocytes from oocytes that are developmentally compromised. Moreover, it is speculated that the replacement of germinal vesicles by somatic cells may result in cells of the haploid genome: the production of germ cells from somatic cells. The preliminary results obtained in our laboratories are discussed in this article.