Cell lines of the same cell type, which were isolated and cultivated under the same conditions, led to significantly different efficiencies after somatic nuclear transfer.
A decrease of the DNA methylation of somatic cells after treatment with the chemical 5-AZA seems possible. The accurate dosage is, however, very difficult to determine since the therapeutically effective dose range is very small.
The demethylation is incomplete and is accompanied by changes in the cell cycle. The exact dosage and application from must be adapted for each cell type and each culture condition.
A non-specific large-scale DNA demethylation of donor cells before transfer to anucleated oocytes generally led to a reduced developmental competence after nuclear transfer as compared to the transfer of untreated cells.
An improvement of the developmental competence of embryos after nuclear transfer can only be expected, if the non-specific DNA demethylation in the donor cell can be combined with an embryo-specific remethylation.