Progress in somatic cloning mammals was made possible by research on the interactions between the nuclear-cytoplasmic enucleated oocyte-taker and giver of exogenous nucleus. An important factor which directly affects the process is the level of MPF activity in the oocyte cytoplasm. This factor affects the microtubular cytoskeleton and nuclear envelope, the spatial form of chromatin enabling coordinated DNA replication in the reconstructed oocyte. This allows the activation of molecular mechanisms responsible for genome reprogramming a somatic cell cytoplasm recipient oocyte.