Reprogramming a somatic nucleus by trans-modification activity in germ cells

The germ cell lineage is totipotent insofar as it provides a link between a n individual and the subsequent generations. There is a series of character istic genomic modifications in germ cells that distinguish this lineage fro m somatic cells. These modifications include extensive demethylation of the genome, erasure of allele-specific methylation of imprinted loci and re-ac tivation of the silent X chromosome To test if this is an active process ca pable of reprogramming a somatic nucleus, toe prepared germ cell-somatic ce ll hybrids. A dominant trans modification activity was detected in germ cel ls that was capable of inducing similar modifications in the somatic nucleu s. This experimental system can therefore be used to study how determined c ell state can be reversed by specific genomic modifications.