"Nuclear Reprogramming" and "Epigenetic Reprogramming"

“Nuclear reprogramming” is a phenomenon regulated by complex mechanisms that lead to the restoration of pluripotential competence in specialized somatic nuclei. Nuclear reprogramming is induced by changes in epigenet ic modif icat ions, known col lect ively as “ep igene t i c rep rog ramming” . I n somat i c ce l l development, on-off switching of certain key genes, which function in determining cell fate in a particular d i r ec t i on , i s r egu la ted t h rough ep igene t i c reprogramming in restricted regions of the genome. In nuclear reprogramming, genome-wide epigenetic reprogramming, which triggers a global restoration of ep igene t i c memory i n the genome lead ing to transformation from a specified to a default nuclear s t a te , i s c ruc ia l . Genome-w ide ep igene t i c reprogramming occurs in nuclear reprogramming with the nuclear transfer of somatic cells to enucleated oocytes and via cell hybridization between embryonic stem cells and adult somatic cells, and also in germ cell and early embryonic development but not in somatic cell development. Global chromatin de-condensation marked by h is tone H3 lys ine 4 methy la t ion is mechanistically linked with the genome-wide epigenetic reprogramming. At least two steps; 1) erasure of the somatic epigenotype induced by the genome-wide epigenetic reprogramming and 2) establishment of a plur ipotent ial cel l -specif ic epigenotype by local epigenetic reprogramming through the activity of key players including Oct4, Sox2, Ehz2 and Nanog, may be required for conferring and maintaining pluripotential competence in the reprogrammed somatic nuclei. Nuclear Reprogramming in Early Embryonic Development