Germ Line, Stem Cells, and Epigenetic Reprogramming

Thegermcelllineagehastheuniqueattributeofgeneratingthetotipotentstate.Developmentofblastocystsfromthetotipo tentzygoteresultsintheestablishmentofpluripotentprimitiveectodermcellsintheinnercellmassofblastocysts,whichsub sequently develop into epiblast cells in postimplantation embryos. The germ cell lineage in mice originates from these pluripotent epiblast cells of postimplantation embryos in response to specific signals. Pluripotent stem cells and unipotent germ cells share some fundamental properties despite significant phenotypic differences between them. Additionally, early primordialgermcellscanbeinducedtoundergodedifferentiationintopluripotentembryonicgermcells.Investigationsonthe relationship between germ cells and pluripotent stem cells may further elucidate the nature of the pluripotent state. Furthermore,comprehensiveepigeneticreprogrammingofthegenomeinearlygermcells,includingextensiveerasureofepigenetic modifications, is a critical step toward establishment of totipotency. The mechanisms involved may be relevant for gaininginsightintoeventsthatleadtoreprogrammingofsomaticcellsintopluripotentstemcells.