Lipid droplets are formed in 2-cell-like cells.

Embryonic stem (ES) cells, derived from the inner cell mass of a blastocyst, are believed to pluripotent cells and give rise to embryonic, but not extraembryonic, tissues. In mice, totipotent 2-cell stage embryo-like (2-cell-like) cells, which are identified by reactivation of murine endogenous retrovirus with leucin transfer RNA primer (MuERV-L), arise at a very few frequencies in ES cell cultures. Here, we found that a lipid droplet forms during the transition from ES cells to 2-cell-like cells, and we propose that 2-cell-like cells utilize a unique energy storage and production pathway.

DNA hypomethylation circuit of mouse rDNA repeats in the germ cell lineage.

DNA methylation is dynamically reprogrammed at two developmental periods, in primordial germ cells and pre-implantation embryos, via distinct phases of DNA demethylation and de novo methylation. Here we show that ribosomal DNA (rDNA) promoters are hypomethylated in sperm and oocytes; this hypomethyaltion was maintained during pre-implantation development. A DNA methylation analysis of embryonic and extra-embryonic cells on embryonic day 7.