Fig. 5.

Germ-line–poised genes as a foundation for totipotency in the germ line. Critical developmental genes are continuously maintained in a poised state (purple and orange circles), with transcription repressed. Loss of either H3K4me3 (resolution toward the active state, with associated increases in gene expression) or H3K27me3 (resolution toward the repressed state) at specific promoters results in terminal differentiation. Those cells that maintain a complete set of poised developmental regulators throughout development constitute the germ cells.