Irreversible gene repression model for control of development.

As the pluripotent cells of early embryos differentiate, each progressively loses the potency to develop into several phenotypes. Ultimately, each cell becomes irreversibly restricted to the expression of a single phenotype. Although in many instances details regarding those restriction events are well known, there is little information concerning the nature of the gene transcription changes involved. A model that accounts for the diminution of developmental potential as resulting from progressive, irreversible repression of previously active genes is presented. A scheme of progressive gene repression, rather than selective gene activation, is most consistent with observations from experimental embryology as well as from more recent biochemical experimentation.