PNAS - November 03 2010
Embryonic stem cells can generate all the cell types of the adult organism. Their properties are controlled by the action of a gene network that formed during the evolution of mammals, indicating that embryonic pluripotency arose in mammals and does not exist in birds and other animal species.
This cells grow indefinitely in culture and retain the capacity to give rise to all the lineages and cell types of the adult organism. These properties are determined by the action of a small group of genes that act as cellular switches, activating other genes important for pluripotency and at the same time shutting down the expression of genes implicated in the first steps of differentiation that occur during embryonic development. These genes are organized into a network in the embryos of mammals, and act in a similar manner during the formation of the blastocyst.
Knowledge in this field has advanced rapidly in recent years, due in large part to the drive to tap the enormous therapeutic potential of embryonic stem cells. But despite efforts in this area, we still know little about how this gene network evolved and whether it carries out similar functions in all vertebrates, or is limited to mammals like mice and humans. In a new study published in the journal PNAS, the team led by Miguel Manzanares at the CNIC compared pluripotency genes in mouse and chick embryos. The team found that although the central gene components of the embryonic pluripotency network are present in birds, their expression in the early embryo is incompatible with the function identified for them in mouse embryos. When the team examined the genomes of mice and chickens, they found that the regulatory elements in mice that control the targets of the pluripotency network?switching them on or off?are not present in chickens. All of this suggests that the gene network that acts in the pluripotent cells of mouse embryos was assembled during the evolution of mammals. Knowledge of how this occurred will provide greater understanding of how pluripotency is genetically controlled in the embryo, and will broaden our understanding of the fascinating potential of stem cells.