They studied sea-urchin embryos over a 24-hour period, beginning at hour eight of the embryo's existence. During this period, different physical domains exist in the embryo, each of which represents a future structure in the body, like the gut. All the regulatory genes known to exist in the sea-urchin genome and to be expressed in the embryo have been studied, and it was found that certain regulatory genes are expressed in the cells of each domain. Some of the domains will express certain regulatory genes in common, but the combination of genes found in each domain is unique. In addition, they found that this process is dynamicwhere the genes are expressed changes over time. For example, two genes that are coexpressed in one domain at an early stage of the process may then be expressed in different domains at a later stage.
"It's like you are building a complicated edifice," explains Davidson. "And before anything is actually there, the building instructions have already been handed to all the workers. They all know what they are going to have to do once the bulldozer comes in and starts moving earth around."
The team focused on pinning down the precise regulatory genes in the progression of pre-gut cells (which eventually form the gut), following them from their initial stage as undifferentiated cells, to the point of gastrulation. During gastrulation the endoderm cells reorganize from a single layer into an internal tube with three regions that serve as the foundation for the future foregut, midgut, and hindgut structures. The researchers were able to pinpoint which regulatory genes were expressed at which specific times in the 24-hour period, and how thos
|Contact: Deborah Williams-Hedges|
California Institute of Technology