'Tree of life' constructed for all living bird species

Scientists have mapped the evolutionary relationships among all 9,993 of the world’s known living bird species. The study, published today in Nature, is an ambitious project that uses DNA-sequence data to create a phylogenetic tree — a branching map of evolutionary relationships among species — that also links global bird speciation rates across space and time.

“This is the first dated tree of life for a class of species this size to be put on a global map,” says study co-author Walter Jetz, an evolutionary biologist at Yale University in New Haven, Connecticut.

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About face: Study shows long-ignored segments of DNA play role in coordinating early stages of face development

The human face is a fantastically intricate thing. The billions of people on the planet have faces that are individually recognizable because each has subtle differences in its folds and curves. How is the face put together during development so that, out of billions of people, no two faces are exactly the same?

School of Medicine researcher Joanna Wysocka, PhD, and her colleagues have discovered key genetic elements that guide the earliest stages of the process.

Their research, published in the Sept. 13 issue of Cell Stem Cell, provides a resource for others studying facial development and could give insights to the cause of some facial birth defects. Because there is not enough genetic information in the body to define exactly where each cell will go, development of the face proceeds much like origami: genes provide instructions for folding, crimping, and movement of cells. As with origami, following a sequence of simple instructions can result in a complex, intricate object.

Wysocka focused on the first critical fold in the process of making an embryo, when the whole of the embryo is a flat sheet of cells that creases and closes over on itself to make a tube. Much of the tube eventually becomes the foundation of the brain and the spinal column, but one end sets the stage for the formation of the head and face. This process is driven by a small population of remarkable cells called neural crest cells.

"We were interested in identifying the portions of the human genome that are responsible for the behavior of the neural crest," Wysocka said.

What they discovered is that the modification of a collection of DNA sequences called “enhancers” can dial up or down the activity of the genes governing which cells eventually become the face. It’s almost as if they have discovered how the instructions for a piece of origami can be modified — slightly change how a fold is made and you may end up with something very different looking.