Cell doi:10.1016/j.cell.2009.04.017 (2009)

In a broad-ranging study, Thomas Boehm of the Max Planck Institute of Immunobiology in Freiburg, Germany, and his colleagues attempt to reconstruct the evolutionary history of the thymus, the immune-system organ where T cells accumulate and mature.

The authors looked at the expansion and diversification of genes implicated in T-cell and thymus development in 13 species spanning the chordate phylogenetic tree. They paid special attention to the jawed vertebrates, which have a thymus, and jawless fishes such as lampreys, which do not. The authors conclude that the latter have many but not all of the genes required to develop a thymus. The study begins to show how the duplication and cooption of genetic pathways leads to the development of a complex organ.