Making HoxD waves

When developmental biologists first got their hands on DNA, perhaps the most remarkable finding was that the order of genes on the chromosome reflected the genes' time and location of expression. Genes at the tail end of each cluster were expressed proximally and early; those at the front of the cluster were expressed distally and later. Now, Basile Tarchini and Denis Duboule (University of Geneva, Switzerland) find that simple placement of two gene regulatory elements explains the entire expression sequence for the HoxD cluster, which patterns forelimb development.

Two waves of HoxD expression control limb formation in vertebrates: an early wave, which generates proximal structures such as the forearm, and a later wave, which forms distal structures such as digits. By breeding mouse strains...