Intercalation of cell fates during tarsal development in Drosophila

The process of proximal-distal (PD) patterning in animal appendages requires the generation of positional values as they grow away from the main body axes. In the Drosophila leg some PD fates are intercalated between previously existing ones. In a recent study, Kojima et al. describe a role for the homeobox gene Bar in patterning of the distal region of the leg. Their work highlights fundamental aspects of PD development, such as the fashion in which new PD values appear, the importance of regulatory relationships between PD genes, and correlation of their patterns of expression with morphogenesis and differentiation.