 PBX1 and PBX2 are two proteins that are present in all vertebrate embryos but have different functions depending on their location. In some cases, they work together to control the expression of genes involved in the development of specific body parts such as the hindlimb. They also interact with another protein called hand2, which helps them target certain areas of the embryo. This allows them to direct the formation of the hindlimb in a way that is unique from other body parts. This article was authored by Marta Losa, Iros Barossi, Marco Osterwalder, and others.