Evolutionary history of the iroquois/Irx genes in metazoans.

Background: The iroquois (iro/Irx) genes encode transcriptional regulators that belong to the TALE superclass of homeodomain proteins and have key functions during development in both vertebrates and insects. The Irx genes occur in one or two genomic clusters containing three genes each within the Drosophila and several vertebrate genomes, respectively. The similar genomic organization in Drosophila and vertebrates is widely considered as a result of convergent evolution, due to independent tandem gene duplications.

Prepatterning the Drosophila notum: the three genes of the iroquois complex play intrinsically distinct roles.

The Drosophila thorax exhibits 11 pairs of large sensory organs (macrochaetes) identified by their unique position. Remarkably precise, this pattern provides an excellent model system to study the genetic basis of pattern formation. In imaginal wing discs, the achaete-scute proneural genes are expressed in clusters of cells that prefigure the positions of each macrochaete.