The establishment of the anteroposterior axis is an important early event in embryogenesis. Many of the molecular components of this process are conserved through evolution. However, Bicoid - the master organiser of anterior development in Drosophila - is not present in non-dipteran insects. So, to study the evolution of body plan patterning, Olesnicky and co-workers have turned to the wasp Nasonia (see ). Wasps lack Bicoid but their embryos are patterned completely within a syncytial environment like fly embryos. The researchers report that a gradient of localised caudal mRNA directs posterior patterning in Nasonia embryos in contrast to Drosophila embryos, in which the translational repression of caudal mRNA by Bicoid establishes a gradient of Caudal protein. The researchers also show that Nasonia caudal activates the expression of gap genes, which then activate pair-rule gene expression; in Drosophila, caudal mostly regulates pair-rule gene expression. These results suggest that caudal is an ancestral master organiser of patterning but that its role has been reduced in dipterans.
