Conserved usage of gap and homeotic genes in patterning the CNS

The homeotic and cephalic gap genes play central roles in the specification of the anteroposterior animal body axis. Genetic studies carried out in Dr osophila and mouse now demonstrate that these genes are also involved in em bryonic brain development. The homeotic genes act in posterior brain patter ning, and the cephalic gap genes act in anterior brain patterning. Moreover , striking cross-phylum gene replacement experiments show that invertebrate and vertebrate members of the orthodenticle gene family can functionally r eplace each other. These findings indicate that the genetic mechanisms invo lved in embryonic brain development are conserved and suggest a common evol utionary origin of the insect and vertebrate brain.