Silencing of an abdominal Hox gene during early development is correlated with limb development in a crustacean trunk

SUMMARY We tested whether Artemia abd-A could repress limbs in Drosophila embryos, and found that although abd-A transcripts were produced, ABD-A protein wasnot. Similarly, developingArtemiaepidermal cells showed expression of abd-A transcripts without accumulation of ABDA protein. This finding in Artemia reveals a new variation in Hox gene function that is associated with morphological evolution. In this case, a HOX protein expression pattern is completely absent during early development, although the HOX protein is expressedat laterstages in thecentral nervous system in a ‘‘homeotic-like’’ pattern. The combination of an absence of ABD-A protein expression in the Artemia limb primordia and the weak repressive function of Artemia UBX protein on the limb-promoting gene Dll are likely to be two reasons why homonomous limbs develop throughout the entire Artemia trunk.