Patterning mechanisms in the body trunk and the appendages of Drosophila

During evolution, many animal groups have developed specialised outgrowths of the body wall, limbs or appendages. The type of appendage depends on the identity of the segment where they appear, indicating that the Hox genes c ontribute to appendage specification. Moreover, work carried out principall y in Drosophila has identified the gene products and the mechanisms involve d in pattern formation in the appendages. In this essay, we compare the mor phogenetic processes in the appendages and the body wall; the function of t he Box genes and the response to the signalling molecules involved in local patterning. We speculate that, although the basic mechanisms are similar, there are significant differences in the manner the body trunk and appendag es respond to them.