Compartmental organization of the Drosophila genital imaginal discs.

We have investigated the anterior and posterior compartmental organization of the genital imaginal disc. Unlike the thoracic discs, the genital disc is a compound disc consisting of three primordia--the female genital, male genital, and anal primordia. Here we provide evidence that each primordium is divided into anterior and posterior compartments. Genes that are known to be expressed in compartment-specific manners in other discs (engrailed, hedgehog, patched, decapentaplegic, wingless and cubitus interruptus) are expressed in analogous patterns in each primordium of the genital disc. Specifically, engrailed and cubitus interruptus are expressed in complementary domains, while patched, decapentaplegic and wingless are expressed along the border between the two domains. Mitotic clones induced at the beginning of the second larval instar do not cross the boundary between the engrailed-expressing and cubitus interruptus-expressing domains, indicating that these domains are true genetic compartments. Furthermore, we examined the phenotypes of mutant clones of the cAMP-dependent protein kinase A and engrailed-invected, genes that are known to play compartment-specific functions in other discs. These experiments demonstrate that the anterior/posterior patterning functions of these genes are conserved in the genital disc. The adult clonal phenotypes of protein kinase A and engrailed-invected mutants also provide a more detailed map of the adult genitalia and analia with respect to the anterior/posterior compartmental subdivision. Our results lead us to propose a new model to describe the anterior and posterior compartmental organization of the genital disc.