The tricornered gene, which is required for the integrity of epidermal cell extensions, encodes the drosophila nuclear DBF2-Related kinase

During their differentiation epidermal cells of Drosophila form a rich vari ety of polarized structures. These include the epidermal hairs that decorat e much of the adult cuticular surface, the shafts of the bristle sense orga ns, the lateral extensions of the arista, and the larval denticles. These c uticular structures are produced by cytoskeletal-mediated outgrowths of epi dermal cells, Mutations in the tricornered gene result in the splitting or branching of all of these structures. Thus, tricornered function appears to be important for maintaining the integrity of the outgrowths. tricornered mutations however do not have major effects on the growth ol shape of these cellular extensions. Inhibiting actin polymerization in differentiating ce lls by cytochalasin D or latrunculin A treatment also induces the splitting of hairs and bristles, suggesting that the actin cytoskeleton might be a t arget of tricornered. However, the drugs also result in short, fat, and occ asionally malformed hails and bristles. The data suggest that the function of the actin cytoskeleton is important for maintaining the integrity of cel lular extensions as well as their growth and shape. Thus, if tricornered ca uses the splitting of cellular extensions by interacting with the actin cyt oskeleton it likely does so in a sutle way. Consistent with this possibilit y we found that a weak tricornered mutant is hyper-sensitive to cytochalasi n D. We have cloned the tricornered gene and found that it encodes the Dros ophila NDR kinase. This is a conserved ser/thr protein kinase found in Caen orhabditis elegans and humans that is related to a number of kinases that h ave been found to be important in controlling cell structure and proliferat ion.