Genetic interactions between Protein Kinase D and Lobe mutants during eye development of Drosophila melanogaster

BACKGROUND: In Drosophila, the development of the fly eye involves the activity of several, interconnected pathways that first define the presumptive eye field within the eye anlagen, followed by establishment of the dorso-ventral boundary, and the regulation of growth and apoptosis. In Lobe (L) mutant flies, parts of the eye or even the complete eye are absent because the eye field has not been properly defined. Manifold genetic interactions indicate that L influences the activity of several signalling pathways, resulting in a conversion of eye tissue into epidermis, and in the induction of apoptosis. As information on the molecular nature of the L mutation is lacking, the underlying molecular mechanisms are still an enigma. RESULTS: We have identified Protein Kinase D (PKD) as a strong modifier of the L mutant phenotype. PKD belongs to the PKC/CAMK class of Ser/Thr kinases that have been involved in diverse cellular processes including stress resistance and growth. Despite the many roles of PKD, Drosophila PKD null mutants are without apparent phenotype apart from sensitivity to oxidative stress. Here we report an involvement of PKD in eye development in the sensitized genetic background of Lobe. Absence of PKD strongly enhanced the dominant eye defects of heterozygous L(2) flies, and decreased their viability. Moreover, eye-specific overexpression of an activated isoform of PKD considerably ameliorated the dominant L(2) phenotype. This genetic interaction was not allele specific but similarly seen with three additional, weaker L alleles (L(1), L(5), L(G)), demonstrating its specificity. CONCLUSIONS: We propose that PKD-mediated phosphorylation is involved in underlying processes causing the L phenotype, i.e. in the regulation of growth, the epidermal transformation of eye tissue and apoptosis, respectively.