A molecular characterization of selected cecropins and cysteine proteinases in Drosophila

Sammanfattning: Insects that have been infected with bacteria produce antibacterial peptides. Among the most potent antibacterial peptides in Drosophila are the cecropins. This work describes the cloning and expression studies of the CecC gene, which completes the picture of the cecropin locus in Drosophila melanogaster. Inducible CecC gene expression has been detected in the fat body and potential hemocytes, by RNase protection and in situ hybridizations. The CecC gene reaches its highest levels in early pupae, where gene expression can also be detected in the hindgut. A conserved region in the promoter regions of the Drosophila cecropin genes has been identified, consisting of three elements. A suitable plasmid for P element-mediated transformation in Drosophila has been constructed, pWimm. By cloning any gene into a pWimm restriction site, it can be put under the tightly regulated CecA2 gene control. CecA2 mediated pWimm expression has been shown to be induced by bacterial infection of transgenic flies. In addition to the previously described expression in the fat body, we detected inducible expression in the female reproductive tract, and constitutive expression in the male reproductive tract.This thesis also describes two new, blood cell expressed, cysteine proteinases in Drosophila. Calpains are specific cytosolic endopeptidases, with a putative regulatory function. This thesis presents the cloning of a new calpain, that is expressed in hemocytes, the central nervous system and the midgut. Immunostaining experiments show that the protein is only detected in a subset of the cells that express the mRNA. Differential splicing of CalpA gene transcripts results in two different calpains, of which one lacks a calcium-binding domain. We also present the cloning of a cathepsin-like cyteine proteinase gene, CP1, from Drosophila. We show that hemocytic Drosophila mbn-2 cells express CP1 in high amounts, and the protein is localized to small granules by immunofluorescence experiments. These data indicates that the CP1 might have a role in the degradation of phagocytosed material in Drosophila.