Germ line specific expression of a protein phosphatase Y interacting protein (PPYR1) in Drosophila.

PPYR1, the product of the CG15031 gene, was identified as a protein phosphatase Y (PPY) interacting protein in Drosophila melanogaster using a yeast two-hybrid screen. PPYR1 displays a biphasic expression pattern: the maternal protein is abundant in the developing egg chambers and in the early embryos, while the zygotic protein appears later in development and is localized specifically in the testes of the males. The maternal and zygotic gene products differ from each other in their size having apparent molecular masses of 47 and 66 kDa, respectively. The maternal PPYR1 is localized in the cytoplasm of the follicular and nurse cells and is deposited as a ribonucleoprotein complex in the oocyte. In the early embryos, the PPYR1 is distributed evenly, and it gradually diminishes during embryonic development. Zygotic PPYR1 is expressed exclusively in the testes, predominantly in the cytoplasm of the spermatocytes. PPY is localized in the nuclei of the same cells. Our results suggest that PPYR1 has two distinct developmental isoforms: a maternal protein the expression of which is independent of PPY and a zygotic protein which is co-expressed with PPY.

Expression pattern of Filamin-240 in Drosophila blood cells.

The expression pattern of Filamin-240 was studied in subsets of Drosophila blood cells by means of immunofluorescent staining and Western blot analysis with use of an antibody specific to a "filamin-folding domain", a consensus motif profile generated from the 20 existing filamin repeats. Expression of Filamin-240 is restricted to lamellocytes - a special blood cell type of the cellular immune response - and is involved in the regulation of lamellocyte development. In the cher1 homozygous larvae, which lack Filamin-240 protein, a vigorous lamellocyte differentiation occurs which is further enhanced upon in vivo immune challenge by a parasitic wasp, Leptopilina boulardi. By introducing a full-length transgene encoding the Drosophila Filamin-240 protein into the cher1 Filamin-deficient homozygous mutant, the mutant blood cell phenotype was rescued. These data demonstrate that the expression of Filamin-240 is strictly lamellocyte specific in Drosophila blood cells and that the protein is a suppressor of lamellocyte development.

Tissue- and developmental stage-specific changes in the subcellular localization of the 26S proteasome in the ovary of Drosophila melanogaster.

The intracellular localization of the 26S proteasome in the different ovarian cell types of Drosophila melanogaster was studied by means of immunofluorescence staining and laser scanning microscopy, with the use of antibodies specific for regulatory complex subunits or the catalytic core of the 26S proteasome. During the previtellogenic phase of oogenesis (stages 1-6), strong cytoplasmic staining was observed in the nurse cells and follicular epithelial cells, but the proteasome was not detected in the nuclei of these cell types. The subcellular distribution of the 26S proteasome was completely different in the oocyte. Besides a constant, very faint cytoplasmic staining, there was a gradual nuclear accumulation of proteasomes during the previtellogenic phase of oogenesis. A characteristic subcellular redistribution of the 26S proteasome occurred in the ovarian cells during the vitellogenic phase of oogenesis. There was a gradual decline in the concentration of the 26S proteasome in the nucleus of the oocyte, and in the stage 10 oocyte the proteasome could barely be detected in the nucleus. This was accompanied by a massive nuclear accumulation of proteasomes in the follicular epithelial cells. These results demonstrate that the subcellular distribution of the 26S proteasome in higher eukaryotes is strictly tissue- and developmental stage-specific.

CG15031/PPYR1 is an intrinsically unstructured protein that interacts with protein phosphatase Y.

Protein phosphatase Y (PPY) is a Drosophila testis-specific enzyme of unknown function. In a yeast two-hybrid screen we identified CG15031/PPYR1 as a PPY interacting protein. The specificity of the protein-protein interaction was proven by directed two-hybrid tests. The complex formation between PPY and PPYR1 was confirmed under in vitro and in vivo conditions by plasmon resonance spectroscopy, co-immunoprecipitation, and pull down experiments. Recombinant PPYR1 expressed in Escherichia coli is a heatstable, protease sensitive, intrinsically unstructured RNA-binding protein that migrates anomalously in SDS-polyacrylamide gel electrophoresis. It can be phosphorylated by cAMP-dependent protein kinase in vitro. PPYR1 moderately inhibits PPY activity, the inhibitory potential of the protein is slightly increased by phosphorylation. We suggest that PPYR1 may function as a scaffolding protein that targets PPY to RNA and other protein partners in Drosophila melanogaster.