Characteristics of genes up-regulated and down-regulated after 24 h starvation in the head of Drosophila.

Starvation is a common experience under fluctuating food conditions in nature, and response to it is vital for many organisms. Many studies have investigated the response at physiological and behavioral level, whereas the studies on starvation-induced transcriptional changes in the brain and the surrounding tissues are still limited. We here investigated global changes in transcript abundance in the head after 24 h starvation by microarray expression profiling of 2 wild-derived inbred strains of Drosophila melanogaster, and identified a core set of 65 up-regulated and 48 down-regulated genes upon starvation. Among these up-regulated genes, 22 genes were circadian oscillating genes previously identified in the head of Drosophila. Interestingly, most (86%) of these circadian genes show their expression peak in a narrow time range of ZT7.0-12.0, when flies are relatively restless and less feeding in the normal condition. Among the down-regulated genes, 2 genes with highest fold-differences, fit and CG8147, are known to have female-biased expression in the head, and 1 gene, Obp99b, is known to be male-biased. Together with the realtime qPCR experiments on female and male transcripts, our data suggest that these sex-specific genes are candidate genes mediating a possible trade-off between starvation resistance and reproduction. Eleven down-regulated genes are known to be involved in the immune response. These changes in head transcriptome upon starvation reflect modulation of expression in some normally oscillating rhythmic genes and reduction in the resource allocation toward sexual activity and immunity.

A novel Takeout-like protein expressed in the taste and olfactory organs of the blowfly, Phormia regina.

In insects, the functional molecules responsible for the taste system are still obscure. The gene for a 28.5 kDa protein purified from taste sensilla of the blowfly Phormia regina belongs to a gene family that includes takeout of Drosophila melanogaster. Molecular phylogenetic analysis revealed that the Phormia Takeout-like protein is most similar to the protein encoded by a member of the Drosophila takeout gene family, CG14661, whose expression and function have not been identified yet. Western blot analyses revealed that Phormia Takeout-like protein was exclusively expressed in antennae and labellum of the adult blowfly in both sexes. Immunohistochemical experiments demonstrated that Takeout-like protein was localized around the lamella structure of the auxiliary cells and in the sensillar lymph of the labellar taste sensillum. In antennae, Takeout-like protein was distributed at the base of the olfactory sensilla as well. No significant differences in Takeout-like protein expression were found between the sexes. Our results suggest that Phormia Takeout-like protein is involved in some early events concerned with chemoreception in both the taste and olfactory systems.

An odorant-binding protein facilitates odorant transfer from air to hydrophilic surroundings in the blowfly.

Chemical sense-related lipophilic ligand-binding protein (CRLBP) is an insect odorant-binding protein (OBP) found abundantly in the taste and olfactory organs of the blowfly, Phormia regina. Through computational construction, a three-dimensional molecular model of a CRLBP indicated good fitting to a fluorescent ligand, 7-hydroxycoumarin (7-HC), in its ligand-binding pocket. By showing that the fluorescence of 7-HC bound to CRLBP migrated in a native electrophoresis gel, we confirmed that CRLBP formed a stable complex with 7-HC. In an odorant-binding experiment, 7-HC vapor odor was introduced by aeration to the aquatic solution containing CRLBP and its binding to CRLBP fluorospectrometrically quantified. Because olfactory organs as well as taste organs of flies respond to vapors, we suggest that CRLBP effectively transfers odorants from the air into aquatic surroundings by forming stable complexes with airborne molecules in both chemosensory organs.

Ant nestmate and non-nestmate discrimination by a chemosensory sensillum.

In animal societies, chemical communication plays an important role in conflict and cooperation. For ants, cuticular hydrocarbon (CHC) blends produced by non-nestmates elicit overt aggression. We describe a sensory sensillum on the antennae of the carpenter ant Camponotus japonicus that functions in nestmate discrimination. This sensillum is multiporous and responds only to non-nestmate CHC blends. This suggests a role for a peripheral recognition mechanism in detecting colony-specific chemical signals.

Gq alpha subunit mediates receptor site-specific adaptation in the sugar taste receptor cell of the blowfly, Phormia regina.

The gustatory system is essential for almost all animals. The recent identification of G protein-coupled receptor proteins (GPCRs) has progressed molecular biological studies of gustatory systems, although the signal transduction mechanisms have not yet been fully elucidated. In vision and olfactory receptor cells, Gq class G protein is known to be a major signal transducer. By functional blocking of intrinsic Gq with an anti-Gq/11alpha antibody, we investigated the roles of Gq in the sugar receptor cell of the blowfly, Phormia regina. Before and after introduction of the anti-Gq/11alpha antibody into the cell through the DOC-permeabilized cell membrane, we recorded the responses of the receptor cell to sucrose and d-fructose, which stimulate different receptor sites, respectively. The initial impulse frequency in response to either sucrose or D-fructose was not changed by antibody introduction, whereas the adaptation rate in sucrose stimulation, but not fructose stimulation, became slower after antibody introduction. These results indicate that: (1) Gq is a regulator of adaptation in the sugar receptor cell of Phormia, rather than a transducer, and (2) different adaptation mechanisms are promoted by stimulations with sucrose and D-fructose.

Molecular and functional characterization of a unique Rab protein, RABRP1, containing the WDIAGQE sequence in a GTPase motif.

Rab proteins of the small G-protein superfamily are known to be involved in intracellular vesicle transport. Here, we describe the unique characteristics of a novel Rab protein, RABRP1 (Rab-Related Protein 1). The Drosophila RabRP1 gene is mainly transcribed in the eyes and testes, where the 3-kb and 1.5-kb mRNAs, respectively, are the predominant gene products. The amino-acid sequence deduced from the longer cDNA indicated that the C-terminal 1/3 of the sequence shares homology with Rab proteins, whereas the rest of the peptide shows no significant homology with any other proteins. Immunoblot analysis using antiserum against the Rab-domain indicated that the multiple translates (94 k, 53 k, 30 k, 29 k and 27 k) were expressed in the eyes. In contrast, only smaller peptides (30 k, 29 k and 27 k) were identified in the testes. Molecular phylogenetic analysis revealed that RABRP1 forms a subgroup with Dictiostelium RabE and mammalian Rab29, Rab32, Rab38 proteins, whose functions have not been identified yet. RABRP1 and its relatives were characterized by the amino acid substitution occurring in the conserved GTP-binding motifs. Immunohistochemical studies demonstrated that RABRP1 was localized on the subrhabdomeric cisternae of photoreceptor cells and on the pigment granules in photoreceptor and pigment cells in the retina. The expression of the dominant negative RABRP1 caused the abnormal accumulation of autophagosome-like vesicles. These data suggest that RABRP1 is involved in the lysosomal vesicle transport pathway, including the biogenesis or degradation of pigment granules.