Functional coupling of acoustic and chemical signals in the courtship behaviour of the male Drosophila melanogaster

During courtship, the male Drosophila melanogaster sends signals to the female through two major sensory channels: chemical and acoustic. These signals are involved in the stimulation of the female to accept copulation. In order to determine the respective importance in the courtship of these signals, their production was controlled using genetical and surgical techniques. Males deprived of the ability to emit both signals are unable to mate, demonstrating that other (e.g. visual or tactile) signals are not sufficient to stimulate the female. If either acoustic or chemical signals are lacking, the courtship success is strongly reduced, the lack of the former having significantly more drastic effects. However, the accelerated matings of males observed with males bearing wild-type hydrocarbons compared with defective ones, whichever the modality of acoustic performance (wing vibration or playback), strongly support the role of cuticular compounds to stimulate females. We can conclude that among the possible factors involved in communication during courtship, acoustic and chemical signals may act in a synergistic way and not separately in D. melanogaster.     

Elaboration and characterization of whey protein beads by an emulsification/cold gelation process: application for the protection of retinol

Whey protein beads were successfully produced using a new emulsification/cold gelation method. The principle of this method is based on an emulsifying step followed by a Ca(2+)-induced gelation of pre-denatured (80 degreesC/30 min) whey protein. Beads are formed by the dropwise addition of the suspension into a calcium chloride (CaCl(2)) solution. IR results show that bead formation has a pronounced effect on the secondary structure of whey protein, which leads to the formation of intermolecular hydrogen-bonded beta-sheet structures. Their preparation conditions (CaCl(2) concentrations of 10, 15, and 20% (w/w)) influence their sphericity and homogeneity: an increase in CaCl(2) favors regular-shaped beads. The physicochemical and mechanical characterizations of beads were also carried out. Their properties, such as swelling, elasticity, deformability, and resistance at fracture, change according to pH levels (1.9, 4.5, and 7.5) and preparation conditions. Indeed, protein chain networks exhibit different behavior patterns with respect to their charge. Finally, bead degradation by enzymatic hydrolysis reveals that beads are gastroresistant and form good matrixes to protect fat-soluble bioactive molecules such as retinol, that have in vivo intestinal absorption sites. The experiment demonstrated the potential of whey protein beads to protect molecules sensitive (i.e., vitamins) to oxidation.     

Modulation of lipid synthesis,apolipoprotein biogenesis,and lipoprotein assembly by butyrate

Short-chain fatty acids (SCFAs) are potent modulators of the growth, function, and differentiation of intestinal epithelia. In addition, high-fiber diets may protect against the development of atherosclerosis because of their cholesterol-lowering effects due, in large part, to SCFA production, liver sterol metabolism, and bile acid excretion. Although the small gut plays a major role in dietary fat transport and contributes substantially to plasma cholesterol and lipoprotein homeostasis, the impact of SCFAs on intestinal lipid handling remains unknown. In the present study, the modulation of lipid synthesis, apolipoprotein biogenesis, and lipoprotein secretion by butyrate was investigated in Caco-2 cells plated on permeable polycarbonate filters, which permit separate access to the upper and lower compartments of the monolayers. Highly differentiated and polarized cells (20 days of culture) were incubated for 20 h with 20 mM butyrate in the apical medium. In the presence of [14C]oleic acid, butyrate led to a significant reduction of secreted, labeled triglycerides (27%; P < 0.01) and phospholipids (25%; P < 0.05). Similarly, butyrate significantly decreased the incorporation of [14C]acetate into exported cholesteryl ester (49%; P < 0.005). As expected from these results, with [14C]oleic acid as a precursor, butyrate significantly (P < 0.05) diminished the delivery of radiolabeled chylomicrons and very low-density lipoproteins. In parallel, [35S]methionine pulse labeling of Caco-2 cells revealed the concomitant inhibitory effect of butyrate on the synthesis of apolipoproteins B-48 (28%; P < 0.05) and A-I (32%; P < 0.01). Collectively, our data indicate that butyrate may influence lipid metabolism in Caco-2 cells, thus suggesting a potential regulation of intestinal fat absorption and circulating lipoprotein concentrations.     

Role of helix 3 in pore formation by the Bacillus thuringiensis insecticidal toxin Cry1Aa

Helix 3 of the Cry1Aa toxin from Bacillus thuringiensis possesses eight charged amino acids. These residues, with the exception of those involved in intramolecular salt bridges (E90, R93, E112, and R115), were mutated individually either to a neutral or to an oppositely charged amino acid. The mutated genes were expressed, and the resultant, trypsin-activated toxins were assessed for their toxicity to Manduca sexta larvae and their ability to permeabilize M. sexta larval midgut brush border membrane vesicles to KCl, sucrose, raffinose, potassium gluconate, and N-methyl-D-glucamine hydrochloride with a light-scattering assay based on osmotic swelling. Most mutants were considerably less toxic than Cry1Aa. Replacing either E101, E116, E118, or D120 by cysteine, glutamine, or lysine residues had only minor effects on the properties of the pores formed by the modified toxins. However, half of these mutants (E101C, E101Q, E101K, E116K, E118C, and D120K) had a significantly slower rate of pore formation than Cry1Aa. Mutations at R99 (R99C, R99E, and R99Y) resulted in an almost complete loss of pore-forming ability. These results are consistent with a model in which alpha-helix 3 plays an important role in the mechanism of pore formation without being directly involved in determining the properties of the pores.     

Calcium fluxes in human trophoblast (BeWo) cells: calcium channels,calcium-ATPase,and sodium-calcium exchanger expression

Although placental transfer of maternal calcium (Ca(2+)) is a crucial process for fetal development, the biochemical mechanisms are poorly understood. In the current study, we have investigated the characteristics of Ca(2+) fluxes in relation with cell Ca(2+) homeostasis in the human placental trophoblast cell line BeWo. Time-courses of Ca(2+) uptake by BeWo cells displayed rapid initial entry (initial velocity (V(i)) of 3.42 +/- 0.35 nmol/mg protein/min) and subsequent establishment of a plateau. Ca(2+) efflux studies with (45)Ca(2+)-loaded cells also showed rapid declined of cell-associated (45)Ca(2+) with a V(i) of efflux (Ve(i)) of 3.30 +/- 0.08 nmol/mg protein/min. Further identification of membrane gates for Ca(2+) entry in BeWo cells was carried out. Expression of Ca(2+) transporter/channel CaT1 and L-type alpha(1S) subunit was showed by RT-PCR. However, mRNA for CaT2 channel and L-type alpha(1C) and alpha(1D) subunits were not revealed. Membrane systems responsible for intracellular Ca(2+) extrusion from BeWo cells were also investigated. Plasma membrane Ca(2+)-ATPases (PMCA) and Na/Ca exchangers (NCX) were detected by Western blot in BeWo cells. Expression of specific isoforms of PMCA and NCX was further investigated by RT-PCR. Messenger RNAs of four isoforms of PMCA (PMCA 1-4) were detected. The presence of messenger RNAs of two NCX isoforms (NCX1 and NCX3) was observed. Ca(2+) flux studies in Na-free incubation medium indicated that NCX played a minimal role in the cell Ca(2+) fluxes. Inorganic ions such as cadmium and manganese did not modify the Ca(2+) fluxes, however, barium increased cell-associated (45)Ca(2+) by, in part, by reducing radiolabel exit.     

The mixed lineage kinase DLK is oligomerized by tissue transglutaminase during apoptosis

Current evidence suggests that the mixed lineage kinase family member dual leucine zipper-bearing kinase (DLK) might play a significant role in the regulation of cell growth and differentiation, particularly during the process of tissue remodeling. To further explore this working model, we have investigated the regulation of host and recombinant DLK in NIH3T3 and COS-1 cells undergoing apoptosis. Using calphostin C, a potent and selective inhibitor of protein kinase C and a recognized apoptosis inducer for various cell types, we demonstrate, by immunoblot analysis, that DLK protein levels are rapidly and dramatically down-regulated during the early phases of apoptosis. Down-regulation in calphostin C-treated cells was also accompanied by the appearance of SDS- and mercaptoethanol-resistant high molecular weight DLK immunoreactive oligomers. Experiments aimed at elucidating the mechanism(s) underlying DLK oligomerization revealed that the tissue transglutaminase (tTG) inhibitor monodansylcadaverine antagonized the effects of calphostin C almost completely, thereby suggesting the involvement of a tTG-catalyzed reaction as the root cause of DLK down-regulation and accumulation as high molecular weight species. In support of this notion, we also show that DLK can serve as a substrate for tTG-dependent cross-linking in vitro and that this covalent post-translational modification leads to the functional inactivation of DLK. Taken together, these observations suggest that transglutamination and oligomerization may constitute a relevant physiological mechanism for the regulation of DLK activity.     

Penguins use the two-voice system to recognize each other

The sound-producing structure in birds is the syrinx, which is usually a two-part organ located at the junction of the bronchi. As each branch of the syrinx produces sound independently, many birds have two acoustic sources. Thirty years ago, we had anatomical, physiological and acoustical evidence of this two-voice phenomenon but no function was known. In songbirds, often these two voices with their respective harmonics are not activated simultaneously but they are obvious in large penguins and generate a beat pattern which varies between individuals. The emperor penguin breeds during the Antarctic winter, incubating and carrying its egg on its feet. Without the topographical cue of a nest, birds identify each other only by vocal means when switching duties during incubation or chick rearing. To test whether the two-voice system contains the identity code, we played back the modified call of their mate to both adults and also the modified call of their parents to chicks. Both the adults and the chicks replied to controls (two voices) but not to modified signals (one voice being experimentally suppressed). Our experiments demonstrate that the beat generated by the interaction of these two fundamental frequencies conveys information about individual identity and also propagates well through obstacles, being robust to sound degradation through the medium of bodies in a penguin colony. The two-voice structure is also clear in the call of other birds such as the king penguin, another non-nesting species, but not in the 14 other nesting penguins. We concluded that the two-voice phenomenon functions as an individual recognition system in species using few if any landmarks to meet. In penguins, this coding process, increasing the call complexity and resisting sound degradation, has evolved in parallel with the loss of territoriality.