Direct sensing of systemic and nutritional signals by haematopoietic progenitors in Drosophila.

The Drosophila lymph gland is a haematopoietic organ in which progenitor cells, which are most akin to the common myeloid progenitor in mammals, proliferate and differentiate into three types of mature cell--plasmatocytes, crystal cells and lamellocytes--the functions of which are reminiscent of mammalian myeloid cells. During the first and early second instars of larval development, the lymph gland contains only progenitors, whereas in the third instar, a medial region of the primary lobe of the lymph gland called the medullary zone contains these progenitors, and maturing blood cells are found juxtaposed in a peripheral region designated the cortical zone. A third group of cells referred to as the posterior signalling centre functions as a haematopoietic niche. Similarly to mammalian myeloid cells, Drosophila blood cells respond to multiple stresses including hypoxia, infection and oxidative stress. However, how systemic signals are sensed by myeloid progenitors to regulate cell-fate determination has not been well described. Here, we show that the haematopoietic progenitors of Drosophila are direct targets of systemic (insulin) and nutritional (essential amino acid) signals, and that these systemic signals maintain the progenitors by promoting Wingless (WNT in mammals) signalling. We expect that this study will promote investigation of such possible direct signal sensing mechanisms by mammalian myeloid progenitors

Pvr expression regulators in equilibrium signal control and maintenance of Drosophila blood progenitors.

Blood progenitors within the lymph gland, a larval organ that supports hematopoiesis in Drosophila melanogaster, are maintained by integrating signals emanating from niche-like cells and those from differentiating blood cells. We term the signal from differentiating cells the 'equilibrium signal' in order to distinguish it from the 'niche signal'. Earlier we showed that equilibrium signaling utilizes Pvr (the Drosophila PDGF/VEGF receptor), STAT92E, and adenosine deaminase-related growth factor A (ADGF-A) (Mondal et al., 2011). Little is known about how this signal initiates during hematopoietic development. To identify new genes involved in lymph gland blood progenitor maintenance, particularly those involved in equilibrium signaling, we performed a genetic screen that identified bip1 (bric à brac interacting protein 1) and Nucleoporin 98 (Nup98) as additional regulators of the equilibrium signal. We show that the products of these genes along with the Bip1-interacting protein RpS8 (Ribosomal protein S8) are required for the proper expression of Pvr

Genetic Analysis of Fibroblast Growth Factor Signaling in the Drosophila Eye

The development of eyes in Drosophila involves intricate epithelial reorganization events for accurate positioning of cells and proper formation and organization of ommatidial clusters. We demonstrate that Branchless (Bnl), the fibroblast growth factor ligand, regulates restructuring events in the eye disc primordium from as early as the emergence of clusters from a morphogenetic front to the cellular movements during pupal eye development. Breathless (Btl) functions as the fibroblast growth factor receptor to mediate Bnl signal, and together they regulate expression of DE-cadherin, Crumbs, and Actin. In addition, in the eye Bnl regulates the temporal onset and extent of retinal basal glial cell migration by activating Btl in the glia. We hypothesized that the Bnl functions in the eye are Hedgehog dependent and represent novel aspects of Bnl signaling not explored previously

Alamethicin: Secondary Structure in Solution and Interactions with Phospholipid Membranes

The icosapeptide alamethicin [sequence included in scanned thesis' abstract, p. v] isolated from the fungus Trichoderma viride induces voltage-gated ionic conductance in black lipid film membranes (Latorre, R. &#38; Alvarez, D. (1981) Physiol. Rev. 61, 77). Single-channel measurements have indicated that passive ion transport across membranes is mediated by alamethicin channels that fluctuate between several conduction states. While these studies provide phenomenological description of the nature of alamethicin-assisted ionic conduction, very few studies probed the molecular structure of this peptide and the nature of its interaction with lipid membranes. These issues are addressed in the present investigation. An analysis of the proton magnetic resonance spectrum is undertaken. Two-dimensional NMR is employed to achieve a complete assignment of the protons in the molecule to NMR resonances. The spectral assignment is a necessary first step towards molecular interpretations. Measurement of coupling constants and two-dimensional NOE's suggest a half-helical, half-extended dimeric structure for the molecule in methanol. This proposed model for the secondary structure, consistent with the NMR data as well as a line of other experimental observations erstwhile published, predicts that (a) the amide protons of residues 15 through 20 are intermolecularly hydrogen-bonded with the corresponding residues of the opposing molecule to create a rigid, extended parallel β-pleated structure for the C-terminal end of the molecule; (b) the proline at position 14 breaks the continuity of this structure, and amino acids 10 through 14 are forced into an open, non-hydrogen-bonded conformation, and (c) amino acids 3 through 9 are folded into an α-helix, with Gln-7 side chains from the two strands in the right juxtaposition to facilitate a hydrogen bond between them. The resultant structure is highly amphipathic: one face is completely hydrophobic with the aliphatic side chains exposed, whereas the other face is primarily hydrophilic with polar side chains and peptide groups lining the extended β-sheet region. The dimeric structure is further supported by relaxation measurements that indicate that the N-acetyl methyl groups at the N-termini of the two helices in the dimer have distinct proton spin-spin relaxation times. This difference is eliminated once the dimers are dissociated with urea. Spectral assignments in water are complicated by broadened NMR signals due to aggregation. Standard two-dimensional and decoupling techniques for assignments are inadequate for this case. A successful assignment is achieved by solvent titration from methanol. No changes in coupling constants are noted during the titration, and it is expected that the conformation in water is similar if not identical, to that in methanol. Relaxation measurements in water are consistent with a tightly bound dimeric unit that micellises to larger aggregates. The interaction of alamethicin with multilayers is inferred from a spectroscopic investigation of the phospholipid bilayer prepared from dimyristoyllecithin (DML) in the presence and absence of alamethicin, and, for contrast, in the presence of other membrane active molecules. The dynamics and conformation of phospholipid head group and chains are examined by P31 and H2 NMR. A P31 line shape calculation has helped identify the dependence of the spectrum on various motional, relaxation and conformational parameters. As part of the investigation of lipid packing and dynamics in membranes, small bilayer vesicles are also studied. Proton NMR indicates that the outside-facing and inside-facing leaflets of the bilayer in small vesicles have lipids packed in different densities. This is due to the differences in the extent and sign of curvature of the two leaflets. At the high field at which this NMR study is undertaken, the differences in packing show up as distinct proton peaks from the inside and outside chain methylene and methyl groups nthat differ in width and in chemical shift. Finally, the interaction of alamethicin with DML multilayers is characterized by P31, H2 and H1 NMR and Raman spectroscopy. The reduction in chemical shift anisotropy (Δσ) of the P31 signal is interpreted in terms of an interaction of the peptide at the water-membrane interface that causes a change in the average head group orientation. Deuterium NMR shows no changes in quadrupolar splittings (and hence C-D order parameters) of the chain deuterons, and Raman spectroscopy shows no change in the gauche-trans ratio of methylene segments in the chain. These results are contrasted with P31 and H2 NMR of the gramicidin S/DML system that shows polymorphism due to partial disruption of the multilayer structure and the chlorophyll A/DML system that exhibits a 7° C change in phase transition temperature as a clear indication of incorporation of the phytol chain into the bilayer. Taken together, these experiments unequivocally indicate that the peptide interacts with lipid bilayers at the lipid-water interface. The proposed amphiphilic aggregated solution structure for the peptide is ideally suited for such an interaction. Inasmuch as the conductance characteristics of alamethicin are only explained in terms of transmembrane pore formation, it is proposed that the large dipole moment of this aggregate facilitates the transfer of the peptide into the bilayer once a gradient of field is applied.</p

Systemic control of immune cell development by integrated carbon dioxide and hypoxia chemosensation in Drosophila.

Drosophila hemocytes are akin to mammalian myeloid blood cells that function in stress and innate immune-related responses. A multi-potent progenitor population responds to local signals and to systemic stress by expanding the number of functional blood cells. Here we show mechanisms that demonstrate an integration of environmental carbon dioxide (CO2) and oxygen (O2) inputs that initiate a cascade of signaling events, involving multiple organs, as a stress response when the levels of these two important respiratory gases fall below a threshold. The CO2 and hypoxia-sensing neurons interact at the synaptic level in the brain sending a systemic signal via the fat body to modulate differentiation of a specific class of immune cells. Our findings establish a link between environmental gas sensation and myeloid cell development in Drosophila. A similar relationship exists in humans, but the underlying mechanisms remain to be established

Design and Development of an Energy Efficient Multimedia Cloud Data Center with Minimal SLA Violation

Multimedia computing (MC) is rising as a nascent computing paradigm to process multimedia applications and provide efficient multimedia cloud services with optimal Quality of Service (QoS) to the multimedia cloud users. But, the growing popularity of MC is affecting the climate. Because multimedia cloud data centers consume an enormous amount of energy to provide services, it harms the environment due to carbon dioxide emissions. Virtual machine (VM) migration can effectively address this issue; it reduces the energy consumption of multimedia cloud data centers. Due to the reduction of Energy Consumption (EC), the Service Level Agreement violation (SLAV) may increase. An efficient VM selection plays a crucial role in maintaining the stability between EC and SLAV. This work highlights a novel VM selection policy based on identifying the Maximum value among the differences of the Sum of Squares Utilization Rate (MdSSUR) parameter to reduce the EC of multimedia cloud data centers with minimal SLAV. The proposed MdSSUR VM selection policy has been evaluated using real workload traces in CloudSim. The simulation result of the proposed MdSSUR VM selection policy demonstrates the rate of improvements of the EC, the number of VM migrations, and the SLAV by 28.37%, 89.47%, and 79.14%, respectively

Minimization of Handoff Failure Probability for Next-Generation Wireless Systems

During the past few years, advances in mobile communication theory have enabled the development and deployment of different wireless technologies, complementary to each other. Hence, their integration can realize a unified wireless system that has the best features of the individual networks. Next-Generation Wireless Systems (NGWS) integrate different wireless systems, each of which is optimized for some specific services and coverage area to provide ubiquitous communications to the mobile users. In this paper, we propose to enhance the handoff performance of mobile IP in wireless IP networks by reducing the false handoff probability in the NGWS handoff management protocol. Based on the information of false handoff probability, we analyze its effect on mobile speed and handoff signaling delay.Comment: 16 Page

Variation of NimC1 expression in Drosophila stocks and transgenic strains.

The NimC1 molecule has been described as a phagocytosis receptor, and is being used as a marker for professional phagocytes, the plasmatocytes, in Drosophila melanogaster. In studies including tumor-biology, developmental biology, and cell mediated immunity, monoclonal antibodies (P1a and P1b) to the NimC1 antigen are used. As we observed that these antibodies did not react with plasmatocytes of several strains and genetic combinations, a molecular analysis was performed on the structure of the nimC1 gene. In these strains we found 2 deletions and an insertion within the nimC1 gene, which may result in the production of a truncated NimC1 protein. The NimC1 positivity was regained by recombining the mutation with a wild-type allele or by using nimC1 mutant lines under heterozygous conditions. By means of these procedures or using the recombined stock, NimC1 can be used as a marker for phagocytic cells in the majority of the possible genetic backgrounds

Mitochondrial Regulation of Cell Cycle Progression during Development as Revealed by the tenured Mutation in Drosophila

SummaryThe precise control of the cell cycle requires regulation by many intrinsic and extrinsic factors. Whether the metabolic status of the cell exerts a direct control over cell cycle checkpoints is not well understood. We isolated a mutation, tenured (tend), in a gene encoding cytochrome oxidase subunit Va. This mutation causes a drop in intracellular ATP to levels sufficient to maintain cell survival, growth, and differentiation, but not to enable progression through the cell cycle. Analysis of this gene in vivo and in cell lines shows that a specific pathway involving AMPK and p53 is activated that causes elimination of Cyclin E, resulting in cell cycle arrest. We demonstrate that in multiple tissues the mitochondrion has a direct and specific role in enforcing a G1-S cell cycle checkpoint during periods of energy deprivation