Transplanted wing and leg imaginal discs in Drosophila melanogaster demonstrate interactions between epidermis and myoblasts in muscle formation

 Adult muscle development in Drosophila is intimately associated with the development of the nervous system and epidermis. During metamorphosis, myoblasts from the wing imaginal disc reach target sites on the developing pupal epidermis and begin the formation of multinucleate myofibres of the dorsal thorax. The paths taken by pupal myoblasts could be specified by the nervous system and/or the epidermis. Using genetically marked donor pupal wing and leg discs transplanted onto pupal hosts, we have generated animals that have ectopic wings or legs and have examined the formation of adult muscle types. We show that thoracic myoblasts migrate over both host and donor epidermis when the transplant site on the host is thoracic. However, when the transplant site is on the abdomen, thoracic myoblasts do not migrate over abdominal epidermis. Our results show that the epidermis plays an important role in determining the migration pattern of myoblasts. Since muscles are multinucleate cells that form by the fusion of myoblasts, one way in which their molecular characteristics could be achieved is by some myoblasts acting as ”founders”. These myoblasts could influence the pattern of gene expression of those nuclei that fuse with them. We have examined, again using disc transplant experiments, if myoblasts on discs have the capacity to express fibre-specific genes as distinct from this property being conferred by other extra-discs myoblasts. Our results demonstrate that disc-associated myoblasts can indeed fuse with each other to express fibre-specific genes. We synthesize the results presented here with those from earlier experiments to suggest a mechanism for muscle patterning in the adult thorax. Received: 8 January 1995 / Accepted in revised form: 22 January 1996     

Mono- and bi-phasic Salmonella typhi: genetic homogeneity and distinguishing characteristics

Several lines of evidence indicate a relatively low genetic heterogeneity in the natural Salmonella typhi population. However, some S. typhi isolates found in Indonesia express, instead of the usual fliC-d flagellin gene, a different flagellar gene fliC-j. In addition, Indonesian strains may have a second flagellar antigen fliC-z66. We have previously suggested, on the basis of the flagellar antigen constitution, that S. typhi evolved in an isolated human population in Indonesia. In order to test this hypothesis, we have gathered S. typhi isolates from around the world and tested the genetic heterogeneity among them. In general, polymorphism was greater in isolates from the Far East, as was indicated by Southern hybridizations with rDNA and fliC DNA probes. Gene fliC-j was not found in S. typhi isolates, other than those from Indonesia. However, the one-clone origin of S. typhi was indicated by a common DNA fingerprint pattern and by the occurrence, in the 5' end region of the fliC gene, of 10 scattered nucleotides that differ from the corresponding 10 nucleotides in other fliC alleles studied. These nucleotides were present in all isolates tested but did not change the amino acid sequence of the flagellin polypeptide.     

HIV quasispecies dynamics during pro-active treatment switching: impact on multi-drug resistance and resistance archiving in latent reservoirs

The human immunodeficiency virus (HIV) can be suppressed by highly active anti-retroviral therapy (HAART) in the majority of infected patients. Nevertheless, treatment interruptions inevitably result in viral rebounds from persistent, latently infected cells, necessitating lifelong treatment. Virological failure due to resistance development is a frequent event and the major threat to treatment success. Currently, it is recommended to change treatment after the confirmation of virological failure. However, at the moment virological failure is detected, drug resistant mutants already replicate in great numbers. They infect numerous cells, many of which will turn into latently infected cells. This pool of cells represents an archive of resistance, which has the potential of limiting future treatment options. The objective of this study was to design a treatment strategy for treatment-naive patients that decreases the likelihood of early treatment failure and preserves future treatment options. We propose to apply a single, pro-active treatment switch, following a period of treatment with an induction regimen. The main goal of the induction regimen is to decrease the abundance of randomly generated mutants that confer resistance to the maintenance regimen, thereby increasing subsequent treatment success. Treatment is switched before the overgrowth and archiving of mutant strains that carry resistance against the induction regimen and would limit its future re-use. In silico modelling shows that an optimal trade-off is achieved by switching treatment at days after the initiation of antiviral therapy. Evaluation of the proposed treatment strategy demonstrated significant improvements in terms of resistance archiving and virological response, as compared to conventional HAART. While continuous pro-active treatment alternation improved the clinical outcome in a randomized trial, our results indicate that a similar improvement might also be reached after a single pro-active treatment switch. The clinical validity of this finding, however, remains to be shown by a corresponding trial.     

Subunit assembly and domain analysis of electrically silent K+ channel alpha-subunits of the rat Kv9 subfamily

Alpha-subunits of the voltage-gated potassium channel (Kv) subfamily Kv9 show no channel activity after homomultimeric expression in heterologous expression systems. This report shows that heteromultimeric expression of rKv9.1 and rKv9.3 specifically suppresses the currents mediated by alpha-subunits of the Kv2 and Kv3 subfamilies but does not affect currents mediated by alpha-subunits of the Kv1 and Kv4 subfamilies. To understand the molecular basis of the electrical silence of Kv9 homomultimeric channels, crucial functional domains (amino and carboxy terminus, S4 segment, and pore region) were exchanged between Kv9 alpha-subunits and rKv1.3. Electrophysiological studies of these chimeras revealed that the pore region is involved in determining the nonconductive behavior of homomultimeric Kv9 channels. This analysis was extended by protein interaction assays, aiming to identify the region of Kv9 subunits responsible for the specific suppression of rKv2.1- and rKv3.4-mediated currents. We could show that the amino-terminal domain of Kv9 alpha-subunits does not support homomultimeric assembly but interacts specifically with the rKv2.1 amino-terminal region. Conversely, the specific intersubfamily assembly of rKv3.4 with rKv9.1 or rKv9.3 is governed by the hydrophobic core and not the amino-terminal domain.     

Effect of reactive oxygen and carbonyl species on crucial cellular antioxidant enzymes

Numerous reactive oxygen species (ROS) and reactive carbonyl species (RCS) issuing from lipid and sugar oxidation are known to damage a large number of proteins leading to enzyme inhibition and alteration of cellular functions. Whereas studies in literature only focus on the reactivity of one or two of these compounds, we aimed at comparing in the same conditions of incubations (4 and 24 h at 37 °C) the effects of both various RCS (4-hydroxynonenal, 4-hydroxyhexenal, acrolein, methylglyoxal, glyoxal, malondialdehyde) and ROS (H₂O₂, AAPH) on the activity of key enzymes involved in cellular oxidative stress: superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH). This was realized both in vitro on purified proteins and MIAPaCa-2 cells. Incubation of these enzymes with RCS resulted in a significant time- and concentration-dependent inhibition for both pure enzymes and in cell lysates. Among all RCS and ROS, hydroxynonenal (HNE) was observed as the most toxic for all studied enzymes except for SOD and is followed by hydrogen peroxide. At 100 μM, HNE resulted in a 50% reduction of GPx, 56% of GST, 65% of G6PDH, and only 10% of Cu,Zn-SOD. Meanwhile it seems that concentrations used in our study are closer to biological conditions for ROS than for RCS. H₂O₂ and AAPH-induced peroxyl radicals may be probably more toxic towards the studied enzymes in vivo.     

The organization of the chemosensory system in Drosophila melanogaster: a rewiew

This review surveys the organization of the olfactory and gustatory systems in the imago and in the larva of Drosophila melanogaster, both at the sensory and the central level. Olfactory epithelia of the adult are located primarily on the third antennal segment (funiculus) and on the maxillary palps. About 200 basiconic (BS), 150 trichoid (TS) and 60 coeloconic sensilla (CS) cover the surface of the funiculus, and an additional 60 BS are located on the maxillary palps. Males possess about 30% more TS but 20% fewer BS than females. All these sensilla are multineuronal; they may be purely olfactory or multimodal with an olfactory component. Antennal and maxillary afferents converge onto approximately 35 glomeruli within the antennal lobe. These projections obey precise rules: individual fibers are glomerulus-specific, and different types of sensilla are associated with particular subsets of glomeruli. Possible functions of antennal glomeruli are discussed. In contrast to olfactory sensilla, gustatory sensilla of the imago are located at many sites, including the labellum, the pharynx, the legs, the wing margin and the female genitalia. Each of these sensory sites has its own central target. Taste sensilla are usually composed of one mechano-and three chemosensory neurons. Individual chemosensory neurons within a sensillum respond to distinct subsets of molecules and project into different central target regions. The chemosensory system of the larva is much simpler and consists essentially of three major sensillar complexes on the cephalic lobe, the dorsal, terminal and ventral organs, and a series of pharyngeal sensilla.     

The organization of the chemosensory system in Drosophila melanogaster: a rewiew

This review surveys the organization of the olfactory and gustatory systems in the imago and in the larva of Drosophila melanogaster, both at the sensory and the central level. Olfactory epithelia of the adult are located primarily on the third antennal segment (funiculus) and on the maxillary palps. About 200 basiconic (BS), 150 trichoid (TS) and 60 coeloconic sensilla (CS) cover the surface of the funiculus, and an additional 60 BS are located on the maxillary palps. Males possess about 30% more TS but 20% fewer BS than females. All these sensilla are multineuronal; they may be purely olfactory or multimodal with an olfactory component. Antennal and maxillary afferents converge onto approximately 35 glomeruli within the antennal lobe. These projections obey precise rules: individual fibers are glomerulus-specific, and different types of sensilla are associated with particular subsets of glomeruli. Possible functions of antennal glomeruli are discussed. In contrast to olfactory sensilla, gustatory sensilla of the imago are located at many sites, including the labellum, the pharynx, the legs, the wing margin and the female genitalia. Each of these sensory sites has its own central target. Taste sensilla are usually composed of one mechano-and three chemosensory neurons. Individual chemosensory neurons within a sensillum respond to distinct subsets of molecules and project into different central target regions. The chemosensory system of the larva is much simpler and consists essentially of three major sensillar complexes on the cephalic lobe, the dorsal, terminal and ventral organs, and a series of pharyngeal sensilla.     

Combined rather than separate pathways for hedonic and sensory aspects of taste in fly larvae?

In mammals, the hedonic aspects (good versus bad) and sensory aspects (i.e., the molecular quality) of taste are associated with different brain regions. Anatomical data argue against such a separation in the primary taste center of Drosophila larvae. Is only one aspect of taste represented or do both co-exist at the same location? I present evidence for a hedonic representation in the larval taste center and review anatomical and behavioral data which support the co-existence of a sensory representation of taste with a hedonic representation.     

A novel linear plasmid mediates flagellar variation in Salmonella Typhi

Unlike the majority of Salmonella enterica serovars, Salmonella Typhi (S. Typhi), the etiological agent of human typhoid, is monophasic. S. Typhi normally harbours only the phase 1 flagellin gene (fliC), which encodes the H:d antigen. However, some S. Typhi strains found in Indonesia express an additional flagellin antigen termed H:z66. Molecular analysis of H:z66+ S. Typhi revealed that the H:z66 flagellin structural gene (fljB(z66)) is encoded on a linear plasmid that we have named pBSSB1. The DNA sequence of pBSSB1 was determined to be just over 27 kbp, and was predicted to encode 33 coding sequences. To our knowledge, pBSSB1 is the first non-bacteriophage-related linear plasmid to be described in the Enterobacteriaceae.