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H Steller

Publications and source records attributed to H Steller.

At least 55 records · Page 3Linked to original sources
PubMed1993

Programmed cell death during Drosophila embryogenesis.

The deliberate and orderly removal of cells by programmed cell death is a common phenomenon during the development of metazoan animals. We have examined the distribution and ultrastructural appearance of cell deaths that occur during embryogenesis in Drosophila melanogaster. A large number of cells die during embryonic development in Drosophila. These cells display ultrastructural features that resemble apoptosis observed in vertebrate systems, including nuclear condensation, fragmentation and engulfment by macrophages. Programmed cell deaths can be rapidly and reliably visualized in living wild-type and mutant Drosophila embryos using the vital dyes acridine orange or nile blue. Acridine orange appears to selectively stain apoptotic forms of death in these preparations, since cells undergoing necrotic deaths were not significantly labelled. Likewise, toluidine blue staining of fixed tissues resulted in highly specific labelling of apoptotic cells, indicating that apoptosis leads to specific biochemical changes responsible for the selective affinity to these dyes. Cell death begins at stage 11 (approximately 7 hours) of embryogenesis and thereafter becomes widespread, affecting many different tissues and regions of the embryo. Although the distribution of dying cells changes drastically over time, the overall pattern of cell death is highly reproducible for any given developmental stage. Detailed analysis of cell death in the central nervous system of stage 16 embryos (13-16 hours) revealed asymmetries in the exact number and position of dying cells on either side of the midline, suggesting that the decision to die may not be strictly predetermined at this stage. This work provides the basis for further molecular genetic studies on the control and execution of programmed cell death in Drosophila.

Acridine Orange↗
PubMed1993

Independent guidance of retinal axons in the developing visual system of Drosophila.

The development of the adult visual system of Drosophila requires the establishment of precise retinotopic connections between retinal photoreceptor cell axons and their synaptic partners in the optic lobe of the brain. To assess the role of axon-axon interactions in retinal axon guidance, we used genetic methods to disrupt the normal spatiotemporal order of retinal axon ingrowth. We examined retinal axon projections to the developing first optic ganglion, the lamina, in two mutants in which reduced numbers of ommatidia develop in the eye imaginal disk. We find that in the developing lamina of these mutants, sine oculis and Ellipse, retinal axons project to proper dorsoventral positions despite the absence of the usual array of neighboring retinal axons. In a second approach, we examined animals that were somatic mosaics for the mutation, glass. In glass- animals, retinal axons project aberrantly and the larval optic nerve is absent. We find that in the developing lamina of glass mosaic animals, wild-type retinal axons project to proper dorsoventral positions despite the misrouted projections of neighboring glass- retinal axons. In addition, wild-type retinal axons project normally in the absence of the larval optic nerve, indicating that the latter is not an essential pioneer for retinal axon navigation. Our observations support the proposal that axon fascicles can make at least some pathfinding decisions independently of other retinal axon fascicles. We suggest that positional guidance cues that might label axon pathways and target destinations contribute to retinotopic pattern formation in the Drosophila visual system.

Animals↗
PubMed1992

Macrophages in Drosophila embryos and L2 cells exhibit scavenger receptor-mediated endocytosis.

Mammalian macrophage scavenger receptors exhibit unusually broad binding specificity and are implicated in atherosclerosis and host defense. Scavenger receptor-like endocytosis was observed in Drosophila melanogaster embryos and in primary embryonic cell cultures. This receptor activity was expressed primarily by macrophages. The Drosophila Schneider L2, but not the Kc, cell line also exhibited a scavenger receptor-mediated endocytic pathway similar to its mammalian counterpart. L2 receptors mediated high-affinity internalization and subsequent temperature- and chloroquine-sensitive degradation of 125I-labeled acetylated low density lipoprotein and displayed characteristic ligand specificity. These findings suggest that scavenger receptors mediate important, well-conserved functions and raise the possibility that they may be pattern recognition receptors that arose early in the evolution of host defense mechanisms. They also establish additional systems for the investigation of endocytosis in Drosophila and scavenger receptor function in disease, host defense, and development.

Animals↗
PubMed1992

Survival of photoreceptor neurons in the compound eye of Drosophila depends on connections with the optic ganglia.

The importance of retinal innervation for the normal development of the optic ganglia in Drosophila is well documented. However, little is known about retrograde effects of the optic lobe on the adult photoreceptor cells (R-cells). We addressed this question by examining the survival of R-cells in mutant flies where R-cells do not connect to the brain. Although imaginal R-cells develop normally in the absence of connections to the optic lobes, we find that their continued survival requires these connections. Genetic mosaic studies with the disconnected (disco) mutation demonstrate that survival of R-cells does not depend on the genotype of the eye, but is correlated with the presence of connections to the optic ganglia. These results suggest the existence of retrograde interactions in the Drosophila visual system reminiscent of trophic interactions found in vertebrates.

Animals↗
PubMed1992

Generation and early differentiation of glial cells in the first optic ganglion of Drosophila melanogaster.

We have examined the generation and development of glial cells in the first optic ganglion, the lamina, of Drosophila melanogaster. Previous work has shown that the growth of retinal axons into the developing optic lobes induces the terminal cell divisions that generate the lamina monopolar neurons. We investigated whether photoreceptor ingrowth also influences the development of lamina glial cells, using P element enhancer trap lines, genetic mosaics and birthdating analysis. Enhancer trap lines that mark the differentiating lamina glial cells were found to require retinal innervation for expression. In mutants with only a few photoreceptors, only the few glial cells near ingrowing axons expressed the marker. Genetic mosaic analysis indicates that the lamina neurons and glial cells are readily separable, suggesting that these are derived from distinct lineages. Additionally, BrdU pulse-chase experiments showed that the cell divisions that produce lamina glia, unlike those producing lamina neurons, are not spatially or temporally correlated with the retinal axon ingrowth. Finally, in mutants lacking photoreceptors, cell divisions in the glial lineage appeared normal. We conclude that the lamina glial cells derive from a lineage that is distinct from that of the L-neurons, that glia are generated independently of photoreceptor input, and that completion of the terminal glial differentiation program depends, directly or indirectly, on an inductive signal from photoreceptor axons.

Animals↗
PubMed1991

Isolation and characterization of the disconnected gene of Drosophila melanogaster.

Mutations in the disco (disconnected) gene prevent the establishment of stable connections between the larval optic nerves, the Bolwig's nerves, and their target cells in the brain during embryonic development. The failure of this initial connection is associated with aberrant development of the optic lobes which are largely degenerate in the mutant adult fly. In order to understand the role of disco in establishing this connection, we isolated and characterized the disco gene. A 22 kb DNA fragment can completely rescue the mutant phenotype. A single transcript, 2.9 kb in length, is found in this region and is expressed throughout development of the fly. We determined the nucleotide sequence of the disco gene to be unique when compared with sequences in a number of databases. The predicted amino acid sequence contains a region with similarity to the consensus established for the zinc finger motif. Mobilization of a P-element inserted near the gene resulted in the deletion of the 5' end of the gene and produced flies indistinguishable from those carrying the disco allele.

Amino Acid Sequence↗
PubMed1991

Expression of the disconnected gene during development of Drosophila melanogaster.

Proper development of the larval visual nerve, Bolwig's nerve, of Drosophila melanogaster requires the wild type function of the disconnected (disco) gene. In disco mutants, the nerve does not make stable connections with its targets in the larval brain. We have begun to explore the role of disco in the formation of the nervous system by examining the distribution of disco mRNA and protein in embryos and third instar larvae using in situ hybridization and antibody staining respectively. No differences between the distribution patterns of the two products are detected; disco is expressed in many tissues including both neural and non-neural cells. Many of the cells which express disco undergo extensive movement during development as they participate in major morphogenetic movements. Antibody staining shows that the protein is found in the cell nucleus. Products of the disco gene are detected in cells near the terminus of the growing Bolwig's nerve. In embryos homozygous for either of two mutant alleles of disco, the disco protein is absent near the nerve terminus, although protein distribution elsewhere is indistinguishable from wild type.

Animals↗
PubMed1991

The influence of retinal innervation on neurogenesis in the first optic ganglion of Drosophila.

We have examined the influence of retinal innervation on the development of target neurons in the first optic ganglion, the lamina, of D. melanogaster. Mitotically active lamina precursor cells (LPCs), which normally produce lamina neurons, are absent in mutants that lack retinal innervation, while other proliferative centers appear unaffected. Reducing the number of innervating photoreceptor axons results in fewer mitotic LPCs. In glass mutants photoreceptors project to abnormal locations and LPCs are found adjacent to these aberrant projections. We conclude that the arrival of photoreceptor axons in the larval brain initiates, directly or indirectly, cell division to produce lamina neurons. Our results provide an explanation for how the synchronous development of these two interacting systems is coordinated.

Animals↗
PubMed1991

Ablation of Drosophila photoreceptor cells by conditional expression of a toxin gene.

We have used toxin-mediated ablation to study some aspects of visual system development in Drosophila melanogaster. To devise a method that permits the conditional expression of a cellular toxin, we introduced an amber mutation into the diphtheria toxin-A-chain gene. In transgenic animals, this toxin gene can be activated by providing the gene for an amber suppressor tRNA. By coupling this toxin gene to the photoreceptor cell-specific promoter of the chaoptic gene, photoreceptor cells could be specifically ablated during development. Photoreceptor cell-specific markers normally activated during pupal development failed to appear after midpupation. Photoreceptor cells were absent from the retinas of adult flies at eclosion. We have assessed the consequences of photoreceptor cell ablation for eye and optic lobe development. We suggest that the larval photoreceptor nerve is not essential, in the late larval stages, for retinula photoreceptor cell axons to achieve their proper projection pattern in the brain. Moreover, while retinula photoreceptor innervation is initially required for the development of normal optic ganglia, the ablation of these cells in midpupation has no discernible effect. This approach to cell-specific ablation should be generally applicable to the study of cellular functions in development and behavior.

Animals↗
PubMed1988

Isolation of a putative phospholipase C gene of Drosophila, norpA, and its role in phototransduction.

Severe norpA mutations in Drosophila eliminate the photoreceptor potential and render the fly completely blind. Recent biochemical analyses have shown that norpA mutants lack phospholipase C (PLC) activity in the eye. A combination of chromosomal walking and transposon-mediated mutagenesis was used to clone the norpA gene. This gene encodes a 7.5 kb RNA that is expressed in the adult head. In situ hybridizations of norpA cDNA to adult tissue sections show that this gene is expressed abundantly in the retina. The putative norpA protein is composed of 1095 amino acid residues and has extensive sequence similarity to a PLC amino acid sequence from bovine brain. We suggest that the norpA gene encodes a PLC expressed in the eye of Drosophila and that PLC is an essential component of the Drosophila phototransduction pathway.

Amino Acid Sequence↗
PubMed1987

Disconnected: a locus required for neuronal pathway formation in the visual system of Drosophila.

Mutations at the X-linked disconnected locus of D. melanogaster lead to the failure of adult photoreceptor axons to innervate their target cells in the developing optic lobes of the third instar larva, resulting in flies that have rudimentary optic ganglia. The cascade of epigenetic events leading to the adult disconnected phenotype is caused by the misrouting of a larval pioneer nerve, Bolwig's nerve, during embryonic development. In the disconnected mutant this nerve fails to recognize and establish stable connections with its correct synaptic partners. In addition, disconnected affects both the proper aggregation and the movement of the Bolwig neurons to their final location in the embryo. Finally, similar but more subtle defects can be found in a subset of other peripheral neurons in the thoracic and abdominal segments. The different aspects of the phenotype suggest that the disconnected gene plays a role in neuronal cell recognition.

Animals↗
PubMed1986

P transposons controlled by the heat shock promoter.

We have transformed Drosophila melanogaster with modified P-element transposons, which express the transposase function from the heat-inducible hsp70 heat shock promoter. The Icarus transposon, which contains a direct hsp70-P fusion gene, behaved like a very active autonomous P element even before heat shock induction. Although heat shock led to abundant somatic transcription, transposition of the Icarus element was confined to germ line cells. To reduce the constitutive transposase activity observed for the Icarus element, we attenuated the translational efficiency of the transposase RNA by inserting the transposon 5 neomycin resistance gene between the hsp70 promoter and the P-element sequences. The resulting construct, called Icarus-neo, conferred resistance to G418, and its transposition was significantly stimulated by heat shock. Heat shocks applied during the embryonic or third instar larval stage had similar effects, indicating that transposition of P elements is not restricted to a certain developmental stage. Both Icarus and Icarus-neo destabilized snw in a P-cytotype background and thus at least partially overcome the repression of transposition. Our results suggest that the regulation of P-element transposition occurs at both the transcriptional and posttranscriptional levels.

Animals↗
PubMed1986

[Quantitative studies of Salmonella in the sewage system of Kiel over a one-year period].

In the course of 1983 the contents of salmonellae was investigated as to quantity in the Kiel sewage water system by samples taken off-hand every fourteen days. Determining the numbers of salmonellae by mpn-method the canalisation of the west-side of Kiel fjord proved to be dominated by the abbatoir of Kiel-Wellsee. Additional evidence for that was given by the differing annual distribution of the numbers of salmonellae on the east-side of Kiel fjord. In total there was a remarkable reduction of salmonellae during the first and the fourth quarter of 1983 and a strong augmentation during summer. A reduction of salmonellae during the passage of the pump and pressure conduit-pipe, combining east- and west-side of Kiel fjord, could be seen.

Abattoirs↗
PubMed1986

[Various Salmonella serotypes in the sewage system of Kiel over a one-year period].

During one whole year (1983) Salmonella investigations were carried out in a total of 54 water samples taken from the sewage system of the town Kiel (FRG). Salmonella were present in 47 samples. 6181 strains were biochemically and serologically identified. The predominant serotypes isolated were S. typhi-murium, S. panama, S. schwarzengrund and S. hadar. A correlation could be demonstrated between salmonella found in sewage and registered human excreters.

Abattoirs↗
PubMed1985

Expression of the Drosophila white gene under the control of the hsp70 heat shock promoter.

We have used P-mediated transformation to introduce into the Drosophila genome transposons containing the hsp-70 heat shock promoter (hsp) placed at different distances upstream of the white gene. Using these constructions we found a strong terminator 250 nucleotides upstream of the white transcription start. When all white upstream sequences are deleted and the hsp is fused to the white leader region, white transcription is under hsp control, however, flies carrying this construction have red eyes even at low temperature, due to the basal level of activity of the hsp. High levels of transcription are obtained after heat shock but about half of the transcripts are incompletely spliced. One transformed line carries the transposon integrated near the heterochromatin. These flies have very pale eyes but develop strongly pigmented, variegated eyes if heat shocked in the first 2 days of the pupal stage. Heat shocks after eclosion have no effect on eye pigmentation. The properties of these transposons also indicated that the control sequences required for Zeste interaction lie > 1 kb upstream of the white transcription start while those required for dosage compensation are close to the gene.

Journal Article↗
PubMed1985

Multiple upstream regulatory elements control the expression of the Drosophila white gene.

Constructions containing the Drosophila white gene and different amounts and arrangements of its regulatory region were introduced into the germ line of white mutant flies by P-mediated transformation. The results obtained with the different transposon constructions show that different parts of the 1.8-kb region preceding the transcription start are required for the expression of the gene in different tissues and at different developmental stages. Different sequences independently control the expression of the gene in the adult testes, in the larval and adult Malpighian tubules and in the eye. Another sequence located greater than 1080 bp upstream of the transcription start is the target of zeste interaction. The results also suggest that sequences required for dosage compensation are contained between -216 and the transcription start site. We show that at least some of these regulatory elements are equally functional if their distance from the promoter is varied or if their orientation is inverted. Their properties suggest that they act as enhancer-like elements to regulate the activity of the white promoter and, at least in the case of the zeste regulatory site, that they can act also in 'trans' on a white promoter locked in close physical proximity by homologous chromosome pairing.

Animals↗
PubMed1985

A transposable P vector that confers selectable G418 resistance to Drosophila larvae.

Drosophila larvae are rapidly killed by food containing the antibiotic G418. The bacterial gene for neomycin resistance introduced in the genome by P-mediated transformation renders larvae resistant to G418 and able to grow to fertile adults. The neo gene transcribed from the herpes thymidine kinase promoter gives low levels of resistance but high levels can be obtained using the hsp70 heat-shock promoter. We have constructed a vector for P-mediated transformation which uses this finding to allow dominant selection of transformed progeny. Features of this vector also facilitate cloning and allow the rapid recovery of the inserted transposon from transformed flies. We have also constructed a cosmid vector for P-mediated transformation that incorporates the hsp70-neo gene.

Journal Article↗