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Biomedical subjects

O Schmidt

Publications and source records attributed to O Schmidt.

At least 73 records · Page 4Linked to original sources
PubMed1996

Working experience with a new vacuum-accelerated microwave histoprocessor.

Methods of microwave and vacuum-accelerated fixation, dehydration, and paraffin embedding are described, using a new type of vacuum and temperature stabilizable microwave histoprocessor: MFX-800. The whole histoprocessing cycle lasts 3.5-5.5 h, depending on the thickness of the tissue blocks. Well-preserved structural detail, intense staining, and good antigen preservation were achieved with various tissues. This new histoprocessing facility is recommended for routine pathology laboratories in speeding up their processing procedures.

Decalcification Technique↗
PubMed1996

[Reconstruction of scar hernias--intraoperative tensiometry for objective determination of procedure of choice].

The reappearance of incisional hernias after reconstruction depends on the size and tension of the hernia. An additional risk factor is the number of operations that have been performed before. There are two decisive factors that influence the rate of recurrence: the operation technique and the tension applied. To reach a functional reconstruction the incisional hernia must be closed and the abdominal wall must be joined together in an anatomical way. The technique used must be able to tolerate the tension which is necessary to close the abdominal wall. Application of arbitrary tension produces a high rate of recurrence, irrespective of the kind of reconstruction used. Through the intraoperative measurement of the tension applied one can match each hernia (according to size, value and tension) to the most suitable technique. Here the inlay/onlay technique tolerates the highest tension, up to 3.5 kp. With this method and a maximum tension of 3.5 kp we achieved a complete functional reconstruction in 65% of cases and our rate of recurrence amounted to 2.3%.

Abdominal Muscles↗
PubMed1996

Visual results of progressive multifocal posterior chamber intraocular lens implantation.

PURPOSE: To evaluate corrected and uncorrected near, intermediate, and distance visual acuities in eyes with a progressive multifocal intraocular lens (IOL) and to determine the effect of the lens on contrast sensitivity. SETTING: Multicenter study. METHODS: This prospective study comprised 59 eyes that had uneventful cataract surgery and implantation of a progressive multifocal IOL at three study centers. Uncorrected and corrected near, intermediate, and distance visual acuities were measured, as was contrast sensitivity at different frequencies. One year results are reported. Patient satisfaction was assessed using a subjective questionnaire. RESULTS: Distance visual acuity improved from 0.13 Snellen lines uncorrected and 0.23 with best correction preoperatively to 0.77 and 0.96 lines, respectively, postoperatively. Uncorrected preoperative near acuity was 13.28 Jaeger lines and best corrected acuity, 8.93 lines. These improved to 4.75 and 2.69 lines, respectively. The differences between visual acuity at intermediate distances and best distance and near acuities were not significant. Patient satisfaction was highest with vision under good light conditions and when viewing larger objects. CONCLUSION: Visual performance with the multifocal progressive IOL was adequate at various distances without additional correction. It was less satisfactory under poor light conditions.

Accommodation, Ocular↗
PubMed1996

Host haemocyte inactivation by an insect parasitoid: transient expression of a polydnavirus gene.

Polydnaviruses produced by the hymenopteran endoparasitoid Cotesia rubecula are deposited together with the egg into the lepidopteran host Pieris rapae and are apparently involved in the suppression of the host's defence system. Around 6 h post-parasitization host haemocytes change their surface properties, actin cytoskeleton structure and adhesion properties. Here we show that a single polydnavirus gene is expressed inside the caterpillar haemocytes in a transient fashion between 4 to 8 h post-parasitization.

Amino Acid Sequence↗
PubMed1996

Multiple alleles encoding a virus-like particle protein in the ichneumonid endoparasitoid Venturia canescens.

Hymenopteran endoparasitoids produce nuclear secretions from ovarian glands, which are deposited into the host insect together with the egg, protecting the developing parasitoid against the host's defence reactions. In the ichneumonid Venturia canescens, virus-like particles (VLPs), are attached to the egg surface and provide passive protection against encapsulation by the host. One of the four major particle proteins (p40) is expressed not only in the calyx gland but also in tissues that are not involved in particle production. The p40 coding DNA from V. canescens was cloned and sequenced. Within the coding DNA a tandem repeat sequence, coding for a putative proteolytic cleavage site of the PEST type, is rearranged in a significant portion of the wasp population. A corresponding polymorphism was also detected in the protein. The amino-terminal region of the deduced protein contains a putative type II transmembrane domain. The carboxy-terminal region shows similarity to the phospholipid hydroxyperoxide glutathione peroxidase (PHGPX) of vertebrates. A peroxidase function of the p40, although not ruled out, is unlikely due to the absence of a reactive centre which is typical for many vertebrate peroxidases. The overall conservation of the hydropathic region is discussed in the context of the formation of the viral envelope and its possible function in the immune protection.

Alleles↗
PubMed1995

A prokaryotic potassium ion channel with two predicted transmembrane segments from Streptomyces lividans.

We report the identification, functional expression, purification, reconstitution and electrophysiological characterization of an up to now unique prokaryotic potassium ion channel (KcsA). It has a rectifying current-voltage relationship and displays subconductance states, the largest of which amounts to A approximately equal to 90 pS. The channel is blocked by Cs- ions and gating requires the presence of Mg2+ ions. The kcsA gene has been identified in the gram-positive soil bacterium Streptomyces lividans. It encodes a predicted 17.6 kDa protein with two potential membrane-spanning helices linked by a central domain which shares a high degree of similarity with the H5 segment conserved among eukaryotic ion channels. Multiple alignments of deduced amino acids suggest that the novel channel has the closest kinship to the S5, H5 and S6 regions of voltage-gated K+ channel families, mainly to the subfamily represented by the Shaker protein from Drosophila melanogaster. Moreover, KcsA is most distantly related to eukaryotic inwardly rectifying channels with two putative predicted transmembrane segments.

Amino Acid Sequence↗
PubMed1994

Cloning of a VLP-protein coding gene from a parasitoid wasp Venturia canescens.

Virus-like particles (VLPs) that are bound to the egg surface of a parasitic wasp Venturia canescens are void of nucleic acid and unable to infect host tissue but instead provide a passive protection against the host's immune recognition. To investigate evolutionary and functional properties of Venturia particles, we isolated cDNAs coding for a VLP-protein by screening an expression library of the wasp, using antibodies against purified VLPs. The corresponding coding DNA is present in the wasp genome as a single-copy gene.

Animals↗
PubMed1990

Hemolin: an insect-immune protein belonging to the immunoglobulin superfamily.

Insects have an efficient defense system against infections. Their antibacterial immune proteins have been well characterized. However, the molecular mechanisms by which insects recognize foreignness are not yet known. Data are presented showing that hemolin (previously named P4), a bacteria-inducible hemolymph protein of the giant silk moth Hyalophora cecropia, belongs to the immunoglobulin superfamily. Functional analyses indicate that hemolin is one of the first hemolymph components to bind to the bacterial surface, taking part in a protein complex formation that is likely to initiate the immune response.

Amino Acid Sequence↗
PubMed1990

The genetic control of cell proliferation in Drosophila imaginal discs.

The imaginal discs of Drosophila provide a favorable system for the analysis of the mechanisms controlling developmental cell proliferation, because of the separation in time between cell proliferation and differentiation, and the facility with which controlling genes can be identified and characterized. Imaginal discs are established in the embryo, and grow by cell proliferation throughout the larval period. Proliferation terminates in a regular spatial pattern during the final stages of larval development and the first day of pupal development. Cell proliferation can be locally reactivated in growth-terminated imaginal discs by removing part of the disc and culturing the remaining fragment in an adult host. The pattern of proliferation in these fragments suggests that cell proliferation in imaginal discs is controlled by direct interactions between cells and their neighbors. Proliferation appears to be stimulated by positional information differences, and these differences are reduced by the addition of new cells during tissue growth. Genes involved in cell proliferation control have been identified by collecting and analyzing recessive lethal mutations which cause overgrowth of imaginal discs. In some of these mutants (fat, lgd, c43, dco) the overgrowing tissue is hyperplastic; it retains its single-layered epithelial structure and is capable of differentiating. In two of the hyperplastic mutants (dco and c43), the imaginal discs show a failure of gap-junctional cell communication, suggesting that this form of cell communication may be involved in termination of proliferation. In other mutants the overgrowing disc tissue is neoplastic: it loses its structure and ability to differentiate, becoming a tumorous growth. The two genes that give a neoplastic phenotype (dlg and lgl) have been cloned and cDNAs of one of them (lgl) sequenced. The lgl gene encodes a cell surface molecule with significant homology to calcium-dependent cell adhesion molecules (cadherins). The expression of lgl at the time of termination of cell proliferation suggests that there are changes in the way that cells interact with one another at these times, and that these changes may be implemented by cell adhesion molecules. Direct cell contact within the epithelium, as well as signalling through gap junctions, appears to be involved in the cell interactions needed for the termination of cell proliferation. Mutations in genes encoding the Drosophila homologs of growth factors, growth factor receptors and oncogenes usually show an effect on cell-fate decisions rather than cell proliferation control, but this may be because oncogenic mutations in these genes would be dominant lethals and would therefore not be identified by conventional genetic analysis.

Aging↗
PubMed1989

Role of virus-like particles in parasitoid-host interaction of insects.

Insect endoparasitoids are capable of suppressing the immune reaction of their habitual hosts in a specific way. Salt (1968) characterized some of the implications: This seeming contradiction--that defence reactions against all kinds of foreign bodies are available to insects and that endophagous parasitoids are nevertheless able to develop in insect hosts--is resolved by recourse to one of the principles of host specificity. Although insects as a group react to every foreign body in the sense that any organism or substance evokes a reaction in most insects, each species of insect fails to make a reaction (or makes an ineffective reaction) to a small group of organisms, its habitual parasites. It is the common paradox of parasitology that defence reactions are least effective against the most noxious parasites, involving the tautology that the most noxious parasites are those against which defence reactions are least effective. Recently, VLP of hymenopteran wasps have been shown to play a crucial part in suppressing the cellular encapsulation reaction (Stoltz and Vinson, 1979a). In some parasitoid wasps, polydnavirus particles are involved in the phenotypic transformation of hemocytes, reducing the capability of the host to mount an immune reaction towards the parasitoid egg (Stoltz and Guzo, 1986; Davies et al., 1987). However, at least in Venturia, the eggs are effectively protected by VLP that lack significant amounts of nucleic acids, precluding any virus expression in the host. The question was raised whether VLP could have acquired properties of the host immune system, which allows specific suppression of the immune response. The finding of structural similarities between VLP proteins and a host component indicated that a host function is expressed in VLP (Feddersen et al., 1986) and this observation has subsequently permitted the identification and characterization of a protein in caterpillars, which appears to inhibit cellular defense reactions (Berg et al., 1987). On the basis of these results we continue to approach this parasitoid-host interaction, assuming that VLP have evolved in the host organism and eventually acquired the coding sequences of a host protein with properties of an inhibitor of encapsulation. Although there are several ways to explain the emergence of VLP in endophagous parasitoid wasps, a simple proposal would be that such hypothetical viruses, which were able to suppress immune reaction in lepidopteran hosts, were incorporated into a parasitoid wasp to become part of the life cycle of the parasitoid.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

The Drosophila melanogaster l(2)gl gene encodes a protein homologous to the cadherin cell-adhesion molecule family.

Mutations in the recessive Drosophila tumor gene l(2)gl affect growth and structural properties of neural tissues and imaginal discs during larval development. We have analyzed the cellular localization of transcripts and a 130-kDa protein encoded by the l(2)gl gene, using in situ hybridization and immunofluorescence techniques. Transcripts of maternal origin are detected in freshly laid eggs and are homogeneously incorporated into blastoderm cells. The protein is found at low levels in all embryonic tissues after blastoderm formation. In later stages differential expression of the protein is observed, particularly in cells of the nervous system. The protein is located at the cell surface of dissociated embryonic cells. Anti-l(2)gl sera show cross-reaction to a mouse protein that is localized at cell-cell contact sites in tissue culture cells. Moreover, amino acid sequence homology to deduced amino acid sequences of members of the vertebrate cadherin cell-adhesion molecule family suggests that the l(2)gl gene product may have properties of a cell-adhesion molecule.

Amino Acid Sequence↗
PubMed1989

A recessive tumor gene function in Drosophila is involved in cell adhesion.

The phenotypic effects of lethal (2) giant larvae mutations are due to unstructured growth of brain and imaginal disc cells in homozygous mutant larvae. Molecular properties of the wildtype l (2) gl protein and its tissue specificity of expression suggest that the protein is required for the adhesion of cells which are about the stop cell division and undergo terminal differentiation.

Animals↗
PubMed1987

A protein product of the Drosophila recessive tumor gene, l (2) giant gl, potentially has cell adhesion properties.

In the fruitfly Drosophila melanogaster the recessive mutation lethal (2) giant larvae affects cell growth and cell adhesion properties of neural and imaginal disc cells during embryonic and larval development. Here we report the nucleotide sequence of a cDNA from one of the two major transcripts of the l (2) gl gene containing a 3.5-kb open reading frame. From the deduced amino acid sequence we predict a 130-kd protein with certain sequence similarities to proteins with cell adhesion properties. We have raised antibodies against bacterial fusion proteins encoded by cDNA subfragments. Affinity-purified specific antibodies recognize a 130-kd protein in wild-type protein extracts and in situ, which is missing in the mutant. Localization of the l (2) gl protein in tissue sections indicates that the l (2) gl protein is associated with cellular membranes and probably involved in cell-cell interaction.

Journal Article↗
PubMed1986

Developmental expression and tissue distribution of the lethal (2) giant larvae protein of Drosophila melanogaster.

Recessive mutations in the Drosophila tumor gene lethal (2) giant larvae affect the growth and tissue specificity of determined cells in imaginal discs and presumptive optic centers of the brain. To analyse the function of the l (2) gl gene during development, we have raised monoclonal antibodies against the l (2) gl protein. These antibodies detect a 130-kd protein in wild-type tissue which is absent in homozygous mutant tissues. The protein is detected in increasing amounts up to mid-embryonic stages. Antibody binding to embryo sections and indirect immunofluorescence labeling indicate that the protein is localized at the cellular membranes or in the intercellular matrix of the embryonic cells. The primordia of all larval tissues are labeled in the embryo. Much less labeling is found in the neural primordia of the central nervous system, except that within the supraoesophageal ganglion the regions of the presumptive optic centers are distinctly labeled. Moreover, the axon bundles of the ventral cord are labeled in the embryo, apparently a reflection of the accumulation of cell membranes here. After embryogenesis the l (2) gl protein is found at a low level until the end of the 3rd larval instar, when it is preferentially seen in the brain and imaginal discs. The protein distribution in embryonic and larval tissues correlates with already known proliferation patterns, which could indicate that the l (2) gl protein is involved in proliferation arrest of cells.

Animals↗