Biomedical subjects

A S Menko

Publications and source records attributed to A S Menko.

25 records · Page 2Linked to original sources

PubMed1984

Chicken embryo lens cultures mimic differentiation in the lens.

Embryonic chicken lenses, which had been disrupted by trypsin, were grown in culture. These cultures mimic lens development as it occurred in vivo, forming lens-like structures known as lentoids. Using a variety of techniques including electron microscopic analysis, autoradiography, immunofluorescence, and polyacrylamide gel electrophoresis, it was shown that the lentoid cells had many characteristics in common with the differentiated cells of the intact lens, the elongated fiber cells. These characteristics included a shut off of DNA synthesis, a loss of cell organelles, an increase in cell volume, an increase in delta-crystallin protein, and the development of extensive intercellular junctions. The cultures began as a simple epithelial monolayer but then underwent extensive morphogenesis as they differentiated. This morphogenesis involved three distinctive morphological types which appeared in sequence as an epithelial monolayer of polygonal shaped cells with pavement packing, elongated cells oriented end to end, and the multilayered, multicellular lentoids. These distinct morphological stages of differentiation in culture mimic morphogenesis as it occurs in the lens.

Animals↗

PubMed1983

Altered cell spreading in cytochalasin B: a possible role for intermediate filaments.

Trypsinized chicken embryo dermal fibroblasts plated in the presence of cytochalasin B (CB) quickly attached to the substrate and within 24 h obtained an arborized morphology. This morphology is the result of the pushing out of pseudopodial processes along the substrate from the round central cell body. There were no microfilament bundles in the processes of these cells plated in the presence of CB; however, the processes were packed with highly oriented, parallel-aligned intermediate filaments. Only a few scattered microtubules were seen in these processes. These results demonstrated that in CB, cells are capable of a form of movement, i.e., the extension of pseudopodial processes, without the presence of the microfilament structures usually associated with extensions of the cytoplasm and pseudopodial movements. We also found that arborization did not depend on fibronectin since cells plated in CB did not have fibronectin fibers associated with the processes. Chicken fibroblasts transformed with tsLA24A, a Rous sarcoma virus which is temperature sensitive for pp60src, formed arborized cells with properties similar to those of uninfected fibroblasts when plated in the presence of CB at the nonpermissive temperature (41 degrees C). At the permissive temperature for transformation (36 degrees C), the cells attached to the substrate but remained round. These round cells were not only deficient in microfilament bundles but also lacked the highly organized intermediate filaments found in the processes of the arborized cells at 41 degrees C. Although both microfilament bundles and the fibronectin matrix were decreased after transformation with Rous sarcoma virus, neither was involved in the formation of processes in normal cells plated in CB. Therefore, the inability of the transformed cells to form or maintain processes in CB must be the result of another structural alteration in the transformed cells, such as that of the intermediate filaments.

Actins↗

PubMed1982

The response of chicken embryo dermal fibroblasts to cytochalasin B is altered by Rous sarcoma virus-induced cell transformation.

The drug cytochalasin B (CB), which disrupts the cellular microfilament network, allows the identification of as yet unclassified structural differences between normal and Rous sarcoma virus-transformed chicken embryo fibroblasts. When exposed to CB, normal chick fibroblasts attain an arborized or dendritic morphology. This results as the cytoplasm collapses upon the remaining structural and adhesive components of the cell. Rous sarcoma virus-transformed cells did not form or maintain these dendritic-like processes in the presence of CB and, as a result, rounded up but still remained attached to the substrate. With a temperature-sensitive mutant of Rous sarcoma virus, LA24A, it was possible to show that these effects are completely reversible and dependent on the expression of pp60src. The cytoskeleton in these CB-treated cells was examined by both immunofluorescence and electron microscopy. After exposure to CB, the microfilaments were found to be disrupted similarly throughout both the transformed and the nontransformed cells. In the nontransformed cells arborized by exposure to CB, the extended processes were found to contain intermediate filaments in an unusually high concentration and degree of organization. The distribution of these filaments in the central body of the arborized cells was random. This lower concentration and random distribution was similar to that seen throughout the transformed cells rounded up by exposure to CB. The failure of these transformed cells to arborize in CB indicates that the structural component(s) which is necessary for the formation or maintenance or both of the arborized state is altered by the expression of pp60src.

Animals↗

PubMed1981

Rapid and reversible reduction of junctional permeability in cells infected with a temperature-sensitive mutant of avian sarcoma virus.

The transformed or normal phenotype of cultured normal rat kidney cells infected with a temperature-sensitive mutant of avian sarcoma virus is conditional on the temperature at which the cells are grown. Using dye injection techniques, we show that junction-mediated dye transfer is also temperature-sensitive. The extent and rate of transfer between infected cells grown at the transformation-permissive temperature (35 degrees C) is significantly reduced when compared to infected cells grown at the nonpermissive temperature (40.5 degrees C) or uninfected cells grown at either temperature. Infected cells subjected to reciprocal temperature shifts express rapid and reversible alterations of dye transfer capacities, with responses evident by 15 min and completed by 60 min for temperature shifts in either direction. These results suggest that altered junctional capacities may be fundamental to the expression of the ASV-induced, transformed phenotype.

Alpharetrovirus↗

PubMed1980

Nuclear tubulin of tissue culture cells.

Tubulin has been implicated as a nuclear protein because of the role it plays in mitosis. In this paper we examined the role of tubulin in the nuclei of nonmitotic cells. Tubulin was found distributed throughout the nucleus and particularly in association with the chromatin. It comprised about 6.5% of the nonhistone chromosomal proteins. Nuclear tubulin appeared to be nonmicrotubular in form. Fluorescence microscopy data on metaphase chromosomes revealed that tubulin was present on the outside of the chromosomes. These data suggest a structural role for chromatin-associated tubulin.

Animals↗

PubMed1976

Structural and enzymatic characterization of viper C-type virus.

The structural polypeptides of purified viper range in molecular weight from 11,000 to 97,000 daltons and consist of 3 major and about 13 minor polypeptides. The virus contains both protein kinase and reverse transcriptase activities. Several of the structural polypeptides are phosphorylated in vitro by the virus-associated protein kinase. However, most (possibly all) of the viral structural polypeptides are not phosphorylated in vivo. DeoxyATP is as efficient as ATP in donating phosphate for in vitro phosphorylation of viral proteins. In vitro protein phosphorylation always precedes transcription and the virus-associated protein kinase and reverse transcriptase activities can be partially separated by sedimentation in a sucrose gradient.

Adenosine Triphosphate↗

PubMedDate not supplied

Neuroadaptive responses in brainstem noradrenergic nuclei following chronic morphine exposure.

Opiate dependence and withdrawal involve neuroadaptive responses in the central nervous system. A host of studies have previously implicated the A6 noradrenergic neurons of the pontine nucleus locus coeruleus (LC) as an important mediator of somatic signs observed upon withdrawal from opiates. Recent studies, however, are showing that noradrenergic neurons of the LC may not be solely involved in mediating somatic signs of withdrawal. The A2 noradrenergic neurons of the nucleus of the solitary tract (nucleus tractus solitarius [NTS]) in the caudal brainstem may be another possible site. Neurons in the nucleus paragigantocellularis lateralis (PGi), located in the rostral ventral medulla, which are known to send collateral projections to both the LC and the NTS, may co-modulate both noradrenergic nuclei in a parallel fashion, which may represent an anatomical substrate underlying the behavioral expression of opiate withdrawal. The PGi provides glutamatergic and opioid innervation to LC neurons. Hyperactivity of LC during opiate withdrawal arises, in part, from increased glutamate transmission in this pathway. The authors have recently shown that the excitatory transmitter, glutamate, co-exists with the endogenous opioid peptide, enkephalin, in a subset of axon terminals in the LC. Decreases in endogenous opioids in afferents to LC and NTS, following chronic opiate administration, may be equally important in modulating noradrenergic neurons following chronic opiate exposure, by removing a neurochemical system that would inhibit noradrenergic neurons. A persistent decrease in opioid peptide release from afferents during withdrawal would result in glutamate acting on postsynaptic targets, in an unopposed fashion. A parallel effect in opioid projections from PGi to the NTS would potentially support similar actions in this noradrenergic nucleus. The authors' recent data show that opioid-containing neurons in the PGi project to the NTS, and that enkephalin levels are decreased in opioid afferents to the NTS. This review summarizes data that the authors have collected regarding opioid expression changes in brainstem circuits (PGi-LC and PGi-NTS), following chronic morphine treatment, which may represent a model for understanding of adaptations in endogenous opioid circuits during drug dependence and withdrawal.

Analgesics, Opioid↗