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P Linser

Publications and source records attributed to P Linser.

12 recordsLinked to original sources
PubMed2000

Kinetic characterization of outer-ring deiodinase activity (ORD) in the liver, gill and retina of the killifish Fundulus heteroclitus.

Conversion of T4 to T3 is the first step in TH action and deiodinases are the major determinants of TH tissue availability and disposal. We here report the kinetic characterization of the outer-ring deiodinating (ORD) enzymes in the liver, gill and retina of sea water-adapted killifish, by using both rT3 and T4 as substrates. In liver, by using rT3, we detected a high Km (84 nM) and a low Km (1.3 nM) component with kinetic characteristics similar to mammalian deiodinases DI and DII. In contrast, T4-ORD only generated a low Km (0.5 nM) component. As judged by its Vmax (920 fmol 125I/mg per h) this DII enzyme is very abundant, approximately five and 20 times higher than that found in trout liver and hypothyroid rat, respectively. Kinetic analysis in killifish gill showed only one enzymatic component, with a high rT3 Km (430 nM) and a relatively low Vmax (4.3 pmol 125I/mg per h). Our results in killifish retina show the expression of a T4-low Km (0.6 nM) deiodinase with high cofactor requirements akin to the mammalian DII. The Vmax value for this enzyme is 182 fmol 125I/mg per h, five times lower than the one found in killifish liver, but comparable to that in hypothyroid rat pituitary. The biochemical similarities between fish and mammalian deiodinases could reflect their high conservation during vertebrate evolution and thus their importance in the regulation of thyroid hormone action.

Animals↗
PubMed1992

Carbonic anhydrase III is expressed in bovine lens.

A highly basic protein isolated from bovine lens has been shown to be carbonic anhydrase III by immunological and peptide sequencing techniques. This is the first demonstration of the presence of this isoenzyme, which is primarily found in skeletal muscle, in the lens or other ocular tissues. The physiological function of this enzyme in the lens is unknown.

Amino Acid Sequence↗
PubMed1984

Variable CA II compartmentalization in vertebrate retina.

We have generated a series of polyclonal and monoclonal antibodies to mammalian, avian, and osteichthian CA II for the purpose of studying its distribution in vertebrate nervous systems. In mature chicken retina, CA II is immunohistochemically detectable only in Müller glial cells. However, during embryonic development, CA II expression is suddenly "switched-on" early as a general constituent of all retinoblasts, later becoming restricted to Müller cells and transiently to a distinct type of amacrine neuron. A similar developmental pattern occurs in mouse. However, at maturity high CA II levels remain in certain amacrine neurons in addition to Müller cells. Comparative analyses of mature retinas of lower vertebrates show that reptiles parallel chicken with high CA II only in Müller cells, certain amphibians show CA II staining in Müller cells, amacrine neurons as in mouse, and in horizontal neurons, teleost and elasmobranch fish possess high CA II in Müller cells and the horizontal neurons, and lamprey eel shows CA II staining primarily in horizontal cells. An evolutionary sequence that will be discussed is thus suggested.

Aging↗
PubMed1983

Hormonal induction of glutamine synthetase in cultures of embryonic retina cells: requirement for neuron-glia contact interactions.

Cortisol induces glutamine synthetase (GS) in gliocytes of chick embryo neural retina. Using adherent cultures of retina cells we have demonstrated that responsiveness of the gliocytes to GS induction by the hormone requires contact with neurons. GS is not inducible in high-density cultures depleted of neurons and consisting only of gliocytes. In neuron-containing cultures, induced GS was detected immunohistochemically only in those gliocytes that were closely juxtaposed with clusters of neurons. Unlike the induction of GS, the expression of carbonic anhydrase-C (which does not require cortisol) persisted in these glia cells also in the absence of neurons. The nature and role of glia-neuron interactions in the hormonal induction of GS are briefly discussed.

Animals↗
PubMed1982

Cell contact-dependent regulation of hormonal induction of glutamine synthetase in embryonic neural retina.

Glutamine synthetase (GS) is a differentiation marker in the neural retina of the chick embryo. GS is localized specifically in Müller glia cells, and it can be precociously induced by adrenal corticosteroids (such as cortisol). The induction depends on cortisol-elicited gene expression and results in de novo synthesis of GS and in a multifold increase in its level. GS is inducible only when Müller cells are closely associated with retina neurons. When retina tissue from 10-day embryos is dissociated into single cells and these are maintained either in suspension or in monolayer culture, GS cannot be induced. However, if identically prepared cells are reaggregated and allowed to reconstruct retinotypic associations, they are inducible for GS. Measurements of cytoplasmic cortisol-receptors showed that cell dissociation results in a rapid and marked reduction in the level (or activity) of these receptors. Their low level persists if the cells are maintained in a dispersed state. However, if the cells are reaggregated and reestablish tissue-like contacts, the level of cortisol receptors increases, as does GS inducibility. The results indicate that, in the embryonic neural retina, histotypic cell contacts are involved in regulating the level of cytoplasmic cortisol receptors and of the responsiveness of Müller glia cells to the induction of GS. Whether the two aspects are causally related is a matter for future study.

Animals↗
PubMed1981

Carbonic anhydrase C in the neural retina: transition from generalized to glia-specific cell localization during embryonic development.

The developmental profile and cellular localization of carbonic anhydrase C (carbonate dehydratase; carbonate hydro-lyase, EC 4.2.1.1) in the neural retina of chicken embryos and adults were investigated by immunochemical and immunohistochemical methods. Carbonic anhydrase C is present in the retina by the 3rd day of embryonic development. In the undifferentiated retina, it is detectable in virtually all the cells; however, as cell specialization progresses, its level declines rapidly in the emerging neurons and increases in Müller glia cells. An exception is certain amacrine neurons that contain carbonic anhydrase C to about the 16th day of development. In the adult retina, the enzyme is confined exclusively to Müller cells (the only gliocytes in the retina). Their identification was confirmed by immunostaining for glutamine synthase, an established Müller cell "marker." The presence in the mature retina of both these enzymes in Müller cells indicates that retinal gliocytes combine functional features that, in the brain, are segregated in astrocytes and oligodendrocytes. In the embryonic retina, carbonic anhydrase C and glutamine synthase differ markedly in their developmental profiles, cellular distribution, and susceptibility to regulation by cortisol and by cell interactions. Such differences make these two enzymes an attractive "marker team" for studying developmental mechanisms in embryonic retina and specific functions of Müller cells.

Animals↗
PubMed1981

Developmental changes in the distribution of S-100 in avian neural retina.

Localization of S-100 in cells of embryonic and mature chick neural retina was studied by immunostaining of tissue sections with antiserum to S-100 and indirect immunofluorescence. Immunostaining was found to be localized predominantly in the neurons. In embryonic retina, the intensity of immunostaining increased transiently in each class of neurons at the time when they were undergoing organization within their stratum. Late embryonic and mature retina reacted weakly with the antiserum, with the exception of certain 'giant' ganglion cells that immunostained intensely. Müller cells, the only kind of glia cells in the chicken transiently in each class of neurons at the time when they were undergoing organization within their stratum. Late embryonic and mature retina reacted weakly with the antiserum, with the exception of certain 'giant' ganglion cells that immunostained intensely. Müller cells, the only kind of glia cells in the chicken transiently in each class of neurons at the time when they were undergoing organization within their stratum. Late embryonic and mature retina reacted weakly with the antiserum, with the exception of certain 'giant' ganglion cells that immunostained intensely. Müller cells, the only kind of glia cells in the chicken retina, did not react prominently with the antiserum at any of the stages examined and could not be discerned by immunostaining either in embryonic or in mature retina. The results indicate that in chick neural retina S-100 is found predominantly in neurons, and it increases and declines in different subpopulations of neurons coordinately with changes in the development and maturation if this tissue.

Animals↗
PubMed1979

Induction of glutamine synthetase in embryonic neural retina: localization in Müller fibers and dependence on cell interactions.

The cellular localization of glutamine synthetase [GSase; L-glutamate:ammonia ligase(ADP)-forming), EC 6.3.1.2] induced by cortisol in the neural retina of chicken embryos was investigated by immunostaining with GSase-specific antiserum and indirect immunofluorescence. In organ cultures of retina tissue, and in the retina in vivo, hormone-induced GSase was found to be confined only to the Müller fibers (retinoglia). Also, in mature chicken retina, which contains a very high level of GSase, the enzyme was detected solely in Müller fibers. In short-term monolayer cultures of dispersed embryonic retina cells, there was no GSase induction and no immunodetectable increase in enzyme level. However, when the dispersed cells were reaggregated and they restituted retinotypic cell associations, GSase could be induced and it was localized in Müller fibers. The results suggest that, in addition to the hormonal stimulus, contact-dependent interactions between Müller glia cells and retina neurons are involved in the mechanism of GSase induction in the retina.

Animals↗
PubMed1979

Uptake of minute virus of mice into cultured rodent cells.

The uptake of minute virus of mice into cells in tissue culture was examined biochemically and by electron microscopy. Cell-virus complexes were formed at 4 degrees C, and uptake of virus was followed after the cells were shifted to 37 degrees C. The infectious particles appeared to enter cells at 37 degrees C by a two-step process. The first and rapid phase was measured by the resistance of cell-bound virus to elution by EDTA. The bulk of the bound virus particles became refractory to elution with EDTA within 30 min of incubation at 37 degrees C. The infectious particles became resistant to EDTA elution at the same rate. The second, slower phase of the uptake process was measured by the resistance of infectious particles to neutralization by antiserum. This process was complete within 2 h of incubation at 37 degrees C. During this 2-h period, labeled viral DNA became progressively associated with the nuclear fraction of disrupted cells. The uptake of infectious virus could occur during the G1 phase of the cell cycle and was not an S phase-specific event. The uptake process was not the cause of the S phase dependence of minute virus of mice replication. In electron micrographs, virus absorbed to any area of the cell surface appeared to be taken into the cell by pinocytosis.

Adsorption↗
PubMed1977

Kinetics of assembly of a parvovirus, minute virus of mice, in synchronized rat brain cells.

The rates of assembly of the three classes of particles of minute virus of mice were examined in synchronized rat brain cells by a combination of electron microscopy and biochemical techniques. We observed a burst of virus assembly beginning about 8 h after the end of cellular S phase. Labeled thymidine incorporated into the 1.46 g/cm3 class of full virus particles was transferred almost quantitatively to the 1.42 g/cm3 class. The 1.46 g/cm3 virus appeared to be an immediate precursor to the 1.42 g/cm3 class. Conversion of the 1.46 density virus to the 1.42 density particles was observed at the time of virus assembly. The processing was rapid and occurred primarily in the nucleus. Infected cells did not contain significant pools of viral DNA in a form that could be encapsulated in the absence of DNA synthesis. The role of the empty virus capsids in the assembly process is discussed.

Animals↗
PubMed1977

Specific binding sites for a parvovirus, minute virus of mice, on cultured mouse cells.

The early interactions between parvoviruses and host cells have not been extensively described previously. In this study we have characterized some aspects of viral binding to the cell surface and demonstrated the existence of specific cellular receptor sites for minute virus of mice (MVM) on two murine cell lines that are permissive for viral growth. The interaction had a pH optimum of 7.0 to 7.2, and both the rate and extent of the reactions were slightly affected by temperature. Mouse A-9 cells (L-cell derivative) had approximately 5 X 10(5) specific MVM binding sites per cell, and Friend erythroleukemia cells had 1.5 X 10(5) MVM sites per cell. In contrast, the nonpermissive mouse lymphoid cell line L1210 lacked specific viral receptors. Also, cloned lines of A-9 cells resistant to viral infection have been isolated. One of these lines lacked the "specific" virus attachment sites but exhibited low levels of nonsaturable virus binding. Based on these examples, infectivity is correlated with the presence of specific viral receptors on the cell surface.

Animals↗