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Biomedical subjects

E Huebner

Publications and source records attributed to E Huebner.

At least 19 recordsLinked to original sources
PubMed2000

The catalytic DNA topoisomerase II inhibitor dexrazoxane (ICRF-187) induces endopolyploidy in Chinese hamster ovary cells.

The bisdioxopiperazines, including dexrazoxane (ICRF-187), are catalytic or noncleavable complex-forming inhibitors of DNA topoisomerase II that do not produce DNA strand breaks. In this study we show that dexrazoxane inhibits the division of Chinese hamster ovary (CHO) cells resulting in marked increases in cell size (up to 80 microm in diameter), volume (up to 150-fold greater), and ploidy (as high as 32N). This last result indicates that the dexrazoxane-induced DNA reduplication was restricted to once per cell cycle. Kinetic analysis of the flow cytometry data indicated that the conversion between successively higher ploidy levels was progressively slowed at longer times of exposure to dexrazoxane. Both the protein and DNA content of dexrazoxane-treated CHO cells increased linearly over time in the same proportion. Light and electron microscopic studies of dexrazoxane-treated cells showed ring-like multilobulated nuclei. Immunohistochemical staining of dexrazoxane-treated cells showed that F-actin and acetylated alpha-tubulin were present in large, highly organized networks. Immunohistochemical staining of the dexrazoxane-treated CHO cells also showed that the topoisomerase II alpha colocalized with the DNA of the multilobulated nuclei. Staining of gamma-tubulin revealed that the dexrazoxane-treated cells contained multiple centrosomes, indicating that dexrazoxane prevents cytokinesis but not centrosome reduplication. It is concluded that dexrazoxane inhibits CHO cytokinesis in cells by virtue of its ability to inhibit topoisomerase II.

Animals↗
PubMed1997

Unipolar microtubule array is directly involved in nurse cell-oocyte transport.

The telotrophic ovariole of Rhodnius prolixus is richly endowed with microtubules (MTs). An extensive, stable array of MTs packs the trophic core and trophic cords which link the nurse cell compartments to the growing oocytes. This system is excellent to study MT-based transport as the MTs are believed to play a role in transport of nurse cell-produced mitochondria, ribosomes, and mRNAs to the oocytes. We investigated MT polarity and molecular MT motors in this unidirectional transport system. Hook decoration revealed that the MTs of the trophic core and cords have their plus (+) ends in the tropharium and minus (-) ends in the oocytes. Video differential interference optics (DIC) microscopy showed that vesicle transport was saltatory, ATP-dependent, and had an average velocity of 0.77 micron/sec toward the oocyte. Transport was sensitive to 2 mM N-ethylmaleimide (NEM) and 50 microM vanadate and resistant to 1 mM 5'-adenylylimidodiphosphate (AMP-PNP) and 5 microM vanadate. We report that the unipolar, acetylated trophic cord MTs play a direct role in nurse cell-oocyte transport via a cytoplasmic dynein-like retrograde motor.

Adenosine Triphosphate↗
PubMed1994

Oogenesis in a placental viviparous onychophoran.

This first ultrastructural study of oogenesis in a placental viviparous onychophoran describes oocyte differentiation, cell interactions and reveals various unusual cellular features. The viviparous onychophoran Plicatoperipatus jamaicensis has paired ovaries medially located, attached to the dorsal body wall by muscular terminal filaments. The rest of the female reproductive tract consists of paired spermathecae oviduct/uteri (hereafter referred to as uterus). Bulbous spermathecae are joined to the oviducts by ducts. Also continuous with the oviduct lumen are two tubular structures whose lumina open to the hemolymph. The uteri contain a progression of developmental stages from implantation through stalked morulae, blastocysts, larvae and juveniles about to be born. Growing oocytes are characterized by large germinal vesicles showing synaptonemal complexes. Oocytes are surrounded by flattened follicle cells that possess extensive bundles of thick and thin filaments. Mature oocytes contain little or no yolk, but are unique among organisms in accumulating a large central reservoir of stored glycogen. The lack of yolk reflects the placental viviparous nature of the reproductive process. The glycogen reservoir provides a rapidly accessible energy source for early developmental stages. Particularly prominent also are unusually extensive and highly elaborate Golgi complexes in the cortical and peri-nuclear ooplasm. While extensive Golgi complexes have been described in oocytes of a variety of species, the particularly exaggerated size and amount of Golgi in these onychophorans suggests they may provide excellent material for the study of Golgi function. The features of the oocyte and placental viviparity show this is an ideal model to investigate the nature of the placental reproductive process analogous to mammals in an invertebrate and its implications to oogenesis.

Animals↗
PubMed1994

In vitro exposure of a novel polyesterurethane graft to enzymes: a study of the biostability of the Vascugraft arterial prosthesis.

The biostability of the Vascugraft arterial prosthesis, a porous synthetic graft made by a novel spinning process from a unique poly(ester urethane) polymer, has been studied by means of an in vitro enzyme incubation technique. Samples of the Vascugraft were exposed to buffered solutions of collagenase and pancreatin, as well as the buffer solutions alone, for periods of up to 100 days at 37 +/- 1 degrees C. On removal and after cleaning, a number of different analytic methods, including X-ray photoelectron spectroscopy for chemical analysis (ESCA), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), size exclusion chromatography (SEC), scanning electron microscopy (SEM), interference microscopy, moisture content and contact angle measurements, were used to examine the changes in chemical structure and surface morphology of the samples. During incubation in both enzymes the molecular weight of the polyurethane appeared to decrease in the presence of enzyme but increase in the presence of buffer. Further microphase separation in the polyurethane material developed during incubation in buffer solutions. Such changes in microstructure were associated with increased surface hydrophilicity, increased moisture content and a significant improvement in the extent of order and preferred orientation of the hard segment domains within the fibres. In the sampling depth of about 5 nm, both enzymes decreased the carbonate group content at the surface of the prosthesis to as little as 40% of their original values. The results from ATR-FTIR and DSC demonstrated that this phenomenon was limited primarily to the soft segment phase. While the Vascugraft prosthesis did exhibit some limited chemical modifications on exposure to concentrated enzyme solutions, nevertheless such changes were confined to the surface layer of the polyurethane microfibres. The importance and significance of those results will be more adequately determined by in vivo investigation.

Blood Vessel Prosthesis↗
PubMed1994

Managing change--the challenge of the '90s.

Everyone knows that changes of all types are occurring in health care. Whatever those changes are, and whatever necessitates them, does not diminish the resistance that individuals may have to them. What can managers or administrators do to diminish the resistance and manage the changes they are making?

Attitude of Health Personnel↗
PubMed1993

Ionic basis of bioelectric currents during oogenesis in an insect.

Transmembrane bioelectric currents around insect ovaries are well documented but as yet poorly understood. In the present study we describe the ionic basis of such currents around the telotrophic ovariole of Rhodnius prolixus using a two-dimensional vibrating probe and ion-substituted media and inhibitors. Current efflux from the base and apex of the terminal follicle is carried by electrogenic Na+ transport, and the return circuit over the middle of the terminal follicle is the result of Na+ influx/Cl- efflux. We further show that a transient inward current at the apex of midvitellogenic terminal follicles is carried by Ca2+ ions and broadly correlates both spatially and temporally with trophic cord closure. A distinct current loop over the tropharium arises at the base via electrogenic Na+ efflux and returns over the middle and apical regions of the tropharium via Na+ and Ca2+ influx. These findings serve as a basis for the further dissection of the physiological relevance of transcellular ion currents around developing insect ovarian follicles.

Adenosine Triphosphatases↗
PubMed1992

Spatial and temporal transcellular current patterns during oogenesis.

We have used the two-dimensional vibrating probe to examine spatial and temporal patterns in the transcellular current flow around telotrophic ovarioles of the insect Rhodnius prolixus. We demonstrate a dynamic pattern of currents which correlates with various stages of vitellogenesis. Asymmetries exist in the radial current pattern around intact ovarioles, particularly around the terminal follicle, and may correlate with early developmental axes. The extra-cellular current pattern is largely reflected by a similar, though weaker pattern of currents over the germ cell membranes, indicating that both germ cell and somatic cell membranes are involved in current generation. Current enters previtellogenic oocytes and leaves oocytes entering vitellogenesis. We speculate that current reversal and loss of trophic cord contact may represent an electrophysiological feedback control mechanism during oogenesis.

Animals↗
PubMed1989

The development of microtubular arrays in the germ tissue of an insect telotrophic ovary.

The microtubular arrays characteristic of the trophic core and cords of the adult Rhodnius prolixus ovary develop prior and during the larval--adult transformation. Development of the microtubules was revealed by immunocytochemistry, electron microscopy and polyacrylamide electrophoresis and Western blot analysis. Microtubular arrays were first detected in the trophic cords and presumptive trophic core 6 days before the adult molt. Cord microtubules increase in length and numbers as the trophic cords grow. Three microtubule packed cords have formed by 1 day post molt. The microtubule distribution in the presumptive core is non-uniform. Microtubule packed areas are interspersed with areas devoid of microtubules. The adult core begins forming between 1 day before molt and molting. This early adult core arises from the fusion of the anterior portions of microtubule packed cords. A fully mature adult core is not present by 2 days post molt. The microtubule packing density in the core increases from 2 days before to 2 days post molt. Tubulin increases from 6 days to 1 day before the adult molt.

Animals↗
PubMed1986

Intracellular electrical potential measurements in Drosophila follicles.

We measured the intracellular electrical potential in oocyte and nurse cells of Drosophila follicles at different developmental stages (6-14) and determined the intrafollicular potential difference. During stages 8-10B, when intrafollicular transport is known to occur, no significant potential difference was found. During late vitellogenic stages the nurse cells assume a more positive potential than the oocyte. This result contrasts with the published data on Hyalophora follicles, in which intercellular electrophoresis of negatively charged proteins occurs from nurse cells to oocyte as a result of an intrafollicular potential difference (nurse cells more negative than the oocyte). Such a potential difference was not observed in Drosophila follicles at any stage, not even after application of juvenile hormone. The extrafollicular electrical field is described with a dipole model. The hypothetical dipole is located in the long axis of the follicle and changes its calculated length stage-specifically.

Action Potentials↗
PubMed1986

Comparison of microfilament patterns in nurse cells of different insects with polytrophic and telotrophic ovarioles.

The localization of F-actin (microfilaments) in the nurse cells of ovarian follicles has been studied in 12 different insect species by fluorescence microscopy after specifically staining F-actin with rhodamine-conjugated phalloidin. In the analysed species with polytrophic ovaries (Apis mellifica, Pimpla turionellae, Bradysia tritici, Ephestia kuehniella, Protophormia terraenovae) a dense F-actin network was found to be associated with the nurse cell membranes. Only in Protophormia were microfilament bundles seen to extend from the cell membrane into the nurse cell cytoplasm and in a few cases appeared to make contact with the nuclear membrane. In the analysed coleopteran species with telotrophic ovarioles (Strangalia melanura, Leptinotarsa decemlineata, Oryzaephilus surinamensis) the fluorescence was also concentrated at the nurse cell membranes only. However, in all analysed hemipteran species (Lygus pratensis, Calocoris affinis, Graphosoma lineatum, Euscelis plebejus) the microfilament pattern was very different: while the nurse cells stained only weakly, we always found a characteristic (in some species massive) microfilament network surrounding the trophic core, a central area in the germarium from where material is transported through the trophic cords into the oocytes. The observed differences in the microfilament patterns are likely to reflect different mechanisms for transporting macromolecules and organelles within the ovariole.

Actin Cytoskeleton↗
PubMed1981

Development of nurse cell-oocyte interactions in the insect telotrophic ovary (Rhodnius prolixus).

The establishment of reorganization of intercellular bridges during larval-adult ovarian differentiation is the basis of the syncytial nature of the adult hemipteran telotrophic ovary. The formation, in the late differentiation phase, of groups of closely arranged nurse cell nuclei occupying a common cytoplasm results from membrane fusions. Oocyte-oocyte intercellular bridge systems later are modified to form the trophic cords. The trophic core, which undergoes a restructuring during the late differentiation phase, mediated nurse cell-oocyte interactions in this system. Material, transported to and accumulated by late differentiation phase pre-vitellogenic oocytes, originates from trophic core restructuring and zone III nurse cell production.

Animals↗
PubMed1981

Nurse cell-oocyte interaction in the telotrophic ovarioles of an insect, Rhodnius prolixus.

Microinjection of intracellular tracers fluorescein, Procion Yellow, Lucifer Yellow and horseradish peroxidase unequivocally showed the syncytial structure of the tropharium and its interaction with the oocytes. The tropharium tip is a separate isolated compartment. Finger-like nurse cell projections comprising the syncytial tropharium interact via gap junctions along their abutting membranes and also via large cytoplasmic continuities at the central trophic core. The trophic cords connecting the tropharium to oocyte vary in diameter relative to oocyte stage. Continuity of the tropharium with the oocytes is lost at approximately 1000 micron oocyte length and the severed cords then regress from the oocyte to the tropharium base. Variation in cord diameters and timing of cord closure may account for the highly regulated sequential oocyte growth.

Animals↗