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F Kretzer

Publications and source records attributed to F Kretzer.

11 recordsLinked to original sources
PubMed1997

The mitochondrion in dividing Leishmania tarentolae cells is symmetric and circular and becomes a single asymmetric tubule in non-dividing cells due to division of the kinetoplast portion.

Kinetoplastid protozoa have a single mitochondrion that extends throughout the cell. The disk-shaped portion of the mitochondrion adjacent to the basal body of the flagellum contains the kinetoplast DNA nucleoid body which consists of thousands of catenated minicircles and a smaller number of catenated maxicircles. The maxicircles contain structural genes and cryptogenes, rRNA genes, and a few guide RNA genes The minicircles contain the majority of the guide RNA genes. The long slender non-dividing stationary phase Leishmania tarentolae cells in culture have an asymmetric mitochondrion that consists of a single tubule extending from one edge of the kinetoplast portion. This presents a problem for cell division, in that one daughter cell will receive significantly less mitochondrial membranes than the other cell. We show in this paper that the solution to this problem is that dividing cells, which are normally shorter and rounder than stationary phase cells, possess a symmetric circular mitochondrion that has mitochondrial tubules extending from both edges of the kinetoplast which are joined in the posterior region of the cell. This implies that growth of the mitochondrion occurs after cell division, either from elongation of the longitudinal tubule towards the anterior of the cell, or from elongation of the kinetoplast portion of the mitochondrion towards the posterior region and fusion of the tubules.

Animals↗
PubMed1982

Imaging of outer segment periodicities in unstained cryoultramicrotomy sections of the frog retina.

Frog retinas were examined following cryoultramicrotomy. The extent of glutaraldehyde cross-linking ranged from maximally 2% for 2 h to no cross-linking. When the tissue was cryoprotected, the effects of hypotonic, isotonic and hypertonic media on outer segment banding periodicities were studied. The specimen was cryosectioned at 193 K to 113 K with sections collected on a dry knife (213 K to 123 K). The sections were freeze-dried and only rehydrated with phosphotungstic acid section stain when transmission electron microscopy was used to establish the extent of gross retinal morphology for each fixation protocol employed. As the extreme of no cross-linking and no cryoprotection was approached and reached, conventional sections which displayed extensive retinal morphology were not obtained. Instead, fragments of retinal tissue resulted which showed periodicities of alternating light and dark bands. These periodicities are interpreted as photoreceptor outer segment discs with contrast formation depending upon an interplay between three factors: mass density differences between disc and interdisc space, section cutting angle, and section thickness.

Animals↗
PubMed1980

Bacterial collagenase. Proposed adjunct to vitrectomy with membranectomy.

Clostridiopeptidase A digested preretinal cicatricial tissue without causing morphological alteration of normal retina during a 30-minute incubation in the rabbit. Light and transmission electron microscopy were used to determine effects on the inner limiting membrane and retinal ganglion and Müller's cells and to evaluate enzyme digestion of preretinal scarring. Removal of the injected collangenase by vitrectomy resulted in normal electroretinograms and retinal morphology 48 hours postoperatively. If the enzyme was left in the eye for 24 hours, lens opacities, partial erosion of the inner limiting membrane, and extensive hemorrhage resulted. The specificity of action of the collagenase is due to the high degree of purity of the enzyme used and a substantial biochemical difference between scar collagen and basement membrane collagen. The injection of purified collagenase capable of digesting vitreal scar tissue while leaving the retina undamaged could represent a new approach to vitrectomy, specifically to facilitate certain cases of membranectomy.

Animals↗
PubMed1980

Comparative responses of normal and malignant mouse mammary cells to modulation of surface properties.

We previously demonstrated that epithelial cells growing in primary cultures derived from normal and neoplastic mouse mammary tissues are indistinguishable on the basis of morphology, surface topography, agglutinability by concanavalin A, or of number, cytoplasmic location, or organization of microtubules and actin-containing microfilaments. In the present study, the modulation and interrelationships of these features were investigated using the drugs colchicine and cytochalasin B and the enzymes trypsin, collagenase, and hyaluronidase. Untreated cells of both types were only weakly agglutinable by concanavalin A. Pretreatment of the cells with colchicine, cytochalasin B, or hyaluronidase increased cytoagglutination by the lectin dramatically, whereas neither trypsin nor collagenase significantly altered reactivity of the cells. Binding studies utilizing fluorescein-tagged concanavalin A indicated that the enhanced agglutinability did not correlate with any particular distribution of lectin receptors on the cells. At the doses used, colchicine and cytocholasin B induced disruption of microtubules and microfilament networks, respectively, but no effects on either type of cytoskeletal element were observed after hyaluronidase, trypsin, or collagenase. The increased agglutinability was not associated with any specific surface conformation since scanning electron microscopy revealed that untreated cells and cells exposed to colchicine, hyaluronidase, and collagenase were flat and possessed variable numbers of small microvilli. In contrast, following incubation with cytochalasin B or trypsin, the cells underwent retraction and rounding, and developed complex surface structures such as blebs, ruffles, and filopodia. Thus, no single factor appeared responsible for determining the agglutinable or nonagglutinable state of the mammary cells. Morover, no differences were detected in the surface responses of the normal and malignant cells under any of the conditions used.

Animals↗