Werner W. Franke

Simultaneous glutaraldehyde-osmium tetroxide fixation with postosmication - An improved fixation procedure for electron microscopy of plant and animal cells

SummaryA fixation procedure for electron microscopy is described which includes a simultaneous glutaraldehyde-OsO4 fixation followed by postosmication. This procedure was found to have considerable advantages in preserving structures of plant and animal cells.

On the universality of nuclear pore complex structure

SummarySubstructural details of the nuclear pore complex were studied in diverse plant and animal cells with both section technique and negative staining of isolated nuclear envelope pieces. The structures observed after the different techniques, including a variety of fixation procedures, are compared and their significance is discussed. It is shown that, down to the 15–20 Å level, the architecture of the nuclear pore complex is universal among such diverse cell types as from, e. g., onion root tips, bean leaves, mammalian liver parenchyma, HeLa cell cultures, and amphibian germ material. The fundamental substructures of the pore complex such as (1) the annular granules, (2) the fibrils attached to the annuli, (3) the central granules, (4) the fibrils in the pore interior including those which make up the “inner ring” and/or those which connect the central granule to the pore margin, are recognized in all cell types studied. The dynamic variability of the central granule morphology is emphasized and observations are presented which suggest that the view of such centrally located material as representing ribonucleoproteins in a transitory state of nucleocytoplasmic migration can be extended to generality. General concepts of the nuclear pore complex structure are presented as alternative model views revealing either a more compact, predominantly granular, or a more fibrillar aspect.

Zur Feinstruktur isolierter Kernmembranen aus tierischen Zellen

SummaryA method developed for isolating pieces of nuclear envelopes from plant tissue (Franke, 1966) can also be applied to animal cells. The procedure consists of a treatment of highly purified nuclei with hypotonical shock and subsequent gentle sonication, followed by a fractionation of the nuclear membranes in a combined differential and discontinuous density gradient centrifugation. This method was successful with such diverse kinds of animal cells as mouse liver tissue and logarithmically growing Tetrahymena pyriformis, micronucleus-less strain GL. Suspensions of the isolated envelope pieces were examined with electron microscopical techniques, especially in negatively stained preparations.1.The pieces of nuclear envelopes isolated from mouse liver show pore complexes with well developed annuli and inner annulus diameters of 65 ± 7 nm. In the majority of the pieces the frequency of the pores per nuclear surface unit is from 35 to 55 pores per μ2. The annulus is composed of globular subunits with diameters in the range of 7 to 18 nm and more diffuse material which also extends into the pores lumen. Testing the number of these subunits and their center-to-center-spacing with Markhams rotation-technique, it was found that in general either eight or nine subunits are arranged in an eight- or ninefold radial symmetry. This result considered together with the findings previously reported for onion root tip nuclei and some observations of other authors strongly suggests that the regular arrangement of eight or nine globular subunits in a circular pattern within the annulus is of widespread occurrence among the karyobions.2.In the fraction of envelope pieces from Tetrahymena macronuclei two types, differing in the appearance of their pore complexes, can be distinguished. In both types extraordinarily high pore frequencies of 95 to 135 pores per μ2 were counted. Type B, however, shows very well developed annuli around the pores with inner annulus diameters of about 20 nm, while almost no annular material is present in type A, where only the delineated perimeter of the pore shows up as negatively stained. The pore diameters of type A range from about 55 to 60 nm. It is assumed that these types represent different structural states of the pore complex relating to changes in the pores functional role as a system regulating the nucleocytoplasmic interactions.ZusammenfassungDie Methode zur Isolierung von Zellkernmembranen aus pflanzlichem Gewebe (Franke, 1966) ist auch auf tierische Zellen anwendbar: von Mäuseleber wie von logarithmisch wachsender Tetrahymena pyriformis konnten Fraktionen gut erhaltener Kernhüllenstücke erhalten werden. Die isolierten Membranen wurden elektronenmikroskopisch untersucht (Negativkontrast). Zellkerne aus Mäuseleber haben eine Porenhäufigkeit von 35–55 Poren pro μ2, der innere Annulusdurchmesser der Porenkomplexe beträgt 65 ± 7 nm. Der Annulus besteht aus 8 oder 9 globulären Untereinheiten mit Durchmessern von 7–18 nm, die streng radiärsymmetrisch angeordnet sind, und diffuserem Material, das sich auch in das Lumen der Pore hinein erstrecken kann. Makronuclei von Tetrahymena weisen eine bemerkenswert hohe Porenhäufigkeit von 95–135 Poren pro μ2 auf. Man findet hier zwei Kernmembran-Typen, die sich vor allem im Ausbildungszustand des Annulus unterscheiden: Typ A (innerer Annulusdurchmesser etwa 55–60 nm) besitzt kaum Annulusmaterial, Typ B (innerer Annulusdurchmesser etwa 20 nm) ist durch einen äußerst stark entwickelten Annulus mit distinkten Untereinheiten charakterisiert. Diese Strukturunterschiede werden in Zusammenhang mit der Vorstellung von den Kernporen als Regulationssysteme der Kern-Cytoplasma-Wechselbeziehung diskutiert.

Identification of renal podocytes in multiple species: higher vertebrates are vimentin positive/lower vertebrates are desmin positive

Abstractu2002We sought to characterize podocytes in the kidneys of numerous species from amphibians to mammals because of the pivotal function of these cells in renal diseases. For this purpose, intermediate filament (IF) proteins of podocytes were examined by immunofluorescence microscopy using antibodies against vimentin, cytokeratins, and desmin. These staining patterns were then compared to those of parietal cells of Bowman’s capsule and tubular cells of the first portion of the proximal tubule from the same sources. As a result, podocytes from mammals (rat, rabbit, dog, cow, and human) and birds (chicken) showed intense vimentin staining without exception, but rarely staining for cytokeratins or desmin. Parietal cells from all these animals were highly heterogeneous with respect to cytokeratin or vimentin staining. Of the tubular cells, only those from humans and chickens were reactive and then only with anti-cytokeratin antibodies. In the reptiles (Chrysemys scripta elegans, Chinemys reeveri, Elaphe quadrivirgata, and Anolis carolinensis), podocytes and other epithelial cells were positive for cytokeratins. Vimentin staining differed among the species, but was not characteristic for podocytes. Anti-desmin antibody reacted strongly only with podocytes from Anolis. In amphibians (Rana catesbeiana and Xenopus laevis), anti-desmin antibody stained podocytes more intensely than any other cell. Cytokeratin and vimentin staining did not differentiate podocytes from the other cell types. These findings indicate that podocytes are characterized by intense vimentin staining in the higher vertebrates and by desmin staining in the lower vertebrates denoting potentially distinctive physiological functions of IF proteins in podocytes from each of these groups.

Cell and lorica fine structure of the chrysomonad alga, Dinobryon sertularia Ehr. (Chrysophyceae)

SummaryThe fine structure of wild living organisms of the chrysophycean alga, Dinobryon sertularia, has been studied after fixation with glutaraldehyde. A description of the cell body as revealed from serial sections is given. The similarity of the cellular organization to that of the related genus, Ochromonas, is emphasized. In addition, the microfibrillar arrangement of the lorica has been studied in negative staining. Possible modes of lorica formation are discussed, especially with the evidence presented that the mid region of the cell body is in direct, although perhaps transitory, contact with the lorica and shows a variety of vesicles suggesting secretory membrane flow.

Annulate lamellae in plant cells: Formation during microsporogenesis and pollen development in Canna generalis Bailey

SummaryThe occurrence of stacked annulate lamellae is documented for a plant cell system, namely for pollen mother cells and developing pollen grains of Canna generalis. Their structural subarchitecture and relationship to endoplasmic reticulum (ER) and nuclear envelope cisternae is described in detail. The results demonstrate structural homology between plant and animal annulate lamellae and are compatible with, though do not prove, the view that annulate lamellar cisternae may originate as a degenerative form of endoplasmic reticulum.

Actinomycin D and the central granules in the nuclear pore complex: Thin sectioning versus negative staining

SummaryThin section electron microscopy of Actinomycin D treated Tetrahymena cells and amphibian oocytes (Xenopus laevis, Triturus alpestris) reveal no reduction in the central granules in the nuclear pore complexes. Possible reasons for the diversity between these results and earlier observations using negatively stained isolated nuclear envelopes from the same objects are discussed. The results clearly show that the presence of central granules within the nuclear pores does neither depend on nuclear RNA synthesis nor does indicate nucleocytoplasmic RNA transport. This conclusion leads to a reconsideration of the nature of the central granule. The functioning of the central granule of the nuclear pore complexes is further discussed in connection with recent studies on the ultrastructure of various types of cisternal pores.

Natural segregation of nucleolar components in the course of a plant cell differentiation.

SummarySegregation of the nucleolar components is described in the differentiated nucleus of the generative cell in the growing Clivia and Lilium pollen tubes. This finding of a natural nucleolar segregation is discussed against the background of current views of the correlations of nucleolar morphology and transcriptional activity.

Central dilations in maturing Golgi cisternae -a common structural feature among plant cells?

SummaryCentrally located dilations of the first or second distal-most Golgi cisternae can be observed in diverse plant cells. Their significance and distribution as well as a possible functional correlation to polysaccharide formation is discussed.

Structure and function of the stimulated adrenal cortex. 2. Early effects of ACTH on the ultrastructure of the zona fasciculata in dexamethasone--treated rats.

Summary The effect of ACTH on the ultrastructure of the zona fasciculata of the rat adrenal cortex has been examined by electron microscopic morphometry. A detailed description of fine structural changes is presented, with special attention to the „early” (i. e., 20 minutes after ACTH application) effects. Significant changes were noted in mitochondria as well in the relative area increase of the condensed chromatin. The possible significance of these ultrastructural changes is discussed against the background of the current concepts of ACTH action on corticoid hormone production and secretion.