Observations on the dynamics of argyrophilic nucleolar material in the nuclei of mice spermatids

Summary Applying a new silver staining technique it could be shown that in very early spermatids strong argyrophilia in nucleoli is confined to their granular and fibrillar components; fibrillar centers are devoid of silver. During subsequent developmental stages remnants of these nucleolar components are present in the form of intensively silver stained clusters of coiled fibers. As chromatin condensation proceeds, these fibrous structures decrease in size and density and are finally completely absent. The nucleus of the mature sperm contains only the space in which they formerly existed, now silver negative, as the so-called nuclear vacuole.Acknowledgment. This investigation was supported partly by grant from the Universitätspreis der Wiener Wirtschaft.     

Observations on the dynamics of argyrophilic nucleolar material in the nuclei of mice spermatids

Applying a new silver staining technique it could be shown that in very early spermatids strong argyrophilia in nucleoli is confined to their granular and fibrillar components; fibrillar centers are devoid of silver. During subsequent developmental stages remnants of these nucleolar components are present in the form of intensively silver stained clusters of coiled fibers. As chromatin condensation proceeds, these fibrous structures decrease in size and density and are finally completely absent. The nucleus of the mature sperm contains only the space in which they formerly existed, now silver negative, as the so-called 'nuclear vacuole'.     

Ultrastructural identification of the nucleolus organizer by the silver staining technic]

The nucleolus organizer regions can be selectively stained in metaphase chromosome preparations by the Goodpasture and Bloom's technique which was adapted to electron microscopy analysis of cells during interphase. Using this technique, a selective accumulation of silver grains was observed over nucleolus light areas. This selective accumulation allows the identification of the interphase fibrillar centers as the nucleolus organizer regions. Ultrastructural relationships between fibrillar centers and dense fibrillar component are discussed.     

Effect of actinomycin D on the quail oocyte nucleolus during meiotic prophase I

Summary Actinomycine D alters profoundly the distribution of the nucleolar constituents in the quail oocyte at prophase I of meiosis. As a consequence of nucleolar segregation the normally existing relations between the nucleolus fibrillar centers and the microchromosomes are ruptured. The relations between the fibrillar center and the dense fibrills which surround it remain intact, suggesting that they constitute together a functional unit.With the technical assistance of Mrs A. Calisti.     

The crystalline phase of cellulose changes under developmental control in a marine chordate

The native form of cellulose is a fibrillar composite of two crystalline phases, the triclinic I_α and monoclinic I_β allomorphs. Allomorph ratios are species-specific, and this gives rise to natural structural variations in cellulose crystals. However, the mechanisms contributing to crystal formation remain unknown. We show that the two crystalline phases of cellulose are tailored to distinct structures during different developmental stages of the tunicate chordate Oikopleura dioica. Larval cellulose consisting of I_α allomorph constitutes the body cuticle fin, whereas adult cellulose consisting of I_β allomorph frames a mucous filter-feeding device, the “house.” Both structures are secreted from the epidermis in accordance with the mutually exclusive expression patterns of two distinct putative cellulose synthase genes. We discuss a possible linkage between structural variations of the crystalline phases of cellulose and the underlying evolutionary genetics of cellulose biosynthesis.     

Characteristics of the nucleolini observed under the electron microscope

Summary Observations with the electron microscope permitted us to ascertain that in molluscs and echinoderms oocytes and in malignat tumour cells, the nucleolini, already seen with the phonton microscope, correspond to the clear fibrillar zones. These present fibrils 40–60 Å thick, spread throughout a very clear matrix. All around these zones there are other closely thickened and interlacing fibrils.     

Amyloid fibrils from the viewpoint of protein folding

In amyloid related diseases, proteins form fibrillar aggregates with highly ordered -sheet structure regardless of their native conformations. Formation of such amyloid fibrils can be reproducible in vitro using isolated proteins/peptides, suggesting that amyloid fibril formation takes place as a result of protein conformational change. In vitro studies revealed that perturbation of the native structure is important for the fibril formation, and it is suggested that the mechanisms of amyloid fibril formation share the mechanisms of protein folding. In particular, amyloid fibril formation is similar to one of the common features of proteins, i.e. amorphous aggregation upon partial unfolding, which is likely driven by hydrophobic interactions through exposed protein interior. However, these molecular associations are distinct phenomena, and identifying factors that lead to amyloid fibril formation would precede our understanding of the mechanisms of amyloid fibrillization. The necessity of understanding the nature of protein denatured states is also suggested.Received 6 July 2003; accepted 19 August 2003     

ADAMTS-2 functions as anti-angiogenic and anti-tumoral molecule independently of its catalytic activity

ADAMTS-2 is a metalloproteinase that plays a key role in the processing of fibrillar procollagen precursors into mature collagen molecules by excising the amino-propeptide. We demonstrate that recombinant ADAMTS-2 is also able to reduce proliferation of endothelial cells, and to induce their retraction and detachment from the substrate resulting in apoptosis. Dephosphorylation of Erk1/2 and MLC largely precedes the ADAMTS-2 induced morphological alterations. In 3-D culture models, ADAMTS-2 strongly reduced branching of capillary-like structures formed by endothelial cells and their long-term maintenance and inhibited vessels formation in embryoid bodies (EB). Growth and vascularization of tumors formed in nude mice by HEK 293-EBNA cells expressing ADAMTS-2 were drastically reduced. A similar anti-tumoral activity was observed when using cells expressing recombinant deleted forms of ADAMTS-2, including catalytically inactive enzyme. Nucleolin, a nuclear protein also found to be associated with the cell membrane, was identified as a potential receptor mediating the antiangiogenic properties of ADAMTS-2.     

Ultrastructural aspects of nucleolar fibrillar centres in meristematic cells ofAllium cepa

Summary This paper deals with the fine structure of the fibrillar centres of the nucleolus inAllium cepa cells in ultrathin, sections of in vivo fixed roots. The ultrastructural observations have allowed us to consider each nucleolar fibrillar centre as an active zone in the nucleolar chromatin loop, and to propose a possible model for the organization of the different components of the nucleolus within it.Acknowledgments. The author wishes to thank Dr.M. C. Risueño for her valuable comments and discussion. This work has been partially supported by the III Plan de Desarrollo of Spain and by a grant of the Foundation Rodriguez Pascual.     

Detection of fibrillary bodies in human and experimental leukemias by polarizing microscopy]

An optical polarizing microscope with a good coefficient of extinction permits the visualization of the cytoplasmic fibrillar body in living preparations and smears of leukemic cells (human leukemias and the L 5222 experimental leukemia). These inclusions are not visible by phase contrast microscopy nor in fixed and stained smears.     

Mikrofibrillenbau der pflanzlichen Zellwände

Summary Primary and secondary cell walls display a beautiful fibrillar texture under the electron microscope. Microfibres of cell walls from many plants and from cultures of cellulose-forming bacteria have a remarkably constant diameter of 250–300 Å.     

Changes to cellular water and element content induced by nucleolar stress: investigation by a cryo-correlative nano-imaging approach

The cell is a crowded volume, with estimated mean mass percentage of macromolecules and of water ranging from 7.5 to 45 and 55 to 92.5 %, respectively. However, the concentrations of macromolecules and water at the nanoscale within the various cell compartments are unknown. We recently developed a new approach, correlative cryo-analytical scanning transmission electron microscopy, for mapping the quantity of water within compartments previously shown to display GFP-tagged protein fluorescence on the same ultrathin cryosection. Using energy-dispersive X-ray spectrometry (EDXS), we then identified various elements (C, N, O, P, S, K, Cl, Mg) in these compartments and quantified them in mmol/l. Here, we used this new approach to quantify water and elements in the cytosol, mitochondria, condensed chromatin, nucleoplasm, and nucleolar components of control and stressed cancerous cells. The water content of the control cells was between 60 and 83 % (in the mitochondria and nucleolar fibrillar centers, respectively). Potassium was present at concentrations of 128–462 mmol/l in nucleolar fibrillar centers and condensed chromatin, respectively. The induction of nucleolar stress by treatment with a low dose of actinomycin-D to inhibit rRNA synthesis resulted in both an increase in water content and a decrease in the elements content in all cell compartments. We generated a nanoscale map of water and elements within the cell compartments, providing insight into their changes induced by nucleolar stress.     

Cerebral amyloidosis: amyloid subunits, mutants and phenotypes

Cerebral amyloid diseases are part of a complex group of chronic and progressive entities bracketed together under the common denomination of protein folding disorders and characterized by the intra- and extracellular accumulation of fibrillar aggregates. Of the more than 25 unrelated proteins known to produce amyloidosis in humans only about a third of them are associated with cerebral deposits translating in cognitive deficits, dementia, stroke, cerebellar and extrapyramidal signs, or a combination thereof. The familial forms reviewed herein, although infrequent, provide unique paradigms to examine the role of amyloid in the mechanism of disease pathogenesis and to dissect the link between vascular and parenchymal amyloid deposition and their differential contribution to neurodegeneration.     

On the structural definition of amyloid fibrils and other polypeptide aggregates

Amyloid fibrils occur inside the human body, associated with ageing or a group of diseases that includes, amongst others, Alzheimer’s disease, atherosclerosis and type II diabetes. Many natural polypeptide chains are able to form amyloid fibrils in vivo or in vitro, and this ability has been suggested to represent an inherent consequence of the chemical structure of the polypeptide chain. Recent literature has provided a wealth of information about the structure of aggregates, precipitates, amyloid fibrils and other types of fibrillar polypeptide assemblies. However, the biophysical meaning associated with these terms can differ considerably depending on the context of their usage. This overview presents a structural comparison of amyloid fibrils and other types of polypeptide assemblies and defines amyloid fibrils, based on structural considerations, as fibrillar polypeptide aggregates with a cross-β conformation. Received 1 March 2007; received after revision 15 March 2007; accepted 25 April 2007     

Lectin receptors in snail proteogalactans. II.Archachatina marginata andAchatina achatina (preliminary report)

Summary The lectin receptor sites on the proteogalactans from the albumin glands of West African land snails,Archachatina marginata andAchatina achatina have been studied by precipitin reactions using the agar-gel double diffusion technique with various lectins. The proteogalactans from both snails have predominantly terminal -D-galactose structures; but they show characteristic differences in the topographical features at the surfaces of the carbohydrate structures presumed to be compatible with the combining site for these lectins.     

Immunogenetics

Summary The 1985 Catalog of Mapped Genes (Human Gene Mapping 8; 33) has been used to pick out the known, immunologically important genes; these are then discussed in the following order: 1. genes controlling organs, tissues and cells of the immune apparatus, 2. genes determining self structures, 3. genes determining the structures of immunological specificity, 4. genes determining substances with immunoregulatory and effector properties. The symbols for the genes and the biological functions of their products are explained. The genetics of the ABO blood groups, of the HLA-system and of antibody formation are given in rather more detail.     

DNA repair nucleases

Stability of DNA largely depends on accuracy of repair mechanisms, which remove structural anomalies induced by exogenous and endogenous agents or introduced by DNA metabolism, such as replication. Most repair mechanisms include nucleolytic processing of DNA, where nucleases cleave a phosphodiester bond between a deoxyribose and a phosphate residue, thereby producing 5-terminal phosphate and 3-terminal hydroxyl groups. Exonucleases hydrolyse nucleotides from either the 5 or 3 end of DNA, while endonucleases incise internal sites of DNA. Flap endonucleases cleave DNA flap structures at or near the junction between single-stranded and double-stranded regions. DNA nucleases play a crucial role in mismatch repair, nucleotide excision repair, base excision repair and double-strand break repair. In addition, nucleolytic repair functions are required during replication to remove misincorporated nucleotides, Okazaki fragments and 3 tails that may be formed after repair of stalled replication forks.Received 12 June 2003; received after revision 29 July 2003; accepted 16 September 2003     

Crystal structure of <Emphasis Type="Italic">Enterobacter cloacae</Emphasis> 908R class C β-lactamase bound to iodo-acetamido-phenyl boronic acid,a transition-state analogue

The structures of the class C -lactamase from Enterobacter cloacae 908R alone and in complex with a boronic acid transition-state analogue were determined by X-ray crystallography at 2.1 and 2.3 Å, respectively. The structure of the enzyme resembles those of other class C -lactamases. The structure of the complex with the transition-state analogue, iodo-acetamido-phenyl boronic acid, shows that the inhibitor is covalently bound to the active-site serine (Ser64). Binding of the inhibitor within the active site is compared with previously determined structures of complexes with other class C enzymes. The structure of the boronic acid adduct indicates ways to improve the affinity of this class of inhibitors. This structure of 908R class C -lactamase in complex with a transition-state analogue provides further insights into the mechanism of action of these hydrolases.Received 16 May 2003; accepted 4 June 2003     

Energy flow and community structure in freshwater ecosystems

The goal of this article is twofold: 1) It aims at providing an overview on some major results obtained from energy flow studies in individuals, populations, and communities, and 2) it will also focus on major mechanisms explaining community structures. The basis for any biological community to survive and establish a certain population density is on the one hand energy fixation by primary producers together with adequate nutrient supply and the transfer of energy between trophic levels (bottom-up effect). On the other hand, predator pressures may strongly control prey population densities one or more trophic levels below (top-down effect). Other interpopulation effects include competition, chemical interactions and evolutionary genetic processes, which further interact and result in the specific structuring of any community with respect to species composition and population sizes.     

Thiamin turnover rate in some areas of rat brain and liver: A preliminary note

Summary Thiamin turnover rates in some nervous structures and liver of rats were evaluated in a steady state condition, using thiamin-¹⁴C as a tracer. The radioactivity contents were analyzed by means of a mamillary type compartmental model. Excluding the liver, turnover rate values of the nervous structures were ordered in the following sequence: sciatic nerve (0.58 g/g·h)>cerebellum>hypothalamus>midbrain>corpus striatum>cerebral cortex (0.16 g/g·h).The mathematical section of this work, developed by V.C. and C.R., was supported by C.N.R., Rome, through the Laboratorio di Analisi numerica, Pavia, Italy. We express our thanks to Prodotti Roche, Milan, for the generous gift of labelled and unlabelled thiamin.