Minimum sample sizes for identifying chromosomal fragile sites from individuals: Monte Carlo estimation

A Monte Carlo simulation procedure was used to estimate the exact level of the standardized X ² test statistic (X _s ²) for randomness in the FSM methodology for the identification of fragile sites from chromosomal breakage data for single individuals. A random-number generator was used to simulate 10 000 chromosomal breakage data sets, each corresponding to the null hypothesis of no fragile sites for numbers of chromosomal breaks (n) from 1 to 2000 and at three levels of chromosomal band resolution (k). The reliability of the test was assessed by comparisons of the empirical and nominal α levels for each of the corresponding values of n and k. These analyses indicate that the sparse and discrete nature of chromosomal breakage data results in large and unpredictable discrepancies between the empirical and nominal α levels when fragile site identifications are based on small numbers of breaks (n < 0.5 k). With n≥ 0.5 k, the distribution of X _s ² appears to be stable and non-significant differences in the empirical and nominal α levels are generally obtained. These results are inherent to the nature of the data and are, therefore, relevant to any statistical model for the identification of fragile sites from chromosomal breakage data. For FSM identification of fragile sites at α = 0.05, we suggest that n≥ 0.5 k is the minimum reliable number of mapped chromosomal breaks per individual. Received: 28 April 1997 / Accepted: 1 July 1997     

The ultrastructure of epithelial and myoepithelial oncocytes in the human parotid gland (author's transl)]

Oncocytes are well known to occur in the tissue of many organs for over 30 years. Their origin and function are less well known. We observed different types of oncocytes in a human parotid gland with the electron microscope. Besides a hyperplasia of mitochondria they show more or less advanced signs of membrane degeneration of these organelles. On the basis of our findings we discuss oncocyte formation as a special form of cellular aging in an otherwise healthy gland.     

Amotin and amoenin,two sesquiterpenes of the picrotoxane group from Dendrobium amoenum

Two new sesquiterpenes, amotin and amoenin, of the picrotoxane group were isolated from Dendrobium amoenum. The constitution of amoenin was evident from spectral investigations and by its conversion into α-dihydro-picrotoxinin on oxidation with oxygen in the presence of platinum. The constitution of amotin was shown by its spectral properties and the conversion of aduncin into amotin by hydrogenolysis of its epoxide ring. That the configuration at C-4 in aduncin and amotin is R was supported by circular dichroism measurements on some derivatives of picrotoxinin and aduncin.     

Human pathologies associated with defective RNA transport and localization in the nervous system.

RNA localization is emerging as an important process to restrict certain proteins to specific subcellular domains and thus spatially control the expression of genes within cells. It is used, for instance, to compartmentalize the developing embryo during early embryogenesis. The localization of RNA also plays important roles later during development, such as in asymmetric cell divisions, cell migration and the outgrowth and pathfinding of axons and dendrites. In differentiated cells, it serves to subdivide the cell into functionally distinct compartments. For example, in mature neurons it is believed to contribute to the plastic changes of individual synapses underlying learning and memory. In this review, we highlight the importance of subcellular RNA localization for the function of the nervous system and neurological diseases associated with defective RNA localization and translation. These diseases include fragile X mental retardation syndrome, spinocerebellar ataxia and spinal muscular atrophy.     

Streptacidiphilus hamsterleyensis sp. nov., isolated from a spruce forest soil

Three acidophilic actinobacteria, isolates LSCA2, FGG8 and HSCA14^T, recovered from spruce litter were examined using a polyphasic approach. Chemotaxonomic and morphological properties of the isolates were found to be consistent with their classification in the genus Streptacidiphilus. The isolates were shown to have identical 16S rRNA gene sequences and were most closely related to Streptacidiphilus neutrinimicus DSM 41755^T (99.9 % similarity). However, DNA:DNA relatedness between isolate HSCA14^T and the type strain of S. neutrinimicus was found to be low at 44.0 (±14.1) %. A combination of phenotypic features, including degradative and nutritional characteristics were shown to distinguish the isolates from their nearest phylogenetic neighbours. Data from this study show that the isolates form a novel species in the genus for which the name S. hamsterleyensis sp. nov. is proposed. The type strain is HSCA 14^T (=DSM 45900^T = KACC 17456^T = NCIMB 14865^T).     

Differentiated NSC-34 motoneuron-like cells as experimental model for cholinergic neurodegeneration

Alpha-motoneurons appear to be exceedingly affected in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). Morphological and physiological degeneration of this neuronal phenotype is typically characterized by a marked decrease of neuronal markers and by alterations of cholinergic metabolism such as reduced choline acetyltransferase (ChAT) expression. The motoneuron-like cell line NSC-34 is a hybrid cell line produced by fusion of neuroblastoma with mouse motoneuron-enriched primary spinal cord cells. In order to further establish this cell line as a valid model system to investigate cholinergic neurodegeneration, NSC-34 cells were differentiated by serum deprivation and additional treatment with all-trans retinoic acid (atRA). Cell maturation was characterized by neurite outgrowth and increased expression of neuronal and cholinergic markers, including MAP2, GAP-43 and ChAT. Subsequently, we used differentiated NSC-34 cells to study early degenerative responses following exposure to various neurotoxins (H₂O₂, TNF-α, and glutamate). Susceptibility to toxin-induced cell death was determined by means of morphological changes, expression of neuronal marker proteins, and the ratio of pro-(Bax) to anti-(Bcl-2) apoptotic proteins. NSC-34 cells respond to low doses of neurotoxins with increased cell death of remaining undifferentiated cells with no obvious adverse effects on differentiated cells. Thus, the different vulnerability of differentiated and undifferentiated NSC-34 cells to neurotoxins is a key characteristic of NSC-34 cells and has to be considered in neurotoxic studies. Nonetheless, application of atRA induced differentiation of NSC-34 cells and provides a suitable model to investigate molecular events linked to neurodegeneration of differentiated neurons.     

Functions and regulation of human artemis in double strand break repair

Cells, which lacked the activity of the nuclease Artemis, retained approximately 10% of unrepaired double strand breaks (DSBs) at later timepoints after ionizing radiation. Ionizing radiation induced hyperphosphorylation of Artemis mainly by ATM and in ATM deficient cells to a minor extent by DNA PK. After induction of DSBs with modified ends by a high dose of calicheamicin gamma1, Artemis was phosphorylated by DNA PK. The type of calicheamicin gamma1-induced DSBs is likely to represent a subclass of DSBs induced by ionizing radiation. DNA PK-dependent phosphorylation of Artemis after treatment with DSB inducing agents increased the cellular retention of Artemis, maintained its interaction with DNA ends and activated its endonucleolytic activity. The following model is suggested: ATM-dependent phosphorylation of Artemis after ionizing radiation could prevent DNA PK-dependent phosphorylation and activation of undesired endonucleolytic activity at DSBs, which do not require endonucleolytic processing by Artemis. The Artemis:DNA PK complex could be involved in the repair of DSBs, which carry modified ends and are refractory to repair by otherwise lesion specific enzymes because of the presence of an inhibitory lesion in the opposite strand.     

The GTP-binding protein Septin 7 is critical for dendrite branching and dendritic-spine morphology

Septins, a highly conserved family of GTP-binding proteins, were originally identified in a genetic screen for S. cerevisiae mutants defective in cytokinesis [1, 2]. In yeast, septins maintain the compartmentalization of the yeast plasma membrane during cell division by forming rings at the cortex of the bud neck, and these rings establish a lateral diffusion barrier. In contrast, very little is known about the functions of septins in mammalian cells [3, 4] including postmitotic neurons [5-7]. Here, we show that Septin 7 (Sept7) localizes at the bases of filopodia and at branch points in developing hippocampal neurons. Upon downregulation of Sept7, dendritic branching is impaired. In mature neurons, Sept7 is found at the bases of dendritic spines where it associates with the plasma membrane. Mature Sept7-deficient neurons display elongated spines. Furthermore, Sept5 and Sept11 colocalize with and coimmunoprecipitate with Sept7, thereby arguing for the existence of a Septin5/7/11 complex. Taken together, our findings show an important role for Sept7 in regulating dendritic branching and dendritic-spine morphology. Our observations concur with data from yeast, in which downregulation of septins yields elongated buds, suggesting a conserved function for septins from yeast to mammals.     

Influence of autoclaved saprotrophic fungal mycelia on proteolytic activity in ectomycorrhizal fungi

The production of proteolytic enzymes by several strains of ectomycorrhizal fungi i.e., Amanita muscaria (16-3), Laccaria laccata (9-12), L. laccata (9-1), Suillus bovinus (15-4), Suillus bovinus (15-3), Suillus luteus (14-7) on mycelia of Trichoderma harzianum, Trichoderma virens and Mucor hiemalis and sodium caseinate, yeast extract was evaluated. The strains of A. muscaria (16-3) and L. laccata (9-12) were characterized by the highest activity of the acidic and neutral proteases. Taking the mycelia of saprotrophic fungi into consideration, the mycelium of M. hiemalis was the best inductor for proteolytic activity. The examined ectomycorrhizal fungi exhibited higher activity of acidic proteases than neutral ones on the mycelia of saprotrophic fungi, which may imply the participation of acidic proteases in nutrition.