Interactions of Schwann cells with neurites and with other Schwann cells involve the calcium-dependent adhesion molecule,N-cadherin

During embryogenesis, Schwann cells interact with axons and other Schwann cells, as they migrate, ensheath axons, and participate in organizing peripheral nervous tissues. The experiments reported here indicate that the calcium-dependent molecule, N-cadherin, mediates adhesion of Schwann cells to neurites and to other Schwann cells. Cell cultures from chick dorsal root ganglia and sciatic nerves were maintained in media containing either 2mM Ca⁺⁺ or 0.2 mM Ca⁺⁺, a concentration that inactivates calcium-dependent cadherins. When the leading lamellae of Schwann cells encountered migrating growth cones in medium with 2 mM Ca⁺⁺, they usually remained extended, and the growth cones often advanced onto the Schwann cell upper surface. In the low Ca⁺⁺ medium, the frequency of withdrawal of the Schwann cell lamella after contact with a growth cone was much greater, and withdrawal was the most common reaction to growth cone contact in medium with 2 mM Ca⁺⁺ and anti-N-cadherin. Similarly, when motile leading margins of two Schwann cells touched in normal Ca⁺⁺ medium, they often formed stable areas of contact. N-cadherin and vinculin were co-concentrated at these contact sites between Schwann cells. However, in low Ca⁺⁺ medium or in the presence of anti-N-cadherin, interacting Schwann cells usually pulled away from each other in a behavior reminiscent of contact inhibition between fibroblasts. In cultures of dissociated cells in normal media, Schwann cells frequently were aligned along neurites, and ultrastructural examination showed extensive close apposition between plasma membranes of neurites and Schwann cells. When dorsal root ganglia explants were cultured with normal Ca⁺⁺, Schwann cells migrated away from the explants in close association with extending neurites. All these interactions were disrupted in media with 0.2 mM Ca⁺⁺. Alignment of Schwann cells along neurites was infrequent, as were extended close apposition between axonal and Schwann cell plasma membranes. Finally, migration of Schwann cells from ganglionic explants was reduced by disruption of adhesive contact with neurites. The addition of antibodies against N-cadherin to medium with normal Ca⁺⁺ levels had similar effects as lowering the Ca⁺⁺ concentration, but antibodies against the neuronal adhesive molecule, L1, had no effects on interactions between Schwann cells and neurites.     

A new DNA marker (D4S90) is located terminally on the short arm of chromosome 4, close to the Huntington disease gene

Genetic linkage studies have mapped Huntington's disease (HD) to the distal portion of the short arm of chromosome 4 (4p16.3), 4 cM distal to D4S10 (G8). To date, no definite flanking marker has been identified. A new DNA marker, D4S90 (D5), which maps to the distal region of 4p16.3, is described. The marker was used in a genetic linkage study in the CEPH reference families with seven other markers at 4p16. The study, together with knowledge of the physical map of the region, places D4S90 as the most distal marker, 6 cM from D4S10. A provisional linkage study with HD gave a maximum lod score of 2.14 at a θ of 0.00 and no evidence of linkage disequilibrium. As D4S90 appears to be located terminally, it should play an important role in the accurate mapping and cloning of the HD gene.     

Lipid peroxidation, iron mobilization and radical generation induced by alcohol

Increasing evidence points to a major role for free radicals in the pathogenesis of alcohol-induced liver injury. In vitro, free radicals may be generated during ethanol metabolism by the further metabolism of acetaldehyde by molybdenum-dependent oxidases such as xanthine oxidase. Ferritin iron mobilized by such free radicals may serve as catalytic iron. Increased stores of ferritin iron and induction of microsomal P-450 reductase activity are mechanisms by which chronic alcohol feeding may potentiate the acute effects of alcohol.     

Nucleus-associated microtubules help determine the division plane of plant epidermal cells: avoidance of four-way junctions and the role of cell geometry

To investigate the spatial relationship between the nucleus and the cortical division site, epidermal cells were selected in which the separation between these two areas is large. Avoiding enzyme treatment and air drying, Datura stramonium cells were labeled with antitubulin antibodies and the three-dimensional aspect of the cytoskeletons was reconstructed using computer-aided optical sectioning. In vacuolated cells preparing for division, the nucleus migrates into the center of the cell, suspended by transvacuolar strands. These strands are now shown to contain continuous bundles of microtubules which bridge the nucleus to the cortex. These nucleus-radiating microtubules adopt different configurations in cells of different shape. In elongated cells with more or less parallel side walls, oblique strands radiating from the nucleus to the long side walls are presumably unstable, for they are progressively realigned into a transverse disc (the phragmosome) as broad, cortical, preprophase bands (PPBs) become tighter. The phragmosome and the PPB are both known predictors of the division plane and our observations indicate that they align simultaneously in elongated epidermal cells. These observations suggest another hypothesis: that the PPB may contain microtubules polymerized from the nuclear surface. In elongated cells, the majority of the radiating microtubules, therefore, come to anchor the nucleus in the transverse plane, consistent with the observed tendency of such cells to divide perpendicular to the long axis. In nonrectangular isodiametric epidermal cells, which approximate regular hexagons in section, the radial microtubular strands emanating from the nucleus tend to remain associated with the middle of each subtending cell wall. The strands are not reorganized into a single dominant transverse bar, but remain as a starlike array until mitosis. PPBs in these cells are not as tight; they may only be a sparse accumulation of microtubules, even forming along non-diametrical radii. This arrangement is consistent with the irregular division patterns observed in epidermal mosaics of isodiametric D. stramonium cells. The various conformations of the radial strands can be modeled by springs held in two-dimensional hexagonal frames, and by soap bubbles in three-dimensional hexagonal frames, suggesting that the division plane may, by analogy, be selected by minimal path criteria. Such behavior offers a cytoplasmic explanation of long-standing empirically derived "rules" which state that the new cell wall tends to meet the maternal wall at right angles. The radial premitotic strands and their analogues avoid taking the longer path to the vertex of an angle where a cross wall is already present between neighboring cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Coccidia of Brazilian mammals: Eimeria corticulata n. sp. (Apicomplexa: Eimeriidae) from the anteater Tamandua tetradactyla (Xenarthra: Myrmecophagidae) and Eimeria zygodontomyis n. sp. from the cane mouse Zygodontomys lasiurus (Rodentia: Cricetidae)

Feces from a specimen of Tamandua tetradactyla (Linn.) from Portel, Pará State, north Brazil, contained two different coccidial oocysts; one identified as Eimeria tamanduae Lainson 1968, and the other as a new species, described here as Eimeria corticulata n. sp. Oocysts of E. corticulata are ellipsoidal, 37.4 x 30.4 (31.2-43.7 x 23.7-35.0) microns, shape index (length/width) 1.2 (1.0-1.5). Oocyst wall 2.5-3.7 microns thick and composed of two layers; an outer thick, brown-yellow one with radial striations, and a thin inner smooth one: no visible micropyle. Oocyst residuum a large globule of about 10.7 x 10.3 microns, usually accompanied by a number of smaller attached globules. Sporocysts ellipsoidal, 21.0 x 11.0 (20.0-22.5 x 10.0-12.5) microns, with a conspicuous Stieda body; shape index 1.9 (1.6-2.2). Sporocyst residuum a small number of scattered granules: sporozoites 18.7 x 5.0 microns, with a large posterior refractile body. Eimeria zygodontomyis n. sp. is described in feces from Zygodontomys lasiurus (Lund) from the Serra dos Carajás, Pará. Oocysts ellipsoidal to cylindrical, 16.5 x 12.0 (13.7-18.7 x 11.2-12.3) microns, shape index 1.4 (1.2-1.5). Wall colorless, smooth, single-layered and about 0.6 micron thick: no micropyle. No oocyst residuum, but a polar granule of about 1.8 x 1.0 microns is sometimes present. Sporocysts ellipsoidal, 8.4 x 5.5 (7.5-8.7 x 5.0-6.2) microns, shape index 1.5 (1.4-1.7), with a thin colorless wall and a delicate Stieda body. Sporozoites enclose a compact residuum of about 2.5 x 3.7 microns.     

Relationship of the env genes and the endonuclease domain of the pol genes of simian foamy virus type 1 and human foamy virus.

We have molecularly cloned and sequenced a portion of the simian foamy virus type 1 (SFV-1); open reading frames representing the endonuclease domain of the polymerase (pol) and the envelope (env) genes were identified by comparison with the human foamy virus (HFV). Unlike the HFV genomic organization, the SFV-1 pol gene overlaps the env gene; thus, the open reading frames reported for HFV between pol and env is not present in SFV-1. Comparisons of predicted amino acid sequences of HFV and SFV-1 reveal that the endonuclease domains of the pol genes are about 84% related. The region predicted to encode the SFV-1 extracellular env domain is 569 codons; SFV-1 and HFV have 64% amino acid similarity in this env domain. The predicted hydrophobic transmembrane env proteins of both HFV and SFV-1 show about 73% similarity. A total of 16 potential glycosylation sites are found in SFV-1 env, and 15 are found in HFV; 11 are shared. SFV-1 has 25 cysteine residues, and HFV has 23 residues; all 23 cysteine residues of HFV are conserved in SFV-1. This sequence analysis reveals that the human and simian foamy viruses are highly related.     

Net increase of pluripotential hematopoietic precursors in suspension culture in response to IL-1 and IL-3

A new short-term suspension culture system is described in which pluripotential hematopoietic precursors from mouse bone marrow increase 8 to 12 times in number over a 4-day period. The increase is shown to derive from myeloid precursors undergoing repeated cell divisions prior to definitive lineage restriction. The response, which occurs in the absence of any pre-formed feeder layer, depends on dual stimulation by both IL-1 and IL-3, and the maximum effect depends on the presence of both factors together from the initiation of the cultures. The observations extend the known range of targets of IL-1 and IL-3 to include primitive pluripotential precursors capable of some degree of self-renewal, and provide a specific and relatively simple assay both for the precursors and the soluble factors which regulate them.