Trilobites Calmoniidae de l'Ordovicien supérieur du Maroc et les origines de la Province Malvino-Cafre

A re-examination of the trilobite Baniaspis globosa Destombes (Phacopina) from the Ashgill of the Anti-Atlas (Morocco) shows that it has several derived characters which allow us to classify it in the family Calmoniidae. Calmoniids were characteristic members of the Malvino-Kaffric province during the Lower Devonian. Hence we regard the origins of this palaeogeographic province as located on the northern Gondwanan margin as early as Ashgill, or even Caradoc, times. We agree with those authors who have suggested that the trilobite associations present in the Anti-Atlas, the Montagne Noire (France) and Bohemia during the earlier Ordovician argue against the existence of a 'proto-Tethys' ocean.     

Structural and physicochemical requirements of endotoxins for the activation of arachidonic acid metabolism in mouse peritoneal macrophages in vitro

Lipopolysaccharides of different wild-type and mutant gram-negative bacteria, as well as synthetic and bacterial free lipid A, were studied for their ability to activate arachidonic acid metabolism in mouse peritoneal macrophages in vitro. It was found that lipopolysaccharides of deep-rough mutants of Salmonella minnesota and Escherichia coli (Re to Rc chemotypes) stimulated macrophages to release significant amounts of leukotriene C4 (LTC4) and prostaglandin E2 (PGE2). Lipopolysaccharides of wild-type strains (S. abortus equi, S. friedenau) only induced PGE2 and not LTC4 formation. Unexpectedly, free bacterial and synthetic E. coli lipid A were only weak inducers of LTC4 and PGE2 production. Deacylated Re-mutant lipopolysaccharide preparations were inactive. However, co-incubation of macrophages with both deacylated lipopolysaccharide and lipid A lead to the release of significant amounts of LTC4 and PGE2, similar to those obtained with Re-mutant lipopolysaccharide. The significance of the lipid A portion of lipopolysaccharide for the induction of LTC4 was indicated by demonstrating that peritoneal macrophages of endotoxin-low-responder mice or of mice rendered tolerant to endotoxin did not respond with the release of arachidonic acid metabolites on stimulation with Re-mutant lipopolysaccharide and that polymyxin B prevented the Re-lipopolysaccharide-induced LTC4 and PGE2 release. Physical measurements showed that the phase-transition temperatures of both free lipid A and S-form lipopolysaccharide were above 37 degrees C while those of R-mutant lipopolysaccharides were significantly lower (30-35 degrees C). Thus, with the materials investigated, an inverse relationship between the phase-transition temperature and the capacity to elicit LTC4 production was revealed.     

No evidence for linkage of autosomal dominant proximal spinal muscular atrophies to chromosome 5q markers

Summary Two recent articles have reported the linkage of a gene for recessive spinal muscular atrophy (SMA) on the chromosome region 5q11.2–13.3. Our data show no linkage of the dominantly inherited forms of SMA to this chromosome region.     

High state of order of isolated bacterial lipopolysaccharide and its possible contribution to the permeation barrier property of the outer membrane.

The conformational properties of the isolated S form of Salmonella sp. lipopolysaccharide (LPS), of Re mutant LPS, and of free lipid A were investigated by using X-ray diffraction and conformational energy calculations. The data obtained showed that LPS in a dried, in a hydrated, and probably also in an aqueous dispersion state is capable of forming bilayered lamellar arrangements similar to phospholipids. From the bilayer packing periodicities, a geometrical model of the extensions of the LPS regions lipid A, 2-keto-3-deoxyoctulosonic acid, and O-specific chain along the membrane normal could be calculated. Furthermore, the lipid A component was found to assume a remarkably high ordered conformation: its fatty acid chains were tightly packed in a dense hexagonal lattice with a center-to-center distance of 0.49 nm. The hydrophilic backbone of lipid A showed a strong tendency to form domains in the membrane, resulting in a more or less parallel arrangement of lipid A units. According to model calculations, the hydrophilic backbone of lipid A appears to be oriented approximately 45 degrees to the membrane surface, which would lead to a shed roof-like appearance of the surface structure in the indentations of which the 2-keto-3-deoxyoctulosonic acid moiety would fit. In contrast, the O-specific chains assume a low ordered, heavily coiled conformation. Comparison of these structural properties with those known for natural phospholipids in biological membranes indicates that the high state of order of the lipid A portion of LPS might be an important factor in the structural role and permeation barrier functions of LPS in the outer membrane of gram-negative bacteria.     

Un biofacies à Trilobites Homalonotidae dans I'Ordovicien de la marge nord-gondwanienne: implications paléobiologiques et paléogéographiques

During the Llandeilo, the sandy lithological units which develop locally in the Armorican Massif, Spain and Morocco, are all characterized by similar trilobite associations in which endobenthic homalonotids. well adapted to shallow water and sandy substrate, are predominant. During the Llandeilo, on the northern Gondwanan margin, the wide geographical distribution of most of the trilobites, controlled by environmental factors, shows that the existence of a 'Proto-Tethys' ocean is unlikely. □ North Gondwana, Trilobita, Homalonotidae, Ordovician, Llandeilo. palaeoenvironment.     

Ein Regelwerk für paläontologische Grabungen in der Grube Messel

The “Framework Messel” formulates regulations, recommendations and instructions for planning and carrying out palaeontological excavations in the Messel pit. The excavation of fossils in the Land Hessen is to some extent controlled by the Monument Protection Law. Therefore, the Framework was developed in close cooperation with the Land Monument Office. Administrative, scientific and organizational conditions for the excavations in the Middle Eocene oil-shales of Messel are listed. Instructional pamphlets explain technical details regarding methods of documentation, excavation and preparation of finds and results.     

Molecular mechanisms of endotoxin activity

Endotoxin (lipopolysaccharide, LPS), a constitutent of the outer membrane of the cell wall of gramnegative bacteria, exerts a wide variety of biological effects in humans. This review focuses on the molecular mechanisms underlying these activities and discusses structure-function relationships of the endotoxin molecule, its interaction with humoral and cellular receptors involved in cell activation, and transmembrane and intra-cellular signal transduction pathways.     

No genetic differences between affected and unaffected members of a German family with Leber's hereditary optic neuropathy (LHON) with respect to ten mtDNA point mutations associated with LHON.

In order to investigate possible synergistic influences of different mtDNA mutations on penetrance and severity of Leber's hereditary optic neuropathy (LHON), a large German LHON pedigree is characterized with respect to 10 different mutations associated with LHON. All members of the family carry three different mtDNA mutations (at nucleotide 4,216, 11,778 and 13,708) in a homoplasmic form, regardless of whether or not they are clinically affected. Testing for another 7 mutations reveals negative results in all family members. Hence, the variable disease expression of the family members cannot be explained by varying combinations of LHON-associated mtDNA mutations.     

Support for association of schizophrenia with genetic variation in the 6p22.3 gene,dysbindin, in sib-pair families with linkage and in an additional sample of triad families

Genetic variants in a gene on 6p22.3, dysbindin, have been shown recently to be associated with schizophrenia (Straub et al. 2002a). There is no doubt that replication in other independent samples would enhance the significance of this finding considerably. Since the gene is located in the center of the linkage peak on chromosome 6p that we reported earlier, we decided to test six of the most positive DNA polymorphisms in a sib-pair sample and in an independently ascertained sample of triads comprising 203 families, including the families for which we detected linkage on chromosome 6p. Evidence for association was observed in the two samples separately as well as in the combined sample (P=.00068 for SNP rs760761). Multilocus haplotype analysis increased the significance further to .00002 for a two-locus haplotype and to .00001 for a three-locus haplotype. Estimation of frequencies for six-locus haplotypes revealed one common haplotype with a frequency of 73.4% in transmitted, and only 57.6% in nontransmitted, parental haplotypes. All other six-locus haplotypes occurring at a frequency of >1% were less often transmitted than nontransmitted. Our results represent a first successful replication of linkage disequilibrium in psychiatric genetics detected in a region with previous evidence of linkage and will encourage the search for causes of schizophrenia by the genetic approach.     

Tertiary structure of bacterial murein: the scaffold model

Although the chemical structure and physical properties of peptidoglycan have been elucidated for some time, the precise three-dimensional organization of murein has remained elusive. Earlier published computer simulations of the bacterial murein architecture modeled peptidoglycan strands in either a regular (D. Pink, J. Moeller, B. Quinn, M. Jericho, and T. Beveridge, J. Bacteriol. 182: 5925-5930, 2000) or an irregular (A. Koch, J. Theor. Biol. 204: 533-541, 2000) parallel orientation with respect to the plasma membrane. However, after integrating published experimental data on glycan chain length distribution and the degree of peptide side chain cross-linking into this computer simulation, we now report that the proposed planar network of murein appears largely dysfunctional. In contrast, a scaffold model of murein architecture, which assumes that glycan strands extend perpendicularly to the plasma membrane, was found to accommodate published experimental evidence and yield a viable stress-bearing matrix. Moreover, this model is in accordance with the well-established principle of murein assembly in vivo, i.e., sequential attachment of strands to the preexisting structure. For the first time, the phenomenon of division plane alternation in dividing bacteria can be reconciled with a computer model of the molecular architecture of murein.