Fibronectin promotes formation of the close cell-to-substrate contact in cultured cells

The effects of addition of cellular fibronectin on the cell-to-substrate contacts of a non-transformed adhesion-defective mutant, AD6, of the BALB/ c3T3 cell-line, and of transformed L-929 fibroblasts have been examined by interference reflection microscopy (IRM). We report that formation of the close contact, but not focal contacts, is promoted in parallel with an increase in spreading in both cell types. These results provide strong evidence for a functional role of fibronectin in the formation of the adhesive close contact.     

Analysis of the patterns of inheritance of splenomegaly and serum IgM levels in the Watut of Papua New Guinea

Hyperreactive malarious splenomegaly (HMS) reflects abnormal immune responses to malarial infection. The central question is whether HMS results from unusual patterns of malarial infection or from immune incompetence in the host. Family distributions of two features of the syndrome, splenomegaly and excessively high IgM levels, have been examined in a Papau New Guinea population in which HMS is exceptionally common. Segregation analysis of spleen grade shows that a major sex-linked gene controls hyperresponsiveness to malaria. This finding is supported by additional segregation analysis, which shows that an autosomal locus cannot account for a significant proportion of variation in spleen grade, and by path analysis, which rejects a model that assumes that parents contribute equally to the child's genotype. The sex-linked gene contributing to HMS was not mediated through sex linkage of a major gene for IgM concentrations, as shown by segregation analysis. It has yet to be determined whether this pattern of inheritance also applies to HMS occurring sporadically in other less severely affected populations. The applicability of these findings to the general variability in "normal" IgM responses to malaria also remains to be established.     

Cerebral Metabolic Effects of Monoamine Oxidase Inhibition in Normal and 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Acutely Treated Monkeys

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic cell death in the substantia nigra pars compacta (SNpc) and clinical parkinsonism in humans and experimental animals. Pretreatment with monoamine oxidase inhibitors prevents this cell death and associated parkinsonism by blocking the oxidation of MPTP to a toxic intermediate. The 2-deoxyglucose method was used to study the acute effects of MPTP in the monkey brain and the effects of monoamine oxidase inhibition on local cerebral glucose utilization in both normal and MPTP-treated monkeys. MPTP administration alone caused a major increase in glucose utilization in the SNpc and smaller increases in some subnuclei within the ventral tegmental area in which eventual dopaminergic cell loss also occurs. Pretreatment with pargyline abolished these metabolic increases, a finding suggesting both that the oxidized product of MPTP generates the metabolic increases and that the increased glucose consumption may contribute to cell toxicity. On the other hand, in most cortical, thalamic, striatal, brainstem, and cerebellar areas MPTP alone caused reductions in glucose utilization, and pargyline failed to prevent these effects. Pargyline alone depressed metabolism in the locus coeruleus and a few other monoaminergic structures.     

Production and standing stocks of the kelp Macrocystis laevis Hay at the Prince Edward Islands,Subantarctic

Summary The recently described species Macrocystis laevis Hay is endemic to the Prince Edward Islands. Aerial photographs of Marion Island were used to outline the distribution of the kelp and to assess its cover. M. laevis occurs along the lee shore of the island, between the 5 and 20 m isobaths. Plant densities and gross plant morphology were measured by divers during April/May 1988. Net production was estimated from growth measurements taken in April/May 1988 and 1989 and again during August 1989. The mean biomass of kelp was 0.67 kgC·m^–2 within the kelp beds. Net production was estimated at 7.7 gC·m^–2·d^–1 and 11.5 gC·m^–2d^–1 during the months of April and August respectively. M. laevis had a uniform frond-length frequency distribution, which suggests that only the oldest fronds are lost by wave action or senescence. Based on calculations for M. laevis and Durvillaea antarctica (the two species making up most of the macrophyte biomass) macrophytes are more productive per unit area than the phytoplankton but contribute less to the seas around the Prince Edward Islands by virtue of their small spatial coverage. Neither of the kelps lose much material as particulate or dissolved organic carbon through fragmentation. The extent of grazing on live M. laevis fronds is unknown, and only D. antarctica contributes to a macrofaunal detrital community. The contribution of M. laevis production to the nearshore ecology of the islands seems limited, as we suspect that almost all of its production is exported to the open ocean pelagic system.     

Growth of Octopine-Catabolizing Pseudomonas spp. under Octopine Limitation in Chemostats and Their Potential To Compete with Agrobacterium tumefaciens

The growth characteristics of five octopine-catabolizing pseudomonads have been determined in batch and continuous cultures. All five strains belonged to rRNA homology group I and showed a more psychrotrophic growth pattern than did Agrobacterium tumefaciens B6 and ATCC 15955. In chemostats limited by octopine, either as the source of carbon and nitrogen or the sole source of nitrogen, maximum specific growth rates and substrate affinities were lower than those in chemostats limited by glutamate. These growth dynamics were similar to those observed for Agrobacterium strains B6 and ATCC 15955 even though the catabolic genes and pathways are believed to be different in the two genera. An analysis of the yields in octopine-limited chemostats indicated that the use of octopine as the sole source of carbon and nitrogen was grossly inefficient. Octopine and presumably lysopine and octopinic acid provided a better source of nitrogen than of carbon. One of the Pseudomonas fluorescens strains, E175D, was able to produce its highest yield on octopine as a nitrogen source. Competition models formulated on pure culture parameters indicated that two of the Pseudomonas spp. would dominate A. tumefaciens B6 and ATCC 15955 when in simple competition for octopine as a limiting substrate.     

Ontogeny of an Extracellular Matrix Component of Sea Urchins and its Role in Morphogenesis

A monoclonal antibody, Sp14, recognizes fibers that form a complex meshwork within the blastocoel of embryos of the sea urchin, Strongylocentrotus purpuratus . The fibers first appear as the blastocoel begins to form and increase in density throughout development. Ultrastructural localizations using the immunoperoxidase method show bundles of 20 nm fibers that are continuous with the basal lamina and have an indistinct axial periodicity. Embryos treated with tunicamycin, β-D-xylopyranoside, β-aminoproprionitrile, proline analogues, or deprived of sulfate all form immunoreactive fibers although in some treatments the pattern formed is abnormal. Immunoreactivity of extracted fibers is not affected by digestion with chondroitinase ABC, hyaluronidase, collagenase or heparinase. However, proteinase K readily destroys immunoreactivity. Fibers will form in cultures of micromeres or mesenchyme 24 to 48 hr after plating with or without horse serum. In embryos in which the blastocoelar matrix has been altered by injection with Sp14, there is inhibition of the release of secondary mesenchyme from the tip of the archenteron and in some embryos supernumerary skeletal elements are formed. It is proposed that Sp14 recognizes a component of the blastocoelar extracellular matrix that is required for the migration of mesenchyme.     

Purification of 20α-hydroxysteroid oxidoreductase from bovine fetal erythrocytes

NADPH-dependent 20α-hydroxysteroid oxidoreductase (20α-HSD; EC 1.1.1.149) from bovine fetal erythrocytes was obtained for the first time free of hemoglobin by a new 2,500-fold purification scheme. This was achieved by a sequence of calcium phosphate gel adsorption, ammonium sulfate fractionation, and affinity chromatography. The present results lead us to believe that the NADPH-dependent 3β-hydroxysteroid oxidoreductase activity, which was co-purified with 20α-activity, may originate at the active site of 20α-HSD (2).     

A variation of the smooth septate junction in sea spiders (Pycnogonida)

A new type of septate junction considered to be a variation of the arthropod smooth septate junction is described in pycnogonid (sea spider) endothermal tissue based on the use of conventional thin-section, lanthanum tracer and freeze-fracture techniques. This new type of septate junction is apparently unique to the Pycnogonida but closely resembles septate junctions previously described in the Merostomata and Collembola. This work in conjunction with previous work suggests that the septa of smooth septate junctions may not be as ‘smooth’ as generally thought and probably have a complex substructure.     

On the defence strategy of Physa fontinalis (L.), a freshwater pulmonate snail

Summary Physa fontinalis (L.) gives a characteristic, chemically mediated escape response when stimulated by the majority of British leeches and flatworms. The snail responds rapidly and consistently to contact with all the molluskivorous leeches but also to three species which may be considered harmless. However, no response was given to Erpobdella octoculata, the most abundant and widespread of the harmless leeches. The flatworms generally evoked less strong reactions. The adaptive significance of the pattern of responsiveness is discussed. A weaker shell-shaking response is elicited in conspecifics and it is shown that this antisocial behaviour leads to a relatively spaced-out dispersion pattern. A possible adaptive advantage is the reduction of risk of detection by shell-crushing fish predators, to which the snails are otherwise extremely vulnerable.