Apolipoprotein E3-Leiden. A new variant of human apolipoprotein E associated with familial type III hyperlipoproteinemia

Summary A variant of apolipoprotein E, denoted apo E3-Leiden, has been identified in a 41-year-old male suffering from type III hyperlipoproteinemia with xanthomatosis. Apo E3-Leiden focus in the E3 position. In contrast with normal apo E3, apo E3-Leiden is defective in binding to the low density lipoprotein (LDL) receptor and does not contain cysteine as evaluated by cysteamine treatment of very low density lipoprotein followed by isoelectric focusing and conventional protein staining and by amino acid analysis. On sodium dodecyl sulfate polyacrylamide gel electrophoresis, apo E3-Leiden displays an electrophoretic mobility intermediate to that of normal apo E3 and apo E2 (Arg₁₅₈Cys). The mother and four siblings of the proband also have apo E3-Leiden and hyperlipoproteinemia type III; three of them with xanthomatosis. Two siblings do not show apo E3-Leiden in their VLDL fraction and do not have hyperlipoproteinemia type III. In the VLDL fractions of all affected family members only the presence of apo E3-Leiden could be detected after cysteamine treatment and isoelectric focusing followed by conventional protein staining. However, isoelectric focusing of cysteaminetreated sera followed by immunoblotting, using anti-apo E antiserum as first antiserum, demonstrates the presence of low amounts of normal apo E3 in addition to apo E3-Leiden in serum of the affected family members. These results indicate that all affected family members are heterozygotes E3/E3-Leiden and suggest that in this family type III hyperlipoproteinemia is transmitted as a dominant trait.     

Localization of rat striatal monoamine oxidase activities towards dopamine,serotonin and kynuramine by gradient centrifugation and nigro-striatal lesions

Subfractionation of the crude synaptosomal-mitochondrial fraction of rat striatum in a continuous sucrose gradient in a zonal rotor led to the following results. The distribution pattern of monoamine oxidase (MAO) activity towards dopamine (DA) was very similar to the pattern of MAO activity towards serotonin (5HT), but differed from the pattern of MAO activity towards kynuramine (KYN). As 5HT is specifically deaminated by MAO-A while KYN is a common MAO substrate, this supports earlier suggestions that in rat striatal preparations DA is deaminated preferentially by MAO-A. The patterns of the MAO activities towards DA and 5HT were clearly dissimilar, despite considerable overlap, to the patterns of tyrosine hydroxylase (TH) and DOPA decarboxylase (DD) activity, both marking the presence of striatal dopaminergic synaptosomes. The peak activities were separated and all patterns were symmetrical without showing a shoulder. This indicates that rat striatal MAO activity towards DA and 5HT is not specifically or for the greater part localized in dopaminergic terminals. We also investigated the effects of electrolytic and 6-hydroxydopamine lesions of the substantia nigra, both causing extensive degeneration of striatal dopaminergic terminals as appeared from the large decrease of striatal TH and DD activity. However, neither type of lesion induced a reduction of the MAO activity towards any of the substrates used. It is concluded towards DA and 5HT (probably MAO-A activity) present in dopaminergic terminals is very low compared with the total activity of this enzyme in rat striatal tissue.     

The caveolae in rabbit sinus node and atrium

Summary Caveolae or membrane vesicles are commonly observed in smooth and skeletal muscle as well as in working heart muscle. Using sections of fixed tissue and replicas of freeze-cleaved material, we show in this study that caveolae are also very numerous in sinus node cells of the rabbit, and to a lesser degree, in the atrial cells.Caveolae increase the plasma membrane surface area by 115% in the leading sinus node, and by 56% in the atrial cells. In these two cell types, the membrane of the caveolae contains four times fewer intramembranous particles than the rest of the plasma membrane, and this difference applies to both PF and EF faces. The role of the caveolae is still unclear, but it does not seem that they have a pinocytotic function.     

Ultroser G and brain extract induce a continuous basement membrane with specific synaptic elements in aneurally cultured human skeletal muscle cells

Basement membrane (BM) components were studied on human muscle and skeletal muscle cells cultured on different media by immunofluorescence and electron microscopy. Their topographical relation with acetylcholine receptors was investigated. Myotubes cultured on a combination of the serum substitute Ultroser G and brain extract show a continuous layer of heparan sulfate proteoglycans (HSPGs), laminin, and type IV collagen. In contrast, myotubes cultured on serum-containing media are associated with granular depositions of HSPG and laminin and only with wisps of type IV collagen. Omission of brain extract or substitution by chicken embryo extract results in an intermediate staining pattern. For all types of cultures, fibronectin is localized in and around mononuclear cells, but hardly associated with myotubes. A codistribution between clusters of acetylcholine receptors and HSPG and laminin and Vicia villosa B4 lectin-positive material exists only in Ultroser G/brain extract-based myotubes like in muscle in vivo. No clustering is observed in serum-based myotubes. Electron microscopy reveals that the former myotubes are surrounded by a continuous BM consisting of a lamina lucida, lamina densa, and lamina fibroreticularis. Proteoglycans are present on the external site of the lamina densa and associated in a regular fashion with collagen fibrils. In conclusion, BMs associated with myotubes cultured on Ultroser G/brain extract resemble in many ways the in vivo situation, including synaptic specializations. Cultured myotubes may serve as a model system for studies on the structure and function of human muscular (synaptic) BM under normal and pathological conditions.     

Stress responses and metal tolerance of <Emphasis Type="Italic">Chlamydomonas acidophila</Emphasis> in metal-enriched lake water and artificial medium

Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake-water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium-grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations.     

Effects of native and exotic range‐expanding plant species on taxonomic and functional composition of nematodes in the soil food web

Due to climate warming, many plant species shift ranges towards higher latitudes. Plants can disperse faster than most soil biota, however, little is known about how range‐expanding plants in the new range will establish interactions with the resident soil food web. In this paper we examine how the soil nematode community from the new range responds to range‐expanding plant species compared to related natives. We focused on nematodes, because they are important components in various trophic levels of the soil food web, some feeding on plant roots, others on microbes or on invertebrates. We expected that range expanding plant species have fewer root‐feeding nematodes, as predicted by enemy release hypothesis. We therefore expected that range expanders affect the taxonomic and functional composition of the nematode community, but that these effects would diminish with increasing trophic position of nematodes in the soil food web. We exposed six range expanders (including three intercontinental exotics) and nine related native plant species to soil from the invaded range and show that range expanders on average had fewer root‐feeding nematodes per unit root biomass than related natives. The range expanders showed resistance against rather than tolerance for root‐feeding nematodes from the new range. On the other hand, the overall taxonomic and functional nematode community composition was influenced by plant species rather than by plant origin. The plant identity effects declined with trophic position of nematodes in the soil food web, as plant feeders were influenced more than other feeding guilds. We conclude that range‐expanding plant species can have fewer root‐feeding nematodes per unit root biomass than related natives, but that the taxonomic and functional nematode community composition is determined more by plant identity than by plant origin. Plant species identity effects decreased with trophic position of nematodes in the soil food web.     

Elaborate petals in Australian Spermacoce (Rubiaceae) species: morphology, ontogeny and function

BACKGROUND AND AIMS: Australian Spermacoce species display various types of elaborate petals. Their precise morphology, ontogenetic origin, and function are hitherto unknown. The aim of the present paper is to unravel the development and nature of the diverse types of elaborate petals in Spermacoce through a floral ontogenetic study. METHODS: The floral ontogeny of six species characterized by different types of corolla appendages was studied by scanning electron microscopy and light microscopy. In order to elucidate the possible functions of the elaborate petals, field observations were conducted as well. KEY RESULTS: Scanning electronmicrographs show that full-grown petals of Spermacoce lignosa, S. phaeosperma and S. redacta bear appendages on their ventral side. Despite their different appearance at anthesis, the appendages develop very similarly in all three species. They are initiated at the same developmental stage and are first visible as two arcs of primordia converging from the upper margins of the petal towards its midvein and downwards. In S. brevidens, S. caudata and S. erectiloba, the full-grown petals have two long, concave protuberances, which develop from the tissue at both sides of the petal's mid-vein. In these three species, initiation of appendages on the ventral side of the petals is also observed, but they are hardly visible on the mature petals. The two types of elaborate petals tightly enclose the anthers, both in bud and during most of the flowering period. CONCLUSIONS: Among Australian Spermacoce species, two types of elaborate petals can be distinguished. The former hypothesis that the two types of elaborate petals are essentially homologous is here rejected. Field investigations point out that the elaborate petals might play a role in the pollination biology of the species.     

Subcellular localization of tyrosine-nitrated proteins is dictated by reactive oxygen species generating enzymes and by proximity to nitric oxide synthase

Using high-resolution immuno-electron microscopy the steady-state subcellular distribution of tyrosine-nitrated proteins in different cells and tissues was evaluated. In quiescent eosinophils and neutrophils in the bone marrow intracellular nitrated proteins were mainly restricted to the peroxidase-containing secretory granules. The inducible nitric oxide synthase (iNOS) was expressed in the same granules. Proteins nitrated on tyrosine residues were also abundant in the cytosol of circulating erythrocytes. In the vasculature, nitrated proteins were mainly located in mitochondria and endoplasmic reticulum of the endothelial cells, fibroblasts, and smooth muscle cells. Endogenous nitrated proteins were also found in chondrocytes in cartilage, where it was typically associated with the cytoplasmic interface of the endoplasmic reticulum membrane. Nitrated proteins were also prominent in the peroxisomes of liver hepatocytes and of secretory cells in the lacrimal gland. Challenge of mouse dendritic cells with lipopolysaccharide induced iNOS protein expression in cytosol and peroxisomes and was associated with an increased 3-nitrotyrosine formation in cytosol, mitochondria, and peroxisomes. These data indicate that nitric oxide-dependent protein tyrosine nitration is a physiologically relevant process localized within specific subcellular compartments in close proximity to iNOS and to enzymes capable of peroxidative chemistry and reactive oxygen species production.