Lumican Regulates Collagen Fibril Assembly: Skin Fragility and Corneal Opacity in the Absence of Lumican

Lumican, a prototypic leucine-rich proteoglycan with keratan sulfate side chains, is a major component of the cornea, dermal, and muscle connective tissues. Mice homozygous for a null mutation in lumican display skin laxity and fragility resembling certain types of Ehlers-Danlos syndrome. In addition, the mutant mice develop bilateral corneal opacification. The underlying connective tissue defect in the homozygous mutants is deregulated growth of collagen fibrils with a significant proportion of abnormally thick collagen fibrils in the skin and cornea as indicated by transmission electron microscopy. A highly organized and regularly spaced collagen fibril matrix typical of the normal cornea is also missing in these mutant mice. This study establishes a crucial role for lumican in the regulation of collagen assembly into fibrils in various connective tissues. Most importantly, these results provide a definitive link between a necessity for lumican in the development of a highly organized collagenous matrix and corneal transparency.     

Nouveaux Monocotylidae (Monogenea), parasites branchiaux de Dasyatis pastinaca (L.) (Euselachii,Dasyatidae). Compléments à la description de Heterocotyle pastinacae Scott, 1904

Heterocotyle scotti n. sp. and H. similis n. sp., two gill parasites of Dasyatis pastinaca, are described. H. pastinacae Scott, 1904, is redescribed from the gills of the same Mediterranean host species. New features concerning haptor morphology are reported. The disposition of the sinuous ridges on the haptor of these three species is discussed. All three species possess a spermatophore. The variation in vaginal anatomy of H. pastinacae leads to the suggestion of a sequence explaining the development or destruction of the spermatophore. The specificity of these parasites and their relationships with Heterocotyle from the Atlantic coast of America are discussed.     

Downregulation of connexin32 protein and gap-junctional intercellular communication by cytokine-mediated acute-phase response in immortalized mouse hepatocytes

In the present study, we have analyzed the direct effects of cytokines, which mediate the acute-phase response in liver, on connexin expression and gap-junctional intercellular communication in immortalized MHSV12 mouse hepatocytes. When these cells were stimulated for 24 h with interleukin 1 and interleukin 6, the amount of connexin26 (Cx26) mRNA increased together with β?fibrinogen mRNA, as expected for this positive acute-phase gene. In contrast, connexin32 (Cx32) mRNA expression was not affected under these conditions. Indirect immunfluorescence revealed a drastic decrease in Cx32 signals, whereas slightly more Cx26 signals were found. Stronger stimulation with interleukin 1 and tumor necrosis factor α gave a dose-dependent increase in steady state levels of Cx26 and β-fibrinogen mRNA, but no further change in Cx32 mRNA level was seen. However, when Cx32 protein was analyzed on immunoblots, we found a 5-fold decrease in expression even at low cytokine doses that did not affect Cx32 mRNA expression. Under these conditions, cell to cell transfer of Lucifer yellow, microinjected into immortalized hepatocytes, was decreased by 70%, suggesting that intercellular communication through Cx32 channels was partially inhibited earlier than other genetic alterations characteristic of the acute-phase response. Thus, the major hepatic gap junction protein was largely downregulated at the beginning of the experimental inflammatory reaction, but about 30% of gap-junctional intercellular communication was maintained. This suggests that, during the acute-phase response, the second hepatic Cx26 protein may compensate in part for the downregulation of the Cx32 protein.     

Long-term measurements of boreal forest carbon balance reveal large temperature sensitivity

We present results from two years’ net ecosystem flux measurements above a boreal forest in central Sweden. Fluxes were measured with an eddy correlation system based on a sonic anemometer and a closed path CO₂ and H₂O gas analyser. The measurements show that the forest acted as a source during this period, and that the annual balance is highly sensitive to changes in temperature. The accumulated flux of carbon dioxide during the full two-year period was in the range 480–1600 g CO₂ m^–2. The broad range is caused by uncertainty regarding assessment of the night-time fluxes. Although annual mean temperature remained close to normal, the results are partly explained by higher than normal respiration, due to abnormal temperature distribution and reduced soil moisture during one growing season. The finding that a closed forest can be a source of carbon over such a long period as two years contrasts sharply with the common belief that forests are always carbon sinks.     

Role of sphingosine kinase in Ca(2+) signalling by epidermal growth factor receptor

Contribution of sphingosine kinase (SPK)-catalyzed production of sphingosine-1-phosphate (SPP), in comparison to phospholipase C (PLC), to Ca(2+) signalling by epidermal growth factor (EGF) was studied in two HEK-293 cell clones (HEK2 and HEK3), expressing functional EGF receptors and exhibiting release of stored Ca(2+) by intracellular SPP. In HEK3 cells, EGF increased [Ca(2+)](i) and stimulated both, SPK and PLC. [Ca(2+)](i) increase, but not PLC stimulation, was strongly reduced by SPK inhibition. In HEK2 cells, EGF similarly stimulated PLC, but did not increase [Ca(2+)](i) or stimulate SPK, suggesting that intracellular SPP production plays a major role for Ca(2+) signalling by EGF in HEK-293 cells.     

Molecular cloning and transmembrane structure of hCLCA2 from human lung, trachea, and mammary gland

The CLCA family ofCa²⁺-activatedCl channels has recentlybeen discovered, with an increasing number of closely related members isolated from different species. Here we report the cloning of thesecond human homolog, hCLCA2, from a human lung cDNA library. Northernblot and RT-PCR analyses revealed additional expression in trachea andmammary gland. A primary translation product of 120 kDa was cleavedinto two cell surface-associated glycoproteins of 86 and 34 kDa intransfected HEK-293 cells. hCLCA2 is the first CLCA homolog for whichthe transmembrane structure has been systematically studied.Glycosylation site scanning and protease protection assays revealedfive transmembrane domains with a large, cysteine-rich, amino-terminalextracellular domain. Whole cell patch-clamp recordings ofhCLCA2-transfected HEK-293 cells detected a slightly outwardly rectifying anion conductance that was increased in the presence of theCa²⁺ ionophore ionomycin andinhibited by DIDS, dithiothreitol, niflumic acid, and tamoxifen.Expression in human trachea and lung suggests that hCLCA2 may play arole in the complex pathogenesis of cystic fibrosis.

     

Polyoxovanadates: The missing link between simple paramagnets and bulk magnets?

Oxovanadium clusters provide novel examples of large magnetic clusters, which may showin nuce the typical behavior of bulk magnetic materials.The paper reviews the magnetic properties of V₁₅, comprising fifteen oxovanadium(IV); V₁₄, comprising fourteen oxovanadium(IV); V₃₊₁, comprising three localized oxovanadium(IV), six localized oxovanadium(V), and one oxovanadium(IV) delocalized over three sites; V₄₊₂ and V₄₊₄ which comprise four localized and two and four delocalized oxovanadium(IV), respectively. The different observed magnetic behaviors are discussed on the basis of several models of different sophistication.