EGF receptor-mediated signals are differentially modulated by concanavalin A

NIH 3T3 cells expressing hgh levels of the human epidermal growth factor (EGF) receptor were used to examine the effects of the lectin concanavalin A (Con A) on EGF-mediated signaling events. Proliferation of NIH 3T3 cells expressing high levels of the human EGF receptor was inhibited in a dose-dependent manner by Con A. At the same time, Con A also inhibited both dimerization and tyrosine phosphorylation of the EGF receptor. Tyrosine phosphorylation of the enzyme phospholiphase C-γ, a substrate of the phosphorylated EGF receptor kinase, was also inhibited. In contrast, EGF-stimulated changes in pH, calcium, and levels of inositol phosphates were unaffected by the presence of Con A. These results indicate that certain signals (changes in the levels of intracellular calcium, pH, and inositol phosphates) mediated by EGF binding to its receptor still occur when receptor dimerization and phosphorylation are dramatically decreased, suggesting that multiple independent signals are transmitted by the binding of EGF to its receptor. © 1995 Wiley-Liss, Inc.     

Metabolic inhibitors induce symplastic movement of solutes from the transport phloem of Arabidopsis roots

The distribution of the phloem-mobile fluorescent probe carboxyfluorescein(CF) within the primary root of Arabidopsis thaliana was imagedusing a confocal laser scanning microscope (CLSM) and the tissueand subcellular distribution of the probe was shown to be influencedby treatment with a number of metabolic inhibitors. Sodium azidecompletely inhibited the phloem transport of CF into the treatedregion of root. Treatment with both CCCP and probenecid inducedthe lateral movement of CF from the transport phloem to theadjacent cell layers, and the probe accumulated in the cytoplasmof the pericycle, endodermis, cortex, and epidermis. This lateraltransfer of CF was restricted to the pericycle in the presenceof plasmolysing concentrations of sorbitol. Ultrastructuralinvestigations demonstrated the presence of a plasm odesmatalpathway leading from the sieve elementcompanion cell complex(SE-CC) out into the cortex. The results are consistent withthe operation of this symplastic pathway under conditions ofmetabolic energy reduction and are discussed in relation tothe regulation of plasmodesmatal conductance in the transportphloem. Key words: Arabidopsis, confocal laser scanning microscopy (CLSM), metabolic inhibitors, phloem transport, symplastic phloem unloading     

Response of compressed skinned skeletal muscle fibers to conditions that simulate fatigue

Myburgh, Kathryn H., and Roger Cooke. Response ofcompressed skinned skeletal muscle fibers to conditions that simulate fatigue. J. Appl. Physiol. 82(4):1297-1304, 1997.During fatigue, muscles become weaker, slower,and more economical at producing tension. Studies of skinned musclefibers can explain some but not all of these effects, and, inparticular, they are less economical in conditions that simulatefatigue. We investigated three factors that may contribute to thedifferent behavior of skinned fibers. 1) Skinned fibers have increasedmyofilament lattice spacing, which is reversible by osmoticcompression. 2) A myosin subunit becomes phosphorylated during fatigue.3) Inosine 5-monophosphate (IMP) accumulates during fatigue. We tested the response ofphosphorylated and unphosphorylated single skinned fibers (isometrictension, contraction velocity, and adenosinetriphosphatase activity) to changes in lattice spacing (0-5% dextran) and IMP (0-5 mM)in the presence of altered concentrations ofP_i (3-25 mM),H⁺ (pH 7-6.2), and ADP(0-5 mM). The response of maximally activated skinned fibers tothe direct metabolites of ATP hydrolysis is not altered by osmoticcompression, phosphorylating myosin subunits, or increasing IMPconcentration. These factors, therefore, do not explain the discrepancybetween intact and skinned fibers during fatigue.

     

Infection ofArabidopsis thaliana ecotype columbia by tomato spotted wilt virus

Mechanical inoculation ofArabidopsis thaliana ecotype Columbia with tomato spotted wilt virus led to viral replication and spread as determined by dot blot and ELISA analysis. Severe symptoms were observed three to four weeks post-inoculation. Early symptoms were manifested as chlorotic spots on uninoculated leaves. Later in the infection process, some plants showed complete chlorosis and wilting prior to bolting. Bolts that were developed by infected plants were chlorotic and deformed. These preliminary results suggest thatA. thaliana could become a model system for the genetic analysis of host factors required for the replication of viruses in the family Bunyaviridae, which includes viruses that cause important diseases of both plants and animals.     

Biochemical variation of Cryptococcus neoformans

Ninety-seven strains of Cryptococcus neoformans and C. bacillisporus were examined for 44 biochemical characters and the results were analyzed numerically. One phenon emerged at the 86% level of similarity when strains were clustered according to their M-similarity values. All strains grew in ten carbon sources (D-glucose, D-galactose, arbutin, maltose, sucrose, D-melezitose, D-xylose, D-mannitol, D-glucitol, and meso-inositol), and also grew at 37 ° C and produced urease and phenoloxidase. None of them grew in melibiose, lactose, nor valine, and none reduced nitrate to nitrite. Comparison of selected biochemical characters, creatinine utilization, and serotypes of 49 aberrant strains is presented. Forty-eight of the 97 strains produced the Filobasidiella state either alone or when paired with a strain of compatible mating-type. Filobasidiella neoformans serotypes A and D were interfertile with compatible mating-types of F. bacillispora serotypes B and C. The 44 biochemical characters and 4 serotypes did not predict barriers to mating competence. The present study further substantiates that Filobasidiella neoformans and F. bacillispora are one species.     

Restriction endonuclease mapping of the colicin Ib plasmid

Summary A cleavage site map of the colicin Ib plasmid (ColIb) has been determined for the enzymes Sall, XhoI, and HindIII by analysis of partial digests, double digests, DNA-DNA hybridization, and Tn5-induced insertion mutants. The site of the colicin gene has been determined by probing with cloned DNA coding for colicin production, as well as by analysis of a colicin negative ColIb:Tn5.     

T cell responses to select Ia determinants using the I-A mutant mouse strain B6.C-H-2bm12

The T cell repertoire of B6.C-H-2bm12 mice (an I-A mutant mouse strain) to wild-type Iab antigens was investigated using both secondary proliferative cultures and cloned T cell lines. Because bm12 mice have a gain-loss mutation of their gene encoding the Ia beta-chain polypeptide, bm12 anti-B6 T cell responses are specific for the select component of Iab specificities that was lost as a result of the mutation. Although stimulator cells bearing Iab antigens elicited the strongest responses, Iaq, d, and s antigens also resulted in reproducible stimulations of these bm12 anti-B6-primed T cells. Cloned T cell lines isolated from bm12 anti-b6 cultures revealed similar findings, with most clones recognizing determinants unique for Iab antigens; however, clones showing cross-reactions with Iad and/or q were also selected. Using F1 hybrid responder T cells (mutant x cross-reactive strain), we further dissected this cross-reactivity into several distinct cross-reactive determinants. Because bm12 mice lack the serologically defined Ia differentiation antigen W39, T cell recognition of this determinant was investigated by using bm12 anti-B6-primed cells. Stimulation by Ia.W39+ cells was appreciably better than by Ia.W39- (Xid-defective) cells, suggesting that bm12 T cells recognize an Xid-regulated, W39-like Ia differentiation antigen.     

ULTRASTRUCTURE OF DEVELOPING AND MATURE NONARTICULATED LATICIFERS IN THE MILKWEED ASCLEPIAS SYRIACA L. (ASCLEPIADACEAE)

The ultrastructure of developing and mature nonarticulated laticifers in Asclepias syriaca L. (the common milkweed) was studied by conventional fixation and staining techniques and by osmium impregnation techniques. The mature laticifer protoplast in A. syriaca possesses a large central vacuole with an intact vacuolar membrane. Formation of this vacuole apparently results from dilation and subsequent enlargement of endoplasmic reticulum and possibly in part by fusion of smaller vacuoles and limited cellular-lytic autophagy. Widespread digestion or autophagy of cytoplasm within vacuoles is not evident. Nuclei, mitochondria, dictyosomes, and small vesicles are the most prominent components distributed in the peripheral cytoplasm. Plastids appear to degenerate as the laticifer matures. The specialized cellular component, latex, which is the vacuolar content of the laticifer, is interpreted to be produced in the cytoplasm and subsequently incorporated into the large central vacuole. Rubber globules, the most prominent latex component, are surrounded by a membrane that does not have a trilaminate structure. Globules are associated with an electron-dense fibrillar component in the vacuole.     

Heavy metals (Cu and Zn) in recent sediments of Llangorse Lake,Wales: non-ferrous smelting,Napoleon and the price of wheat — a palaeoecological study

Elevated concentrations of Cu and Zn have been found in the upper part of three sediment cores collected from Llangorse Lake, in south Wales. Palaeomagnetic evidence from one of the cores and ²¹⁰Pb analysis of another, suggests that the increase in sediment Cu and Zn concentrations began during the eighteenth century. A sharp increase in the concentrations of these metals in the sediment profile appears to have occurred during the latter part of the eighteenth century and these concentrations remained high until the mid to late nineteenth century.The absence of known ore deposits and industry around the lake suggests that the lake and catchment soils were increasingly contaminated by long-range aerial transport of emissions from the expanding activity of Cu and Zn smelters located some 80 km upwind in the Swansea area during the Industrial Revolution. Evidence from agricultural crop returns indicates a significant increase in the amount of land devoted to tillage in the catchment, particularly to cereal production, during the late eighteenth and the first half of the nineteenth century which included the Napoleonic Wars. This agricultural shift appears to coincide with increased concentrations of Cu and Zn in the lake sediments. It is suggested that newly ploughed soils, contaminated with metals for many years by long-range aerial transport from the Swansea area, eroded, and were carried into the lake by catchment run-off and added to the sediment burden of Cu and Zn. A subsequent decline of Cu and Zn emissions due to the collapse of the non-ferrous smelting industry and reduced soil erosion because of a 50% reduction of tillage due to an agricultural depression in the second half of the 19th century may explain the fall in Cu and Zn concentrations in the upper part of the sediment profile. The most recent sediments (20th century) show the increase in heavy metals characteristic of many lakes around the world.