Free Edges in Epithelial Cell Sheets Stimulate Epidermal Growth Factor Receptor Signaling

The ability of epithelia to migrate and cover wounds is essential to maintaining their functions as physical barriers. Wounding induces many cues that may affect the transition to motility, including the immediate mechanical perturbation, release of material from broken cells, new interactions with adjacent extracellular matrix, and breakdown of physical separation of ligands from their receptors. Depending on the exact nature of wounds, some cues may be present only transiently or insignificantly. In many epithelia, activation of the epidermal growth factor receptor (EGFR) is a central event in induction of motility, and we find that its continuous activation is required for progression of healing of wounds in sheets of corneal epithelial cells. Here, we examine the hypothesis that edges, which are universally and continuously present in wounds, are a cue. Using a novel culture model we find that their presence is sufficient to cause activation of the EGFR and increased motility of cells in the absence of other cues. Edges that are bordered by agarose do not induce activation of the EGFR, indicating that activation is not due to loss of any specific type of cell–cell interaction but rather due to loss of physical constraints.     

Effect of glucocorticoids on the response of airway smooth muscle to catecholamine and resorcinol beta-agonists

The influence of hydrocortisone (11 beta, 17 alpha, 21-trihydroxy-pregn-4-ene-3,20-dione) or of methylprednisolone (6 alpha-methyl-11 beta, 17 alpha-21-trihydroxy-1,4-pregnadiene-3,20-dione) on the response of airway smooth muscle to a variety of beta-adrenergic bronchodilators was evaluated using incubated guinea pig tracheal rings, preconstricted with histamine. The adrenergic agonists chosen for this study included the nonselective beta 1- and beta 2-catecholamine, isoproterenol, the selective beta 2-catecholamine, rimiterol, and the selective beta 2-resorcinols, fenoterol and terbutaline. When the incubated rings were pretreated with 10-50 micrograms/mL of the steroids, there was a significant enhancement in smooth muscle sensitivity and reactivity to rimiterol and isoproterenol. Tracheal response to fenoterol or terbutaline, on the other hand, was not altered by the glucocorticoids. When used alone, neither steroid exerted an inotropic influence on the tracheal smooth muscle. The results of our study indicate that glucocorticoid enhancement of adrenergic bronchodilators is selective for catecholamines, and not for resorcinols.     

Relative regeneration proficiency ofArabidopsis thaliana ecotypes

We have compared regeneration proficiency for cultured explants from different tissues of different ecotypes ofArabidopsis thaliana. Proficiency varies widely with both tissue and ecotype, and is highest when the flux of light during regeneration is low. Analysis of F1 hybrids suggests that high proficiency is dominant to low proficiency.     

Two-phase species–time relationships in North American land birds

The species–time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analysed STRs for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two‐phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two‐phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most community dynamics were dominated by ecological processes over scales <5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes.     

Transcapillary escape rate of albumin in humans during exercise-induced hypervolemia

Haskell, Andrew, Ethan R. Nadel, Nina S. Stachenfeld, KeiNagashima, and Gary W. Mack. Transcapillary escape rate of albuminin humans during exercise-induced hypervolemia. J. Appl. Physiol. 83(2): 407-413, 1997.To test thehypotheses that plasma volume (PV) expansion 24 h after intenseexercise is associated with reduced transcapillary escape rate ofalbumin (TER_alb) and that localchanges in transcapillary forces in the previously active tissues favorretention of protein in the vascular space, we measured PV,TER_alb, plasma colloid osmoticpressure (COP_p), interstitialfluid hydrostatic pressure (Pi), and colloid osmotic pressure in legmuscle and skin and capillary filtration coefficient (CFC) in the armand leg in seven men and women before and 24 h after intense uprightcycle ergometer exercise. Exercise expanded PV by 6.4% at 24 h (43.9 ± 0.8 to 46.8 ± 1.2 ml/kg, P < 0.05) and decreased total protein concentration (6.5 ± 0.1 to6.3 ± 0.1 g/dl, P < 0.05) andCOP_p (26.1 ± 0.8 to 24.3 ± 0.9 mmHg, P < 0.05), although plasmaalbumin concentration was unchanged. TER_alb tended to decline (8.4 ± 0.5 to 6.5 ± 0.7%/h, P = 0.11) and was correlated with the increase in PV(r = 0.69,P < 0.05). CFC increased in the leg(3.2 ± 0.2 to 4.3 ± 0.5 µl · 100 g¹ · min¹ · mmHg¹,P < 0.05), and Pi showed a trend toincrease in the leg muscle (2.8 ± 0.7 to 3.8 ± 0.3 mmHg, P = 0.08). These datademonstrate that TER_alb isassociated with PV regulation and that local transcapillary forcesin the leg muscle may favor retention of albumin in the vascular spaceafter exercise.

     

Sublocalization of an Ataxia-Telangiectasia Gene Distal to D11S384 by Ancestral Haplotyping In Costa Rican Families

In an effort to localize a gene for ataxia-telangiectasia (A-T), we have genotyped 27 affected Costa Rican families, with 13 markers, in the chromosome 11q22-23 region. Significant linkage disequilibrium was detected for 9/13 markers between D11S1816 and D11S1391. Recombination events observed in these pedigrees places A-T between D11S1819 and D11S1960. One ancestral haplotype is common to 24/54 affected chromosomes and roughly two-thirds of the families. Inferred (ancestral) recombination events involving this common haplotype in earlier generations suggest that A-T is distal to D11S384 and proximal to D11S1960. Several other common haplotypes were identified, consistent with multiple mutations in a single gene. When considered together with all other evidence, this study further sublocalizes the major A-T locus to ≈200 kb, between markers S384 and S535.     

Ornithogenic soils of the Cape Bird adelie penguin rookeries,Antarctica

Summary Ammonia evolution and urease, phosphatase and protease activities were measured after field incubations of soil from 5 sites, differently influenced by penguin guano, from Cape Bird, Antarctica. Rates of NH₃ production were low considering the large amounts of free NH₃ in these soils. Enzyme activities were higher than expected and, under optimum conditions of temperature, moisture and substrate availability, were sufficient to degrade rapidly the accumulated organic matter in these soils. Laboratory incubations confirmed these high levels of activity; they also showed high dehydrogenase, but not sulphatase, activity. The surface horizon from the site that received continuous additions of fresh penguin excreta had considerably more enzyme activity than the other samples. The optimum activity of phosphatase in this sample was at pH 9.5-10. These enzyme activities are compared with those of New Zealand topsoils, and considered in relation to activities likely to occur under field conditions. Recommendations are made for further biochemical studies at Cape Bird.     

T lymphocytes responding to Mls-locus antigens are Lyt-1+, 2− andI-A restricted

We have investigated primary and secondary responses of mouse splenic T cells to strong mixed lymphocyte stimulating antigens controlled by theMls locus using MHC-identical mixtures of cells. Our studies show that strong primaryMls-locus specific responses involve recognition of self I-A antigens, since BUdR and light suicide or F1 into parent radiation bone-marrow chimeras both demonstrate a preference of unprimed F1 T cells to respond to Mis-locus antigens associated with one parent's MHC antigens. Furthermore, conventional anti-I-A antisera and monoclonal anti-I-A antibody both inhibitMls-locus responses in an MHC-specific manner. Finally, as is typical of T cells responding to I-A antigens or to nominal antigens associated with self I-A,Mlslocus responses are mediated by Lyt-1⁺, 2^– cells. One striking finding in these studies was the very high frequency of cells capable of responding to Mls-locus antigens, the highest being 1/300 splenic T cells. This plus evidence for recruitment during primaryMls-locus responses may account for reports of a lack ofI-A restriction in secondary anti-Mls locus responses to strong Mls-locus antigens, a finding with which we concur. The possibility that these secondary responses between noncongenic strains of mice may be directed at other genetic loci is also discussed. These experiments leave open the question of the biological role of theMls-locus and of the very large number of T cells reactive to it.Abbreviations used in this paper MHC Major histocompatibility complex - MIg Mouse immunoglobulin - MLC Mixed lymphocyte culture - TCGF T-cell growth factor     

Soil restoration under pasture after lignite mining: Management effects on soil biochemical properties and their relationships with herbage yields

The recovery of soil biochemical properties under grazed, grass-clover pasture, after simulated lignite mining, was studied over a 5-year period in a mesic Typic Dystrochrept soil at Waimumu, Southland, New Zealand. The restoration procedures involved four replacement treatments, after A, B, and C horizon materials had been separately removed, from all except the control, and stockpiled for 2–3 weeks. In each replacement treatment, the effects of ripping to 1.8 m depth, mole drainage, and the use of fertilizer nitrogen were also investigated.Replacement treatment markedly influenced the recovery of herbage production and soil organic C and total N contents, N mineralization, microbial biomass (as indicated by mineral-N flush) and invertase and sulphatase activities. The effectiveness of replacement treatments decreased in the order: 1. control (no stripping or replacement). 2 A, B, and C horizon materials replaced in the same order. 3. A, B, and C horizon materials each mixed with an equal amount of siltstone overburden and replaced in order, 4. A and B horizon materials mixed before replacing over C horizon material.Ripping increased herbage production, net N mineralization, and to some extent microbial biomass. Drainage had little, if any, effect.Fertilizer N also stimulated herbage production, but depressed clover growth. Over 2.5 years, it had little detectable effect on the soil properties.Increases in soil invertase and, to a lesser extent, sulphatase activity during the trial were closely related to changes in herbage production. Microbial biomass increased more rapidly than did soil organic C in the early stages of the trial.Rates of net N mineralization strongly suggest that N availability would have limited pasture growth, especially in the treatments with mixed soil materials.     

Domination or equilibrium

In the dynamics of an evolutionary game an equilibrium in which all strategy types occur is called an interior equilibrium. Interior equilibria fail to exist only when there is domination among the strategy types.