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.     

Amplified Rnase H Activity in Escherichia coli B/R Increases Sensitivity to Ultraviolet Radiation

Strains of E. coli B/r transformed with the plasmid pSK760 were found to be sensitized to inactivation by ultraviolet radiation (UV) and to have elevated levels of RNase H activity. Strains transformed with the carrier vector pBR322 or the plasmid pSK762C derived from pSK760 but with an inactivated rnh gene were not sensitized. UV-inactivation data for strains having known defects in DNA repair and transformed with pSK760 suggested an interference by RNase H of postreplication repair: uvrA cells were strongly sensitized, wild-type and uvrA recF cells were moderately sensitized and recA cells were not sensitized; and minimal medium recovery was no longer apparent in sensitized uvrA cells. Biochemical studies showed that post-UV DNA synthesis was sensitized and that the smaller amounts of DNA synthesized after irradiation, while of normal reduced size as indicated by sedimentation position in alkaline sucrose gradients, did not shift to a larger size (more rapidly sedimenting) upon additional incubation. We suggest an excess level of RNase H interferes with reinitiation of DNA synthesis on damaged templates to disturb the normal pattern of daughter strand gaps and thereby to inhibit postreplication repair.     

Guidelines for the Control of Human Immunodeficiency Virus Infection in Adolescents

Although adolescents account for only 0.4% of reported cases of the acquired immunodeficiency syndrome (AIDS) in the United States, they are sexually active and, therefore, at risk of acquiring human immunodeficiency virus (HIV) infection. To address issues of HIV control in adolescents, we developed guidelines that emphasize education and medical care and deemphasize antibody testing. For adolescents known to be infected with HIV, we recommend no restrictions on access to educational or treatment programs except when their health providers recommend such restrictions to protect them from exposure to opportunistic infections. For adolescents of unknown antibody status with a possible previous exposure to HIV, we recommend that as long as the incidence of HIV infection and clinical AIDS remains low, there should be no restrictions on residential placements and no routine antibody testing.     

Characterization of monoclonal antibodies to histone 2B. Localization of epitopes and analysis of binding to chromatin

Two mouse monoclonal IgM antibodies have been isolated which bind to histone 2B (H2B), as shown by protein blotting and immunostaining and by solid-phase radioimmunoassay (RIA). One of these (HBC-7) was specific for H2B by both techniques whereas the other (2F8) cross-reacted with histone H1 by RIA. Both antibodies failed to recognize H2B limit peptides from trypsin-digested chromatin and did not bind to Drosophila H2B, which differs extensively from vertebrate H2B only in the N-terminal region. These findings indicate that both antibodies recognize epitopes within the trypsin-sensitive, N-terminal region comprising residues 1-20. Binding of antibody HBC-7 was inhibited by in vitro ADP-ribosylation of H2B at glutamic acid residue 2. This strongly suggests that the epitope recognized by HBC-7 is located at the N-terminus of H2B, probably between residues 1 and 8. We have used solid-phase radioimmunoassay to investigate factors which influence the accessibility of this epitope in chromatin. Removal of H1 ('stripping') from high-molecular-mass chromatin had no effect on HBC-7 binding, nor was any difference observed between binding to stripped chromatin and to 146-base-pair (bp) core particles derived from it by nuclease digestion. These results suggest that accessibility of the N-terminal region of H2B is not influenced by H1 itself or by the size or conformation of linker DNA. In contrast, binding of antibody HBC-7 to 146-bp core particles derived from unstripped chromatin was reduced by up to 70%. Binding was restored by exposure of these core particles to the conditions used for stripping. Analysis of the protein content of core particle preparations from stripped and unstripped chromatin suggests that these findings may be attributable to redistribution of non-histone proteins during nuclease digestion. Pre-treatment of high-molecular-mass chromatin or 146-bp core particles with the intercalating dye ethidium bromide resulted in a severalfold increase in binding of HBC-7. The major changes in nucleosome morphology induced by ethidium are therefore accompanied by an increase in accessibility of the N-terminal region of H2B, possibly as a direct result of changes in the spatial relationship between H2B and core DNA.     

Stomatal movement in Zea mays: Shuttle of potassium and chloride between guard cells and subsidiary cells

Summary When stomates of Zea mays open K and Cl migrate from the subsidiary cells into the guard cells; when the stomates close both elements return to the subsidiary cells. Subsidiary cells function as reservoirs for K and Cl. Import of K and Cl into the guard cells and loss of both elements from the guard cells become observable 1 or 2 min after light is turned on or off, both when histochemical methods and the electron-probe microanalyzer are used for detection. Each stomatal complex of maize contains on the average 10±3×10^-13 gram equivalents (eq) of K and 4±1×10^-13 eq of Cl. Guard cells accumulate K in the light and CO₂-free air at an average rate of 10×10^-15 eq K per minute, and Cl at approximately half that rate.     

Rat RI beta isoform of type I regulatory subunit of cyclic adenosine monophosphate-dependent protein kinase: cDNA sequence analysis, mRNA tissue specificity, and rat/mouse difference in expression in testis

A rat complementary DNA (cDNA) for the RI beta isoform of type I cyclic adenosine monophosphate (cAMP)-dependent protein kinase regulatory subunit was cloned and sequenced and was found to contain the entire protein coding and 3'-untranslated regions, with a single (ATTAAA) poly-adenylation site. The largest open reading frame was preceded by a short out-of-phase open reading frame, which is not seen in the corresponding mouse RI beta cDNA due to a single base substitution. The rat RI beta cDNA clone was 2,374 bases long and detected a rat mRNA of approximately 2.8 kilobases. Rat RI beta mRNA was abundant in adult rat brain and testis but was undetectable in other rat tissues. The rat RI beta cDNA also detected RI beta mRNA in mouse brain, but not mouse testis, from 10-week-old BALB/c or 10- and 6-week-old Swiss Webster mice. Thus, despite a 96% nucleotide identity in the coding region of RI beta in rat vs. mouse, there are at least two differences in these closely related species. First, there is a short open reading frame, which precedes the coding region in the rat but not the mouse. Second, unlike the mouse testis, the rat testis contains abundant levels of RI beta mRNA.     

Root traits of perennial C4 grasses contribute to cultivar variations in soil chemistry and species patterns in particulate and mineral-associated carbon pool formation

Recent studies have indicated that the C₄ perennial bioenergy crops switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) accumulate significant amounts of soil carbon (C) owing to their extensive root systems. Soil C accumulation is likely driven by inter- and intraspecific variability in plant traits, but the mechanisms that underpin this variability remain unresolved. In this study we evaluated how inter- and intraspecific variation in root traits of cultivars from switchgrass (Cave-in-Rock, Kanlow, Southlow) and big bluestem (Bonanza, Southlow, Suther) affected the associations of soil C accumulation across soil fractions using stable isotope techniques. Our experimental field site was established in June 2008 at Fermilab in Batavia, IL. In 2018, soil cores were collected (30 cm depth) from all cultivars. We measured root biomass, root diameter, specific root length, bulk soil C, C associated with coarse particulate organic matter (CPOM) and fine particulate organic matter plus silt- and clay-sized fractions, and characterized organic matter chemical class composition in soil using high-resolution Fourier-transform ion cyclotron resonance mass spectrometry. C₄ species were established on soils that supported C₃ grassland for 36 years before planting, which allowed us to use differences in the natural abundance of stable C isotopes to quantify C₄ plant-derived C. We found that big bluestem had 36.9% higher C₄ plant-derived C compared to switchgrass in the CPOM fraction in the 0–10 cm depth, while switchgrass had 60.7% higher C₄ plant-derived C compared to big bluestem in the clay fraction in the 10–20 cm depth. Our findings suggest that the large root system in big bluestem helps increase POM-C formation quickly, while switchgrass root structure and chemistry build a mineral-bound clay C pool through time. Thus, both species and cultivar selection can help improve bioenergy management to maximize soil carbon gains and lower CO₂ emissions.     

Studies on the growth of Saccharomycopsis fibuliger on pectic materials

Growth experiments have indicated that the yeast Saccharomycopsis fibuliger is able to utilize pectic materials as a carbon source for cell growth. Small quantities of yeast extract or mycological peptone and maltose are necessary to initiate growth. Cell yields of 35 g/100 g pectin were obtained after modification of the pH value, the concentration of calcium ions and pectin in the growth medium. The optimum pH for cell growth was 4.8, which is similar to the reported optimum for cell growth on starch. Cell yields declined at higher concentrations of pectin, as a result of the reduced rate of oxygen absorption into the growth medium. Neither the concentration of ammonium and phosphate ions nor the type of inorganic nitrogen source significantly affected cell growth within the experimental conditions employed.