Isolation of monoclonal antibodies specific for human c-myc proto-oncogene product.

Six monoclonal antibodies have been isolated from mice immunized with synthetic peptide immunogens whose sequences are derived from that of the human c-myc gene product. Five of these antibodies precipitate p62c-myc from human cells, and three of these five also recognize the mouse c-myc gene product. None of the antibodies sees the chicken p110gag-myc protein. All six antibodies recognize immunoblotted p62c-myc. These reagents also provide the basis for an immunoblotting assay by which to quantitate p62c-myc in cells.     

Inhibition by theophylline of phagocytosis in Acanthamoeba castellanii.

Theophylline inhibited the phagocytosis of latex beads by Acanthamoeba castellanii (Neff). The cells recovered the ability to engulf beads after 1-2 hr of exposure to theophylline. Cells which have been exposed to 25 mM theophylline for a period of inhibition and recovery were not inhibited further by incubation with a fresh medium containing the same concentration of theophylline. However, the medium in which the cells recovered was as effective as a fresh medium in inhibiting phagocytosis in a fresh batch of cells, suggesting that the development of insensitivity to theophylline inhibition resides with the cells themselves. Dibutyryl cyclic AMP also inhibited bead uptake.     

Widespread desert affiliation of trebouxiophycean algae (Trebouxiophyceae,Chlorophyta) including discovery of three new desert genera

Unlike most other green algae, trebouxiophyceans are predominantly aerophytic and contain many symbiotic representatives. In recent years, a number of new terrestrial trebouxiophycean taxa were described from soils, tree bark, and lichens. The present phylogenetic study reveals three new lineages of free‐living trebouxiophyceans found in North American desert soil crusts and proposes new generic names to accommodate them: Desertella, Eremochloris, and Xerochlorella. This survey of desert isolates also led to discovery of representatives of seven existing genera of trebouxiophyceans. Two of these genera have never been reported to contain desert representatives and one was known previously only from aquatic habitats. Furthermore, we expand the known geographic range of the recently described genus Chloropyrula, heretofore only known from the Ural Mountains. We demonstrate that the diversity of trebouxiophyceans is still underestimated and poorly understood, and that most major trebouxiophycean lineages contain desert‐dwelling taxa.     

Endothelial cells are activated by angiopoeitin-1 gene transfer and produce coordinated sprouting in vitro and arteriogenesis in vivo

RATIONAL AND OBJECTIVES: Activation of fully differentiated vascular cells using angiogenic genes can lead to phenotypic changes resulting in formation of new blood vessels. We tested whether Ang-1 gene transfer to endothelial cells (EC) activates these cells. METHODS AND RESULTS: EC and SMC were transduced using retroviral or adenoviral vectors to produce Ang-1 or vascular endothelial growth factor (VEGF). EC Tie-2 receptor was phosphorilated by autologous secretion of Ang-1. Transduced EC and SMC sprouting capacity was tested using collagen embedded spheroids assay and capacity to produce arteriogenesis was tested in a hind limb model of ischemia. EC expressing Ang-1 in the presence of SMC expressing VEGF exhibited high levels of sprouting of the two cell types. Flow and numbers of arteries were increased after transduced cells implantation in vivo. CONCLUSIONS: Autologous secretion of Ang-1 by transduced EC resulted in Tie-2 activation and in the presence of SMC expressing VEGF resulted in coordinated sprouting in vitro and increase in flow and number of arteries in vivo.     

Energy and predation costs of firefly courtship signals

Animal courtship signals include many highly conspicuous traits and behaviors, and it is generally assumed that such signals must balance the benefits of attracting mates against some fitness costs. However, few studies have assessed the multiple costs potentially incurred by any one courtship signal, so we have limited understanding of the relative importance of different costs. This study provides the first comprehensive assessment of signal costs for Photinus fireflies (Coleoptera: Lampyridae), using controlled experiments to measure both the energy and predation costs associated with their bioluminescent courtship signals. We measured energy required to generate bioluminescent flashes, using differential open-flow respirometry, and found that flash signaling results in only a nominal increase in energy expenditure above resting levels. These results suggest that the energy required to generate bioluminescent flashes represents a minor component of the total cost of firefly courtship. However, controlled field experiments revealed that visually oriented predators imposed major costs on firefly courtship signals, with higher signaling rates significantly increasing the likelihood of predation. Together with previous results demonstrating that female fireflies prefer more conspicuous courtship signals, these results support the importance of multiple-receiver communication networks in driving signal evolution.     

Calorimetric and spectroscopic studies of the phase behavior and organization of lipid bilayer model membranes composed of binary mixtures of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol

The thermotropic phase behavior of hydrated bilayers derived from binary mixtures of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) was investigated by differential scanning calorimetry, Fourier-transform infrared spectroscopy and 31P-nuclear magnetic resonance spectroscopy. Binary mixtures of DMPC and DMPG that have not been annealed at low temperatures exhibit broad, weakly energetic pretransitions (approximately 11-15 degrees C) and highly cooperative, strongly energetic gel/liquid-crystalline phase transitions (approximately 23-25 degrees C). After low temperature incubation, these mixtures also exhibit a thermotropic transition form a lamellar-crystalline to a lamellar gel phase at temperatures below the onset of the gel/liquid-crystalline phase transition. The midpoint temperatures of the pretransitions and gel/liquid-crystalline phase transitions of these lipid mixtures are both maximal in mixtures containing approximately 30 mol% DMPG but the widths and enthalpies of the same thermotropic events exhibit no discernable composition dependence. In contrast, thermotropic transitions involving the Lc phase exhibit a very strong composition dependence, and the midpoint temperatures and transition enthalpies are both maximal with mixtures containing equimolar amounts of the two lipids. Our spectroscopic studies indicate that the Lc phases formed are structurally similar as regards their modes of hydrocarbon chain packing, interfacial hydration and hydrogen-bonding interactions, as well as the range and amplitudes of the reorientational motions of their phosphate headgroups. Our results indicate that although DMPC and DMPG are highly miscible, their mixtures do not exhibit ideal mixing. We attribute the non-ideality in their mixing behavior to the formation of preferential PC/PG contacts in the Lc phase due to the combined effects of steric crowding of the DMPC headgroups and charge repulsion between the negatively charged DMPG molecules.     

Factors regulating cladoceran dynamics in a Venezuelan floodplain lake

Five cladoceran zooplankton species in a Venezuelan floodplainlake, Laguna la Orsinera, were analyzed to identify factorscontrolling their dynamics over a period encompassing isolation,inundation by the Orinoco River and drainage. The abundanceof each species increased rapidly to a maximum associated withflooding of the lake by the Orinoco River. We calculated birth,death and population growth rates, and developed a method forestimating uncertainty in these parameters, in order to interpretobserved cladoceran abundance patterns. Rapid increases in populationsizes resulted both from high birth rates associated with decreasingturbidity following inundation and from the hatching of restingeggs. Birth rates remained high throughout the study, but highdeath rates restricted each population to a brief maximum andthen maintained small population sizes throughout the remainderof the study. Our demographic analyses suggest that high mortalityresulted from intense predation by fish and by Chaoborus larvae,rather than from resource limitation, and that this mortalitywas the major factor regulating cladoceran abundance duringinundation and drainage in this tropical floodplain lake.