Polymorphonuclear leukocytes regulate the plasminogen-activating system of cultured endothelial cells

Exposure of bovine pulmonary artery endothelial cells (BEC) to polymorphonuclear leukocytes (PMN) (1 x 10(6)/ml) stimulated by opsonized zymosan (OZ-PMN) decreased plasminogen activator (PA) activity in conditioned medium by as much as 98% as compared to controls. Unstimulated PMN (U-PMN) (1 x 10(6)/ml), after an initial enhancement, decreased PA activity 95%. Low concentrations of U-PMN and OZ-PMN enhanced and high concentrations depressed PA activity. The decline in PA activity was not associated with an increased endothelial cell injury. The suppression of PA activity by OZ-PMN was associated with a 7-fold increase in activity of PA inhibitor 1 (PAI-1). PMN did not affect PA after its secretion, suggesting that modulation of endothelial cells by PMN changes the net activities of PA and PAI-1 in the conditioned medium.     

A Toxoplasma MORN1 Null Mutant Undergoes Repeated Divisions but Is Defective in Basal Assembly,Apicoplast Division and Cytokinesis

The membrane occupation and recognition nexus protein 1 (MORN1) is highly conserved among apicomplexan parasites and is associated with several structures that have a role in cell division. Here we dissected the role of MORN1 using the relatively simple budding process of Toxoplasma gondii as a model. Ablation of MORN1 in a conditional null mutant resulted in pronounced defects suggesting a central role for MORN1 in apicoplast segregation and in daughter cell budding. Lack of MORN1 resulted in double-headed parasites. These Janus-headed parasites form two complete apical complexes but fail to assemble a basal complex. Moreover, these parasites were capable of undergoing several more budding rounds resulting in the formation of up to 16-headed parasites conjoined at the basal end. Despite this segregation defect, the mother''s cytoskeleton was completely disassembled in every budding round. Overall this argues that successful completion of the budding is not required for cell cycle progression. None of the known basal complex components, including a set of recently identified inner membrane complex (IMC) proteins, localized correctly in these multi-headed parasites. These data suggest that MORN1 is essential for assembly of the basal complex, and that lack of the basal complex abolishes the contractile capacity assigned to the basal complex late in daughter formation. Consistent with this hypothesis we observe that MORN1 mutants fail to efficiently constrict and divide the apicoplast. We used the null background provided by the mutant to dissect the function of subdomains of the MORN1 protein. This demonstrated that deletion of a single MORN domain already prevented the function of MORN1 whereas a critical role for the short linker between MORN domains 6 and 7 was identified. In conclusion, MORN1 is required for basal complex assembly and loss of MORN1 results in defects in apicoplast division and daughter segregation.     

Sexual selection and the evolution of obligatory sex

Background  

Among the long-standing conundrums of evolutionary theory, obligatory sex is one of the hardest. Current theory suggests multiple factors that might explain the benefits of sex when compared with complete asexuality, but no satisfactory explanation for the prevalence of obligatory sex in the face of facultative sexual reproduction.     

Pollinator‐mediated selection on floral size and tube color in Linum pubescens: Can differential behavior and preference in different times of the day maintain dimorphism?

Diversity of flower traits is often proposed as the outcome of selection exerted by pollinators. Positive directional pollinator‐mediated selection on floral size has been widely shown to reduce phenotypic variance. However, the underlying mechanism of maintaining within‐population floral color polymorphism is poorly understood. Divergent selection, mediated by different pollinators or by both mutualists and antagonists, may create and maintain such polymorphism, but it has rarely been shown to result from differential behavior of one pollinator. We tested whether different behaviors of the same pollinators in morning and evening are associated with dimorphic floral trait in Linum pubescens, a Mediterranean annual plant that exhibits variable within‐population frequencies of dark‐ and light‐colored flower tubes. Usia bicolor bee‐flies, the major pollinators of L. pubescens, are mostly feeding in the flower in the morning, while in the evening they are mostly visiting the flowers for mating. In 2 years of studying L. pubescens in a single large population in the Carmel, Israel, we found in one year that dark‐centered flowers received significantly higher fraction of visits in the morning. Fitness was positively affected by number of visits, but no fitness differences were found between tube‐color morphs, suggesting that both morphs have similar pollination success. Using mediation analysis, we found that flower size was under positive directional pollinator‐mediated selection in both years, but pollinator behavior did not explain entirely this selection, which was possibly mediated also by other agents, such as florivores or a‐biotic stresses. While most pollinator‐mediated selection studies show that flower size signals food reward, in L. pubescens, it may also signal for mating place, which may drive positive selection. While flower size found to be under pollinator‐mediated selection in L. pubescens, differential behavior of the pollinators in morning and evening did not seem to explain flower color polymorphism.     

Visual characterization of recombination at FRT-gusA loci in transgenic tobacco mediated by constitutive expression of the native FLP recombinase

FLP/FRT-mediated site-specific recombination was studied with a recombination-reporter gene system which allows visualization of -glucuronidase (GUS) expression after site-specific excisional activation of a silent gusA gene. This system was used for characterization of the functional activity of the Saccharomyces cerevisiae native FLP recombinase driven by the cauliflower mosaic virus (CaMV) 35s promoter [linked to the tobacco mosaic virus (TMV) omega translational leader] in mediating site-specific recombination of chromosomal FRT sites in tobacco FLP x FRT-reporter hybrids. Six hybrids were generated from crosses of lines containing either a stably integrated recombination-reporter or a FLP-expression construct. The activated gusA phenotype was specific to hybrid progenies and was not observed in either parental plants or their selfed progenies. Recombination efficiency in whole seedlings was estimated by the percent of radioactivity on a Southern blot which was incorporated into the recombined DNA product. Estimated efficiency mean values for the six crosses ranged from 5.2 to 52.0%. Histochemical analysis in hybrid plants visualized GUS activity with variable chimeric patterns and intensities. Recombination efficiency and GUS expression varied both among and within crosses, while higher recombination efficiency coincided with larger and more intense patterns of GUS activity. These data suggest that recombination is induced randomly during somatic developmental stages and that the pattern and intensity generated in a given plant are affected by factors imposing varibility not only between but also within crosses. Additionally, while recombination in a population of FLP/FRT hybrids may occur in all plants, recombination efficiency may still be low in any given plant. The activity of the native, as compared to a modified, FLP (Kilby et al. 1995) in the activation of transgenic traits in tobacco is discussed.     

Photonastic Control of Leaflet Orientation in Melilotus indicus (Fabaceae)

Leaflet orientation in Melilotus indicus (L.) All. Is under photonastic control during the day and nyctinastic control during the night, but also exhibits a diaphototropic (solar-tracking) response. Detached leaves with the two lateral leaflets excised were used to study the solar-tracking capability of the terminal leaflet. Perception of the photonastic excitation is located in the pulvinule. The lower (abaxial) and upper (adaxial) surfaces perceive photonastic excitation, which results in concomitant contraction of the side exposed to light and/or expansion of the opposite side. Steady state laminar elevation is determined by the fluence rates of the light incident simultaneously on the opposite sides. Light sensitivity of the lower side exceeds that of the upper. Response to photonastic excitation of either side is affected by angle of incidence of the light, but angular dependence is restricted to a limited range of angle of incidence, which differs for the two sides. This may be accounted for by the different topography of the two pulvinar surfaces and the localization in them of the light-sensitive tissues.     

Increased catecholamine output in the hypertensive fawn-hooded rat

The total 24 hour urinary outputs of the catecholamines norepinephrine (NE), epinephrine (E), dopamine (DA) and the DA metabolite homovanillic acid (HVA) were measured in hypertensive fawn-hooded rats and compared to the ancestral strain of normotensive Wistar rats. The hypertensive fawn-hooded rats demonstrated significantly higher urinary outputs of the catecholamines NE and DA, and of the DA metabolite HVA. Following treatment with the antihypertensive, debrisoquin sulfate, the blood pressure of the fawn-hooded rats decreased until it approached the levels observed in normotensive Wistar rats. By inhibiting sympathetic nervous activity and monoamine oxidase, the debrisoquin treatment significantly decreased the output of DA, NE and HVA but not E. The data suggest the fawn-hooded rat is a model of neurogenic hypertension which is characterized by an increased sympathetic output.     

Molecular motions and phase transitions. NMR relaxation times studies of several lecithins.

The spin-lattice relaxation time, T1, and the dipolar energy relaxation time, TD, were measured as a function of temperature. The materials studied were samples of anhydrous L-dipalmitoyl lecithin, DL-dipalmitoyl lecithin, L-dimyristoyl lecithin, DL-dimyristoyl lecithin and their monohydrates, and of anhydrous egg yolk lecithin. It is shown that TD is a much more sensitive parameter than T1 for the determination of the Chapman phase transition. Comparison between T1 and TD provides information about new types of slow molecular motions below and above the phase transition temperature. It is suggested that the relaxation mechanisms for T1 and TD in the gel phase are governed by segmental motion in the phospholipid molecule. A new metastable phase was detected in dimyristoyl lecithin monohydrates. This phase could only be detected from the dipolar energy relaxation times.     

Use of 23Na nuclear magnetic resonance spectroscopy to determine the true intracellular concentration of free sodium in a halophilic eubacterium.

We present new data obtained by 23Na nuclear magnetic resonance spectroscopy, which can distinguish free intracellular sodium from cell-bound sodium, showing that the intracellular concentration of Na+ the halophilic eubacterium Vibrio costicola is only 5 to 20% of that in the extracellular medium. Previous methods could not distinguish free intracellular Na+ from that bound to cell structures, and it was believed that in halophilic eubacteria the total monovalent cation concentration inside matched that of the NaCl outside. Information obtained by the newer technology raises fundamental questions about the ways in which these organisms and others which live in hypersaline environments function and cope with osmotic stress.