Allochtonous input and trophic level heterogeneity: impact on an aquatic food web

The impact of food web complexity in open and closed food webs was explored experimentally under controlled laboratory conditions. We used an aquatic model community consisting of two forms of primary producers, phytoplankton ( Scenedesmus obtusiuscusculus ) and periphyton ( Nitzschia perminuta ) and two types of consumers, Daphnia pulex feeding on phytoplankton and Chydorous sphaericus feeding on both periphyton and phytoplankton. Three different food webs all having the phytoplankton and periphyton, but having either one of the consumers or both were set up. These food webs were studied in an open and closed treatment. In the open treatment, phytoplankton was continuously flowing through the aquaria whereas in the closed system all the phytoplankton was delivered at the start of the experiment.
D. pulex had a positive effect on the density of C. sphaericus in both the open and closed treatments. In the open treatment C. sphaericus increased to very high numbers and was able to depress phytoplankton and thereby negatively affect D. pulex . Our study shows that the explicit handling of the population dynamics of both grazers allowed us to show how a compensatory increase in one primary producer due to increased grazing on another primary producer creates a negative feedback between consumers: C. sphaericus increased and negatively affected D. pulex .     

DC temperature-regulating device for anesthetized experimental animals.

A temperature-regulating device for anesthetized experimental animals is presented. The rectal temperature of the animal is measured with a thermistor and this variable controls via nonlinear amplification the power fed to the heating pad on which the animal is placed. Rectal temperature variations of not more than +/- 0.1 degrees C are reached after 30 min of operation.     

Direct and indirect measurement of somatic cell count as indicator of intramammary infection in dairy goats

Background  

Mastitis is the most important and costly disease in dairy goat production. Subclinical mastitis is common in goats and is mainly caused by contagious bacteria. Several methods to diagnose subclinical mastitis are available. In this study indirect measurement of somatic cell count (SCC) by California Mastitis Test (CMT) and direct measurement of SCC using a portable deLaval cell counter (DCC) are evaluated. Swedish goat farmers would primarily benefit from diagnostic methods that can be used at the farm. The purpose of the study was to evaluate SCC measured by CMT and DCC as possible markers for intramammary infection (IMI) in goats without clinical symptoms of mastitis. Moreover to see how well indirect measurement of SCC (CMT) corresponded to direct measurement of SCC (DCC).     

Purification of recombinant and human apolipoprotein A-1 using surfactant micelles in aqueous two-phase systems: recycling of thermoseparating polymer and surfactant with temperature-induced phase separation.

An effective system has been developed for purification of apolipoprotein A-1 from Escherichia coli fermentation solution and human plasma using aqueous two-phase extraction and thermal-phase separation. The system included non-ionic surfactants (Triton or Tween) and as top phase-forming polymer a random copolymer of ethylene oxide (50%) and propylene oxide (50%), Breox PAG 50A 1000, was used. The bottom phase-forming polymer was either hydroxypropyl starch, Reppal PES 100 and PES 200, or hydroxyethyl starch, Solfarex A 85. The top-phase-forming polymer and the surfactants are thermoseparating in water solution, i.e., when heated a water phase and a polymer/surfactant phase are formed. Recombinant apolipoprotein A-1, the Milano variant, was extracted from E. coli fermentation solution in a primary Breox-starch phase system followed by thermal separation of the Breox phase where the target protein was recovered in the water phase. Both in the Breox-starch system and in the water-Breox system Triton X-100 was partitioned to the Breox phase. The addition of non-ionic surfactants to the Breox-starch system had strong effect on the purification and yield of the amphiphilic apolipoprotein A-1. In a system containing 17% Breox PAG 50A 1000, 12% Reppal PES 100 and addition of 1% Triton X-100 the purification factor was 7.2, and the yield 85% after thermal separation of the Breox phase. Recycling of copolymer and surfactant was possible after thermal separation of copolymer phase. Approximately 85% of the copolymer and surfactant could be recycled in each extraction cycle. DNA could be strongly partitioned to the starch phase in the primary-phase system. This resulted in a 1000-fold reduction of E. coli DNA in the apolipoprotein A-1 solution obtained after thermoseparation. In extraction from human plasma containing low concentrations of apolipoprotein A-1, it was possible to reach a purification factor of 420 with 98% yield. By reducing the volume ratio to 0.1 Apo A-1 could be concentrated in a small volume of top phase (concentration factor 10) with a yield of 85% and a purification factor of 110.     

Labelling of proteins with [35S]methionine in monolayer cultures of rat hepatocytes

Optimal conditions for the labelling of proteins with [35S]methionine in monolayers of rat hepatocytes have been established. The ability to incorporate the radioactive amino acid was constant for at least 26 h and independent of whether the medium was buffered with CO2/HCO3 or with 4-(2-hydroxyethyl)-1-piper-azineethanesulphonic acid (Hepes). Preincubation in methionine-free medium for up to 30 min yielded increasing, and from 60 to 180 min decreasing, rates of incorporation. An apparent Km value of 0.06 mM was obtained for the incorporation reaction in cells preincubated for 40 min.     

Highly reiterated non-coding sequence in the genome of Plasmodium falciparum is composed of 21 base-pair tandem repeats

Clones containing highly reiterated DNA sequences were isolated from a Plasmodium falciparum genomic library. One clone, Rep2, was selected for further characterization by nucleotide sequence analysis. The results revealed that the insert of this clone is composed of tandemly arranged 21 base-pair imperfect repeats. These repeats are estimated to comprise approximately 1% of the P. falciparum genome and there are 10(4) to 2 X 10(5) copies, depending on the genome size estimate used for calculation. Moreover, the repeats are organized in clusters and do not appear to be transcribed in non-synchronized P. falciparum cultures.     

Primary structure of the hemolglobin β-chain of Rose-ringed Parakeet (Psittacula krameri)

The primary structure of Rose-ringed Parakeet hemoglobin β-chain was established, completing the analysis of this hemoglobin. Comparisons with other avian β-chains show variations smaller than those for the corresponding α-chains. There are 11 amino acid exchanges in relationship to the only other characterized psittaciform β-chain, and a total of 35 positions are affected by differences among all avian β-chains analyzed (versus 61 for the α-chains). At three positions, the Psittacula β-chain has residues unique to this species. Three α₁β₁ contacts are modified, by substitutions at positions β51, β116, and β125.     

Glioma Cell Proliferation Controlled by ERK Activity-Dependent Surface Expression of PDGFRA

Increased PDGFRA signaling is an essential pathogenic factor in many subtypes of gliomas. In this context the cell surface expression of PDGFRA is an important determinant of ligand sensing in the glioma microenvironment. However, the regulation of spatial distribution of PDGFRA in glioma cells remains poorly characterized. Here, we report that cell surface PDGFRA expression in gliomas is negatively regulated by an ERK-dependent mechanism, resulting in reduced proliferation of glioma cells. Glioma tumor tissues and their corresponding cell lines were isolated from 14 patients and analyzed by single-cell imaging and flow cytometry. In both cell lines and their corresponding tumor samples, glioma cell proliferation correlated with the extent of surface expression of PDGFRA. High levels of surface PDGFRA also correlated to high tubulin expression in glioma tumor tissue in vivo. In glioma cell lines, surface PDGFRA declined following treatment with inhibitors of tubulin, actin and dynamin. Screening of a panel of small molecule compounds identified the MEK inhibitor U0126 as a potent inhibitor of surface PDGFRA expression. Importantly, U0126 inhibited surface expression in a reversible, dose- and time-dependent manner, without affecting general PDGFRA expression. Treatment with U0126 resulted in reduced co-localization between PDGFRA and intracellular trafficking molecules e.g. clathrin, RAB11 and early endosomal antigen-1, in parallel with enhanced co-localization between PDGFRA and the Golgi cisternae maker, Giantin, suggesting a deviation of PDGFRA from the endosomal trafficking and recycling compartment, to the Golgi network. Furthermore, U0126 treatment in glioma cells induced an initial inhibition of ERK1/2 phosphorylation, followed by up-regulated ERK1/2 phosphorylation concomitant with diminished surface expression of PDGFRA. Finally, down-regulation of surface PDGFRA expression by U0126 is concordant with reduced glioma cell proliferation. These findings suggest that manipulation of spatial expression of PDGFRA can potentially be used to combat gliomas.