Strain-specific Influence of Microcystis Aeruginosa on Food Ingestion and Assimilation of some Cladocerans and Copepods

Ingestion rates where estimated for daphnids, Cyclops spp. and Bosmina (Eubosmina) coregoni thersites fed hepatotoxic and non-toxic M. aeruginosa either separate or mixed with the readily available food alga Ankistrodesmus falcatus. The ingestion rates of hepatotoxic strains of M. aeruginosa are very low compared with those of A. falcatus or non-toxic M. aeruginosa HUB 5-3 fed to Daphnia magna or D. longispina. However, a close relationship between ingestion rate of different M. aeruginosa strains and their toxicity could not be observed. Addition of the toxic strain M. aeruginosa HUB 5-2-4 reduces the ingestion rates of A. falcatus progressively due to increased food rejection by D. magna. Additionally, the assimilation efficiency of M. aeruginosa HUB 5-2-4 is two times lower compared with A. falcatus and M. aeruginosa HUB 5-3 leading to strong starvation.     

Daphnia and Toxic Blooms of Microcystis aeruginosa in Bautzen Reservoir (GDR)

As a part of a whole-lake, long-term experiment in biomanipulation in. the hypertrophic Bautzen reservoir (G.D.R.), during three years (1984–1986) the dynamics of mouse-related LD 50 of Microcystis aeruginosa was compared with the biomass development of this blue-green and the grazing pressure exerted by Daphnia galeata. Since the three summer averages of the biomass of D. galeata revealed strong differences due to decreasing predation activity of fish from 1984 to 1986, the effects of different grazing pressure on Microcystis toxicity could be investigated under field conditions. Microcystis was nontoxic at the beginning of the growing season and developed high toxicity during its first strong biomass increase in summer in all three years. But this decrease of the LD 50 together with the first biomass increase of the season is found in quite different periods in different years (1984: August, 1985: July, 1986: June). It is obvious that the higher the mean effective filtration rate of D. galeata during summer is found the faster the toxicity of Microcystis is formed. If these observations are combined with findings of other authors, the conclusion can be drawn that the development of toxic Microcystis blooms seems to be promoted by a combination of five conditions: (1) Presence of a mixture of toxic and nontoxic Microcystis strains at the beginning of the growing season even if the portion of toxic strains is very low, (2) physical and chemical growth conditions which favour Microcystis over other phytoplankton, (3) high grazing pressure by zooplankton on edible food particles over a rather long period, (4) patchy distribution of the different Microcystis strains if nonselective filtrators such as Daphnia dominate the zooplankton, and (5) absence of defense mechanisms of Microcystis against grazing which are not coupled with toxicity (e.g. large colony size). These conclusions contribute to a better understanding of the possibilities and limits of in-lake eutrophication control by biomanipulation and emphasize the need to combine top-down and bottom-up control mechanisms in eutrophic and hypertrophic waters.     

Resuspension studies in cylindrical microcosms: Effects of stirring velocity on the dynamics of redox sensitive elements in a coastal sediment

Effects of resuspension on the release of dissolved, redox sensitive elements (Fe, Mn) was studied in cylindrical microcosms. Effects from changing water stirring velocity in sediment pools were evaluated through measurements of pore water profiles of dissolved Mn, Fe and redox potential. Mn was a good natural marker to follow such effects. At current velocities below the threshold velocity for resuspension (37 cm s-1), Mn release rates to overlying water were 100 times higher compared to steady-state values. Pulse increases in Mn concentration were the result of convective currents inside flow chambers. These results were strongly supported by measurements of Eh profiles in the sediment pore water. Furthermore, impacts from increasing stirring velocity were found down to 1.9 cm depth below the resuspended layer of sediment.     

Caspase-10 is recruited to and activated at the native TRAIL and CD95 death-inducing signalling complexes in a FADD-dependent manner but can not functionally substitute caspase-8

The involvement of the death adaptor protein FADD and the apoptosis-initiating caspase-8 in CD95 and TRAIL death signalling has recently been demonstrated by the analysis of the native death-inducing signalling complex (DISC) that forms upon ligand-induced receptor cross-linking. However, the role of caspase-10, the other death-effector-domain-containing caspase besides caspase-8, in death receptor signalling has been controversial. Here we show that caspase-10 is recruited not only to the native TRAIL DISC but also to the native CD95 DISC, and that FADD is necessary for its recruitment to and activation at these two protein complexes. With respect to the function of caspase-10, we show that it is not required for apoptosis induction. In addition, caspase-10 can not substitute for caspase-8, as the defect in apoptosis induction observed in caspase-8-deficient cells could not be rescued by overexpression of caspase-10. Finally, we demonstrate that caspase-10 is cleaved during CD95-induced apoptosis of activated T cells. These results show that caspase-10 activation occurs in primary cells, but that its function differs from that of caspase-8.     

Connections of the olfactory bulb in the piranha (Serrasalmus nattereri)

Summary The connections of the olfactory bulb were studied in the piranha using the Nauta and horseradish-peroxidase methods. Three olfactory tracts project to seven terminal fields in the telencephalon and one in the diencephalon, all of them bilaterally. The contralateral olfactory bulb also receives a small input. All contralateral projections decussate in the anterior commissure and are relatively weak compared to the ipsilateral projections. HRP-containing cells were found in all of the ipsilateral telencephalic aggregates receiving an olfactory tract projection; the contralateral side was free of labeled cell bodies. Although only about one fourth of the entire telencephalon receives a direct olfactory input, the high degree of differentiation of the olfactory system suggests that the piranha depends substantially on the sense of olfaction and that this species may be a good model for further studies on olfactory mechanisms.     

Angiotensin II Protects Primary Rat Hepatocytes against Bile Salt-Induced Apoptosis

Angiotensin II (AT-II) is a pro-fibrotic compound that acts via membrane-bound receptors (AT-1R/AT-2R) and thereby activates hepatic stellate cells (HSCs). AT-II receptor blockers (ARBs) are thus important candidates in the treatment of liver fibrosis. However, multiple case reports suggest that AT-1R blockers may induce hepatocyte injury. Therefore, we investigated the effect of AT-II and its receptor blockers on cytokine-, oxidative stress- and bile salt-induced cell death in hepatocytes. Primary rat hepatocytes were exposed to TNF-α/Actinomycin D, the ROS-generating agent menadione or the bile salts: glycochenodeoxycholic acid (GCDCA) and tauro-lithocholic acid-3 sulfate (TLCS), to induce apoptosis. AT-II (100 nmol/L) was added 10 minutes prior to the cell death-inducing agent. AT-1R antagonists (Sartans) and the AT-2R antagonist PD123319 were used at 1 µmol/L. Apoptosis (caspase-3 activity, acridine orange staining) and necrosis (Sytox green staining) were quantified. Expression of CHOP (marker for ER stress) and AT-II receptor mRNAs were quantified by Q-PCR. AT-II dose-dependently reduced GCDCA-induced apoptosis of hepatocytes (−50%, p<0.05) without inducing necrosis. In addition, AT-II reduced TLCS-induced apoptosis of hepatocytes (−50%, p<0.05). However, AT-II did not suppress TNF/Act-D and menadione-induced apoptosis. Only the AT-1R antagonists abolished the protective effect of AT-II against GCDCA-induced apoptosis. AT-II increased phosphorylation of ERK and a significant reversal of the protective effect of AT-II was observed when signaling kinases, including ERK, were inhibited. Moreover, AT-II prevented the GCDCA-induced expression of CHOP (the marker of the ER-mediated apoptosis).

Conclusion

Angiotensin II protects hepatocytes from bile salt-induced apoptosis through a combined activation of PI3-kinase, MAPKs, PKC pathways and inhibition of bile salt-induced ER stress. Our results suggest a mechanism for the observed hepatocyte-toxicity of Sartans (angiotensin receptor blockers, ARBs) in some patients with chronic liver injury.     

Pseudouridine residues in the 5′-terminus of uridine-rich nuclear RNA I (U1 RNA)

The primary nucleotide sequence was reported earlier for U1 RNA (Reddy et al, (1974) J. Biol. Chem. $\text{249}$, 6486–6494), an snRNA implicated in splicing of HnRNAs. In view of the presence of homologous pseudouridine (ψ) residues in 5′-ends of several highly conserved U-snRNAs and the recent report of modified bases in the U1 RNA structure (Branlant et al, (1980) Nucleic Acids Res. $\text{8}$, 4143–4154) a study was made for the presence of ψ and other modified nucleotides in the 5′-end of the U1 RNA. Identification of ψ residues at positions 6 and 7, shows the 5′-sequence of U1 RNA is: m₃², 2,7 GpppAm-Um-A-C-ψ-ψ-A-C-C-U-G-G-C-A-G-G-G-G-A-G-A-U-A-C. The ψ residues in place of U at positions 6 and 7 may affect the binding of U1 RNA at intron-exon splice junctions.     

Primary and secondary structure of U2 snRNA

With the improved rapid sequencing techniques, the earlier sequence of U2 RNA of Novikoff hepatoma (Shibata et al, J. Biol. Chem. 250, 3909-3920, 1975) was reanalyzed and modified. The improved sequence of U2 RNA is 188 (or 189) nucleotides long and is in register with a characterized U2 RNA pseudogene (Denison et al, PNAS 78, 810-814, 1981) except for an 11 nucleotide sequence (nucleotides 147-157) which is absent from the pseudogene. From these results, a secondary structure of U2 RNA is proposed which is supported by the preferred cleavage sites with T1-RNase, RNase A and S1 nuclease. Isolated U2 RNA was cleaved by T1-RNase preferentially at positions 64 and 164, whereas U2 RNA in U2-snRNP was cleaved only at position 64, indicating that position 164 is protected in U2-snRNP. As with U1 RNA (Epstein et al, PNAS 78, 1562-1566, 1981) the 5'-end of isolated U2 RNA was not preferentially cleaved by T1-RNase.     

Aperiplasmic protein (Skp) of Escherichia coli selectively binds a class of outer membrane proteins

A search was performed for a periplasmic molecular chaperone which may assist outer membrane proteins of Escherichia coli on their way from the cytoplasmic to the outer membrane. Proteins of the periplasmic space were fractionated on an affinity column with sepharose-bound outer membrane porin OmpF. A 17kDa polypeptide was the predominant protein retained by this column. The corresponding gene was found in a gene bank; it encodes the periplasmic protein Skp. The protein was isolated and it could be demonstrated that it bound outer membrane proteins, following SDS-PAGE, with high selectivity. Among these were OmpA, OmpC, OmpF and the maltoporin LamB. The chromosomal skp gene was inactivated by a deletion causing removal of most of the signal peptide plus 107 residues of the 141-residue mature protein. The mutant was viable but possessed much-reduced concentrations of outer membrane proteins. This defect was fully restored by a plasmid-borne skp gene which may serve as a periplasmic chaperone.