The dynamic recruitment of TRBP to neuronal membranes mediates dendritogenesis during development

MicroRNAs are important regulators of local protein synthesis during neuronal development. We investigated the dynamic regulation of microRNA production and found that the majority of the microRNA‐generating complex, consisting of Dicer, TRBP, and PACT, specifically associates with intracellular membranes in developing neurons. Stimulation with brain‐derived neurotrophic factor (BDNF), which promotes dendritogenesis, caused the redistribution of TRBP from the endoplasmic reticulum into the cytoplasm, and its dissociation from Dicer, in a Ca²⁺‐dependent manner. As a result, the processing of a subset of neuronal precursor microRNAs, among them the dendritically localized pre‐miR16, was impaired. Decreased production of miR‐16‐5p, which targeted the BDNF mRNA itself, was rescued by expression of a membrane‐targeted TRBP. Moreover, miR‐16‐5p or membrane‐targeted TRBP expression blocked BDNF‐induced dendritogenesis, demonstrating the importance of neuronal TRBP dynamics for activity‐dependent neuronal development. We propose that neurons employ specialized mechanisms to modulate local gene expression in dendrites, via the dynamic regulation of microRNA biogenesis factors at intracellular membranes of the endoplasmic reticulum, which in turn is crucial for neuronal dendrite complexity and therefore neuronal circuit formation and function.     

PAR‐3 controls endothelial planar polarity and vascular inflammation under laminar flow

Impaired cell polarity is a hallmark of diseased tissue. In the cardiovascular system, laminar blood flow induces endothelial planar cell polarity, represented by elongated cell shape and asymmetric distribution of intracellular organelles along the axis of blood flow. Disrupted endothelial planar polarity is considered to be pro‐inflammatory, suggesting that the establishment of endothelial polarity elicits an anti‐inflammatory response. However, a causative relationship between polarity and inflammatory responses has not been firmly established. Here, we find that a cell polarity protein, PAR‐3, is an essential gatekeeper of GSK3β activity in response to laminar blood flow. We show that flow‐induced spatial distribution of PAR‐3/aPKCλ and aPKCλ/GSK3β complexes controls local GSK3β activity and thereby regulates endothelial planar polarity. The spatial information for GSK3β activation is essential for flow‐dependent polarity to the flow axis, but is not necessary for flow‐induced anti‐inflammatory response. Our results shed light on a novel relationship between endothelial polarity and vascular homeostasis highlighting avenues for novel therapeutic strategies.     

Studies on the aerobic utilization of synthesis gas (syngas) by wild type and recombinant strains of Ralstonia eutropha H16

The biotechnical platform strain Ralstonia eutropha H16 was genetically engineered to express a cox subcluster of the carboxydotrophic Oligotropha carboxidovoransOM5, including (i) the structural genes coxM, ‐S and ‐L, coding for an aerobic carbon monoxide dehydrogenase (CODH) and (ii) the genes coxD, ‐E, ‐F and ‐G, essential for the maturation of CODH. The cox_Oc genes expressed under control of the CO₂‐inducible promoter P_L enabled R. eutropha to oxidize CO to CO₂ for the use as carbon source, as demonstrated by ¹³CO experiments, but the recombinant strains remained dependent on H₂ as external energy supply. Therefore, a synthetic metabolism, which could be described as ‘carboxyhydrogenotrophic’, was established in R. eutropha. With this extension of the bacterium's substrate range, growth in CO‐, H₂‐ and CO₂‐containing artificial synthesis gas atmosphere was enhanced, and poly(3‐hydroxybutyrate) synthesis was increased by more than 20%.     

Pollen germination and in vivo fertilization in response to high‐temperature during flowering in hybrid and inbred rice

High‐temperature during flowering in rice causes spikelet sterility and is a major threat to rice productivity in tropical and subtropical regions, where hybrid rice development is increasingly contributing to sustain food security. However, the sensitivity of hybrids to increasing temperature and physiological responses in terms of dynamic fertilization processes is unknown. To address these questions, several promising hybrids and inbreds were exposed to control temperature and high day‐time temperature (HDT) in Experiment 1, and hybrids having contrasting heat tolerance were selected for Experiment 2 for further physiological investigation under HDT and high‐night‐time‐temperature treatments. The day‐time temperature played a dominant role in determining spikelet fertility compared with the night‐time temperature. HDT significantly induced spikelet sterility in tested hybrids, and hybrids had higher heat susceptibility than the high‐yielding inbred varieties. Poor pollen germination was strongly associated with sterility under high‐temperature. Our novel observations capturing the series of dynamic fertilization processes demonstrated that pollen tubes not reaching the viable embryo sac was the major cause for spikelet sterility under heat exposure. Our findings highlight the urgent need to improve heat tolerance in hybrids and incorporating early‐morning flowering as a promising trait for mitigating HDT stress impact at flowering.     

Novel mutations in an otherwise strictly conserved domain of CuZn superoxide dismutase

All mutations in the human gene for CuZn superoxide dismutase (CuZnSOD) reported to date are associated with the disease amyotrophic lateral sclerosis (ALS). These mutations, mostly of a familial nature (ALS 1, MIM 105400), span all of the coding region of this enzyme except for a highly conserved centrally located domain that includes all of exon III. We describe the identification and characterization of two mutations in this region, both found in mice. One mutation, a glutamate to lysine amino acid substitution was found in position 77 (E77K) of the strain SOD1/Ei distributed by the Jackson Laboratory. The other mutation, a lysine to glutamate substitution at position 70 (K70E) of a human transgene, was discovered in mouse line TgHS/SF-155. Enzyme activity measurements and heterodimer analysis of the CuZn SOD variant in SOD1/Ei suggest a mild loss of activity, which differs from the enzyme activity losses detected in patients with autosomal dominant ALS 1. Similarly, the presence of the mutant transgene in TgHS/SF 155 does not produce any phenotypic manifestations.     

Epizoic bacteria on the foot of the Antarctic bivalve, Lissarca notorcadensis Melville and Standen, 1907 (Filibranchia: Philobryidae)

Specimens of the epizoic bivalve Lissarca notorcadensis Melville and Standen, 1907 (Philobryidae) were collected from the spines of cidaroid sea-urchins in the Weddell Sea during austral summer 1991. Soft tissues were investigated by means of transmission electron microscopy. Epizoic bacteria were discovered on the foot in 14 out of 15 specimens of the bivalve, and in juveniles as well as in adults. The presence of bacteria was restricted to a certain area of the foot's surface, where they were populating the brushborder of the epidermal epithelium. This is the first time that epizoic bacteria have been described, either from an Antarctic bivalve or from the foot epithelium of any bivalve species. Aspects of the fine structure were studied with regard to future work on this symbiosis. The bacteria undergo a full life-cycle in the brushborder. Whereas young or dividing bacteria are found more distally between the microvilli, senescent stages seem to disintegrate and be absorbed between their bases. The bacteria could contribute to the nutrition of their host by breaking down macromolecular or particulate organic matter, which would facilitate parenteral absorption by the bivalve, as well as eventual digestion. The ultrastructural findings suggest that the bacteria are neither sulphidotrophic nor methylotrophic. Based on their appearance, they are classified as sub-cuticular bacteria, which have been recently described from the surface epithelia in various marine invertebrate species. The phenomenon is discussed in respect to seasonal food limitation for Antarctic suspension feeders and the brooding behaviour of the host species and its ecological success. Received: 26 April 1996 / Accepted: 8 September 1996     

Similar Organization of the Lipopolysaccharide-Binding Protein (LBP) and Phospholipid Transfer Protein (PLTP) Genes Suggests a Common Gene Family of Lipid-Binding Proteins

The transfer of lipids in aqueous environments such as serum has been attributed to a recently characterized class of proteins. Abnormal regulation of serum lipids by these proteins is thought to be a key event in the pathophysiology of cardiovascular diseases. Lipopolysaccharide (endotoxin) binding protein (LBP) was identified by virtue of its ability to bind bacterial lipid A. We have analyzed the exon–intron organization of the LBP gene and the nucleotide sequence of its approximately 20 kb spanning 5′- and 3′-untranslated regions. When comparing the genomic organization of LBP with that of two other genes coding for lipid transfer proteins, significant homologies were found. The LBP gene includes 15 exons, and the 2-kb promoter contains recognition elements of acute phase-typical reactants and a repetitive 12-mer motif with an as yet unknown protein-binding property. Detailed sequence comparison revealed a closer relatedness of LBP with PLTP than with CETP as demonstrated by an almost identical intron positioning. This high degree of similarity supports functional studies by others suggesting that like LBP, PLTP may also be able to bind and transport bacterial lipopolysaccharide.     

The γ-Glutamyl Transpeptidase Inhibitor Acivicin Preserves Glutathione Released by Astroglial Cells in Culture

The release of glutathione from astroglial cells was investigated using astroglia-rich primary cultures prepared from the brains of newborn rats. These cells release glutathione after onset of an incubation in a glucose-containing minimal medium. The amount of extracellular glutathione increased with the time of incubation, although the accumulation slowed down gradually. An elevated rate of increase of the glutathione concentration in the incubation medium was found if the astroglial ectoenzyme -glutamyl transpeptidase was inhibited by acivicin. The activity of -glutamyl transpeptidase in astroglia-rich primary cultures, which was found to be 1.9 ± 0.3 nmol/(min × mg protein), was markedly reduced if the cells had been incubated in the presence of acivicin. After 2 h of incubation with acivicin half-maximal and maximal inhibition of -glutamyl transpeptidase activity was found at concentrations of about 5 M and 50 M, respectively. In the presence of acivicin at a concentration above 10 M the glutathione content found released from astroglial cells apparently increased almost proportional to time for up to 10 h. Under these conditions the average rate of release was 2.1 ± 0.3 nmol/(h × mg protein) yielding after a 10 h incubation an extracellular glutathione content three times that of the medium of cells incubated without inhibitor. Half-maximal and maximal effects on the level of extracellular glutathione were found at 4 M and 50 M acivicin, respectively. After a 10 h incubation with acivicin the intracellular content of glutathione was reduced to 75% of the level of untreated astroglial cultures. These results suggest that glutathione released from astroglial cells can serve as substrate for the ectoenzyme -glutamyl transpeptidase of these cells.