The putative moss 3'-phosphoadenosine-5'-phosphosulfate reductase is a novel form of adenosine-5'-phosphosulfate reductase without an iron-sulfur cluster

Sulfate assimilation provides reduced sulfur for synthesis of the amino acids cysteine and methionine and for a range of other metabolites. Sulfate has to be activated prior to reduction by adenylation to adenosine 5'-phosphosulfate (APS). In plants, algae, and many bacteria, this compound is reduced to sulfite by APS reductase (APR); in fungi and some cyanobacteria and gamma-proteobacteria, a second activation step, phosphorylation to 3'-phosphoadenosine 5'-phosphosulfate (PAPS), is necessary before reduction to sulfite by PAPS reductase (PAPR). We found previously that the moss Physcomitrella patens is unique among these organisms in possessing orthologs of both APR and PAPR genes (Koprivova, A., Meyer, A. J., Schween, G., Herschbach, C., Reski, R., and Kopriva, S. (2002) J. Biol. Chem. 277, 32195-32201). To assess the function of the two enzymes, we compared their biochemical properties by analysis of purified recombinant proteins. APR from Physcomitrella is very similar to the well characterized APRs from seed plants. On the other hand, we found that the putative PAPR preferentially reduces APS. Sequence analysis, analysis of UV-visible spectra, and determination of iron revealed that this new APR, named PpAPR-B, does not contain the FeS cluster, which was previously believed to determine the substrate specificity of the otherwise relatively similar enzymes. The lack of the FeS cluster in PpAPR-B catalysis is connected with a lower turnover rate but higher stability of the protein. These findings show that APS reduction without the FeS cluster is possible and that plant sulfate assimilation is predominantly dependent on reduction of APS.     

Deficiency in mTORC1‐controlled C/EBPβ‐mRNA translation improves metabolic health in mice

The mammalian target of rapamycin complex 1 (mTORC1) is a central regulator of physiological adaptations in response to changes in nutrient supply. Major downstream targets of mTORC1 signalling are the mRNA translation regulators p70 ribosomal protein S6 kinase 1 (S6K1p70) and the 4E‐binding proteins (4E‐BPs). However, little is known about vertebrate mRNAs that are specifically controlled by mTORC1 signalling and are engaged in regulating mTORC1‐associated physiology. Here, we show that translation of the CCAAT/enhancer binding protein beta (C/EBPβ) mRNA into the C/EBPβ‐LIP isoform is suppressed in response to mTORC1 inhibition either through pharmacological treatment or through calorie restriction. Our data indicate that the function of 4E‐BPs is required for suppression of LIP. Intriguingly, mice lacking the cis‐regulatory upstream open reading frame (uORF) in the C/EBPβ‐mRNA, which is required for mTORC1‐stimulated translation into C/EBPβ‐LIP, display an improved metabolic phenotype with features also found under calorie restriction. Thus, our data suggest that translational adjustment of C/EBPβ‐isoform expression is one of the key processes that direct metabolic adaptation in response to changes in mTORC1 activity.     

Phylogenetic constraints vs. ecology in the nectar composition of Acanthaceae

Nectar composition and concentration were analyzed for 75 samples of 70 species of Acanthaceae representing all major intrafamiliar groups. Analyses of variance were conducted to test for significant differences between pollination syndromes and between taxonomical or phylogenetic groups (genera). The available data indicate that the characteristics of nectar in Acanthaceae are predominantly determined by adaptation to needs of the pollinators rather than by phylogenetic constraints.     

Adaptive differentiations of the skin of the head in a subterranean rodent,Spalax ehrenbergi

The skin of macroscopically distinct regions (hairy skin, vibrissal fields, buccal ridge, and rhinarium) of the head of the blind mole-rat, Spalax ehrenbergi, was studied by routine histological methods. Few guard and several soft vellus hairs are organized into tufts that grow from a group of hair follicles localized in an invaginated compound cavity. We suggest that this hair arrangement may be a burrowing adaptation to match frictional resistance. The follicles and the compound cavity possess either well developed complex striated musculature or errector pili muscles. There are no structural specializations (sweat glands, glomus bodies) to enhance thermo-regulatory (heat dissipative) capacities in the hairy skin of the head. Vibrissae penetrate the epidermal surface as single hairs. They are microscopically normally developed are arranged in vibrissal fields according to a basal mammalian pattern. Most of them are, however, relatively short and inconspicuous. The mystical vibrissal field is horizontally divided by a prominent buccal ridge which is probably involved in bulldozing. The hairs in the ridge leave the compound cavity singularly. The follicles of guard hairs and bristles are equipped with well developed pilo-Ruffini complexes indicating that the buccal ridge may serve also as a tactile organ. The glabrous skin of the rhinarium has a highly interdigitated dermal-epidermal interface. The dermal papillae possess simple lamellated and/or simple Meissner's corpuscles and few Merkel cell-axon-complexes indicating that the skin of the rhinarium may be particularly sensitive to perception of vibrations. J Morphol 233:53–66, 1997. © 1997 Wiley-Liss, Inc.     

Neuroblast ablation in Drosophila P[GAL4] lines reveals origins of olfactory interneurons

Hydroxyurea (HU) treatment of early first instar larvae in Drosophila was previously shown to ablate a single dividing lateral neuroblast (LNb) in the brain. Early larval HU application to P[GAL4] strains that label specific neuron types enabled us to identify the origins of the two major classes of interneurons in the olfactory system. HU treatment resulted in the loss of antennal lobe local interneurons and of a subset of relay interneurons (RI), elements usually projecting to the calyx and the lateral protocerebrum (LPR). Other RI were resistant to HU and still projected to the LPR. However, they formed no collaterals in the calyx region (which was also ablated), suggesting that their survival does not depend on targets in the calyx. Hence, the ablated interneurons were derived from the LNb, whereas the HU-resistant elements originated from neuroblasts which begin to divide later in larval life. Developmental GAL4 expression patterns suggested that differentiated RI are present at the larval stage already and may be retained through metamorphosis. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 443–456, 1997     

Phospholipid transfer protein enhances removal of cellular cholesterol and phospholipids by high-density lipoprotein apolipoproteins

High-density lipoprotein (HDL) apolipoproteins remove excess cholesterol from cells by an active transport pathway that may protect against atherosclerosis. Here we show that treatment of cholesterol-loaded human skin fibroblasts with phospholipid transfer protein (PLTP) increased HDL binding to cells and enhanced cholesterol and phospholipid efflux by this pathway. PLTP did not stimulate lipid efflux in the presence of albumin, purified apolipoprotein A-I, and phospholipid vesicles, suggesting specificity for HDL particles. PLTP restored the lipid efflux activity of mildly trypsinized HDL, presumably by regenerating active apolipoproteins. PLTP-stimulated lipid efflux was absent in Tangier disease fibroblasts, induced by cholesterol loading, and inhibited by brefeldin A treatment, indicating selectivity for the apolipoprotein-mediated lipid removal pathway. The lipid efflux-stimulating effect of PLTP was not attributable to generation of preβ HDL particles in solution but instead required cellular interactions. These interactions increased cholesterol efflux to minor HDL particles with electrophoretic mobility between α and preβ. These findings suggest that PLTP promotes cell-surface binding and remodeling of HDL so as to improve its ability to remove cholesterol and phospholipids by the apolipoprotein-mediated pathway, a process that may play an important role in enhancing flux of excess cholesterol from tissues and retarding atherogenesis.     

Novel iso-branched ether lipids as specific markers of developmental sporulation in the myxobacterium Myxococcus xanthus

Iso-fatty acids (FAs) are the dominant FA family in all myxobacteria analyzed. Furthermore, it was postulated that iso-FAs or compounds derived thereof are involved in fruiting body formation in Myxococcus xanthus, since mutants with a reduced level of iso-FA due to a reduced level of the precursor isovaleryl-CoA, are delayed in aggregation and produce only few myxospores. To elucidate the function of iso-FAs and their corresponding lipids we have analyzed the developmental phenotype of mutants having different levels of iso-FAs resulting in a clear correlation between the amount of iso-FAs and the delay of aggregation and reduction in spore yield. Addition of either isovalerate or 13-methyltetradecanoic acid resulted in restoration of the wild-type FA profile and normal development. Detailed analysis of the fatty acid (FA) profile during fruiting body formation in Myxococcus xanthus wild-type revealed the specific accumulation of 13-methyltetradecanal and 1-O-13-methyltetradecylglycerol which were produced specifically in the myxospores and which are derived from 1-O-(13-methyl-1-Z-tetradecenyl)-2-O-(13-methyltetradecanoyl)-glycero-3-phosphatidylethanolamine (VEPE) and 1,2-di-(13-methyltetradecanoyl)-3-(13-methyltetradecyl)glycerol (TG-1), respectively. The structures of these unusual ether lipids have been determined by spectrometric methods and synthesis (for TG-1). Analysis of several mutants blocked at different stages of development indicated that the biosynthesis of TG-1 is developmentally regulated and that VEPE might be an intermediate in the TG-1 biosynthesis. Finally, addition of TG-1 to mutants blocked in the biosynthesis of isovaleryl-CoA could restore aggregation and sporulation emphasizing the important role of iso-branched lipids for myxobacterial development.     

Über die Sehschärfe der Elritze (Phoxinus laevis) Bei verschiedenen Helligkeiten

Zusammenfassung Zwischen Sehschärfe und Beleuchtungsintensität bestehen bei den Fischen kurz folgende Beziehungen: Die Sehschärfe der Elritze wächst ungefähr proportional dem Logarithmus der Beleuchtungsstärke. Ihr Maximum ist bei einer relativ geringen Helligkeit erreicht. Der Übergang vom Tages-zum Dämmerungssehen ist durch eine Änderung der Sehschärfe gekennzeichnet, die bei der Elritze — umgekehrt wie beim Menschen — im Bereich des Stäbchensehens eine etwas schnellere Abnahme erfährt als im Bereich des Zapfensehens.     

REACTIONS OF LIMULUS TO ILLUMINATED FIELDS OF DIFFERENT AREA AND FLICKER FREQUENCY

In phototropic tests with young Limulus, the phototropic reactions to flickering fields were studied. If the two fields are equal in area and brightness but different in flicker frequency, the number of animals going to the two fields is proportional to their flicker frequencies. Equal stimulating effects of two fields differing in flicker frequency are obtained by reduction of the area of the faster flickering field. The areas for equal effect must be inversely proportional to their flicker frequencies. It seems that equal effects are dependent upon equality of the number of active excitation elements per unit of time.