Synthesis and metabolism of vertebrate-type steroids by tissues of insects: a critical evaluation

This review covers the synthesis and the metabolism of vertebrate-type steroids (progesterone, testosterone, estradiol, corticosteroids) by insect tissues and discusses the significance of the reactions for insect physiology. Biosynthesis of vertebrate-type steroids from cholesterol hitherto has been demonstrated in only two insect species, i.e. the water beetle Acilius sulcatus (Coleoptera) and the tobacco hornworm Manduca sexta (Lepidoptera). In Acilius, steroid synthesis is associated with exosecretion (chemical defense). Nothing, however, is known about a physiological role of the C21 steroid conjugate present in ovaries and eggs of Manduca. No synthesis of vertebrate-type steroids was observed in any other insect investigated to date. Most metabolic conversions of steroids by insects concerned oxidoreduction of oxygen groups (hydroxysteroid dehydrogenase activity) and (polar and apolar) conjugate formation. All important enzymatic steps involved in synthesis and catabolism, as known from studies with tissues of vertebrates, were not, or hardly observed. The conclusion is drawn that typical vertebrate-type (C21, C19 and C18) steroids probably do not act as physiologically active substances in insects.     

Phyletic affinities among Polystomatidae (Monogenea)]

The chaetotaxy and ciliated cells in two Monogenean larvae of marine fishes are described for the first time: a Monopisthocotylea Diplectanum aequans (Wagener, 1857) Diesing, 1858 parasite of Dicentrarchus Labrax (L) and a Polyopisthocotylea, Microcotyle mormyri Lorenz, 1878 parasite of Pagellus mormyrus (L). A comparative study with the known larvae shows evidence of two larval types in the Monogenea of fishes, related to the two great phyla of the class: the Monopisthocoytylea and Polyopisthocotylea. The Polystomatidae, Monogenea from Amphibia and Chelonia, belong to the Polyopisthocotylea on account of their larval chaetotaxy. But the proximity of the Polystomatidae with the Tetraonchidae, within the Polyonchoinea Bychowsky, 1975 is not confirmed.     

Eine neue gegen Bilharziose und Amoebiase wirksame Verbindung

Summary 5-[nitro-thiazolyl-(2)]-2-oxo-tetrahydroimidazole was found to possess schistosomicidal and amoebicidal properties. In mice this substance exhibited a curative effect in experimental infections withS. mansoni andS. japonicum. Preliminary clinical trials indicated that the compound is effective and well tolerated in the treatment of vesical bilharziasis.     

Small molecule activators of SIRT1 as therapeutics for the treatment of type 2 diabetes

Calorie restriction extends lifespan and produces a metabolic profile desirable for treating diseases of ageing such as type 2 diabetes. SIRT1, an NAD+-dependent deacetylase, is a principal modulator of pathways downstream of calorie restriction that produce beneficial effects on glucose homeostasis and insulin sensitivity. Resveratrol, a polyphenolic SIRT1 activator, mimics the anti-ageing effects of calorie restriction in lower organisms and in mice fed a high-fat diet ameliorates insulin resistance, increases mitochondrial content, and prolongs survival. Here we describe the identification and characterization of small molecule activators of SIRT1 that are structurally unrelated to, and 1,000-fold more potent than, resveratrol. These compounds bind to the SIRT1 enzyme-peptide substrate complex at an allosteric site amino-terminal to the catalytic domain and lower the Michaelis constant for acetylated substrates. In diet-induced obese and genetically obese mice, these compounds improve insulin sensitivity, lower plasma glucose, and increase mitochondrial capacity. In Zucker fa/fa rats, hyperinsulinaemic-euglycaemic clamp studies demonstrate that SIRT1 activators improve whole-body glucose homeostasis and insulin sensitivity in adipose tissue, skeletal muscle and liver. Thus, SIRT1 activation is a promising new therapeutic approach for treating diseases of ageing such as type 2 diabetes.     

Asymmetric inheritance of centrosomally localized mRNAs during embryonic cleavages

During development, different cell fates are generated by cell-cell interactions or by the asymmetric distribution of patterning molecules. Asymmetric inheritance is known to occur either through directed transport along actin microfilaments into one daughter cell or through capture of determinants by a region of the cortex inherited by one daughter. Here we report a third mechanism of asymmetric inheritance in a mollusc embryo. Different messenger RNAs associate with centrosomes in different cells and are subsequently distributed asymmetrically during division. The segregated mRNAs are diffusely distributed in the cytoplasm and then localize, in a microtubule-dependent manner, to the pericentriolar matrix. During division, they dissociate from the core mitotic centrosome and move by means of actin filaments to the presumptive animal daughter cell cortex. In experimental cells with two interphase centrosomes, mRNAs accumulate on the correct centrosome, indicating that differences between centrosomes control mRNA targeting. Blocking the accumulation of mRNAs on the centrosome shows that this event is required for subsequent cortical localization. These events produce a complex pattern of mRNA localization, in which different messages distinguish groups of cells with the same birth order rank and similar developmental potentials.     

Secular variation in carbon isotope ratios from Upper Proterozoic successions of Svalbard and East Greenland

Analyses of stratigraphically continuous suites of samples from Upper Proterozoic sedimentary successions of East Greenland, Spitsbergen and Nordaustlandet (Svalbard) provide an approximation to the secular variation in carbon isotope ratios during a geologically and biologically important period of change from around 900 million years ago to the beginning of the Cambrian period. Late Riphean carbonates and organic material show a stratigraphically useful pattern of enrichment in 13C relative to Phanerozoic or earlier Proterozoic samples. Isotopic compositions of isolated samples from other localities are consistent with a worldwide extended interval of enhanced organic burial and consequent net survival of oxidized material, probably O2, just before the initial radiation of metazoans.