Differential induction of regulatory genes during mesoderm formation in Xenopus laevis embryos

Mesoderm development in Xenopus laevis depends on inductive cell interactions mediated by diffusible molecules. The mesoderm inducer activin is capable of redirecting the development of animal explants both morphologically and biochemically. We have studied the induction of four regulatory genes, Mix. 1, goosecoid (gsc), Xlim-1 and Xbra in such explants by activin, and the influence of other factors on this induction. Activin induction of gsc is strongly enhanced by dorsalization of the embryo by LiCl, while expression of the other genes is only slightly enhanced. The protein synthesis inhibitor cycloheximide (CHX) inhibits the activin-dependent induction of Xbra partially, while induction of Mix. 1 and Xlim- 1 is essentially unaffected. In contrast, gsc shows strong superinduction in the presence of activin and CHX, and can be induced in animal explants by CHX alone. Induction and superinduction by CHX have previously been observed for immediate early genes in a variety of systems, notably for the activation of c-fos expression by serum stimulation, but have not been reported in early amphibian embryos. © 1993Wiley-Liss, Inc.     

The biostratigraphic and palaeoenvironmental significance of Lower Cambrian (Botomian) trilobites from the Ak-Kaya section of the Altai Mountains (southern Siberia,Russia)

The presence of one of the oldest records of polycystine Radiolaria in the Lower Cambrian sedimentary sequence of the Ak-Kaya section (Gorny Altai) requires a biostratigraphic dating. The trilobites found recently a few tens of meters below the radiolarian-bearing level belong to Calodiscus resimus Repina, Serrodiscus fossuliferus Repina and Alacephalus aff. contortus Repina; they suggest that this part of the Shashkunar Formation can be correlated with the lower part of the Botomian stage. The absence of eyes in the two former species suggests a mode of life buried in the fine pelagic sediments. Indications of the presence of a strongly developed musculature on the third species point to a palaeoenvironment characterized by a relatively high hydrodynamic regime.     

Dermal carotenoid measurements via pressure mediated reflection spectroscopy

We describe a reflection‐based method for the quantitative detection of carotenoid antioxidants in living human skin. The skin tissue site of interest is illuminated with broad‐band white light spanning the spectral range from 350–850 nm and the spectral composition of the diffusively reflected light is analyzed in real time. Topical pressure is applied to temporarily squeeze blood out of the illuminated tissue volume. In this way the influence of oxy‐hemoglobin on the reflection spectra is effectively reduced. After a short optical clearing time the carotenoid absorption becomes easily discernable in a 460–500 nm spectral window and its optical density can be calculated with high accuracy. Our empirical methodology provides a non‐invasive rapid determination of skin carotenoid levels, can be used to monitor skin carotenoid concentration changes over time in response to carotenoid containing natural or supplemental diets, and is easily adaptable for applications in clinical and field settings. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The role of microtubules in the maintenance of regular localization and arrangement of Golgi apparatus in root cells of Triticum aestivum L.

In plant cells Golgi apparatus organization, maintenance and distribution differ from that in mammalian cells and the mechanisms for this are not clearly understood. Here we investigate the role of microtubules in the positioning and arrangement of Golgi apparatus in the root cells of Triticum aestivum L. by using dual immunofluorescent labeling and laser confocal microscopy to localize both throughout the cell cycle. We observed that Golgi stacks (i) in interphase cells predominantly occupied the perinuclear region, (ii) during mitosis they redistributed to the spindle periphery and/or areas above spindle poles, and (iii) in telophase accumulated around the phragmoplast and the chromosomes/nuclei of daughter cells. Inhibition of microtubule assembly by colchicine resulted in aggregation of Golgi in the cortical cytoplasm of interphase cells and accumulation around the chromosomes in C-mitotic cells, in stark contrast with the distribution in untreated cells. Electron microscopy revealed that in colchicine treated cells many Golgi units became disorganized, yet others were abnormally enlarged. Overall, our results indicate that in plant cells microtubules play a key role in restricting the position and maintaining the arrangement and structural integrity of the Golgi apparatus.     

A long way to stemness

Comment on: Tanaka Y, et al. Proc Natl Acad Sci USA 2012; 109:4515-20.     

Hydrogen bonded supramolecular structures of cationic and anionic module assemblies containing square-planar oximate complex anions

The formation of the molecular assemblies consisting of anionic and cationic molecules may lead to their interesting structural properties. In this work, we present three new structures based on the tetradentate oxime and amide open-chain ligand CH₃-C(NOH)-C(O)-NH-(CH₂)₃-NH-C(O)-C(NOH)-CH₃ (PAP). All the structures contain the complex cations, complex anions [M(PAP-3H)]⁻ and solvating water molecules. These are H-bonded complex anions: [Ni(1,3-pn)₂(H₂O)₂][Ni(PAP-3H)]₂ · 4 H₂O (1), [Ni(Im)₄(H₂O)₂][Ni(PAP-3H)]₂ (2) and [Cu(Im)₄(H₂O)₂][Cu(PAP-3H)]₂ · 2H₂O (3) (Im=imidazole; 1-3-pn=1,3-diaminopropane). All compounds were synthesised by co-crystallisation of octahedral amine-containing cationic complex with oxime-containing anionic complexes in methanol solution. They were compared with some earlier reported assemblies based on the same ligand (PAP). The comparison of the structures reveals one distinct difference in the separation between the cis-situated oximate oxygen atoms O(1)?O(4) in the copper complexes. The consequence of this effect is the lengthening of the Cu-N distances. In the nickel complexes containing [Ni(PAP-3H)]⁻ anion this effect is much less pronounced.     

Mechanisms of peroxisome proliferator-induced DNA hypomethylation in rat liver

Genomic hypomethylation is a consistent finding in both human and animal tumors and mounting experimental evidence suggests a key role for epigenetic events in tumorigenesis. Furthermore, it has been suggested that early changes in DNA methylation and histone modifications may serve as sensitive predictive markers in animal testing for carcinogenic potency of environmental agents. Alterations in metabolism of methyl donors, disturbances in activity and/or expression of DNA methyltransferases, and presence of DNA single-strand breaks could contribute to the loss of cytosine methylation during carcinogenesis; however, the precise mechanisms of genomic hypomethylation induced by chemical carcinogens remain largely unknown. This study examined the mechanism of DNA hypomethylation during hepatocarcinogenesis induced by peroxisome proliferators WY-14,643 (4-chloro-6-(2,3-xylidino)-pyrimidynylthioacetic acid) and DEHP (di-(2-ethylhexyl)phthalate), agents acting through non-genotoxic mode of action. In the liver of male Fisher 344 rats exposed to WY-14,643 (0.1% (w/w), 5 months), the level of genomic hypomethylation increased by approximately 2-fold, as compared to age-matched controls, while in the DEHP group (1.2% (w/w), 5 months) DNA methylation did not change. Global DNA hypomethylation in livers from WY-14,643 group was accompanied by the accumulation of DNA single-strand breaks, increased cell proliferation, and diminished expression of DNA methyltransferase 1, while the metabolism of methyl donors was not affected. In contrast, none of these parameters changed significantly in rats fed DEHP. Since WY-14,643 is much more potent carcinogen than DEHP, we conclude that the extent of loss of DNA methylation may be related to the carcinogenic potential of the chemical agent, and that accumulation of DNA single-strand breaks coupled to the increase in cell proliferation and altered DNA methyltransferase expression may explain genomic hypomethylation during peroxisome proliferator-induced carcinogenesis.     

Characterization of mutations in the GTP-binding domain of IF2 resulting in cold-sensitive growth of Escherichia coli

The infB gene encodes translation initiation factor IF2. We have determined the entire sequence of infB from two cold-sensitive Escherichia coli strains IQ489 and IQ490. These two strains have been isolated as suppressor strains for the temperature-sensitive secretion mutation secY24. The mutations causing the suppression phenotype are located within infB. The only variations from the wild-type (wt) infB found in the two mutant strains are a replacement of Asp409 with Glu in strain IQ489 and an insertion of Gly between Ala421 and Gly422 in strain IQ490. Both positions are located in the GTP-binding G-domain of IF2. A model of the G-domain of E.coli IF2 is presented in. Physiological quantities of the recombinant mutant proteins were expressed in vivo in E.coli strains from which the chromosomal infB gene has been inactivated. At 42 degrees C, the mutants sustained normal cell growth, whereas a significant decrease in growth rate was found at 25 degrees C for both mutants as compared to wt IF2 expressed in the control strain. Circular dichroism spectra were recorded of the wt and the two mutant proteins to investigate the structural properties of the proteins. The spectra are characteristic of alpha-helix dominated structure, and reveal a significant different behavior between the wt and mutant IF2s with respect to temperature-induced conformational changes. The temperature-induced conformational change of the wt IF2 is a two-state process. In a ribosome-dependent GTPase assay in vitro the two mutants showed practically no activity at temperatures below 10 degrees C and a reduced activity at all temperatures up to 45 degrees C, as compared to wt IF2. The results indicate that the amino acid residues, Asp409 and Gly422, are located in important regions of the IF2 G-domain and demonstrate the importance of GTP hydrolysis in translation initiation for optimal cell growth.     

Prevalence of intron gain over intron loss in the evolution of paralogous gene families

The mechanisms and evolutionary dynamics of intron insertion and loss in eukaryotic genes remain poorly understood. Reconstruction of parsimonious scenarios of gene structure evolution in paralogous gene families in animals and plants revealed numerous gains and losses of introns. In all analyzed lineages, the number of acquired new introns was substantially greater than the number of lost ancestral introns. This trend held even for lineages in which vertical evolution of genes involved more intron losses than gains, suggesting that gene duplication boosts intron insertion. However, dating gene duplications and the associated intron gains and losses based on the molecular clock assumption showed that very few, if any, introns were gained during the last ~100 million years of animal and plant evolution, in agreement with previous conclusions reached through analysis of orthologous gene sets. These results are generally compatible with the emerging notion of intensive insertion and loss of introns during transitional epochs in contrast to the relative quiet of the intervening evolutionary spans.