RESUMEN
With respect to sustainable development, the leachability of trace metal from solid materials in contact with water has focused much attention over the years. Portland cements produced in industrial kilns generally contain from 10 to 300 mg/kg of trace metals. The behaviour of these endogenous metals has been, in this regard, the target of different leaching studies. Many of these researches concluded that heavy metals release are lower than analytical detection limits. Although satisfying from an environmental point of view, it induces a lack in the knowledge about the trace metals behavior during the leaching of cement based material. Accordingly, we designed the CTG-LEACHCRETE device, a dynamic leaching system (modified Soxhlet type) that overcomes this difficulty and allows long term monitoring. The experimental procedure is presented and preliminary results are discussed.
Asunto(s)
Materiales Manufacturados , Metales Pesados/química , Contaminantes del Agua/análisis , Metales Pesados/análisis , Modelos Teóricos , Eliminación de ResiduosRESUMEN
One of the most dominant influences in the patterning of multicellular embryos is exerted by the Hedgehog (Hh) family of secreted signaling proteins. Here, we identify a segment polarity gene in Drosophila melanogaster, skinny hedgehog (ski), and show that its product is required in Hh-expressing cells for production of appropriate signaling activity in embryos and in the imaginal precursors of adult tissues. The ski gene encodes an apparent acyltransferase, and we provide genetic and biochemical evidence that Hh proteins from ski mutant cells retain carboxyl-terminal cholesterol modification but lack amino-terminal palmitate modification. Our results suggest that ski encodes an enzyme that acts within the secretory pathway to catalyze amino-terminal palmitoylation of Hh, and further demonstrate that this lipid modification is required for the embryonic and larval patterning activities of the Hh signal.
Asunto(s)
Aciltransferasas/genética , Aciltransferasas/metabolismo , Proteínas de Drosophila , Drosophila melanogaster/genética , Proteínas de Insectos/metabolismo , Ácido Palmítico/metabolismo , Transducción de Señal , Acilación , Aciltransferasas/química , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Animales , Tipificación del Cuerpo , Colesterol/metabolismo , Drosophila melanogaster/embriología , Drosophila melanogaster/crecimiento & desarrollo , Drosophila melanogaster/metabolismo , Expresión Génica , Genes de Insecto , Proteínas Hedgehog , Proteínas de Insectos/química , Proteínas de Insectos/genética , Datos de Secuencia Molecular , Mutación , Estructura Terciaria de Proteína , TransgenesRESUMEN
A review is given of the results and lessons arising from a sustained in situ diffraction study of the structure and performance of functional ceramic/cementitious materials in which synchrotron-based energy-dispersive diffraction has been the central under-pinning technique. Five particular points of discussion emerge: the demands on time resolution; the use of penetrating radiation for the in situ mode; the need for complementary techniques; re-analysing of data; spatially resolved diffraction: a new tomography. These aspects are discussed in turn using illustrative examples taken from the fields of cement hydration, clay intercalation, cation-exchanged zeolites, and particulate/fluid invasion into building and archaeological objects.
RESUMEN
Members of the Hedgehog (Hh) family of secreted signaling proteins function as potent short-range organizers in animal development. Their range of action is limited by a C-terminal cholesterol tether and the upregulation of Patched (Ptc) receptor levels. Here we identify a novel segment-polarity gene in Drosophila, dispatched (disp), and demonstrate that its product is required in sending cells for normal Hh function. In the absence of Disp, cholesterol-modified but not cholesterol-free Hh is retained in these cells, indicating that Disp functions to release cholesterol-anchored Hh. Despite their opposite roles, Disp and Ptc share structural homology in the form of a sterol-sensing domain, suggesting that release and sequestration of cholesterol-modified Hh may be based on related molecular pathways.
Asunto(s)
Colesterol/metabolismo , Proteínas de Drosophila , Drosophila/metabolismo , Proteínas de Insectos/metabolismo , Proteínas de la Membrana/metabolismo , Secuencia de Aminoácidos , Animales , Clonación Molecular , Drosophila/embriología , Drosophila/genética , Embrión no Mamífero , Proteínas Hedgehog , Inmunohistoquímica , Proteínas de Insectos/genética , Larva , Proteínas de la Membrana/genética , Datos de Secuencia Molecular , Mutación , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , Alineación de Secuencia , Transducción de Señal/fisiología , TransgenesRESUMEN
Epigenetic silencing of gene expression is often correlated with extensive DNA methylation at cytosine residues in the promoter and the coding region of silenced genes. Increasing evidence indicates that, in such cases, DNA methylation can also occur in sequence contexts other than CG and CNG, resulting in genomic regions with almost complete modification of cytosines. Whether this nonconventional methylation at CNN sites also contributes to gene repression is not known. We constructed genes with a promoter and a coding region devoid of the conventional methylation acceptor sites CG and CNG in addition to constructs with the corresponding wild-type sequences containing these sites. We generated unmethylated and completely methylated DNA by the polymerase chain reaction and performed expression assays in plant protoplasts. Quantification of transcript levels by RNase protection assay demonstrated that DNA methylation at positions other than CG or CNG sites contributes to the reduction in gene expression.